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Resurrecting the IBM 5150

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First post, by KIsmay

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I have an IBM 5150, that used to work a dozen years ago. It was stored in my garage for a while, so I brought it in the house to have a look. I took it apart and cleaned everything. There aren't any signs of leaky capacitors or battery leakage etc. Things look like it should work. It no longer displays anything on the screen. On start up, it seems to power on and go through a POST routine, including a single beep after about 20 seconds.

Components include:
- 1 floppy drive
- 1 hard drive
- printer card
- memory expansion card
- floppy and hard drive controller cards
- Original Color Graphics Adapter
- I have a generic amber monochrome monitor and a green Tandy monochrome monitor. Both work fine on my Tandy 1000, and the amber monochrome screen used to work with the 5150

I have a working Tandy 1000, a 486 computer (in pieces), and a AMD K6-2 system with ISA slots (in pieces) that can be used to test individual components. Unfortunately, the CGA card doesn't fit in any of them. I have experience with electronics and soldering, so I can replace capacitors etc if needed. I'm just reluctant to start replacing stock components unless I can prove they've actually failed.

Are there any good ways to test and verify that the mainboard is working? I've looked at buying replacement video cards, but the price is steep at $80-$100.

Thanks!

Reply 1 of 3, by kdr

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There's an excellent troubleshooting guide for the 5150/5160 at minuszerodegrees.net:

http://www.minuszerodegrees.net/5150_5160/MDC … diag_config.htm

If you think it's the CGA card that isn't working (a good guess) then I'd suggest trying a minimal configuration: just the motherboard and the floppy controller card plus the keyboard and floppy drive. See if the drive motor and light activate after booting. It's also possible that you have a keyboard error. You can try blindly pressing F1 a few times and see if that gets past any error codes to the point where the BIOS will try to boot from the floppy. But I reckon that the motherboard is fine, given that you get a beep out of it.

Reply 2 of 3, by KIsmay

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I've done some further testing. In the Minimum Diagnostic Configuration (as above) with no cards, I get 1 long beep and 2 short beeps.
With the CGA Card installed, and the dip switches reconfigured for CGA, I get 1 beep.

I've also reinstalled the floppy drive and controller, and the drive seems to be accessed on boot.

I'm going to try to make a dos boot disk with an autoexec.bat file that just beeps the speaker a few times to see if it will run some code.

I do have a logic probe, but not a lot of experience with using it.

Reply 3 of 3, by kdr

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KIsmay wrote on 2021-03-15, 00:32:

I've done some further testing. In the Minimum Diagnostic Configuration (as above) with no cards, I get 1 long beep and 2 short beeps.
With the CGA Card installed, and the dip switches reconfigured for CGA, I get 1 beep.

I've also reinstalled the floppy drive and controller, and the drive seems to be accessed on boot.

Great news! This means that your 5150 is alive and happy. The BIOS has detected the CGA card (by poking the registers of the 6845 CRTC and testing access to the video RAM).

Since the CGA card doesn't seem to output any video to a TTL monitor, have you tried connecting a monitor (or TV) to the composite output yet?

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