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Nice PET but garbage screen

I'd also make sure that the buffers (that would be E7 and E8 ) separating the video logic from the cpu bus is working as they should. If they are defective, by either letting data through although they are disabled or forcing a data pin in some direction, it would garble the data on the data bus while the processor is reading data from the PROM's.

/PacMan
 
E7 & E8 & general question

E7 & E8 & general question

PacMan said...(that would be E7 and E8 )
Click to expand...
I think they've already done this somewhere along the line, at least, I've made a note that they've checked that, so it might just be me misremebering. Anyway, would that bring the bus grinding to a halt, expecially since it isn't happening immediately ?

Anyways, a question for the original fearless duo:
Further suggestions are probably going to go in the direction of injecting pulses at various parts of the board, so unless you're really motivated to fix the board...
And another question, assuming you guys really want to fix the board, can you guys get hold of a pulse/function generator ?

And one last question, which might have already been answered, so please forgive me if I missed it, and that's supposedly the PET has a built-in diagnostic mode. Have you guys heard of that and tried running it ?

patscc
 
tezza said:
Anders's board should be here soon.
Click to expand...
I get the feeling you should already have it?

Code: 
   Time     Date    Status 
 9.23 PM  12/01/09  Picked up  
 8.41 AM  14/01/09  Left country of origin  
11.53 AM  19/01/09  Arrived in New Zealand  
 7.00 AM  20/01/09  Delivery Complete  
Your item has been successfully delivered.
 
Progress ?

Progress ?

While checking system ROMS, I found no power at D9 (F000-FFFF) at Pin 24 (but there was at Pin 21). Another clean of pins of that ROM has restored power to the chip. The display has changed somewhat. Still a screen of garbage, but about 12 different character positions change rapidly (like 5 times a sec). Too quick for a normal cursor. They appear to alternate between 2 different chars. It's always the same 12 positions (after Resets) and they are positioned all over the screen.

The Address & Data lines appear to no longer hang.

The SEL line of D9 appears to flicker active after Reset, then stays inactive. The other SEL to D5-D8 appear never to go active.

Perhaps I shall have a further clean of the other socketed chips?


patscc said:
Possibly the binary representation of the character set. Let me ask you a question. What are you triggering off of when looking at the waveforms ?

You've tried all the obvious stuff, like reseating the ROMS & character ROM, right ?

At this point I'd go get a cup of coffee or a lager, and start checking the SEL lines going to the sytem ROMS (pin 20 on the ROMS) (Don't know if you've done this yet).
Pick a line, reset, observe, next line, etc.

Too bad you guys don't live closer.

I'd also solder a wire to something, or a switch, or something like that so you can do a reset without turning it on/off, if you haven't done this already, so that you don't fry your CRT.

patscc
Click to expand...

Using Auto Trigger off Ch 1, off + edge. Yeap, got a Reset switch going.

Philip
 
patscc said:
When you guys did the repeated cleanings, did you pull the socketed chips out at all ?
patscc
Click to expand...

Philip, it looks like you're making progress.

I pulled out all socketed pins initially and cleaned the pins with fine sandpaper. Then re-inserted them.

Tez
 
carlsson said:
I get the feeling you should already have it?

Code: 
   Time     Date    Status 
 9.23 PM  12/01/09  Picked up  
 8.41 AM  14/01/09  Left country of origin  
11.53 AM  19/01/09  Arrived in New Zealand  
 7.00 AM  20/01/09  Delivery Complete  
Your item has been successfully delivered.
Click to expand...

Cool, then it's probably waiting for me at my local Post Office. I'll check there tomorrow morning.

Tez
 
Corrosion pt. 2

Corrosion pt. 2

Do you have a magnifying glass to check and see if the inside contacts of the sockets are corroded as well, or is it just the IC's ?

patscc
 
patscc said:
Do you have a magnifying glass to check and see if the inside contacts of the sockets are corroded as well, or is it just the IC's ?

patscc
Click to expand...

Philip has the machine but from memory the sockets (like the rest of the board) did not appear to be in the best of shape. I did work the ICs up and down a bit when I re-inserted them to ensure a clean connection and perhaps knock off some of the corrosion but I didn't dose them with any kind of solvent. Maybe I should have?

Tez
 
pins

pins

Well, the pics I went back and looked at looked pretty bad. I was wondering if perhaps some pins might have actually been corroded through. However, all that speculation can wait until you've got the ROM's from the new board in.
patscc
 
Why not try to use the new board as it is, possibly replacing the character generator ROM? At least it is fully tested working, only matter is whether the jumper settings match Tezza's model.
 
New board & sockets

New board & sockets

carlsson said:
Why not try to use the new board as it is, possibly replacing the character generator ROM? At least it is fully tested working, only matter is whether the jumper settings match Tezza's model.
Click to expand...

That's Tezza's call - he may well just do that. On the other hand, the new board provides us with known good ROMs. We could try those in this board. If it turned out we just need another ROM we could probably get that, then Tezza would have two good boards :D

Well, the pics I went back and looked at looked pretty bad. I was wondering if perhaps some pins might have actually been corroded through. However, all that speculation can wait until you've got the ROM's from the new board in.
patscc
Click to expand...

I've just pulled all socketed ics, scraped the pins with a knife - all good. Have reinserted & checked continuity from all pins to circuit board (track side). Still no change. :(

Philip
 
pavery said:
That's Tezza's call - he may well just do that.
Click to expand...

In many ways it's Philip's call as he's doing all the hard diagnostic work! :)

pavery said:
On the other hand, the new board provides us with known good ROMs. We could try those in this board. If it turned out we just need another ROM we could probably get that, then Tezza would have two good boards :D
Click to expand...

Yea, that's the aim really. To get two working boards or at least know what components ARE faulty. Pets are so rare here, it's always good to have a stock of known WORKING spares. Given the very tidy condition of the case and video, it's worth it.

Tez
 
For what it's worth, I've always found it safer to pull chips from a defective board and try them in a known good board instead of the other way around.

Since whatever killed a chip in the first place (corrosion shorted traces, solder ball shorts, etc.) may still be in place on the defective board, it may save killing a known good chip.

Bad chips in a good board will be immediately obvious and you can just shut it down instead of slowly cooking a good chip on a bad board.
 
Druid6900 said:
For what it's worth, I've always found it safer to pull chips from a defective board and try them in a known good board instead of the other way around.

Since whatever killed a chip in the first place (corrosion shorted traces, solder ball shorts, etc.) may still be in place on the defective board, it may save killing a known good chip.

Bad chips in a good board will be immediately obvious and you can just shut it down instead of slowly cooking a good chip on a bad board.
Click to expand...

Thanks Druid6900. I'd say that's worth quite a bit, that advice. I had it mind.

When the other board arrives, I would like to: study it & compare it *very* carefully with the other board to ensure ROMs, jumpers etc are correctly placed. I do realise it is a 4032 not 3032 board, but I believe the difference is just ROM contents.

Then once the PET is going on new board, try socketed chips from old into new - I guess one at a time.

Back to old board: Tried invoking Diagnostics (taking Pin 5 LO on User Port J2) - no change.

Philip
 
On this other forum I started a discussion:
http://landover.no-ip.com/pet/forum/index.php/topic,505.0.html

Check the link posted there:
http://www.amiga-stuff.com/hardware/cbmboards.html

Scroll down to PET 2001, 4xxx, 8xxx, 9xxx. As far as I know, the 3000 series seems just a relabeling of 2001N. The Schematic 320349-01 and PCB fabrication 320350-01 is consistent through a lot of models, only the PCB Assy number differs. I believe this is what is known as the universal board? It was pulled from a 4032 with graphics keyboard, but has Basic 2. As you probably already know, the schematics to 320349 can be found at Zimmers.net FTP. There is some jumper information, although very sparse.

Good luck!
 
pavery said:
Thanks Druid6900. I'd say that's worth quite a bit, that advice. I had it mind.

When the other board arrives, I would like to: study it & compare it *very* carefully with the other board to ensure ROMs, jumpers etc are correctly placed. I do realise it is a 4032 not 3032 board, but I believe the difference is just ROM contents.

Then once the PET is going on new board, try socketed chips from old into new - I guess one at a time.

Back to old board: Tried invoking Diagnostics (taking Pin 5 LO on User Port J2) - no change.

Philip
Click to expand...
--------------------
Do I understand that you're getting a 4032 board? If so, it probably won't help much; AFAIK it's quite a bit different from the 3032, much more than just ROMs, although it should be a direct replacement.

Hmm, just read Anders' discussion and am now thoroughly confused and will be interested whether they are indeed similar; if it really came out of a 4032 it should be an 80320xx PCB and not a 320350, but I don't think 4032s ever came with BASIC2...

Maybe someone replaced the 4032 board with a 3032 (or maybe it's just one of those things ;-) ) And who knows what they did "over there"... ;-)

So, never mind; just get them working! Good luck!
 
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