Ibm pc 5150a..... Possibly a pre-release build???

[PCFreek]

No apology is expected/required from someone such as yourself, a 'learner'.

but I understand the need for clear and accurate posts. I do not want to waste your time when you are trying to help me... and I GREATLY appreciate the help. I read that the slow refresh can be the 8237 (DMA)... I am going to go ahead and unsolder that from the Olivetti clone. I am getting good at unsoldering and it helps hone my skills. Even if I don't need the chip, I feel like I am accomplishing something by unsoldering it : )

 

[PCFreek]

So now I am trying to correct the "slow refresh to 10000" failure. I have swapped power supplies with the working motherboard and that did not help. I broke pin 1 off the 8237 DMA chip from the Olivetti clone, but I have a 2nd Olivetti clone that I can cannibalize... if that is even a possible source of this error as I have read online.

EDIT: Never mind the DMA 8237 (U35)... that passed earlier in the diagnostic ROM test

 

[modem7]

So now I am trying to correct the "slow refresh to 10000" failure.

The bottom-right corner of the screen shot suggests that the problem is at 8000 (32 KB).

So now I am trying to correct the "slow refresh to 10000" failure. I have swapped power supplies with the working motherboard and that did not help. I broke pin 1 off the 8237 DMA chip from the Olivetti clone, but I have a 2nd Olivetti clone that I can cannibalize... if that is even a possible source of this error as I have read online.

Something in the back of my mind tells me that the "SLOW REFRESH" message in these diagnostics can be a red herring.
I think what the diagostics does is slows down the RAM refresh rate to something that it expects should still work (i.e. runnng at the speed spec of the RAM chips).
You could have a RAM chip that isn't quite up to spec, but runs okay at the speed that the motherboard BIOS runs the chip at.

What do you see on-screen if you remove the diagnostic and try the IBM BIOS chip ?

 

[PCFreek]

The bottom-right corner of the screen shot suggests that the problem is at 8000 (32 KB).


Something in the back of my mind tells me that the "SLOW REFRESH" message in these diagnostics can be a red herring.
I think what the diagostics does is slows down the RAM refresh rate to something that it expects should still work (i.e. runnng at the speed spec of the RAM chips).
You could have a RAM chip that isn't quite up to spec, but runs okay at the speed that the motherboard BIOS runs the chip at.

What do you see on-screen if you remove the diagnostic and try the IBM BIOS chip ?

No cursor or anything... I also tried minimum diagnostic configuration and get no beeps. I get other memory failure codes so I need to address that: 08000, 00E80, 00E84, and 00E86 (different errors with each run of the diagnostic utility). I have replaced the parity chip on bank 2... will replace it again as I still get the 8000 error.

I have read the RAM note on minuszerodegrees and assume that the combo of codes above indicate chips 1, 2, and 7 in bank 0.

Edit: 8000 obviously does not indicate bank 2 parity chip. I mis-read that...

 

[PCFreek]

By piggybacking RAM onto chips in bank 0 I get the 16k critical memory to pass intermittently.
I replaced all of bank 2 and still get the 8000 error.

 

[modem7]

I knew the SLOW REFRESH error was a red herring. I just got the reason wrong.

I was able to produce the screen shot that you last posted (at post #118) simply by removing the bit 0 chip in bank 2 of a working 16KB-64KB motherboard.
So the "16K CRITICAL MEMORY REGION" failure can be misleading, as can be the "SLOW REFRESH" failure.

As expected though (because the first 16K of RAM is good), if I then restored the original IBM BIOS ROM, at power on, I saw a 201 memory error followed by "PARITY CHECK 1".

You are seeing different error addresses each time you run the diagnostic. That suggests a much larger issue than one or more faulty RAM chips.

 

[PCFreek]

I consistently pass the 16k critical memory test (at least the last 6 or so power cycles anyway), but it does not display anything to the monitor with the regular BIOS chip in U33. I do feel like I am chasing my tail sometimes as chips I have replaced with known good chips (0400 and 0C00) still report errors and I still get the 8000 error. Another oddity... sometimes the U28 passes and sometimes it fails but it is always empty.

EDIT: U28 only seems to fail when 16K critical memory passes.
EDIT 2: Occasionally fails the 16k critical memory test... I tell myself that this is due to the piggybacking not being a perfect solution, but I am not sure.

 

[PCFreek]

You are seeing different error addresses each time you run the diagnostic. That suggests a much larger issue than one or more faulty RAM chips.

It actually cycles through these errors during diagnostics, not different ones each cycle... although some do change. Example: 0E80, 0E84, 0E86 do not always pop up every diagnostic cycle. It is usually one or 2 of these.

I consistently get 8000 and 8001 even though I have replaced all of bank 2.

I probed chip U12 (LS245) and see pulses on all pins 1-9, but few pulses from pins on the 11-20 side. the pulses that I do get are random as if it is only when processing certain data?

 

[modem7]

Another oddity... sometimes the U28 passes and sometimes it fails but it is always empty.
EDIT: U28 only seems to fail when 16K critical memory passes.

With no changes to the motherboard, I am seeing that test sometimes pass and sometimes fail.
If we had the diagnostic documentation, it may even point out the peculiarity, indicating that one should only worry about a negative result if U28 is in place.

 

[modem7]

I probed chip U12 (LS245) and see pulses on all pins 1-9, but few pulses from pins on the 11-20 side. the pulses that I do get are random as if it is only when processing certain data?

Yes, some pins are only 'active' during specific events.

 

[modem7]

but it does not display anything to the monitor with the regular BIOS chip in U33.

The diagnostic screen shows that switches 5 and 6 on SW1 are being read correctly (set to CGA).

Because the base 16K RAM test only passes sometimes, you will need to try a few power ons, hoping that the test passes on one of the power-ons.
Did you try a few times, or only once ?

 

[PCFreek]

After snuggly piggybacking bank 0, I am down to 2 errors:
memory refresh (which prevents the diagnostic routine from continuing the tests on the left side of the screen)
and slow refresh... the red herring...

the only memory error I get now is: 0000 and 8000... can you narrow down which bank/chips that indicates?

EDIT: I'm dumb... bank 0 parity chip is now piggy backed... no more memory errors... slow refresh passes, but memory refresh still FAILS

 

[PCFreek]

Because the base 16K RAM test only passes sometimes, you will need to try a few power ons, hoping that the test passes on one of the power-ons.
Did you try a few times, or only once ?

I have power cycled it repeatedly without success with the BIOS installed even after it says "no memory errors" as noted in #132.

I still get occasional memory errors that are resolved when I apply pressure to the piggy backed chips. I believe that I should solder them in and go from there.
Any idea why the "Memory Refresh" would fail? I can only assume this is what prevents the machine from booting with the regular BIOS ROM inserted.

I am calling it a night tonight... thank you for all of your help.

 

[modem7]

It would be good to get the diagnostic documentation. I expect that that would detail what exactly is being done in each test. Without that, we can only make educated guesses.

I can see that if certain tests fail, the diagnostic skips certain other tests. That makes sense. For example, failure of the 16K CRITICAL MEMORY REGION test results in the diagnostic skipping 13 tests, going on to the SYSTEM MEMORY TO 10000 and SLOW REFRESH TO 10000 tests.

SYSTEM MEMORY TO 10000 is I believe a check of RAM from 16 KB to 64 KB (the 16K CRITICAL MEMORY REGION test having done a check of the first 16 KB).

SLOW REFRESH TO 10000 is I believe the above test done at a slow refresh rate, designed to detect RAM chips that don't quite meet spec.

But there are apparent bugs. For example, if I remove a chip from bank 2 of a good 16KB-64KB motherboard, I see:

16K CRITICAL MEMORY REGION -- FAILED
SYSTEM MEMORY TO 10000 ----- PASSED
SLOW REFRESH TO 10000 ------- FAILED

Instead, I would have expected to see:

16K CRITICAL MEMORY REGION -- PASSED (because the first 16 KB is in fact good)
SYSTEM MEMORY TO 10000 ----- FAILED
SLOW REFRESH TO 10000 ------- N/A (no point doing a slow refresh test if the 'normal' test fails)

Any idea why the "Memory Refresh" would fail?

I guess that the MEMORY REFRESH test is now being done against your motherboard because the 16K CRITICAL MEMORY REGION test now passes.

Again, the diagnostic documentation would I expect tell us what exactly is being tested. Perhaps MEMORY REFRESH is a 'slow' refresh on the first 16 KB. I'm guessing.

I can only assume this is what prevents the machine from booting with the regular BIOS ROM inserted.

It is hard to say. The Supersoft/Landmark diagnostic (having the entire ROM to itself) will be doing testing that the IBM POST does not do.

 

[PCFreek]

It is fixed!! Passes all appropriate diagnostic tests and boots to Basic with the BIOS ROM inserted. Apparently, piggybacking the faulty RAM chip in Bank 0 allows it to pass memory tests with no errors, but prevented the "Memory Refresh" from passing. The faulty chips, even when piggy backed, also apparently prevented it from booting to Basic.

Thank you so much to glitch for the diagnostic ROM and a few very helpful PM's, and a big thanks to modem7 for walking me though this every step of the way...

 

[PCFreek]

To update modem7's database for faulty components, this motherboard had:

Faulty U26 (74LS175) - Motorola (detected w/ logic probe: no data pulses from pin 10)
Faulty U41 and U43 (4116) - both Texas Instruments (located w/ diagnostic ROM as it actually displays the bad bits. Confirmed by piggy backing.)

Of interest: on the 2 very early motherboards that I have, I did not find any AMD 9016 chips that were known to be bad. I did replace all of the Bank 2 9016 chips, but the same memory error persisted (8000) after the swap. Apparently, the diagnostic ROM reports an 8000 parity error for any bad chips in Bank 0.

On the later motherboard the I repaired, the 4164 was made by NEC. The percentages look good for the AMD chips thus far.

 

[PCFreek]

I have two 1981 motherboards. One has fixed chips (not counting removable RAM) with date codes from 8022 through 8137... the other has fixed chips with date codes from 8114 through 8140. On the underside, the PCB's themselves also have a date code machined on the back: 8135 and 8138... both are also marked 94V-0, Pc-A-0 in green with the numbers 5000866 soldered into the corner between the power supply plug and keyboard plug. There are noticeable differences between components on the two (color of the board itself, color of relay, color of capacitors, design change in the potentiometer near the power supply plugs...). How can I upload high resolution images to this site? Would anyone be interested in these photos?

EDIT: this thread was originally titled "possible pre-release build???" That question has been answered definitively. PCB of the earlier machine was manufactured in week 35 of 1981 so the motherboard PCB was created the week of August 24, 1981... early build, but not pre-release.

 

[Ole Juul]

How can I upload high resolution images to this site? Would anyone be interested in these photos?

Don't. It just makes it so that someone has to log in to see it - and that's a nuisance. It's generally best to host images elsewhere and just link. I find photobucket works, but there are many more free services. The thing about those services is that it saves hosting high bandwidth items yourself - or here, for that matter.

 

[PCFreek]

I finally figured this out... Here you go. If you click on a photo and then download it by clicking "options", you can zoom in considerably.

[URL=http://s150.photobucket.com/user/ebigon/media/P1017768_zps8ad195fb.jpg.html]


[/URL]

 

[modem7]

To update modem7's database for faulty components, this motherboard had:
Faulty U26 (74LS175) - Motorola (detected w/ logic probe: no data pulses from pin 10)
Faulty U41 and U43 (4116) - both Texas Instruments (located w/ diagnostic ROM as it actually displays the bad bits. Confirmed by piggy backing.)

Web page updated.