IBM 5150(B) Motherboard or BIOS Differences?

[joekster]

I have two 5150's (64-256k). Both have the 1501476 BIOS (10/27/82). Both have been stripped down to a minimal config - 256k RAM on motherboard and no expansion cards. Both have the switch settings the same.

First system will work 100% with a 16-bit VGA card.
Second system will NEVER work with the same card. System is fine if a CGA card is used (and switch settings changed).

So, there has to be a difference - but what?

 

[SpidersWeb]

One has an 8088 CPU.
One has an NEC V20 CPU.

Something to check for.

 

[modem7]

One has an 8088 CPU.
One has an NEC V20 CPU.

Sounds like the most likely cause.

So, there has to be a difference - but what?

Although an unlikely cause, I would swap the power supplies between the two systems, just to make sure that a power supply is not the cause.

Second system will NEVER work with the same card. System is fine if a CGA card is used (and switch settings changed).

Did the VGA card go into the same slot as was used for the CGA card? If not, perhaps the VGA card was put into a faulty slot.

 

[Timo W.]

Do the motherboards look the same? I had two 5150s as well and both were from 1984 and had the same BIOS. The motherboards however were quite different. One was brown and looked very clean (meaning no patch wires), whereas the other one was green and had lots of patches applied (ex factory). Didn't find out what those patches fixed, but could have something to do with compatibility.

 

[mmruzek]

Hi, I'm wondering what 16-bit VGA card you are using? Also, Can you read the identification on the video chip? I've spent ALOT of time trying to get different VGA cards to work in the 5150 and PC-Retro, is why I ask. Thanks!

 

[Stone]

My 5150 (with the 1501476 BIOS) doesn't like the 16-bit Trident VGA card I use in my 5160.