Here's an anecdote to take to the bank. I have a Rev D ][+ board that was previously damaged and malfunctioned. A while back, I restored it, tested it, did a full burn in, RAM tests, the lot, and it passed them all. I put it into a static bag and put it on a shelf.
Today, when I was putting a board in a system, I selected that one first, as I had marked it 'Restored, 100%, 48K'. After I completely installed the board, I powered it up, and.... Screen of rubbish characters. Might be the 9334, but my point in all of this, is that I did not first bench test it again ere installing it. IDK what would have gone bad in two months sitting on a shelf, but I marked the bag 100% burn in verified--and this board had some suspect issues originally where it had phantom problems that some standard chip swaps seemed to cure.
The takeaway, is even if you tested something two months earlier, test it again ere spending the time installing it.
Shelf time is cruel sometimes.
I've run into that situation more than once. I suspect that it miche be socket or cold-solder joint related. Or maybe a flakey 9334, who knows?
I've got a Microsoft 16K card that doesn't work at all when it's cold. The computer doesn't even recognize that it's there.
Within a minute it's recognized but fails. Over the next minute or so RAM tests performed show fewer and fewer errors until the errors disappear.
Once it's allowed to warm up for evan 3 minutes it works perfectly and passes every single test I can throw at it.
I've been chasing that one for weeks, but since I can only test it when it's stone cold my testing windows are extremely short.
Sounds like internal IC breakdown such as the lead weld to the actual silicone internal to the IC has given up the ghost. Likely makes connection with thermal expansion. My guess anyway.
Very probably an issue that dissipates with heat. Pretty sure that this is what you are pointing toward, and it may likely be this. It's just annoying.
I suppose, that if I solve this, I might post about it, but it isn't high up on my prior5ity list. I more or less simply wanted to share my little anecdote and move on. I have three ][/][+ boards not in cases: One I know is fine, the second (the board in question), I thought was fine, and the third is a misfit Rev 4 board that needs a lot of reworking. I spent one good working board to make me Beltron functional, until I can diagnose and repair the Beltron mainboard, if that ever occurs.
I need one for a B&H, but I expect this to be the story of these boards. Every system that I have had, maintained, or worked on since it was new never had any issues and works as new to this day. Everything that I receive as trade or buy 'as-is' is horribly broken.
This isn't some sort of 'help me' topic. It is more or less me venting about stupid things, such as not triple-checking the working status of a board ere spending an hour installing it. If I had more members on the Apple 77 Discord server, I would have posted it there, but people (for whatever reason) join that, then leave b/c there isn't activity; b ut the only way to generate activity is for people to sign up and post. I suppose that it doesn't appeal as much as forums, and that part, I understand.
I am starting to hate this board. Working perfectly, failed, working perfectly, failed in another way. The CPU is not running (no beep, random RAM on screen), and I am starting to think it might be the NE555 or the Q5 transistor; or the LS02 at A12, but until I fix my oscope or get another one, I am using this cheap chinese multifunction digital probe that likes to power itself off after two minutes, which suffice to say, is particularly irritating.
I need to invest in a 74xx series IC tester, so that I know if the ICs that are on the PCB, or if the ICs that I am using to swap in are good or not. All of the RAM that I am using tested good, but until I have samples of bad 4116s to check if the tester finds internal faults, IDK if I can trust it. (I did try several other 6502s and none changed a thing, so I doubt that the CPU itself is dead unless I am cooking each one that I tested. I suppose I can test the CPU on a known good board next for now.
I have some //e KBs to finish, so I will work on those this week and decide if it is worth investing more time on these boards or if they are to become donors for the future. I would have liked to kept one ][ or ][+ board as a loose PCB for my bench, but if not, fine.
I am pretty sure that a bad 9334 cannot cause a no beep situation, ever. If I am mistaken, feel free to correct me, but I am out of spares for that part, and I have stolen a lot of them off of Disk ][ cards, so I need to resupply.
I don't think the 9334 would cause that issue - it's used for video mode switching.
Probably it's one of the video shift registers that aren't switching properly.
The TL866-II IC programmer works pretty well for testing a lot of 74-series logic chips.
Here's the list from the product website (http://www.autoelectric.cn/EN/index.html)
4000 4001 4002 4007 4009 4010 40106 4011 4012 4013 4015 4016 40161 40162 4017 40174 40175 4018 4019 40193 4022 4023 4024 4025 4026 4027 4028 4029 4030 4031 4034 4040 4041 4042 4043 4044 4048 4049 4050 4051 4053 4066 4067 4068 4069 4070 4071 4072 4073 4075 4076 4077 4078 4081 4082 4093 4099 4501 4503 4506 4510 4511 4512 4514 4515 4518 4519 4520 4529 4532 4543 4572 6821 7400 7401 7402 7403 7404 7405 74HC05(OD) 7406 74HC06(OD) 7407 74HC07(OD) 7408 7409 7410 74107 74109 7411 74112 74113 7412 74123 74125 74126 7413 74132 74133 74136 74137 74138 74139 7414 74140 74147 74148 74149 7415 74151 74153 74154 74157 74158 7416 74160 74161 74162 74163 74164 74165 74166 7417 74173 74174 74175 7418 74181 74182 74190 74191 74192 74193 74194 74195 7420 7421 7422 74237 74240 74241 74242 74243 74244 74245 7425 74251 74253 74257 74258 74259 7426 74260 74266 7427 74273 7428 74280 74283 74292 74293 74294 74298 74299 7430 7432 7433 74354 74356 74365 74366 74367 74368 7437 74373 74374 74375 74377 7438 74386 74390 74393 744053 7440 7442 7447 7450 7451 7452 74533 74534 74540 74541 7455 74563 74564 74573 74574 7458 74589 74595 74597 7460 7461 7462 74640 74643 74646 74648 7465 74688 747266 7473 7474 7475 7476 7485 7486 7490 7492 7493 7497 8155 8255 8259 8279
And if you're willing to pay just a bit more to get one really fast you cna order it from Amazon.
It sucks at programing 2716s but it's dirt cheap and does a lot of other programmable ICs fairly well.
That happens to me with my Apple II and II+ boards. I don't use them regularly, but every few years I pull them out and usually none of them work right. Typically just working chips around in the sockets makes it work again for a while. Rinse and repeat.
I think it's the ROM sockets typically, but sometimes others. It's just oxidation...
Entropy gets all electronics (and us) over time.