Hi all, me again. I am really appreciative of everyones help with things so far. Unfortunately one of my problems got worse!
The machine has never liked sitting since trying to resurrect it, if I leave it overnight unplugged, the next day it will often fail to start without fidding.
I could never figure out what exactly caused it to happen, but removing cards seemed to get it to boot, and after lots of switching it off, unplugging drives from the disk controller, plugging different ones in, swapping things around, etc, it would boot with the disk controller card inserted again. And with the video card, I could unplug it, it would boot, then I could turn it back off, plug it in, and turn it back on again. The disk controller was more commonly the "issue" though.
However it is now doing that with no expansion cards installed, I can't get it to boot at all. I even took the language card out and put a RAM chip from it in the socket where it had previously plugged into the board.
I removed and re-inserted every chip I could get access to, all the RAM chips, the ROMs, the CPU, and all the others, aside from the ones under the keyboard which I can't access without taking the machine fully apart.
If I remove the CPU and power the machine on it behaves exactly the same...
I feel like this might have been my original issue where the cards were causing it not to boot, so it was the machine itself not the cards. (the Videx issue remains though, of course)
Any ideas? Pulling out my hair lol. The RAM including the language card, and all the ROM chips tested OK a few days ago.
Two things I've noticed.The autostart ROM is also on the language card. Does that need to go in the F8 slot with the language card not installed? And also, I'm going to test the PSU with a multimeter tomorrow (its 1AM here now) From what I've read, the PSU is the most likely candidate to be causing an issue like this? If nothing else it will be something else I can eliminate.
Yes, you need to put the autostart ROM in F8.
Thanks, it's sorted now!
PSU tested OK, I just had to reseat all the chips on the language card.
There is definitely some kind of loose connection somewhere. I managed to get it to where if I poked the board one way it stopped booting, and then I poked it the other way it booted again, but that was only a brief phenomenon.
What confuses me is once it is working, it will switch off and on and off and on as many times as needed for the entire usage session.
But when left overnight, powered off at the wall, the next day it won't boot again, having not touched anything inside.
I tested the power supply voltages and have 12.77v, 5.36v, -502v, -11.74v. That seems a little bit out to me, the positive voltages especially. Could that cause issues like this? I am going to test the voltages again tomorrow because I thought I saw 17v from one of the pins. I'm wondering if something happens to the PSU when it sits, and it is unhappy on a "cold start"
There is likely an issue with a socket, pcb trace or an internal chip fault that is temperature related.
If could be any one of the three and is difficult to diagnose. Sometimes you can find the casue of the issue by strategically spraying each chip with "cold spray".
I have a 16K expansion card that does not work cold. It works after about two or three minutes of power-up time.
I can run language card diagnostics over and over and watch as it returns fewer and fewer errors until it passes all tests and works perfectly.
I can then use the card without issue, but if it is allowed to cool down it stops working again.
I have tried over and over to find the cause of the fault and in the end I just gave up and use it as it is.
Ah that sounds like a likely but annoying possibility...
I really want to get this thing working basically 100%
It is a fun little project, but I was really hoping it wouldn't be *too* extreme.
I did think about cooking the whole board to hopefully reflow any very slightly iffy solder joints, but I don't want to risk further issues... It worked for Nvidia 8000 series GPUs... Lol
There is definitely an issue which is linked to the Disk II card.
Sometimes with the card inserted it wont boot, but it will with it removed.
However other times (most of the time) the machine will boot with the card inserted, as long as there is no drive connected to the card.
As soon as I connect a drive to the card, it will fail to boot. (I have tried two seperate working drives)
Just now, it would not boot with a drive connected, but would boot without.
So I moved the card from slot 6 to slot 7, with a drive connected, and the machine booted. Doing PR#7 made the drive seek.
However then once I turned it off, and back on, it wouldn't boot with a drive connected when in slot 7 either...
It started having issues with the Apple Disk II drive first, and I could only use the third party drive. But now neither will allow it to boot.
I have tried swapping some chips on the Disk II card with ones I had in stock. The LS05, LS174, LS132, and the NE556. No change.
I have, with no load (power supply not connected to motherboard) 12.83, 5.41, -5.06, -11.80
Not perfect, but I think its in the "close enough" realm.
I can't test it while connected, I'll have to find some thin probes.
The voltage is fine under load, I rigged up some wires so I can easily test it.
OK so, the machine is at the point now where everything is inserted, and it is almost completely working (knock on wood) but this no beep issue still plagues it at times.
Currently the repeatable issue for days has been that the machine will start up just fine with no drive connected, but will fail to boot with the drive connected.
People pointed me to the power supply, so I set up some probes so I can monitor the voltage at any point, and as soon as the power is switched on, the correct voltages are coming from the PSU.
I haven't tested the voltage at the disk II card yet though, I suppose there might be a drop somewhere between it and the power supply. Which pins do I need to probe?
Look up the pinout of the slots. Make sure you're getting power on the power pins of the slots, especially slot 6. Test with and without the card (careful testing with it in especially).
I do think it is partially a temperature related problem. Or capacitance, or something? Because it doesn't boot when it is "cold". But if I switch it on, leave it for 5 minutes, then switch it off and back on, it boots.
When cold or after warming up, +12v and +5v look absolutely fine on the slots, with or without cards installed, almost exactly 12v and 5v respectively.
The negative voltages look a little less happy but still within spec I believe? At -12.79v when cold and -12.69v when warm, and -5.42v when cold, and -5.38v when warm.
Card insertion / disk drive connection doesn't seem to make a difference.
When you first turn the computer on after being off over night, what is displayed on the screen.
Have you tried just pressing Ctrl Reset to see if it starts ok.
Do you have another working Apple PSU that you could swap.