As an update, I was ... somehow able to get into the reference disk configuration menu, went in and set the time/date and manually set and saved the configuration. On reboot, it was still showing a 162/163 error so I'm guessing there's something wrong with the CMOS/SRAM storage chips identified here (https://ardent-tool.com/8570/Planar_T1.html) maybe? I'm pulling my hair out on this one now...

Needs new battery.

Cheers,

As noted, I've replaced the battery with a brand new one, and even used a benchtop supply in place of the battery to be absolutely sure that's not the problem.

Trace corrosion as mentioned was present, might cause voltage drops/breaks from the battery to the chips needing it, so maybe check all affected lines/solder points inbetween?

Hmm... the trace corrosion was on the floppy drive from the leaked electros, but I guess that is directly above the circuitry between the battery and the RTC. I couldn't see anything obviously damaged on the planar, but I guess I should measure between the VBAT at the RTC/CMOS directly to be absolutely sure!

Okay then, all traces are healthy, no corrosion anywhere on the planar. On the MC146818A itself and during power off, I'm seeing a constant 4V between Vss and Vdd, and 5V when powered on - both are well within the acceptable range for that IC.

Same situation with the SRAM & Vcc? (Since that is where the BIOS settings would be stored)
Looks like a bog-standard 2kbyte chip, never seen one break, but who knows?

Yep sorry, should have mentioned voltages there were fine too. I was able to get into the ref disk system checkout and run tests, and it's definitely finding something wrong on the planar. Not quite sure what this error is though, I can't find a definitive guide to what the diagnostic test error codes mean - closest I can find is that 00010300 as a POST error on a 90/95 system means checksum/clock error... Who knows indeed! Best guess, I'll just replace both the SRAM and RTC chips with either new replacements or NOS and see what happens.

Have you tried a complete clear? Belt and braces style, short jumper, leave battery out overnight style of thing. Once in a handful of blue moons, you get a bit set in the CMOS RAM in a "reserved" area that the setup program can't set, unset or clear, but it screws up the checksum.

I haven't shorted the jumper, but the machine was sitting on a shelf for 4-5 years without a battery or power... but yeah I'll give that a try too. Throwing everything at the wall at the moment, hopefully something sticks!

No luck on the belt and braces clear, unfortunately. Left it overnight with the jumper in and battery and power out, booted up this morning to a 161/163, went through the usual procedure and on reboot it went back to the 162/163 and configuration data error boot loop.

Okay I've had it sitting for a few days now without the battery, and I remade a bunch of copies of the reference disk just in case. Same thing.
I've also switched to a CRT monitor from the LCD I was using above, and the 2401 error I had attributed to the LCD is still there too, so I guess there's definitely something wrong on the planar. I've ordered some replacement RTC and SRAM ICs so will replace those when they arrive, and hope for the best. The 2401 error is making me rethink though and looking more at the video circuitry, but everything there seems physically fine...

can you describe the corrosion damage a bit? That sounds like a probable cause. Does the bios settings stick with a warm boot? if it only doesn't survive a cold boot, it sounds like the battery circuitry is likely to blame.

luckybob wrote on 2021-11-29, 17:12:

can you describe the corrosion damage a bit? That sounds like a probable cause. Does the bios settings stick with a warm boot? if it only doesn't survive a cold boot, it sounds like the battery circuitry is likely to blame.

The corrosion was only on the floppy drive, caused by leaked SMD electrolytics. The main planar has no corrosion that I've been able to find, and I've looked pretty closely now. The main boot loop that I'm referencing here is during warm reboots, after the reference disk restarts during automatic configuration, and I've tested the battery circuits end to end and they're providing correct voltages.

if it were me, at this point, i'd double check and reseat any parts in sockets. looking up the 2401 error...

2401 (PS/2) Planar video error -- it can be the display or the video.
First check for a solid connection -- wiggle the plug at the system end and check for one or more bent pins. Next swap the monitor. If a 2401 error persists after swapping the monitor, then the system board should be replaced next. However if your monitor serial number starts with "72" , is below 72-0374000 and you cannot find the number "61" stamped on the bottom of the display (you may need to remove the display stand), then a replacement monitor will probably fix this error.

If it's definitely on the planar (ie another monitor fails) check the Inmos palette DAC (ceramic DIP module with gold colored middle) for shorts between the pins.

going further, this is beyond my ability. My beard isn't nearly long or grey enough. IBM Museum's majestic facial hair is precisely suited for the task: https://www.youtube.com/channel/UCEfyT_TIXx41xA3U4psqWkw and the secret PS/2 underground where most of us lurk is at https://comp.sys.ibm.ps2.hardware.narkive.com/

https://www.youtube.com/watch?v=Y6UprDq8LAQ

TL;DR, Seems like soldering on PS/2 planars doesn't age up to IBM quality expectations. As seen in the video, it frequently develops micro-cracks and other subtle, but insidious issues.

Just as an update, I ended up replacing both the RTC and SRAM ICs to no avail. After consulting the boffins on comp.sys.ibm.ps2.hardware as recommended, they led me down a good track.

Was able to confirm the RTC functionality perfectly, but the SRAM was not returning anything. Digging and probing with my scope and multimeter led me to find the ~CS line on the SRAM was constantly held high, and I traced that back to the hex inverter MC14069U at U158 which didn't seem to be inverting. I drove it to ground with a jumper wire and all the system issues went away.

Will be looking to replace that hex inverter, but for now the jumper wire seems to be working! Thanks for everyone's suggestions!

I think most of the ibm greybeards have a presence there.

I was watching the CuriousMarc channel fix a very similar system, it was just a borked via.

Wow, good troubleshooting!

Cheers,