• Please review our updated Terms and Rules here

Faulty 8032 - Sodick

J

Jannie

Experienced Member
Joined
Feb 5, 2017
Messages
273
Location
Cape Town
This machine is the 5th in a batch of 5 faulty 8032 boards I'm slowly making my way through with lots of help from this forum and - especially - the Daves. :)
Sodick-1.jpg

Turning it on gave no display. Did hear a very garbled startup tone though. Supply, reset and clock all looks fine.

- The CRTC did not give any sync outputs, so replaced the CRTC and then got H and V-sync on the outputs of the CRTC but still no picture.
- This was caused by the V-Sync level on the video connector sitting at about 1V, even though the input to the XOR is a nice 5V 50Hz. Assumed it's the XOR failing, so replaced the 7486 but the output was still being pulled low by something.
- The only real place V-Sync goes is to the two IRQ inputs on the VIA and Keyboard PIA, so took a guess and lifted the VIA from this signal. This restored the V-Sync to TTL levels and I now get a (very garbled) picture. Removed the VIA completely at this point.
Sodick-2.jpg
Watching the screen, I can see the startup prompt is printed (it's just a complete mess) so the machine is at least booting (with a RAM/ROM replacement card in place.). The Tynemouth PET Diagnostics also print to the screen (again, just super messy).

Would this output indicate something more fundamental than just faulty VRAM? (I did replace the Character ROM with same results.)
 
It could be the VRAM or the bus buffers to VRAM. Is it consistent or does it change each time you reset?
If it is consistent, does it change when swapping the VRAMs around?
Dwight
 
If the image is static, the vram has to be partially working. If it wasn't, the image would constantly change as the video output read stray capacitance off the data bus.

it may help to look at each character and document what the bit pattern is. You might find a stuck bit or two.

Definitely out of my depth on this, just throwing ideas out there.
 
I feel the Dave PETTESTER ROM needs to be installed in place of thecEDIT ROM.

I know exactly what that should be displaying on startup.

But yes, it could be address decoding, video data bus buffers, video RAM or a host of other problems yet...

But you got the video working on your own. Well done for achieving that!

Dave
 
Thanks all,

I had to call it a day earlier just when I got the video to come up. Will tackle the video circuit tomorrow, taking all your feedback into consideration.

I need to make a ROM replacement card that contains Dave's latest PETTESTER. I *think* the version in the Tynemouth ROM replacement board I'm using is far older than the current (V4?) one Dave's got.

I'll map the actual vs expected characters tomorrow, maybe it just is a faulty bit or two in each of the ODD/EVEN VRAM banks.

PS @daver2, also not getting an interrupt coming out the PIA, kinda like deja vu... :) But first want to clean up the display.
 
Last edited:
Chuck(G) said:
Can't help you much with your problem, but is this the same Sodick that manufactures wire EDM tools?
Click to expand...

No, not at all. :)

I'm repairing this machine for a friend, named Sodick. I tend to call the machines by either their owners name or the person from whom I got the machine. Helps to not get confused when working on a number of different machines. :)
 
Got a bit distracted on this repair, especially by a friend who arrived wit a Junior Computer he built up and we had to get going, so that was lots of fun. :)
Stephen-01.jpg
This specific board is interesting as the person who made it, literally traced the original Elektor layout, i.e. it was not a layout done from a circuit diagram. Only found 1 fault in the layout which is actually quite impressive as it was all done visually.
 
To pick up on 'Sodick, the last post above showed a very corrupted display even though I could see the machine running (to some level).

Looking at the display, it seemed that there were faulty bits in all 4 the 2114s, so I started replacing them one by one. With every replaced 2114, the display cleared a little bit till all 4 were replaced and I now get a (nearly) clean screen. There still is a '@' character somtimes visible in the top left corner.

But, now I can see the PETs output.

Original display:
Sodick-10.jpg

After replacing 1st 2114:
Sodick-11.jpg

After replacing all four 2114s:
Sodick-12.jpg

Much better, but some faults immediately evident. :(
 
Last edited:
Running the Tynemouth PET diagnostics board, shows the "stuck bits" on D1, D6 & D7 as per above.

It also shows the CRCs of all the ROMs as "Inconsistent".
Sodick-13.jpg

When plugging the RAM/ROM replacement board in, and with all the ROMs remapped, I get the boot prompt but no cursor due to no interrupt being generated.
Sodick-14.jpg

This is beginning to look suspiciously like the issues we had with the previous 8032 board, "Gary", i.e. something interfering on the data bus and causing the 'stuck bit' and CRC errors.
 
Taking the above symptoms and the experience with the previous 8032, plus the fact that 3 data lines are consistently reported as stuck, I (carefully) removed all the ROMs from the board, assuming one or more of them might be causing the issue.

However......fat chance.....

Now, with all the ROMs gone from the main board, I still get the same stuck bits and inconsistent CRC errors. :(

And, even more unexpected, with the RAM/ROM board in place, the ROM replacement board now boots into the Monitor. :shocked:

Sodick-15.jpg

Am I correct in understanding the PET will boot into the monitor if it can't find the BASIC ROMs?

If so, (and clearly the BASIC ROMs are present in the ROM replacement board), does this mean the main board is interfering with the ROM select of the ROM replacement board?

Basically, what could cause the main board to interfere with the ROM replacement board?

Or, could it still be something interfering on the data bus as shown by the stuck bits report? The RAM seems to be passing tests. Could it be ROM address selection?

Any ideas will be appreciated. :)

I've started tracing the address selection on the ROMs, so far the 154 looks fine, working my way down the circuit.

(PS: I did test the ROM replacement board in a working PET. It *seems* to be working fine.)
 
Last edited:
The ROMs enter the debug monitor when the DIAG pin of one of the I/O devices (I can’t remember exactly which at the moment) is active.

EDIT: UB12 (6520) PA7. This is also an output, and feeds UD5 pin 2 for the sounder.

This could also be as a result of a duff data bus bit...

Dave
 
Ah....that's why I hang out with the clever people :)

/off to measure and test, tx! :)

PS: I just created a new thread re the PETTESTER, if you could weigh in there, please Dave.
 
I pulled the KB PIA but the 'stuck' D1, D6 & D7 did not go away, so I pulled the IEEE PIA as well and replaced both of them with new 6821s.

This cleared all the stuck bits and the machine now boots to the welcome prompt and with a flashing cursor!

Attached an SD drive and could load and run Space Invaders after putting the 8032 into 40 column mode. :)

Sodick-20.jpg

So, it all looks good, but the machine is not stable. Every now and then when I turn it on, there will be no display even though I get the startup chirp.

Next post shows the Pet diagnostic board output. A new stuck bit appeared and there's clear instability with the Diagnostics board installed.
 
To recap, the board is currently in the following state:

1. CRTC, both PIAs and VIA replaced. All these were faulty with the possible exception of the IEEE PIA but I replaced it in any case.
2. All four the 2114 VRAMs were replaced. They were definitely faulty.
3. All the onboard ROMs are removed at this point. Onboard RAM still in place and passing diagnostics.

With a ROM replacement board in place, the machine boots and works, BUT not every time. Sometimes I just get a blank screen. Rebooting then recovers and machine boots correctly. This is quite infrequent.

However, with the PET diagnostic board, I consistently get the following two (possibly three) errors:

1. An '@' character in the top left corner of the display. This appears on most (but not all) of the PET diagnostics screens. It specifically does not appear when the two character maps are printed by the diag board. Furthermore, it does not appear when the ROM replacement board is installed and the machine boots to the normal startup message.

2. Bit D5 of the data bus is now reported as 'stuck high'. Previously it were 3 other bits.

Sodick-21.jpg

3. With no ROMs on the board, the PET Diagnostic report a checksum of B7BE, which is what I always see for an empty ROM slot. However, the Edit ROM slot (which is empty), consistently reports a checksum of 584A. If I plug an Edit ROM into the socket, the diagnostics detect it correctly and displays the correct checksum for it. Could this different checksum just be a function of the slightly more complex chip select circuit for the Edit ROM (or similar) or could it point to another issue?

Sodick-22.jpg

I think if I can first find what's causing the '@' appearing in the top left of the display, it might also resolve the 'stuck' D5.

Thoughts? Also, are there good disk-based diagnostics utility that could help tease this out? I've seen some on Zimmers but not sure which ones are good.
 
I managed to get the PETTESTER working (as per separate thread) and I noticed it also displays the '@' character top left.

Sodick-25.jpg
(Sync issue caused by 60Hz image)

This at least confirms the PET Diagnostic board output that shows the same character (I was beginning to wonder if the diagnostic board might be at fault.)
 
A PETSCII code 00 is an '@'... So this doesn't actually 'prove' anything.

If you can get BASIC to run OK, try and POKE various characters to the top left hand side of the screen and see what you get.

Dave
 
Yup, will do.

When the PETTESTER writes the PETSCII character set to screen, what character should I expect in the first location? (top left).

I see the '@' is the character right before 'a', according to the PETSCII tables.

So, is it normal for PETTESTER to write @ as the first character?

50Hz-1.jpg

I.e., is it coincidental that PETTESTER write the exact same character to the same screen position that the diagboard displays?
 
You must log in or register to reply here.
Back
Top