TRS-80 M4 26-1069 - Revival in progress...

[lanmangler]

For low low price of a single Andrew Jackson I picked up an M4 this week. It's a little out of my 5150/C64/IIe comfort zone, but figured I'd give it a try.
Looking for tips on next steps.

Here's the rundown so far:
Power on gets the blue/gray screen as shown. Several power on cycles have the same result. Both drives spin continuously, but no lights come on the drives. Not sure if the M4 itself has a light, but I dont see one. No luck in III mode with the break key held either. The Astec power supply looks super nice and clean, and I have removed it entirely and inspected both sides. I'm not uber experienced, but don't see any obvious problems inspecting from both sides.
I managed to get these voltages very carefully with the monitor powered/connected:
V1 +6.9
V2 +15.9
V3 +16.0
V4 -16.8
Interestingly, I dont think think a wire is punched on the V4 molex(?) connector. Hopefully shows in the pic.
Without the monitor cable attached, the voltages seem all goofy, mostly low other than V4.

I have not done much of anything with the monitor board or troubleshooting on that side of things. I have inspected as you can see, the mainboard and carefully reseated all socketed chips with no difference in outcome. I also put the Astec bottom under a magnifier and didn't see much of anything that made me want to re-solder, but I'm open to that.
Serial number is 0015890 and case has March 3, 1983 written on the inside, with some QC looking stamps on the case bottom that are April 1983.

I do have a boat, but don't wanna settle for boat anchor.
-Tim

 

[lanmangler]

I think I got it - in absence of better thoughts, I went the isolation route pulling board(Drive, serial?) connectors to no avail. I then pulled the keyboard and gave it a inspection, finding some circuit board damage on the bottom center - there is solid peg riser that comes from the bottom of the case. Apparently somewhere in its lifespan - it held too much weight and broke into the PCB. Something shorting out there was giving it fits. I cleaned it up and at least have bootable machine, though I dont have all the keys yet. Hopefully an easy fix from here.