3 posts / 0 new
Last post
Last seen: 2 hours 15 min ago
Joined: Apr 1 2020 - 16:46
Posts: 950

Welcome to another "secret trick" of Uncle Bernie. Now, this trick is in the public domain and not "secret" anymore, but I'm sure you will find it useful.


Consider this situation: 


You have just finished all the soldering work your newest Apple-1 build. Now you have a PCB with empty IC sockets, but all other components soldered in place. Now, how to proceed to avoid a lot of frustration, pain and suffering ?


This is the procedure:


Step 1)  Check for shorts on the power supply rails


Take a multimeter to the yet unconnected PCB, set it to the "Conductivity" setting (sometimes a "diode" symbol to test the forward voltage of a diode) and check that none of the power supplies has a short to another one. This is where to find them:


+12V: any DRAM pin 8

+5V: any DRAM pin 9

GND: any DRAM pin 16

-5V: any DRAM pin 1

-12V: 2513 character generator, location D2-3, pin 1


You have to check the conductivity between all pairs of these five nets, which are 10 combinations. Any conductivity is a fault condition. Some multimeters beep if they see a short. This is a great feature which costs you $1 to $5 more when you buy the instrument. Be aware that the charge / discharge of the electrolytics will give brief beeps or show conductivity for a while. Just be patient. If you see a "diode" forward drop of 400mV or more, that's OK. But you don't want to see a short.


Step 2): Trial power up with no ICs in sockets 


After you are sure there is no short between any power supplies, plug your PSU (the transformer cable) in and power it up. While doing so, keep the fingers of one hand on the cooling tabs or the body of all the four regulators and when any of those get warmer and warmer after powering up, immediately switch off the power supply and search for the problem. None of these regulators should get hot when no ICs are in the sockets. Be aware in some fault conditions you need to be quick with getting your fingers off the regulators, otherwise you will get a blister. And, if you wired up your transformers wrongly, you may get a shock and die. All your fault and your own stupidity ! I disclaim all liability for injury and death ! Don't try to sue me if you hurt yourself, be warned I will come after you with much more nasty tools if you ever dare to do that ;-)


If you survived so far, then measure all the four power supply voltages to be in spec. These regulators typically are specified to +/-5%, but most good ones are better than that, so if you see a larger error than maybe 3%, this deserves some scrutiny, try to find out what could be wrong or just change the offending regulator.


Now it's time to populate the IC sockets. There is a stupid way to do it, and there are two smart ways to do it.


Let me explain the stupid way first:


Step 3a):  The stupid way to populate Apple-1 sockets:


Plug in all the ICs you bought from surplus places, or found in your stock, or swiped from the floor of your lab. Then cross your fingers and turn the thing on. Most likely, it won't work. Even if you did all the reliability mods I propose here:

The reason is, these parts are old. They were living in a tube or a drawer or on your lab floor for decades. Some will be dead. Some will be limping wounded, which almost work, or work when the moon and the stars are in the right constellation. Some may be Chinese forgeries that are not the part which they pretend to be: too many people got fooled by these MM1404 from China found on alibaba which actually are only re-stamped 555 or some 8-pin opamp. They will only get hot and die in your Apple-1, but won't do their job as a shift register. If you bought one of these nice Rockwell 6502 with the crisp laser lettering from Chinese vendors off Ebay, you may be lucky if it's a 6502 but it may be of any speed grade, and almost certainly it won't be from Rockwell. It also might be just some random DIL-40 IC that was relabled. There are forged 2519 out there, too. But they are rarer as the forger at least needs to find DIL-16 ICs which have the grey mold compound used by Signetics in the 1970s. You can imagine that your chances to debug your Apple-1 build and get it working are slim if you have bought any forged parts. But even the genuine parts may be bad. I once had a problem with no video at all except for the sync. It took me hours to find the one bad 7432 at location C9. And I do understand how the circuit is supposed to work. Maybe it had been less waste of time to just swap ICs instead of trying to interpret oscillograms. Sometimes using brute force instead of brains is more efficient ...


There must be better ways. Here are two options:


Step 3b):  First smart way to populate Apple-1 sockets:


You were smart and have bought an IC set that has been tested for functionality in an actual Apple-1 build. This greatly enhances your chances of success: just plug them in, check that the correct ones are in the right sockets and properly oriented (not plugged in backwards), and you are good to go and power up your Apple-1 build. If you did a good solder job and used a quality PCB, it should work. At least you should get a video and CLR SCREEN and RESET should work. If the WOZMON crashes or behaves erratically, the most likely reason is a /CAS timing problem, which can be remedied by substituting the 27K resistor between locations B2 and B3 with a 50K trimmer. I prefer to use a combination of a 15K resistor and a 20K trimmer in series. You need either an oscilloscope to observe the 480ns pulse width of the oneshot or a DRAM test PROM to adjust this contraption. And, you did put in the reliability mods suggested by Uncle Bernie, and mentioned above, did you ? Otherwise all bets are off.


Step 3c):  Second smart way to populate Apple-1 sockets:


To go this way, you need a functional Apple-1 build that already has been sorted out and works, and your new build with the empty IC sockets. Set the functional build up complete with monitor, keyboard and transformers. The new build is not connected to anything. Power up the functional build we will call "donor" in the following.  Make sure it works. Power it off. Transfer a number of N ICs from the donor to the new build. Replace the N ICs in the donor. Power up the donor again, and see if it works. If it still does work, rinse and repeat, until all the ICs have been transferred from the donor to the new build. If it does not work, the culprit must be a bad IC in the last group of yet untested N ICs that just have been put back into the donor. Since N is a small number (I recommend 5) it's quick to find the bad ones, just replace them until the donor works again.  Once the donor works again, rinse and repeat, until the new build has all the ICs. At this point, all the known good ICs from the donor have been transferred to the new build. And the donor has got a new set of ICs, but since this set was tested incrementally, it also is known good, except for possible infant mortality, thermal problems, etc., but at least for a while, the donor should still work. It is now time to remove the donor from the bench and connect the new build to the monitor, keyboard and transformers to try it out. It's very likely it works the first time it was turned on. If it doesn't, follow the hints and debug procedures of step 3b) above. Once you know your new build is up and running, what is left is to fully burn-in and test both the new build and the donor, which takes a few days or weeks, depending on your standards. It is highly unlikely that the new build will develop problems during that period of time, as it has an IC set that already was burned in in the donor. But expect that at least sometimes, one or more of the yet unproven ICs of the donor may die during burn-in or it may develop faults: thermal faults being the most likely, appearing after the machine has warmed up. A can of electronics grade cold spray  comes very handy if you experience such thermal faults, it may help to identify and replace the offending IC quickly. Any such offenders should be widlarized to prevent them from coming back to haunt you in the future. But in the end, you will have two Apple-1 builds which are burned in and work well. In the next round, the new build with its now proven IC set becomes the donor, and the old donor is given back to the owner or sold or put into a nice wooden encasing. Do not use the same build as a donor again and again as this wears out the IC sockets.


These are all my "secrets" how I populate new Apple-1 builds with minimum effort and minimum time expenditure for hunting down and killing bad ICs. But make no mistake, even such an elaborate and refined plan does not always work without some problems popping up. But this is - so far - the best way to tackle the problems and potential pitfalls with these vintage ICs that may be nearly half a century old.


Comments invited !








Last seen: 2 years 2 months ago
Joined: Mar 31 2020 - 19:55
Posts: 848
Bernie, you should write a

Bernie, you should write a book on this and bring it to market. I think that it'd be a successful seller, and generally useful to anyone who wants to do this, binding all of your experience and advice into one volume. Your posts are always thorough and insightful, with a large amount of practical knowledge, and compiling them all into a publication would be fantastic.

Last seen: 2 hours 15 min ago
Joined: Apr 1 2020 - 16:46
Posts: 950
Dear "Timelord": I'm not going to write a book, sorry !

I don't think I'm qualified to write the "Definite Book of Apple-1", since I ain't no Apple collector at all, and certainly no "expert" on the Apple-1.

I learned about the Apple-1 only last year from a young man who invited me to fly as a safety pilot in his old and scary Piper Tomahawk he got for a song. Seems I was the only one at the airport willing to fly with him in this deathtrap as I'm old enough not to fear death anymore ;-) He mentioned the Apple-1 scene, and told me about the insane amount of money being paid for them, and that tempted me to try building a "real forged" one and auction it off at Bonhams, so I could buy myself the Eclipse 500 which I always had wanted so badly. Little did I know about the existence of "experts" like Corey ... and the damn thing I built as a learning exercise didn't work either, so my grand get-rich-quick plan was foiled. Facing extreme boredom due to the pandemic I then decided it would be a cool idea to investigate the design and building of Apple-1 clones, just to kill time while keeping my skills in electronics sharp. What I have posted above in in this thread is almost all I do know about the care and feeding of Apple-1.

I have built quite a few in the meanwhile, though, to test and refine my theories, mods and methods, and I will make a few more posts about solving some mechanical issues and the power supply unit. I may even make my toolkit available to the builder scene. But that's about all I intend to do in terms of building Apple-1. Writing a book, definitely: no! There are more qualified people out there who should do that !

Log in or register to post comments