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Problems about repairing a PC/XT 5160 motherboard

OctSL

OctSL

Member
Joined
Feb 26, 2022
Messages
39
Location
Fuxin City, LN China
Hello,everyone

This is my first post. I'm new here.

In these days, I bought a 5160 motherboard. It cannot enter the normal display state (but there is a signal on the data bus). I tried to troubleshoot the problem and found that many circuits were disconnected. However, it still does not work after connecting. The ROM address is found stuck in E188 through the test. After checking the Technical Reference, it is found that it is stuck in code C24B (page 5-117), which is about memory work. I changed the BIOS to skip this step (I'll see if it's the problem caused by this step), and it didn't get stuck at this address. I'm sure it must be a memory or memory circuit problem. So I tried to replace the memory chip and replace it with the original BIOS, and found that it was still stuck at this address. However, the motherboard has no circuit disconnected. How can I troubleshoot the chip next?

Thanks for any help with getting this computer working again!
 
Welcome to the forum @OctSL !

You've got yourself quite a project, there. I can't tell from the pictures, but did that board suffer from a leaked battery? If you haven't already seen them, here are some YouTube channels that go through the process of searching for and repairing damaged traces and vias, and the process for finding problems:

CuriousMarc's IBM PS/2 77 restoration (featuring TubeTimeUS):
Adrian's Digital Basement:
Epictronics' Commodore PC-10 extreme battery damage repair:
Necroware repairing a 286 motherboard:

Apologies if you already know all this. I've learned a ton watching videos like these.

- Alex
 
I see that you have the ability to substitute the motherboard's IBM BIOS ROM with code of your choosing.
- Does the Supersoft/Landmark Diagnostic ROM (see [here]) display anything ?
- Does Ruud's Diagnostic ROM (see [here]) display anything ?

If those diagnostics do not display anything, then do all 13 steps at [here] produce the expected results ?

( BTW. Today, I will be testing a new version of Ruud's Diagnostic ROM, one that is expected to fix the "163 KB" bug seen in version 2019-07-23. )
 
modem7 said:
I see that you have the ability to substitute the motherboard's IBM BIOS ROM with code of your choosing.
- Does the Supersoft/Landmark Diagnostic ROM (see [here]) display anything ?
- Does Ruud's Diagnostic ROM (see [here]) display anything ?

If those diagnostics do not display anything, then do all 13 steps at [here] produce the expected results ?

( BTW. Today, I will be testing a new version of Ruud's Diagnostic ROM, one that is expected to fix the "163 KB" bug seen in version 2019-07-23. )
Click to expand...
Thanks a lot for your helping! I will test it now.
 
modem7 said:
I see that you have the ability to substitute the motherboard's IBM BIOS ROM with code of your choosing.
- Does the Supersoft/Landmark Diagnostic ROM (see [here]) display anything ?
- Does Ruud's Diagnostic ROM (see [here]) display anything ?

If those diagnostics do not display anything, then do all 13 steps at [here] produce the expected results ?

( BTW. Today, I will be testing a new version of Ruud's Diagnostic ROM, one that is expected to fix the "163 KB" bug seen in version 2019-07-23. )
Click to expand...
On the SuperSoft ROM, it beeped HI/LO 5 times and short 9 times first(VGA card failure), then beeped HI/LO once and short 7 times(about short: fourth was long but not short, seventh was so long that it did not stop)
On the Ruud's ROM, it beeped once and POST card displayed FF in the end.
What should I do next?
 
OctSL said:
On the Ruud's ROM, it beeped once and POST card displayed FF in the end.
Click to expand...
I presume that you are writing of an ISA POST card. Note that modern ISA POST cards are not expected to work in an IBM 5160, irrespective of what code is sending POST codes. More information about that is at [here].

The single beep is a good sign, although we cannot assume that it is the beep produced by step 25 at [here].

You don't have MDA or CGA video capability? That is expected to show a screen like the one at [here].

If you can get yourself one of [these], that will display the checkpoints codes that Ruud's ROM outputs as it progresses through its checks. And it can display the output of custom code, such as TEST6055/TEST6000/TEST6077 at [here].

OctSL said:
On the SuperSoft ROM, it beeped HI/LO 5 times and short 9 times first(VGA card failure), then beeped HI/LO once and short 7 times(about short: fourth was long but not short, seventh was so long that it did not stop)
Click to expand...
From experience, I know that relying on the beeps from the SuperSoft ROM can be very misleading.
A screen display is ideal, and for the Supersoft ROM, MDA or CGA is required (although EGA sometimes works for the Supersoft ROM).

OctSL said:
What should I do next?
Click to expand...
Get yourself one of [these].

In the meanwhile:
1. Do you see the toggling produced by TEST6083 at [here] ?
2. Do all 13 steps at [here] produce the expected results ?
 
modem7 said:
I presume that you are writing of an ISA POST card. Note that modern ISA POST cards are not expected to work in an IBM 5160, irrespective of what code is sending POST codes. More information about that is at [here].

The single beep is a good sign, although we cannot assume that it is the beep produced by step 25 at [here].

You don't have MDA or CGA video capability? That is expected to show a screen like the one at [here].

If you can get yourself one of [these], that will display the checkpoints codes that Ruud's ROM outputs as it progresses through its checks. And it can display the output of custom code, such as TEST6055/TEST6000/TEST6077 at [here].


From experience, I know that relying on the beeps from the SuperSoft ROM can be very misleading.
A screen display is ideal, and for the Supersoft ROM, MDA or CGA is required (although EGA sometimes works for the Supersoft ROM).


Get yourself one of [these].

In the meanwhile:
1. Do you see the toggling produced by TEST6083 at [here] ?
2. Do all 13 steps at [here] produce the expected results ?
Click to expand...
Though modern POST cannot work here, it showed 07 when beeping on Ruud's ROM.

I used TEST6083 and TEST6082, the corresponding pin is HIGH, but it did not jump to LOW.
Should I replace the 8255 or the 8253?
 
My video card is ISA Super VGA. I have not got a CGA or MDA monitor, it's rare.
Actually, nothing displayed on the VGA monitor on Ruud's ROM or Supersoft's.
Is there a ROM can use VGA video card?
Thanks!
 
Last edited:
Yes, you can use a GBS-8200/8220 to convert from CGA to VGA.

If you want good quality, you can use the excellent GBS-control, available here:
github.com

GitHub - ramapcsx2/gbs-control

Contribute to ramapcsx2/gbs-control development by creating an account on GitHub.
github.com github.com

Documentation on GBS-control, including how to build the hardware, is here:

Welcome to the gbs-control wiki! · GBS Control

Welcome to the gbs-control wiki! Intro GBS Variations RGB Potentiometers Si5351 Clock Generator install notes ESP8266 adapter Hardware Mods Library...
ramapcsx2.github.io ramapcsx2.github.io

- Alex
 
OctSL said:
Though modern POST cannot work here, it showed 07 when beeping on Ruud's ROM.
Click to expand...
Per [here], if you step back through the received codes, you expect to see {00}{01}{02}{03}{04}{05}{06} before the {07}.

OctSL said:
I used TEST6083 and TEST6082, the corresponding pin is HIGH, but it did not jump to LOW.
Should I replace the 8255 or the 8253?
Click to expand...
Not at this point. The code in TEST6083 is small, and I was curious to see if it worked for you.

Given the information that you have presented so far, I think there may be a problem related to the address and/or data buses. Do all 13 steps at [here] produce the expected results? That is not a complete test of the address and data buses, but if you do not see the expected results, the result can lead the way to identifying the problem cause.
 
modem7 said:
Per [here], if you step back through the received codes, you expect to see {00}{01}{02}{03}{04}{05}{06} before the {07}.


Not at this point. The code in TEST6083 is small, and I was curious to see if it worked for you.

Given the information that you have presented so far, I think there may be a problem related to the address and/or data buses. Do all 13 steps at [here] produce the expected results? That is not a complete test of the address and data buses, but if you do not see the expected results, the result can lead the way to identifying the problem cause.
Click to expand...
After some adjustment, I can hear the beep clearly on Supersoft's ROM. The beeps are valid.
Feedbacks(HI/LO+Shorts):
1. 5+9: Cannot initialize monitor
2. 1+8: 16K critical memory region(known)
3. 3+4: System memory at address 00000
After a while,
4. 4+1: System BIOS
5. 4+2: BASIC ROM 1
Then jump to step 2 and start the cycle.
I noticed that from the second cycle, it added a beep event(3+5: Slow refresh at address 00000) between step 3 and step 4.
What's wrong with it?
 
As I guess, there is a problem with Base 16K RAM.
I have changed the RAM chips many times.
How do I troubleshoot memory problems next?
 
OctSL said:
As I guess, there is a problem with Base 16K RAM.
I have changed the RAM chips many times.
How do I troubleshoot memory problems next?
Click to expand...
Do you have a means to independently prove that the memory chips you’re using for swaps are good?

I used one of these to prove bad 4116 and 4164 memory in my 5150 and to validate the replacement stock I bought from EBay also was working correctly.
 
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