IBM P70 portable repair

[agentb]

I recently acquired an IBM P70 portable which I would love to get working. It posted intermittently the first time or two I turned it on and got some error codes in the 161-165 realm (can’t remember exactly which ones). Then it would only post if I let the machine sit for hours. Now it won’t post at all. Lithium battery has been removed so presumably CMOS is blank/garbage. I checked caps in-circuit with an ESR meter and nothing jumped out at me. But they could still be bad I assume. Caps are electrolytic, not surface mount like on the P75. Floppy caps (SMD) are definitely bad, I saw visible leaking, so that’s a problem for the future. Power supply readings all look good.

Any suggestions on what to try next? I was planning to recap the planar board (and plasma board?) as I’m not sure what else to do. I know I need to use the reference floppy to set the CMOS correctly once I can get it to post again.

 

[agentb]

 

[agentb]

Good news, pulled pin 9 from a VGA cable and plugged into the external VGA port. Looks to be booting. So must be a plasma display issue. After the memory count, got errors:
601
162
163

 

[agentb]

These error codes all make sense, I have the floppy unplugged as the caps are toast, and also have the ESDI HDD unplugged (which fortunately sounds like it's spinning up when it is powered).

• 162 AT systems options not set (run SETUP)
• 163 AT time & date not set (run SETUP)
• 601 Diskette power on diagnostics test failed

Not sure what electronics are in the plasma display, I'll have to see if I can find some disassembly or video of that. The plasma display board has some caps, but more interested in what else lives in the actual display piece.

 

[agentb]

well, according to this guy's video, all he did was unplug the plasma display connector, clean it, and re-connect to get his display working again. I tried unplugging and re-plugging and that got the plasma display back! Amazing, certainly not complaining about that. Now I need to re-cap the mess of a floppy drive and see if I can get that somehow working again so I can boot the reference disk.

 

[shrike]

I recently acquired one of these, as well. Mine is in extremely good physical shape, appears to POST and boot, but the screen is completely blank. It gives the 'long beep, then two short beeps' error code that indicated a plasma display card issue. Unfortunately, There's no video output on the external VGA, and pulling the plasma card, cleaning it up and replacing it didn't revive the screen. Now I'm looking at either recapping or replacing the plasma card, if I can come by one.

 

[agentb]

I was going to tackle the re-cap on the floppy today but after studying the floppy control board, I had at least 5 roached SMD caps to replace. It wasn’t looking pretty so I went to Plan B which was the gotek. I was extremely close to buying this nice adapter on feeBay, but came up with a cheaper option which was to just cut pins 3 and 6 off the gotek. These are the pins the P70 powers with +5V and +12V. Sure enough, that got the job done and I can now boot from the HD once the CMOS and time was set by the reference disk.

Not sure where I’ll go from here, OS/2 or AIX are thoughts, but I had a great experience putting recent NetBSD on my SPARCstation so considering that (if possible?) but not sure how to install given no CDROM or network connection.

Any other OS recommendations?

 

[shrike]

Very cool! I managed to get the display on mine up and working last night. I'll post some photos in my own thread. It's a wonder what just 'taking it apart and putting it back together' can do sometimes. On mine, I was thinking about playing around with PC-MOS, which seems like it was a really cool concept for it's time. https://en.wikipedia.org/wiki/PC-MOS/386

 

[agentb]

That’s great you got the display working! That’s all it took for me, just unplugging and replugging the display. Prior to that, it would not turn on anymore. Today I tried installing freedos but it didn’t go well, seemed to be running extremely slowly and eventually crapped out on the first install disk after the boot disk. I then tried MS-DOS 6.22 and all went smoothly. Thinking I may go the wifi modem route instead of an Ethernet card. Looks like latest wifi modem can do some sort of wifi IP over serial, very cool.