"Horror Room" Symptoms of Bad CIs

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"Horror Room" Symptoms of Bad CIs

Hello everyone, I think I'm ripe for writing my first column of my own on this wonderful forum.  Immediately I apologize if the text is a little clumsy, I do not speak English, I use Google translator.  The idea is this: upload here a photo (or even better video) depicting the symptoms of bad microcircuits.  Not too experienced A1 amateur builders like me would be able to identify a "troublemaker" from these photos or videos and replace him on their own without having to purchase expensive equipment.  I am sure that every A1 builder has such situations during debugging, and the presence of a "room of horrors" - the name was invented by Uncle Bernie, will greatly simplify this task.

Video

 I'll start with the Signetics 74123 chip, board location B3.  I had this "grandfather from the 70s", when I pressed reset, it did not stop displaying /////////, with a short hold, @ appeared, but as soon as I let it go, everything continued again.  The selection method was used to find the problem and replace the "troublemaker".

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Actually, my name for this was "Chamber of Horrors",

... but when it goes though Google translate twice, from English to Russian to English, it's amazing how good the translation is.

 

I really appreciate and welcome macintosh_nik for opening this thread and I hope I will soon find some time to post screenshots of my "chamber of horrors" exhibits.

 

Allow me a comment on the 74123: the symptom of '//////////////' appearing on the screen is typical for a marginally working DRAM. The oneshot in the 74123 responsible for the /CAS timing should produce a 480ns wide pulse. But I have found that, more often than not, the 27K resistor at the 74123 will not produce 480ns, but a much longer time, which is bad, and the DRAM will not work. I have found that 74123 from different manufacturers or different lots have great variations in the pulse width they produce, even for the same resistor and capacitor value. Those from my current tube of 74123 all need 20KOhm resistors to make the 480ns, and the variations between ICs from this same tube are very small.

 

So it is not necessarily a "bad" 74123 which macintosh_nik has found, it just did produce the wrong timing. Which may be one of the reasons why digital designers back in the  1970s learned to hate these oneshots. If you want to get any reproducible timing out of them, you need to use a trim pot as the timing resistor, but be careful, if you just use a trimpot, you can adjust it down to near zero, and the 74123 may get damaged by that. Its datasheet specifies a minimum resistor of 5KOhm. So if you experiment with a trim pot in the Apple-1 to replace the (almost always wrong) 27K resistor, use a 5K Ohm fixed resistor in series with a 20K trimpot.

 

You can then adjust the trimpot even without having an oscilloscope. Set the resistance between pins 15 and 16 of the 74123 to 22K (power off of course, and the 74123 not in the socket). Then enter a DRAM test program (if possible, if not, try other settings of the resistance, such as 18K, 20K, 24K, 26K).

 

Let the DRAM test program run for a while, hopefully with no errors yet, and then very slowly adjust the trim pot until the first DRAM errors appear.  Turn power off, remove the 74123, measure and note the resistance between pins 15 and 16. Set resistance again to the value where the DRAM did work. Put the 74123 back and repeat the experiment, but this time turn the trim pot into the other direction until DRAM errors are seen.  Power down, remove 74123, measure resistance. Use the average value between the two values where the error "cliffs" are. Adjust the trim pot until the resistance between pins 15 and 16 is at that optimum value. Re-run the DRAM test. You should not see errors anymore for days / weeks / months. Then you are sure all is OK and you can replace the 5Kfixed/20KTrimpot with a fixed resistor of the same optimum value. If errors still do occur, you may have a bad DRAM chip, or your Apple-1 may need my reliability mods added, seen here in post #4:

 

https://www.applefritter.com/content/part-path-towards-rock-solid-apple-1-builds

 

Entering the DRAM test program several times is tedious, especially if you have no keyboard yet ;-)

 

So I started to provide PROMs with a hidden burn-in firmware page with my IC kits. More on this in a separate post. My notebook battery is running too low now. Stay tuned !

 

 

 

 

 

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Hi Uncle Bernie!

Thanks for the detailed comment!  I already read about a trimmer resistor instead of 27kOhm in your earlier post, but somehow I did not connect it with my "bad" 74123. Now everything becomes clear.  In the near future I will definitely undertake this.  I will write about the results, good luck in all your endeavors!

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Signetics 2504

Hello everyone, we continue the "Horror Room" column, today another exhibit from the 70s is Signetics 2504. There are 7 such IC's on the board, different symptoms appear in each place, so there will be a lot of photos.  As you know, a working Apple 1 appears with a grid when turned on (24 lines of 40 characters each, @ symbols are blinking).

If the bad IC is set to D4B, then the _ will be W (@ symbols are blinking).

D4A, then the _ will be [

D5B, then the _ will be ]

D5A, then the _ will be ^

D14B, then the _ will be ?

D14A, then the _ will be O

Finally, if the bad 2504 is set to C11B, the grid will look fine, but ClearScreen will not work (no single blinking @ symbol appears in the upper right corner).

I hope this information will be useful.

 

 

 

 

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Signetics 2519

Hello all! Another exhibit of the horror room, the most difficult to find Signetics 2519. It's very sad when you're looking for the right chip for a long time (I needed one with vertical markings), you find it, buy it, wait over a month until it's delivered and it turns out not to work. 

 

So, the whole screen is a grid of static question marks, clearscreen doesn't work. Shit happens...
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Uncle Bernie's horror show of bad 2519 ICs ...

Hi Macintosh_nik:

 

Thanks for posting this, but I have had my unfair share of misbehaving 2519, too,  actually, a little pile of them ""worth" several hundred dollars (and people still complain my 100% tested and burned-in ICs kits are too expensive. Idiots. So far I have not made one dime of profit out of these kits, and if I would ever get out of the sea of red ink, I would upgrade the kits to eat these profits away again ... I loathe the taxman that much.)

 

Here are a few more symptoms of bad 2519 (all were outputs of my burn-in firmware in PROM running):

 

 

And here is another one:

 

 

It seems that there is a pattern sensitivity in these "bad" 2519 so they are not 100% dead.

 

But the really bad news is this: with the exception of maybe 2-3 of them which were bad right out of the tube, all the other bad ones appeared to work at the beginning, but then they died during the burn-in. Most died over the first night of burn-in, so I found the mess after breakfast, and could replace them without affecting the schedule, but a few, maybe 3-4, died in the first week.

 

The takeaway from this is that I highly recommend any builder using parts sourced from other vendors to do a full burn-in over weeks to find those ICs which die prematurely so they could ask for a replacement in due time. It's not smart to put a newly built Apple-1 away after running it only briefly.

 

DRAMs are the second worst offenders, and they also like to die during burn-in. But other than these 2519 I saw DRAMs dying in each week of burn-in, so I keep a set of already burned-in ones ready to replace those without disturbing my one-IC-kit-per-week rhythm.

 

In my next post I will show you the true magnitude of these horrors !

 

 

 

 

 

 

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UNCLE BERNIES GRAVEYARD OF DEAD APPLE-1 ICs

 

Here is my "graveyard" which is located on top of the monitor of my "developer's" Apple-1:

 

 

And these are only those ICs who were bad out of the tube. I use the same table to "harvest" and replace the ICs from my burn-in rigs, this is why the bad ones end up there. The burn-in rigs have been moved from my lab upstairs to in front of the open fireplace downstairs, because there they can sit on fireproof bricks, just in case. There is another, smaller pile of ICs there which died during the burn-in, but sorry, no photo for them.

 

Some ICs have gotten dots with nail polish left to me by my ex wife (she took everything else of value). The number of dots allow me to discern them, they all have interesting ill effects, and maybe I find some time later to document these effects in photos.

 

If you look closely you can spot about 9 pcs of bad (but very expensive) 2519, about a dozen bad DRAMs, some 50 bad MM1404, and a few bad PIAs and bad TTLs, too.

 

And now the shocker: all this mayhem and all these dead ICs come from the production of just 25 of my 100% tested and burned-in IC kits !

 

You may now appreciate how much pain, suffering, desperation and monetary losses I save Apple-1 builders from by offering these 100% tested and burned-in IC kits.

 

If I would just sell IC kits (or single ICs) to Apple-1 builders with not testing and not burning-in these ICs to weed the bad ones out,  I'm certain all hell would break loose and I would have lots of unhappy customers who want their money back or threaten me with lawyers. This, Ladies and Gentlemen, may be the root cause why everyone, every single one, vendor of complete Apple-1 kits in the past has given up, except maybe that magical Unicorn, but they ring up very high prices for their "complete" Apple-1 kits (still with no PROMs ?)  and hide them very well on their website, so it's hard to order them from there.

 

I have come to the conclusion that selling untested ICs to Apple-1 builders is not a viable business, because it will cause frustrations and is a phone call generator. One of the companies I worked for as a chip designer had the rule: "Don't design a phone call generator." --- Because if you do, these phone calls will steal all the time you should spend on designing follow up products.

 

With the Apple-1, the two Steves in their garage had created such a phone call generator and worse, they had sold enough of them to have the phone ringing all the time. Which kept Woz - the only person at Apple who could answer these questions and help these disgruntled and/or desperate Apple-1 owners  - from working on the Apple-II. This is why the two Steves (?) decided to "buy back" the Apple-1 to destroy them. This was done in form of a voucher so a customer who turned in his Apple-1 for destruction would get a new Apple-II at a discounted price. And I bet that Steve Jobs even back then was too much of a savvy businessman to have given too much of a discount - meaning that they for sure still made a profit on these discounted Apple-II. But this is only my conjecture. The rest of this paragraph is how the "official" Apple story is being told, but rendered with my own words.

 

Before I did publish my reliability mods here in Applefritter the situation even was probably much worse:

 

I estimate that, prior to these mods, that  from each 3 Apple-1 clones ever built:

 

1/3 did not work at all.

1/3 did work very unreliably and did crash often.

1/3 worked somewhat OK and could run programs for prolonged periods of time.

 

It all depends on the particular combination of ICs , tolerances of timing components, and the type of bypass capacitors. It's a hit-and-miss. But by using a DS0025 clock driver from the original BOM, you could improve your chances towards getting your build into the last class, which worked somewhat OK. But DS0025 are very hard to find, and if you can find them, they are heinously expensive: Rochester Electronics, a chip broker, wants close to $50 each. The DS0026 which is plug-in compatible but has faster rise and fall times (which causes huge current spikes within the 2504/1404 shift registers, via various capacitances of the MOSFETs therein)  is much more abundant and cheaper, but I think no Apple-1 build using a DS0026 will work robustly unless my reliability mods were put in. With my mods, even an Apple-1 using a DS0026 works perfectly robust.

 

Here is the thread with these mods. The picture showing them is in post #4:

 

https://www.applefritter.com/content/part-path-towards-rock-solid-apple-1-builds

 

So far today's contribution of mine to the "CHAMBER OF HORRORS" thread here on Applefritter. The title chosen by Macintosh_nik is what the translation software english->russian->english made out of my original idea, sorry, it's too late to fix it. A "chamber of horrors" or "cabinet of horrors" is a secluded room (i.e. in a University teaching medical doctors) in which they show terrible mostrosities, tumors, etc., all preserved in Formaldehyde. But most industrial companies had such "chamber of horrors", too, full of specimen of parts which had failed in the field, and caused angry (or mutilated or dead) customers, to train young engineers to avoid such bad designs. All this is gone now, due to the bean counters, and due to Globalisation, and so bad designs are coming back to haunt the customers (and the manufacturers).

 

A little personal sidenote about "bad designs" and why nowadays all fields of industry suck more or less:

 

 I'm glad to be retired so I can't design horrible ICs anymore which come back to haunt me. Actually, this never happened to me ... all the 40+ years ... my own designs always were based on paranoia against possible process flaws and they were 100% robust ... but occasionally I had to fix bad designs of others (most of those designers had left the company in question before their SHTF) and, once, my brilliant analysis of a field failure and my proposed fix drew the wrath of a narcisstic psychopathic superior, which cost me my career at that company. Because he himself was the "complete moron" or "cunning saboteur" who had meddled with that circuit design and he had forced  these designers to put his "pet" clamp circuit in, which then later caused field failures (a bandgap reference would not start under certain rare power cycling / ramp up conditions, and then got stuck there, no further power cycles would help, a very nasty effect, you had to wait for 10-30 minutes powered off until the charge on an internal capacitor leaked away enough to allow for another startup attempt, the high quality of today's wafers contributing to the slow decay of that charge).

This director is another example of a lousy engineer who has turned to the "management" career ladder because he knew he's a bad designer, but then, of course, he used his position of power to incompetently meddle with designs again, each circuit block done under his rule had to have his special signature "mark of the beast" in it, even if it was a superflous addition. And, of course, he was not fired even after an ISO9001 auditor exposed the utter incompetence and failure of that psychopath even  in management tasks ... he consequently was promoted, IIRC to the level of vice president. I wished they had made him CTO instead, such that this obnoxious vulture of a semiconductor outfit would go under even quicker ! 

(no, it's not TI, but another very, very big outfit which due to lack of in-house innovation continues to take over and strip mine smaller competitors, just to install their own sh*tty management methods and their Orwellian spyware on all the computers. And stock options only for their management vermin, not for us chip designers who do the actual productive work and the  innovation. Suckers ! I'm glad that I'm out of there.)

 

The global problem, as I see it, is that such effects and mechanisms and "power play" by managers is now everywhere, pervades every company, and the larger the company is, the worse it gets. Back in the day when brilliant engineers seeing such rot and management incompetence at their employer could just walk out, find venture capital, and start their own company where everything was done right, no manager vermin infesting the place yet. Some of the finest and most successful companies came out of that effect, and they are legendary now, but most did not survive as an independent company, and  got swallowed by these much larger vultures mentioned above. How can that happen to a company making stellar products ? The reason is very easy: once a company exceeds a certain size, more managers need to be drawn in to run it. And these come from the outside, often leaving behind a lot of stink at the companies they came from. These new hires more often than not turn into "management vermin" again infesting the place, but the founders in the meanwhile, over the decades,  got too rich and too old to care about that infestation, the same type of infestation they once had walked out from. So, like termites eating your house, rot sets in within the company, and at some point the company is weakened enough to be a takeover candidate for the big ones. Which, of course, only will make matters worse. But they will strip-mine all the assets and all the patents and the technology. And they will drive out all the brilliant but too expensive engineers ... if these can find new employers, or are wealthy enough to retire.

 

This is how companies rise and fall and get eaten by the vultures. The problem today is much worse, because most hi-tech is too expensive nowadays for startups. For instance, in the semiconductor industry of the early 1980s, you could set up a wafer fab using the newest equipment for somewhere between 10-25 Million USD of capital invested. And then you had a very competitive process technology. Nowadays, you need 1-2 Billion USD to do the same. In the 1980s, a single IC designer could design a new IC. More complex ICs, like a microprocessor, needed small teams of maybe half a dozen designers. Nowadays, to really design the 100's of millions of transistors that go into any leading edge IC, you need hundreds if not thousands of IC designers to get the work done in a useful period of time. Hope you can see the problem ! This is why I sold all my semiconductor stocks I had accumulated over the decades from company stock options. The semiconductor industry is now mature, much like the car industry, or the aircraft industry, or the food industry, and the good days are over, and the products suck.

 

 

 

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You should send your

You should send your graveyard to one of the chinese fake chip refurbish processors, they could make some nice sets for none working showcase boards.

Seriously some people might be interested in such a set, but they should be deeple marked on the bottom as none working chips.

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Another bad MM1404 shift register ....

... this one is very peculiar. It almost works but there seems to be a pattern sensitivity, so some characters are wrong:

 

 

The above is the output of the hidden burn-in test page in my A1,A2 PROMs featured here:

 

https://www.applefritter.com/content/uncle-bernies-burn-proms-and-gimmick-switch

 

The takeaway from this is that you really need to watch this screen output closely and not just be happy if you see a marching pattern that seems to be almost right. These pattern sensitive errors normally are not easy to spot (this one is easy !) and they also might happen somewhat randomly, sometimes they manifest (i.e. warm ICs) and sometimes they may not appear (cool ICs, such as after startup).

 

All these 1Kx4 dynamic shift registers are typical mee-too products of the very early 1970s and the companies who were making them wanted to make a quick buck and still sell them cheap.  I don't know which semiconductor outfit made them first, but is certainly wasn't a huge design effort. Their inner circuit is so simple and regular that if you have a modern CAD workstation running Cadence and you can call up library cells for the I/O pads, you probably could do the complete circuit design, layout and simulation of such a chip in one day. In the early 1970s it was not so quick as they had no circuit simulator, no library cells, and no powerful layout tools. Still, they already had the first digitizers and could tell the CAD tool to put one cell down many times in the layout once the hand-drawn cell was digitized.  So, even back then it probably was the quickest and still useful chip you could design. Of course it was PMOS. They had no NMOS process yet, which explains the weird supply voltages. I really wonder where the "huge" market for these stupid shift registers could have been. Being bit serial devices they make very slow RAMs if used as such. Think of a semiconductor "magnetic drum memory" which early 1950s computers had. Some early electronic desktop calculators also used serial memory of a few hundred bits, but this typically was  an acoustic delay line made out of a special wire bent into a spiral. Other than the Apple-1 and the early TV typewriter published by Don Lancaster in the September 1973 issue of "Radio Electronics" magazine I don't know of any applications for these serial shift registers. Maybe that's the reason why we can still buy them today ... all the unsold ones went to the chip brokers.

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And another type of Symptom:

this is caused by a 7404 (half of which are for the clock generator) and the clock is faulty, mainfesting itself in this garbled screen output:

 

 

This happend on the third day of burn-in. (And another IC bites the dust ...)

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And another Signetics 2519 bites the dust ...

This is similar to my post #6 above, but this time there are more diverse characters on the screen:

 

 

And there also is the telltale diagonal bar of blanks:

 

 

This particular 2519 died three days after burn-in start. Which means that a "quick check" for a few seconds does not make you safe.

By now I don't think that making 100% burned-in and tested Apple-1 IC kits is a commercially viable business endavor for anyone.

I just have to do it to be able to dump my overstock of rare Apple-1 ICs into the market without causing lots of angry customers.

There is an iron rule for any company making kits: the kit must yield a fully functional build if put together properly. Every. Single. Time.

No exceptions !

For a relatively complex machine like an Apple-1 having 100% known good ICs is a must.

This applies to all kits if the complexity exceeds a few ICs.

I witnessed the microcomputer kit woes of the 1970s and most kits (like the Nascom) were disastrous. The reason is that one bad IC among 50-100 ICs is enough to doom the build and make the builder very unhappy and disappointed. So word spread and these kit companies went out of business as quickly as they appeared.

So even back then, selling microcomputer kits was no commercially viable business endavor.

And don't get me started on "Sir" Clive Sinclair with his notorious electronic calculator kits, the "Black Watch" kit, the MK-14 and ZX-80 kits. All were utter disasters and more often than not total waste of time and money. Even if they worked (which must have been a rare outcome) they did disappoint due to their lack of capabilities.

But like many experiences, after a generation or so,  memory fades and a new generation of "entrepreneurs" repeat the mistakes of the past. Again and again and again.

But my kits are doing well. No complaints so far and lots of happy builders who succeeded. Seems the 100% test and burn-in does the magic. Alas, this is not commercially viable on any larger scale, IMHO.

 

 

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I mostly agree.I had one of

I mostly agree.

I had one of the Sinclair ZX81 kits, I build together with my father and do not agree about the kits. It was easy to build (I assisted my dad as I was only 6 at that time) , it worked instantly, it is not as incomplete as the Apple I was and with the 16k expansion you could do almost the same as you can do with the Apple 1.

A working cassette interface was on board, there are two disadvantages to mention one is the 32 instad of 40 characters a line and the shaky connection to the 16k extension. But there is also a big advantage ZX81 had a full characterset including graphical elements so gaming was more fun as on Apple 1, the shaky connection to the RAM expansion got solved with some wood and hotglue in the end I had an replacement case with a real keyboard and a printer port.

You are right if you say this kit came 1981 while Apple 1 was 1976 but it's also right that this kit was £49.95 ($110), £69.95 ($155) assembled while the Apple II was 10 times the price £549 ($1100) and the Apple I was 5x this price.

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natas666 wrote:I mostly agree
natas666 wrote:

I mostly agree.

I had one of the Sinclair ZX81 kits, I build together with my father and do not agree about the kits. It was easy to build (I assisted my dad as I was only 6 at that time) , it worked instantly, it is not as incomplete as the Apple I was and with the 16k expansion you could do almost the same as you can do with the Apple 1.

 

The ZX81 is an improved ZX80 with much less parts, as all the TTLs from the ZX80 went into the ULA chip. Just compare the pictures of the PCBs you can find on the internet. Less ICs = less chances of getting a bad one. I was a teen back then and a classmate bought the ZX80 kit.  It was a disaster. It did not work. He brought it to me (I had lots of TTL ICs) and so we started swapping ICs until it did work. The next disappointment was the awkward editor, the horrible membrane keyboard, and the fact that when a BASIC program was running, the screen went black. And almost no memory to do useful things. Much like the MK-14 which only had 256 bytes of RAM. The ZX80 had four times that. My friend said that he got ripped of by a con man (meaning Clive Sinclair). At the time, for slightly less money than the ZX80 kit did cost, you could buy an Ohio Scientific Superboard II computer with 4K RAM installed and a real keyboard. You had to add a 5V supply, though. I had the Superboard II. But I also felt ripped off because when I used strings in any BASIC program, the machine would lock up and only a reset could bring it back. This was the infamous "Garbage Collection Bug" of OSI BASIC. The upside was that this forced me to start programming in 6502 Assembly language (as the BASIC was useless). I later did even analyze and fix the "Garbage Collection Bug". Oh, and despite I had to sell the OSI to buy one of the first Ataris, about 10 years ago I was able to buy a Superboard II off Ebay and about two years ago I proceeded to build another one (a clone) based on the open source Gerbers. Oh, and I have a ZX-81 with that wobbly 16K DRAM module, too. But I didn't pay any money for it. I got it for free as the owner wanted to throw it into th trash can. Had I paid more than $10 for it I would have felt somebody had ripped me off ! The irony with all these pathetic early Sinclair calculators and ZX is that they were stripped down to the absolute minimum (and then they took away even more  parts or functions !) and they were sold at a price point that at the first glance looked like a bargain. The rude awakening came when you found out that you got ripped off. After buying all the additional expansions in hope to turn that turd into a useful computer you had spent a nice sum of money - far more than the intital purchase which had set the trap -  and you still didn't have a decent computer. For the same amount of money you could have bought a nice Taiwanese made Apple-II clone with a real keyboard, the slots, and the same 16K DRAM. They were better quality than the original Apple-II. I have about half a dozen original Apple-II in my collection and none of them works anymore. My sole Apple-II clone still works. Currently I use it to verify my new ACI PROMs which make the Apple-1 recordings Apple-II compatible (and still can be read on a standard ACI). I need that to get my RWTS routines into the Apple-II to be able to test them if they are compatible with the original Apple DOS3.3 --- lots of cute goodies for the Apple-1 under development !

Footnote (to avoid more Sinclair related comments in this Apple-1 thread): the Sinclair Spectrum deserves honorable mention as it really was a nice machine out of the box and *lots* of great programmers cut their teeth on it. So finally, even "Sir" Clive got it right - at least once.

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Uncle Bernie's graveyard of dead Apple-1 ICs ...

... just for a Halloween giggle:

 

 

 

This graveyard is located on top of my period correct B&W monitor. I've put labels on the piles of dead ICs for your reference what they are. Note the pile of 25 pcs of the expensive Signetics 2519N in the rear part (some on the ESB foam having red dots). There also is a huuuge pile of National Semiconductors MM1404 shift registers which refused to shift. Never again I will buy those. There are only about 18 bad AM1404 on the graveyard despite I ran through close to 500 of them.

 

Total money in this graveyard is about $1000.

 

It's the "fallout" from producing 50 of my famous 100% tested and burned-in IC kits, plus about a dozen which went into my own builds. About 80% of the ICs were bad out of the new-old-stock tube, the other 20% died during burn-in, which in my case runs 4 weeks 24/7 on multiple burn-in rigs which really stress the ICs by running my diagnostics page which comes with all the A1,A2 PROMs I sell (just letting the ICs sit powered up but not running a memory intensive program would not stress the DRAMs).

 

Now, let that sink in. What are the odds for a typical Apple-1 builder  who bought his (untested) ICs from various other vendors ?

 

I think these odds are not in their favour.  From this graveyard I can estimate that about 1/3 of the builds fail, if not worse. And this estimate includes all those who are stubborn enough to push through and find all the bad ICs by trial and error. But at which cost in terms of money spent, frustration, suffering, fear and doubt ?

 

I will continue to provide my famous 100% tested and burned-in IC kits to the Apple-1 builder community next year, as long as supplies last. At the moment I have only about a dozen 2519N left, due to the many duds. I do have a source but can't get my IC broker on the phone (try to get any IC broker on the phone, all lines busy all the time). At the moment they are busy trying to find ICs for big industrial customers. It's really that bad !

 

Comments invited !

 

 

 

 

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Screen keeps scrolling

I'm unfortunately here to bring on this horror room thread with my build. When D4 and D5 are fully populated screen keeps scrolling up and can't be stopped. It continue even after a screen clear.

Anyway if you remove one random shift register in these locations the problem disappears.

If I connect the shift register with the output pin out of the socket the screen scrolling problem happens again.

I really have no idea on what is happening and how to solve.

P.S. all the shift registers work. I was filming a non-fresh power up

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Weird scrolling of Apple-1 screen

In post #15, Toms98 wrote:

 

" P.S. all the shift registers work. I was filming a non-fresh power up "

 

Uncle Bernie comments:

 

No, they don't work. At least not all of them. The movie clip you have posted does not play back very well on my side, I had to watch it several times to get a glimpse of the 'scrolling' action, but I got the impression that on the screen there are only either the even or the odd character positions occupied / active.

 

This hints to a problem with the DS0025 clock generator or some upstream logic driving it. But even I am not 100% sure what causes this. And I know the exact function of each and every gate or IC in the Apple-1.

 

None of the 2504/1404 in Row D can have ANY legitimate effect on scrolling. Scrolling is controlled by the cursor state machine in the lower right hand corner of the "Terminal Section" schematic. The only 2504/1404 shift register which enters this logic is the one sitting in Row C under the DS0025 (location C11b). There is one special feature of the cursor state machine, it also feeds back into the counter chain, signal WC1, via the 7432 at location C9. This path can initiate scrolling action at times, when "fake cursors" living in the 2504/1404 at location C11b happen to infest the unused portions of the shift register that correspond to screen locations that never can be reached by characters. The idea Woz had with this obviously is to get rid of "fake cursors" by scrolling them out. I would have blocked them by inserting a gate in the cursor circulating loop.

 

I've seen several instances of unwanted scrolling and one of them even produced a "The Matrix" (meaning the movie)  style character waterfall when running the diagnostics page that comes with my A1, A2 PROMs. Interesting is that this was caused by the 7408 at location C12. Which was bad and screwed up the generation of the two clock phases for the shift registers.

 

I would recommend you to first check that the -12V supply on the DS0025 is right. Then check the PHI3, PHI4 clock phases generated by the DS0025 (they must swing from +5V to -12V and the -12V periods must not overlap). But for this you need an oscilloscope of sufficient performance.

 

I suspect something is wrong with your DS0025 because you say that added load (if the D4 and D5 sockets are populated) causes the scrolling problem to manifest.

 

It also would be interesting to see a close-up photo of your DS0025 and the 2504/1404, such that the manufacturer and date code could be read.

 

- Uncle Bernie

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Weak psu

Thanks Uncle Bernie for your help!I made another video of a fresh start to show you that all shift registers work. You can see the right pattern of "_@" scrolling up.I suspect something not working properly in my psu since I double cheeked my board and I'm having a sum of other strange problems.The high nibble of ram is always corrupt (I can use the terminal if I remove one shift register from D4/D5) if I write "0000" I can read "0000" correctly on display but when I hi return I get "D0D0" as a responce. No other value different from D of F can be stored in ram (only after resettig the computer it reads partly correct address for example "C100" is saved as "C1D0").I read your post about the fake cursors killer circuit and you mentioned that can be caused from the psu.I'm using an SMD replacement for the LM323k (if necessary I can add a pic) and  I have two trasformers that maybe don't match enough the specs (8V-9V @2.5A and 24V-27V @1.2A).

I'm buying two new trasformers that are more matching. In your opinion can these trasformers be too weak for the machine?Thanks,Toms98
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Transformer problems are NOT IC problems !

In post #17, Toms98 wrote:

 

"I'm buying two new transformers that are more matching. "

 

Uncle Bernie comments:

 

Oh no, don't do this before you are absolutely certain it's caused by transformers. I know two types of problems with transformers in the Apple-1 PSU:

 

a) output voltage too high

b) CT ("Center tap") of the 24/28Vac transformer not properly connected.

 

In the first case, the 7812 regulator runs too hot and may go into thermal shutdown. Which impairs functionality of the DRAM. But it won't affect the 2504 shift registers. These live on +5V/-5V/-12V (the latter in their clocks, via the DS0025).

 

In the second case, weird effects can happen and the unregulated voltages on the 2400uF filter capacitors may fluctuate around. This is a slow process leading to intermittent loss or brownout of a regulated voltage (-12V, +12V).

 

Both issues can be easily checked with a multimeter. Measure the DC voltages on the filter capacitors while the Apple-1 is running (after RESET was active and is released). On the 5300uF, there should be ~10V, and on the 2400uF, there should be ~ -20V and ~+20V. These voltages should be fairly stable and not fluctuate around. Note that there is plenty of headroom for the regulators in this case. Actually, too much headroom, which makes them run hot.

 

The problems with the Wozmon you see are almost always rooted in a dysfunctional DRAM. If you have bought one of my kits, the A1, A2 PROMs contain an extra page with a diagnostics program that does NOT need any DRAM at all for doing its job. If will, however, complain about DRAM errors and give you a syndrome message. Everything is coded without use of any subroutines so it can't crash due to bad DRAM. The Wozmon uses subroutines and if the return address off the stack is corrupted, it crashes.

 

I still would be interested in a photo of your 2504/1404 ICs. Some date codes are known to be bad.

 

- Uncle Bernie

 

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Hi Mr. Tom Owad!

Can I ask you to correct the title of this thread, I seem to have made a mistake writing CIs instead of IC's? My English is much better now than before.

 

Thanks in advance!

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Texas Instruments SN74174N

I recently received a batch of SN74174n from aliexpress, they looked pretty good but their functionality was not. The seller seemed to be aware of the problem and made a full refund at once without involving aliexpress. Beware of fake IC's!

 

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I've done the test you said

I've done the test you said.Fortunatley the 7812 won't run hot. On the 5300uF I have a stable 10.35V, on the 1st 2400uF I have form -17.7V to -17.9V, on the 2nd 2400uF I have from 18.05V to 18.25V. Might the voltages on the 2400uF capacitors be too low?

I'm using MM1404AH (code on the side: 814 MM1404AH) shift registers in a TO-99 package adapted to the 2504 sockets, I'm adding some pics
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Hi Toms98!

I am still concerned about 74LS157, I read on the Russian forum that this replacement does not work.

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Hi Mackintosh_nik!I'm having

Hi Mackintosh_nik!I'm having the very same issues on screen with or without both of them so I'm quite they are not the cause of this problem

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In post #21, Toms98 wrote: 

In post #21, Toms98 wrote:

 

"On the 5300uF I have a stable 10.35V, on the 1st 2400uF I have form -17.7V to -17.9V, on the 2nd 2400uF I have from 18.05V to 18.25V. Might the voltages on the 2400uF capacitors be too low?"

 

Uncle Bernie answers:

 

No, these voltages are OK. The positive regulators need about 2.5V headroom and the negative regulators need about 1.5V headroom. If you had ~7.5V on the 5300uF and ~15V on each 2400uF you still would be good.

 

I'amazed that somebody finally found MM1404 in the TO can package. Wow. I never was able to find some, and I tried for years. Alas, I have no datasheet for them so I can't look if the metal can is connected to something. If this is the case, then if the metal can touch anything, there may be a short. Avoid this.

 

About the 74LS157 vs. 74157 controversy, I once built a LSTTL Apple-1. It did not work (screen issues). Finally, I tried it with National Semiconductors MM1404 and it worked ! I got the impression that the 74LS157 were the culprit. They have Schottky input clamping diodes which may interfere with the PMOS logic levels. But I did not get to the bottom of the problem, no reason to experiment more after I found that the MM1404 worked in my LSTTL build ! None of the other 1k x 1 shift registers worked in it, neither the Signetics 2504V/1404 nor the AM1404 nor the AM2804. Only the MM1404 did work. But those had about 50%  bad ones in the lot so I did not buy them again.

 

- Uncle Bernie

 

 

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Hi, The MM1404 in the TO99

Hi, The MM1404 in the TO99 package is the cheapest option available today.

You can buy them on ebay at a very affordable price.

In one of my compilations, I also used them.

View thread  https://www.applefritter.com/content/my-version-apple-1-replica

Regards,

Mateusz SQ9PXB

 

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I have some update on my

I have some update on my build. I removed the high nibble of W bank (E000-EFFF) and now ram is half-working (it can't hold data if you perform other operations but at least I can access all address and see and start the cassette proms). Also I put a 100nF capacitor between D5A pin 4 (-5V) and D6 pin 8 (GND) to reduce noise on -5V line and now the screen don't scroll up but when I hit the screen clear button I can't clear the cursor shift register and the screen won't work. Can this be cause by a defective 7905?

Also I noticed that every 8 characters the 9th is write twice on screen (this problem won't go away with or without the capacitor I added)

P.S. I still need to remove 1 shift register to use the terminal, in the picture I removed D4B, in the video all shift registers are in place.
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The problems of Toms98 are not "defective ICs" !

In post #26, Toms98 wrote:

 

"Can this be cause by a defective 7905 ?"

 

Radio Eriwan answers:

 

In principle, yes. But I've never had a case of a defective 7905 (or any other 78xx or 79xx regulator).  And I used / shipped hundreds of them. These regulators are incredibly robust and they have built-in overcurrent and overtemperature protection. These are very difficult to kill (Don't ask me how, it's evil tricks we used to blow up new IC prototypes from fellow designers --- they only would 'win' if we can't blow them up within the 'rules'. Oh, this was standard practice in that famous company, encouraged by the management).

 

This said, it's unlikely you have a regulator problem, unless you can prove that by measurements.

 

The fact that your added  100nF capacitors improves things is a clue, don't you think ?

 

The Apple-1 in its original form has a very pathetic capacitive bypass on the -5V rail and the kickback from the shift register clocks (and their DS0025 clock driver) often causes trouble for the DRAMs. There has been a well known mod from an Italian guy for many many years involving adding a few bypass capacitors. I came later to the Apple-1 scene and found that the first Apple-1 I built did not work (DRAM issues). The 'Italian mod' helped but there still were occasional DRAM errors. I then worked out a more elaborate 'reliability mod', see here:

 

https://www.applefritter.com/content/part-path-towards-rock-solid-apple-1-builds

 

Over the almost two years I'm selling my Apple-1 IC kits now, I've learned a lot how to compose the ICs and the passive components in a way that - finally - the builds may work without the full reliability mods: with the recent kits having the Intersil DRAMs you typically only need the six damping resistors. But it also depends on the particular PCB recipe.

 

Still, you (meaning Toms98) are another good example for what happens if a 'maverick' builder ventures into building an Apple-1 clone all on his own. You bought your own ICs from various sources, of unknown functionality and fitness for an Apple-1, and now you are in the painful learning process to find out how to make the damn thing work. Which took me more than a year. The builders of my kits do not only get a 100% tested and burned-in IC set (burn-in happens in Apple-1 clones) which has been carefully composed to take some edges out, but also a set of passive components which are proven. The electrical performance of bypass capacitors varies greatly and now with the Chinese manufacturers (the only ones left making the vintage looking disc capacitors) it's a hit-and-miss. You need an instrument called 'Network Analyzer' to measure their performance. I was lucky that I found some which are good. The more modern " boxy" blue bypass capacitors for the "NTI" style builds are still being made by Vishay and some other manufacturers, but even there you need to know which ceramic material to choose. Builders of my kits also get a 69 page "Tips & Tricks" pdf which protects them from common pitfalls and guides them though the building process.

 

Now here is my complaint to you, Toms98: dealing with these issues has nothing to do with "Chamber of Horrors" ICs and their symptoms. This thread was meant for bad ICs and which symptoms they cause and not for common Apple-1 woes caused by its inherent quirks and then not knowing the remedies because being a 'maverick' builder who wants to do and find out everything himself. I understand this attitude (I'm of the same type) but I still would appreciate if you would open a special thread on this forum "Apple-1 maverick builder seeks help" or such, and then post about your problems there, because they do not have to do anything with 'bad' ICs.

 

If you follow my advice and stop posting here in this thread off topic, then I will continue to give you hints. But if you continue here in this thread, I will stop with that. This thread should not be filled up with 'maverick' builder woes. It's meant for which bad IC causes which symptom(s). And for that you need proof that the IC indeed was the culprit.

 

Do we have an agreement ?

 

- Uncle Bernie

 

 

 

 

 

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I'm really sorry. Moved to

I'm really sorry. Moved to "Help needed with strange terminal issue (maverick builder) "

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