• Please review our updated Terms and Rules here

Need help with flaky 2001-N

K

KevinO

Experienced Member
Joined
Apr 13, 2012
Messages
435
Location
Des Moines, IA USA
Hello everyone! Been a while since I've been here, but this is where I come when I have PET problems, because all the knowledge is right here!

I've got this hermaphrodite 2001-N that I'd like to get working. It's in an 8032 case, but it has the 9" monitor. Someone must have put this together with various parts they had on hand. Maybe I'll find some new badges for it so it ends up looking more authentic, but I have to get it working first.

I've fixed this thing once before. But then it failed again later on, so I'm back at it. Right now I have it booting, but no keyboard at all. If I press down even slightly on the board anywhere around the C row, the cursor stops flashing. So do I need to be looking for a bad connection/socket/trace around C7 8520? Do I have that right? Swapping the 8520s makes no difference. Just need a sanity check to see if I'm in the right neighborhood.
 
Well, shoot. Looks like I have bigger problems than I thought. I had Tynemouth's RAM/ROM board (5-dip switch version) installed, and thought I had everything switched out. It turns out that the system only boots if SW4 is in the ON position. I thought that if SW1 and SW2 were switched OFF, I was booting from the stock ROMs, but that's apparently not the case. It does NOT boot with only the 6502 installed. I don't think I remember exactly how this thing works. Does anyone have the user guide for the 5-switch version? I found the 9-switch version online, but not mine. Not sure what SW4 is replacing, but my ROMs (3 replaced and 1 original) all sumcheck ok on my 8032, so I'm not entirely sure what's happening, but I evidently have more than one problem here.

UPDATE: I've checked all the data and address lines to the 74LS244 Buffers, and from those to the ROMs. Also the /CS1 lines from 74154, and everything looks good. Tomorrow I'll check and see if the ROMs are getting selected.

20260401_202754.jpg
 
Last edited:
So it was a PET that was never diagnosed or repaired properly and operating on a diagnostic pcb and with 2732 on adapters rather than 2532's too. It will be a lot of fun to fix this PET and rid it of its bandages and crutches and hopefully get it back to working healthy order.
 
Last edited:
ScottishColin said:
The instructions for the 5-dip switch version are here:


If you only have switch 4 on to boot then there's something interesting going on as that would choose BASIC 2, but only if Switch 2 were on. With switch 2 off, then 3,4 and 5 should have no effect.

The settings signified by switches 3,4 and 5 are on the sticky label on top of the ROM.

Colin.
Click to expand...
Ok, I'm not crazy then! Well, not about THAT anyway. That's exactly how I had understood it. Wonder if I've got a bad DIP switch. I'll check those when I get home from work today. Thanks for the link! I know that is around here somewhere on paper, but I'll be darned if I can locate it.
 
Hugo Holden said:
So it was a PET that was never diagnosed or repaired properly and operating on a diagnostic pcb and with 2732 on adapters rather than 2532's too. It will be a lot of fun to fix this PET and rid it of its bandages and crutches and hopefully get it back to working healthy order.
Click to expand...
Well, I'm the one that replaced 3 ROMs with 27xx on adapters years ago, and as of last night, those all sumcheck ok in my 8032 (plugged in with adapters and all), which isn't necessarily comprehensive, but it's a good quick test.

Also, I only installed the RAM/ROM adapter the other day when I pulled it out of storage and it wasn't booting, just for a quick diag to see what was what. I agree, the RAM/ROM adapter is not a repair, I couldn't just install that and walk away and call it fixed!
 
If the cursor stops flashing, then you are looking at an interrupt issue. Definitely around the 6520 (C7).

If you have an oscilloscope, check pins 18 and 37 of C7.

Pin 18 is the regular interrupt from the video circuitry (that initiates reding of the keyboard and flashing the cursor).

Pin 37 is the interrupt pin to the CPU.

They should both be 'ticking away' nicely. if one (or both) stop, then investigate further as to why.

Since you have EPROM adapters in there, you could replace the EDIT ROM with my freely-available PETTESTER ROM to run some diagnostic tests (not the same as is on the ROM/RAM board you have though).

Dave
 
I agree, put the CPU back in its socket and put in Dave's PETTESTER ROM. Also, when you have removed the RAM/ROM board, double check that the pins on it have not damaged the IC socket. You can check that by taking a pin from a defunct IC, soldering it to a small wire handle, and for each socket claw checking/feeling that there is still reasonable tension/friction on the pin.

I particularly like this Dynamic PET board, it is the one I designed my diagnostic system for, to find faulty soldered in DRAM chips, but, Dave's PETTESTER can too, if it is interpreted correctly.

 
Last edited:
Ok, I think I should focus on the not booting issue first. We can come back to the other issue, assuming there are two different things.

Took the RAM/ROM tester out and went back to just a known good 6502

On the PETTESTER ROM, do I use the adapter or no? Sorry I can't recall...in between fixing these things, I seem to forget everything. I've got it burned onto a 2716, and it definitely works when plugged into my 4032, but not the 2001, with or without the adapter.
Just the standard garbage screen.
Also, other ROMs need to be removed, or left in place?

I can't thank you enough for your help on this!
 
The 2716 is good with Dave's PETTESTER file in it, it doesnot require an adapter.

The 2716 is also good in for the Character rom, witih a small change involving the /INIT connection. All the others, to avoid headaches should be the TMS2532 (not the TMS2532A and not the 2732 to avoid adapters)
 
You need the Kernal ROM installed at address $Fxxx and the PETTESTER ROM installed in place of the EDIT ROM at address $Exxx.

Remove the other ROMs.

Check CPU pin 7 for activity if this doesn't work.

If no activity on CPU pin 7, check all of the power supply voltages, the /RESET signal on CPU pin 40, and the CPU clock pins for a 1 MHz clock.

Dave
 
Hugo Holden said:
The 2716 is good with Dave's PETTESTER file in it, it doesnot require an adapter.

The 2716 is also good in for the Character rom, witih a small change involving the /INIT connection. All the others, to avoid headaches should be the TMS2532 (not the TMS2532A and not the 2732 to avoid adapters)
Click to expand...
 
Hugo Holden said:
The 2716 is good with Dave's PETTESTER file in it, it doesnot require an adapter.

The 2716 is also good in for the Character rom, witih a small change involving the /INIT connection. All the others, to avoid headaches should be the TMS2532 (not the TMS2532A and not the 2732 to avoid adapters)
Click to expand...
This is a good idea. I'm ordering some of those on Ebay right now. No reason not to. I have enough old Commodores that I will undoubtedly use them. Whether my programmer can handle them is another question! Then I can eliminate the adapters!
 
daver2 said:
You need the Kernal ROM installed at address $Fxxx and the PETTESTER ROM installed in place of the EDIT ROM at address $Exxx
Click to expand...
daver2 said:
Remove the other ROMs.

Check CPU pin 7 for activity if this doesn't work.

If no activity on CPU pin 7, check all of the power supply voltages, the /RESET signal on CPU pin 40, and the CPU clock pins for a 1 MHz clock.

Dave
Click to expand...

Because I am 6 hours behind you, we usually end up waiting a day for response, but I wanted to jump in and say that I tried the PETTESTER, but since it was 6AM when I did it, I missed also having the Kernal ROM also plugged in! So my bad on not being able to read first thing in the morning.

But I wanted to tell you about the other signals:
I have good pulses on CPU pin 7
/RES looks good on Pin 40
CPU Clock looks good on pins 37 and 39
PS Voltages are good.

Anyway, this is a PARTIAL update, more later when I get home from work.
 
No problem, I know what you mean...

>>> I missed also having the Kernal ROM also plugged in!

I know this is not the way things are usually done - but I assume you have a copy of my fairly extensive PETTESTER manual, and at least read the first few pages?

Sorry, couldn't resist...

Dave
 
Dave, you KNOW the answer to that question. You don't even have to ask! Of COURSE I haven't read the manual.

<hangs head in shame>

Sorry! But I am getting some luck now. Imagine that, following directions! I promise next time we chat, I will have read the manual.
EDIT: Now that I'm looking at it, I HAVE read this, but forgotten everything I read. At 59, my memory is so bad that I wonder how long until my wife puts me in a home!
 

Attachments

  • 20260403_150800.jpg
    20260403_150800.jpg
    1.8 MB · Views: 8
  • 20260403_150820.jpg
    20260403_150820.jpg
    1.6 MB · Views: 8
  • 20260403_150813.jpg
    20260403_150813.jpg
    2 MB · Views: 8
Last edited:
So, looking better.

Most tests are passing by the looks of it.

I would put the other BASIC ROMs back in now (obviously not the EDIT ROM - leave the PETTESTER in).

Check that the ROM checksums are correct. Although the Kernal ROM checksum doesn't look right off the bat - but I haven't checked my own documentation either!.

EDIT: Ignore that last part. I have checked my own documentation now. A checksum of 7C98 is OK for the BASIC 2 Kernal ROM.

Dave
 
Last edited:
Put all the ROMs back in and here's what I get. Looked up your documentation and they look ok. What about the EDIT ROM? Can I test that by dropping it into another socket? I didn't see the checksum listed though.
 

Attachments

  • 20260403_211949.jpg
    20260403_211949.jpg
    1.9 MB · Views: 10
That's fine. I assume the ROM checksums are stable throughout the test?

Did you check the keyboard out on that screen also?

Also, did you leave the DRAM test run for (say) 20 (hex) iterations to thoroughly test it out? You do have 16K of RAM fitted don't you?

Dave
 
You must log in or register to reply here.
Back
Top