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Nice PET but garbage screen

MikeS: Yes, the computer is labeled 4032 on the front. I haven't checked the back side. Wasn't there two series of those: one with 9" monitor and graphics keyboard, one with 12" monitor and business keyboard? Frankly I'm not fully educated in this business, just trying to pick up bits here and there. The board I ended up installed in the same computer has the same part/assy number but different ROMs, featuring lower case letters.
 
Well, until now I always thought that all 4032s used the 8032 board, and the list at the Amiga site seems to confirm that (i.e. both 9" and 12" 4032s both show the same board).

But if your PCB is the same number as Tezza's then that's all that matters; either someone replaced the board in that 4032 or CBM labelled some 2001N/3032s as 4032s. Not the only confusion in their numbering history... ;-)

Let's see if Philip can use it to debug the other one; I'm mildly curious myself what's stopping that CPU.
 
Jus thought I'd let the people following this thread that I now have the board Anders sent me.

It looks in very good condition, with indeed the same formfactor as the old one. See the picture below. Apart from one bank of ROM being socketed, the only other difference from memory (as the PET is with Philip right now) is that there are three ROM sockets empty. I think mine only had two empty, but I could be wrong.

2009-01-24-new-pet-board.jpg


I'll be driving over to see Philip tomorrow, and we'll see if this replacement board can help us diagnose what's wrong with the original one.

Tez
 
The empty sockets are for application ROMs anyway. Now when I think about it, I believe this is a 2001/3000 series board since it has three empty slots. Lately I read that newer 4000/8000 series boards only has two such application ROM slots. Compare jumper settings J4 and J10 with the old board.
 
It works!

It works!

Hi Tezza here posting under under Philip's username (and from his place):

Progress! Here's what we've found:

  • The board Anders supplied works just fine. No jumper changes were needed.
  • The board Andres supplied is exactly the same type as the original board.
  • The problems in the original board were the 2114 (which Philip diagnosed and changed) AND one of the ROM ICs (we don't know which one). We determine this by swapping the ROMs over. When we did the old ROMS in the Anders board gave the same symptoms as the original board (i.e. boot failure).
  • The ROMs in the original board were BASIC 4.0 while the ROMS in Anders board were 2.0! This means the working ROMS (the BASIC 2.0 ones) are more authentic for the 3032. Good stuff.
  • The keys on the PET don't all work (some are intermittent) but this is probably just a cleaning issue.

More later.

Tez
 
Keyboard

Keyboard

Tezza's been working on the keyboard. From having nearly all keys NOT working, now we have all keys working - albeit a few are a bit stubborn. Perhaps with use, they'll improve.

We used Brasso on the PCB pads and a pencil on the rubber conductive key surfaces.

We've also swapped out the Character ROM, as it was Swedish (there were 3 differences on alpha characters that we found).

All in all a happy PET.

Philip
 
PET photo

PET photo

Well, here it is, now working just as it should...

2009-01-25-commodore-pet-working-large.jpg

This was a real team effort. Apart from myself it involved Philip Avery, who spent many hours isolating and diagnosing the problem(s) on the original board, Anders Carlsson, who kindly sent me a working replacement and all the guys who gave moral support and contributed ideas through this forum.

As always, I'll write up the detail in a repair blog. You never know who might find it useful. I'll also add a blurb on the PET to my collection site soon.
 
Your next project should be to restore your old board, build a video adapter and keyboard adapter, hook up a different power supply and get another, monitor-less PET. I kind of tried that before, found a few diagrams on video adapters but none worked that well. One may need a very special monitor to handle the frequency. Keyboard should be somewhat easier, also power supply.
 
Well, the video is only a problem for folks like Anders & Tezza who live in PAL countries; for us North American folks using NTSC it's no problem at all.

But if you can find a "standard" ten-pin computer monitor or an NTSC-compatible TV it shouldn't be a big problem. A small AT-type PS should work, and PET keyboards and/or PS/2>PET converters are available as well; find a nice unusual enclosure or build one and you'd have a real conversation piece.
 
Post Mortem

Post Mortem

Now that we have found the main cause of trouble with the old board is ROM(s) failure, Tezza & I are both curious if it is only one ROM & which one has failed - there are 4 possibles.

At first I suggested just calculate a checksum on each suspect ROM & compare to that of a good ROM (probably in VICE emulator as the new board's ROMs are different, albeit correct for this model of PET).

But it would be good to know 'how much' of the ROM(s) has gone bad. Is it just a single byte, or an Address or Data line gone down/rusty? What we now propose to do is place each ROM one at a time in a spare socket on the running PET & dump it's contents (probably to cassette), then read back & compare byte for byte in VICE. Then, we maybe able to replace just the faulty component in the spare board - the ultimate repair.

Secondly, remember this:
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.
Click to expand...

Well, when we got the old board working - it still had this fault. About 12 positions on the mainly blank boot-up screen, flashed rapidly alternating between say a 'blank' and another character.

We replaced one 2114 Video Ram previously, but I assume the other one has a few 'sticky bits' causing this. Is that a fair assumption?

Lastly, to satisfy our curiosity we reinserted the faulty 2114 (with stuck data line), just to see what the display would look like. It was pretty much as we anticipated. A photo of this, and more details will appear in Tezza's blog.

Thanks to posters (particulary Patscc), as I wouldn't have attempted the board repair without your knowledge & help. Thanks to Anders for bringing it to a timely end.:D

Philip
 
jitter

jitter

pavery said...flashed rapidly alternating between say a 'blank' and another character
Click to expand...

Earlier somewhere, I've lost track of the thread, didn't you mention something about jitter on one of the lines going to the 4114's ? Anyway, you might try using the R/W signal going to the video RAM area as trigger to see if you spot something weird on either the address or data lines to the 2114's.

After you're done with the ROM, you should make it into a button or tie-pin or something.

patscc
 
patscc said:
Earlier somewhere, I've lost track of the thread, didn't you mention something about jitter on one of the lines going to the 4114's ? Anyway, you might try using the R/W signal going to the video RAM area as trigger to see if you spot something weird on either the address or data lines to the 2114's.
Click to expand...

Well, I was getting a faster signal on the data lines of the new 2114, but it may have been a signal of 1010101 as opposed to 11001100. Just strange that two 2114s start off so differently. We didn't do any scoping once the board was working. Maybe... if we get the ROM(s) rectified... and had the old board back in the PET - then we would re-scope the 2114s & sort that fault too.

After you're done with the ROM, you should make it into a button or tie-pin or something.
Click to expand...

Tezza oughta start a Shrapnel Jar.

Philip
 
latch

latch

pavery said...faster signal on the data lines of the new 2114
Click to expand...
From what I recall tezza posting, the new is a mite faster, so it'll settle quicker, but that should get smoothed out by the latches. Do you see any jitter on the character ROM address lines ?

patscc
 
pavery said:
..What we now propose to do is place each ROM one at a time in a spare socket on the running PET & dump it's contents (probably to cassette), then read back & compare byte for byte in VICE.
Click to expand...

Does anyone know of any diagnostic/ROM-verification programs out there already? I don't think it would take much to write one, but if something is already be out there we could use or adapt it would be quicker.

Actually a diagnostic program which checked out the machine generally (RAM, ROM, etc,) would be nice. Anyone know of one available as a cassette image, which could be converted to audio for loading into the PET?

Tez
 
patscc said:
From what I recall tezza posting, the new is a mite faster, so it'll settle quicker, but that should get smoothed out by the latches. Do you see any jitter on the character ROM address lines ?

patscc
Click to expand...

The PET has left the Hospital and been transferred to the Rest Home (Tezza's place). No scope at Rest Home.

After Tezza has played around with his PET (remember neither of us have ever used one before), downloaded software, etc, then he is allowing me to borrow it for a while so I can evaluate the thing.
I'm particularly interested in seeing it's graphics abilities on it's little beady 9" screen. We may resume action on the old board then.

What were the unforgetable PET games & graphics programs we should be looking at?

Philip
 
You can find a set of PET games here:
http://www.portcommodore.com/petfiles.php?path=main-cbmidx-petidx

Some of those may be repeated here:
http://zimmers.net/anonftp/pub/cbm/pet/games/english/index.html

As you probably has found out, there is no native way to redefine the character set so all programs would have to do with C= character graphics. It took 30 years (!) before Nils Eilers built a 3rd party hardware expansion that will let you load custom graphics.

Regarding diagnostics, I don't know one off-hand. I have come across some harnesses to connect onto the CPU, I/O ports etc which should be usable to get on-screen diagnostics but I never had a chance to try them. Correct me if I am wrong, but wouldn't an EPROM programmer be able to read a real ROM too, given the proper settings? At least it appears some of the ROM slots on the PET would accept either a ROM or an EPROM (2532?).
 
graphics

graphics

pavery said...graphics abilities
Click to expand...
From the schematic you've all been staring at so long, the 2114's act as a page buffer for a page of text, and the data drives the address of the char. ROM.
So, if it ain't in the ROM, it ain't drawin' it.

patscc
 
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