This procedure was written for the IBM 5150 (IBM PC) motherboard.
You are here because you believe that there may be a faulty RAM chip/s in bank 0.
Click here to see a diagram that shows the four RAM banks.
Vintage RAM chips have a relatively high failure rate. The failure of any chip in the 5150's first bank of RAM (bank 0) results in what appears to be a 'dead' motherboard. (Of course, the 'dead' motherboard symptom has many possible causes.)
In the IBM 5150, RAM failure in bank 0 is not easy to diagnose because the bank 0 chips are soldered in.
Technical:
This is because the power-on self test (POST) within the IBM BIOS ROM tests the first 16 KB of RAM, and if found faulty, the POST will halt the 8088 CPU, and to you, the user, the motherboard will appear to be 'dead'. (No video, no beeps, nothing.)
Step 1 of 4 - Examination of RAM chips in bank 0
If you acquired the IBM 5150 motherboard in a faulty state, then you need to cater for the possibility that a previous owner may have done a bad repair to bank 0:
1. Verify that all RAM chips in bank 0 are soldered in the correct orientation; and
2. Verify that all RAM chips in bank 0 are compatible with the IBM 5150 motherboard. See here.
3. Look for bad soldering.
Step 2 of 4 - Isolation
There is a slight possibility that a RAM chip in a bank other than 0 has failed in such a way as to cause a problem reading/writing to bank 0.
So, remove the RAM chips from the banks other than bank 0, leaving only bank 0 populated.
If this step failed to get the motherboard displaying anything on-screen (including only a cursor), then try the next step.
Step 3 of 4 - Piggybacking
The 'piggybacking' technique will sometimes diagnose this particular problem, but because of the hit-and-miss nature of the piggybacking technique, use of a diagnostic ROM is very much preferred. Still, worth a try.
If this step failed to get the motherboard displaying anything on-screen (including only a cursor), then try the next step.
Step 4 of 4 - Diagnostic ROM
At this point, we have to say to ourselves, is there really a RAM bank 0 problem?
Well, if there is only one problem, and it is in RAM bank 0, then the use of a suitable diagnostic ROM in socket U33 (replacing the existing IBM BIOS ROM) will reveal that.
For RAM bank 0 problems, the recommended diagnostic ROM to use is "Ruud's diagnostic ROM". If there is a faulty RAM chip in bank 0, Ruud's diagnostic ROM will display what is shown at here. The use of that ROM on a 16KB-64KB motherboard is described at here.
The Supersoft/Landmark diagnostic ROM is not recommended because of RAM related bugs that are seen when it is used on the 16KB-64KB motherboard. And in regard to RAM related errors, it can be quite misleading.
For RAM bank 0 problems, the recommended diagnostic ROM to use is "Ruud's diagnostic ROM". If there is a faulty RAM chip in bank 0, Ruud's diagnostic ROM will display what is shown at here. The use of that ROM on a 16KB-64KB motherboard is described at here.
The Supersoft/Landmark diagnostic ROM is not recommended because in regard to RAM related errors, it can be quite misleading.