Apple 1 Boot Screen

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Apple 1 Boot Screen

Hi,

This is my first post here. I'm trying to build an Apple 1 replica (I bought the pcb from retroplace a year ago, and started collecting all the parts until I get everything to actually start building). 

My electronic knowledge is far from a professional level but I love learning while doing.

So far, I soldered everything, checked the power supply section. The LM323K I had was a restamped transistor (I guess, since it was giving only 0.67V). So I changed it and now I have all the voltages correct everywhere needed. 

I proceeded with populating the terminal section, powered it up, and got a nice boot screen. At least I thought, until I noticed one of the _ char was a +

I should mention I switched all the 2509v for mm1404an, because I wasn't able to find 2509v for sale.

When I clear the screen, I get the blinking @

I don't want to go into populating the computer section until I figure why there is a + where there should be a _

I tested removing  D2, C3, D4a, D4b, D5a, D5b, D14a, D14b and C11b :

-> 40 x 24 fixed "█" symbols

put back the 2513:

-> 40 x 24 fixed "@" symbols

put back the 2519:

-> 40 x 24 flashing "@" symbols

put back all the mm1404an:

-> flashing "_@" symbols (and can be cleared) but with still that + sign in col 33 line 17

 

Any help to figure it out would be appreciated. Here is a picture of it: 

 

PS: English isn't my first language. Please excuse any weird sentances and mistakes. 

 

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Hi Ben_Aveline!

It seems okay, the starting grid sometimes may not have all the "right characters", this is normal.

 

Set jumpers: "6502" two, "NO DMA", Y-F, Z-D, R-C, W-E, X-0. And also in the KEYBOARD connector a temporary jumper between pins 15 and 16.

Then put all other microcircuits and do Reset (on KEYBOARD connectors connect pins 1 and 9) and see what happens...

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Next Step

Thanks for the details. I went ahead and set jumpers, and put all remaining ICs. I powered it on and... nothing happened on screen, but soon I felt a bad burning smell. So I unplugged it very quickly and touched every component. The only one that was painful hot was the LM320 MP-5 

So I'm guessing a bad IC is making a short somewhere and I didn't identify it by touch. While I'm trying to identify the issue, any help to troubleshoot would be appreciated.

Thanks in advance

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Hi Ben_Aveline!
If the video part worked fine and the problems started after installing the chips in the CPU part I would take a step back and try to insert the chips in the CPU part one by one. As I understand you already had a bad experience with the LM323k? Did you buy it on aliexpress? There's a lot of junk out there... I hope your DRAM chips are not from there? It doesn't work, it's quite possible that your processor or PIA is just a relabeled fake, I've run into that.
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Another well meant warning about Chinese counterfeit ICs !

In post #4, Macintosh_nik wrote:

 

"Did you buy it on aliexpress? There's a lot of junk out there... I hope your DRAM chips are not from there? It doesn't work, it's quite possible that your processor or PIA is just a relabeled fake, I've run into that."

 

Uncle Bernie comments:

 

MUHAHAHAHAHA !  (I nearly spit my morning coffee over the keyboard when reading the above).

 

"Mostek" DRAMs with a date code hinting they were made in the year 1999 ! Hilarious ! These Chinese counterfeiters don't even do their "homework":

 

https://en.wikipedia.org/wiki/Mostek

 

Mostek ceased to exist in 1985 as a brand (it was swallowed by STM) and you can bet they NEVER produced any DRAMs in the year 1999, let alone the long obsolete MK4027 from the mid 1970s !

 

Same thing with the laser engraved "Rockwell" 6502 and 6520 with date codes from the 2000's ... Hilarious !

 

Here is a thread about Chinese counterfeit ICs every prospective Apple-1 builder should know:

 

https://www.applefritter.com/content/warning-counterfeit-ds0025-china-oh-no-surprise

 

Buyer beware !

 

Oh - and the counterfeit MM1404 or Signetics 2504/1404 - especially those in grey mold compound packages - more often than not are based on re-stamped 555 timers, which, when put into the Apple-1 in the 2504 sockets, will only get hot, melt the socket (if they can, depends on the plastic material) and - of course - they also might kill the -5V regulator if this is yet another fake. The real 78xx and 79xx bipolar regulators self protect (they have overcurrent protection and thermal shutdown) and they are very hard to kill, although this is possible by applying enough overvoltage and other mean tricks. But there are *lots* of Asian knock-off three leg regulators which lack the protection circuits, and these are mere junk, designed by idiots who don't know what they are doing. Of course, if you simplify the regulator circuit and take the protection out then you can have a smaller die size and you can sell the part cheaper. But I think the main reason for removing the protection circuits was that these copycats never figured out how to control the process to keep the current limiting set point in the proper range. This is NOT trimmed, it's done by turning knobs in the wafer fab.

 

- Uncle Bernie

 

 

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I feel so stupid, but learning

Yeaah... I bought these dram, with a 2000 timecode... (0038)

I removed all the computer section chips, and tested again, in case it caused damages. Everything still works fine with just the terminal section. 

Thank you both for pointing me to the right direction. 

 

P.S. : @UncleBernie I saw you have some IC kits on ebay. Do you have some DRAMs in stock to sell ?

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Hi Ben_Aveline!
Not problem. Only those who do not do anything are not wrong. I also bought these, immediately after receipt checked and opened a dispute, the money was returned. If Uncle Bernie can not help you with DRAM chips, I can give you a contact for a reliable seller, he is from Europe.
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Giving updates

Ok so I got new DRAMs, and went ahead with 4K and desoldered the w wire. Now it powers on with the boot screen, I press clear, I get a single @. Then reset, and there is something weird.

I get:

/@

@

(Yes 2 @) and when I type in, it writes between the / and the first @.

I also noticed that if I type more than one line, some characters previously entered change. I ignored it a while and typed in the test program from the manual. The chars display but while running it changes some characters 1 or 2 lines above. I assume it's a bad shift register, so today I'll try replacing them one by one (I have 3 spares)

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wrong ICs

After looking at it back from the beggining, I spotted a few ICs being in their LS version: 

- the 74S257 switched to 74LS257. Looking at both documentations, they have small differences (like propagation delay from data input being more than doubled).

- the 7427 switched to 74ls27, which has a different high/low treshold.

I started collecting the parts for this project long time ago, and obviously didn't pay enough attention. I'll get some more precise IC references (each time with a couple spares, as these are cheap enough) before resuming troubleshooting.

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Hi Ben_Aveline!

I don't think it's a bad shift register, they have very different symptoms, you can read more here. The 74ls257 works without problems in one of my assemblies, about the 74ls27 I have to look in my notes, I can do it tomorrow. Tell me, do you use a 27k resistor in the area between B2-B3? Try putting 20-22k, it's not hard.

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I tried replacing the 27k by

I tried replacing the 27k by a 22k then 20k but no change.

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The point is that for the
The point is that for the processor part to work properly the sync pulse must be as close as possible to 480ns, which is almost never the case with a 27k resistor. This value can be measured on pin 13 of 74123. I will attach a screenshot from my oscilloscope.
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Thanks for that precision.I

Thanks for that precision.

I have an old analogic oscilloscope, that goes as low as 500nS/div so the readings are not as precise but, after a few measurements on pin 13 of the 74123, i decided to solder a 20k potentiometer, with a 5k resistor in serie. When I turn the potentiometer, it changes the duty cycle, but not the frequency. 

This is what it looks like with X: 0.5uS/div and Y: 2V/div

 

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Hi Ben_Aveline!

You're getting close. I tried 74ls27 and 74ls257, on my assembly it works. Here's a little video. I still think the solution to your problem is in the area around 74123. Try swapping out the 8t97 and 74ls257, as well as the other 74123 and the 47pH capacitor. The Apple-1 is not exactly an ordinary computer, in the sense that it has never been mass produced and therefore has not undergone the necessary technical checks. Sometimes components that don't work in the Apple-1 are fine in other systems...

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Update

Ok, so far: 

- I changed the 27k resistor for a 22k. 

- I swapped the 74123 for another one

- I changed the 74ls257 for a set of 74s257

Still exact same issue (wasn't able to reset the processor for a moment, due to a bad 74s257, that I've been able to identify)

I'm out of spares for the other chips. They are cheap enough so I ordered a few spare 8t97 and 7427. 

I'll keep this thread updated when everything is delivered.

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I changed the two 8t97 and

I changed the two 8t97 and the 7427.

I also found a digital oscilloscope and fine tuned the pulse on pin 13 of 74123 to 480 nanoseconds with a 18k ohms resistor. 

Still no change.

Maybe I'll start checking all the capacitors. Wondering if it could be a bad prom tho. What do you guys think ?

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Ben_Aveline wrote:I changed
Ben_Aveline wrote:

I changed the two 8t97 and the 7427.

I also found a digital oscilloscope and fine tuned the pulse on pin 13 of 74123 to 480 nanoseconds with a 18k ohms resistor. 

Still no change.

Maybe I'll start checking all the capacitors. Wondering if it could be a bad prom tho. What do you guys think ?

 

Where did you get that PROM from?  How was it programmed?  Those PROMs are hard to find and even harder to find a programmer that can handle them.  This is where buying a tested parts kit from Uncle Bernie might have saved you some trouble.

 

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Hi Ben_Aveline!

The symptoms of bad PROMs are poorly understood... I tried swapping A1 and A2, as well as putting clean chips. In both cases I just didn't get /, so it's unlikely it's the PROMs. But just in case, where did you get them?  I hope not on aliexpress, the probability to buy them there is 0.

Pretty hard to work blind. Can you post a good photo of your assembly here? So you can read the markings on the microcircuits? And the back side too. What do you use as a keyboard? Try to put another 47pF capacitor, I once helped a guy in a Facebook group with a similar problem, it helped him.

You can test your PROMs, but probably not now, but when your build starts interacting with you.

 

<CLEARSCREEN>

<RESET>

FF00.FFFF

<RETURN> 

It should be like this, check every character

FF00: D8 58 A0 7F 8C 12 D0 A9

FF08: A7 8D 11 D0 8D 13 D0 C9

FF10: DF F0 13 C9 9B F0 03 C8

FF18: 10 0F A9 DC 20 EF FF A9

FF20: 8D 20 EF FF A0 01 88 30

FF28: F6 AD 11 D0 10 FB AD 10

FF30: D0 99 00 02 20 EF FF C9

FF38: 8D D0 D4 A0 FF A9 00 AA

FF40: 0A 85 2B C8 B9 00 02 C9

FF48: 8D F0 D4 C9 AE 90 F4 F0

FF50: F0 C9 BA F0 EB C9 D2 F0

FF58: 3B 86 28 86 29 84 2A B9

FF60: 00 02 49 B0 C9 0A 90 06

FF68: 69 88 C9 FA 90 11 0A 0A

FF70: 0A 0A A2 04 0A 26 28 26

FF78: 29 CA D0 F8 C8 D0 E0 C4

FF80: 2A F0 97 24 2B 50 10 A5

FF88: 28 81 26 E6 26 D0 B5 E6

FF90: 27 4C 44 FF 6C 24 00 30

FF98: 2B A2 02 B5 27 95 25 95

FFA0: 23 CA D0 F7 D0 14 A9 8D

FFA8: 20 EF FF A5 25 20 DC FF

FFB0: A5 24 20 DC FF A9 BA 20

FFB8: EF FF A9 A0 20 EF FF A1

FFC0: 24 20 DC FF 86 2B A5 24

FFC8: C5 28 A5 25 E5 29 B0 C1

FFD0: E6 24 D0 02 E6 25 A5 24

FFD8: 29 07 10 C8 48 4A 4A 4A

FFE0: 4A 20 E5 FF 68 29 0F 09

FFE8: B0 C9 BA 90 02 69 06 2C

FFF0: 12 D0 30 FB 8D 12 D0 60

FFF8: 00 00 00 0F 00 FF 00 00

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I went back to my eBay

I went back to my eBay history, to find out that I bought the proms from you Macintosh_Nik (in February)

So I'll assume it's been properly tested.

I have already ordered a new 47pF capacitor. I don't have any spares. I will test changing it. In the mean time, I will provide a high res picture of front and back as soon as possible, and a video of the official manual test program running. I'm using a modern keyboard attached with a appleII to usb keyboard and a cable I modified, but I already know it's not the issue since it does the same with just a jumper between 15 and 16 in the socket and a short to clear and reset (and a jumper between the PIA and the  6502 to avoid random chars)

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Hi Ben_Aveline!

Then you don't have to worry about PROMs. If you bought this in February, you are one of my last buyers.

 

I would also like to make sure that your keyboard adapter is not causing this phenomenon. It would be great to check how ClearScreen works (pins 12 and 16 have to be shorted in the keyboard connector) and Reset without it (pins 1 and 9). It is better to do it with some old button and a couple of wires.

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Pictures of the board

Yes, I tested without keayboard, with a jumper between 15 and 16 and a wire to briefly short between pins to ClearScreen and then Reset, with the exact same output.

Here are large pictures (clickable) of my board: 

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Hi Ben_Aveline!

Is 1ЛБ554 a legal replacement for 7410? I understand this is a Soviet microcircuit, in my records I found that К155ЛА4 = 7410...

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It's the same, but yeah, it's

It's the same, but yeah, it's one of those I'm still waiting for the real reference to be delivered. I must confess I've had a hard time finding all the exact IC references for months and I took some replacement chips sometimes, which I'm trying to replace now. I'm not surprised that with "almost" the right chips, it "almost" works :D

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I desoldered the 47pF and

I desoldered the 47pF and measured it. It reads 21pF. So I guess I'll wait for the new ones to be delivered. You pointed at it several times, I should have verified it earlier. My bad

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I've changed the 47pF

I've changed the 47pF capacitor and the two 1ЛБ554 for two 5410 I had spare (7410 for military use), and still the same issue.

In the mean time, I'm trying to understand more about the whole thing. I came accross this webpage.

Here is a video I made for everyone to see what happens when I type in.

I typed the program given by the manual, trying to ignore weird things on screen: 

0:A9 0 AA 20 EF FF E8 8A 4C 2 O (RET)

0.A (RET)

R (RET)

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Reliability mod
Ben_Aveline wrote:

I've changed the 47pF capacitor and the two 1ЛБ554 for two 5410 I had spare (7410 for military use), and still the same issue.

In the mean time, I'm trying to understand more about the whole thing. I came accross this webpage.

Here is a video

I think you probably have power spikes on +12 -12 +5 -5 lines.  Did you test components before and after installing on the bare unpopulated board?  Specifically the 22 uF capacitors? I would suggest adding the 6 resistors on the bottom of the board as shown in post #4 of this link.  You probably won't need the small capacitors shown all over the board.

 

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

 

Justin

 

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