• Please review our updated Terms and Rules here

"seek error" on a TRS-80 Model 4P

retrobecanes

Experienced Member
Joined
Apr 11, 2017
Messages
181
Location
Florida, USA
My TRS-80 model 4P is giving me some trouble with the secondary (i.e. defective) drive, here are my findings:

- the drives are TANDON TM-50-1
- the head moves freely, is clean, and the drive spins at 300rpm
- there is proper voltage going to the drive
- visual inspection of the defective drive doesn't show anything obvious
- the defective drive doesn't read any disks (tried with many different "known to be good" disks)
- when I set up the defective drive as a primary/boot drive, I consistently get a "seek error"
- the primary/good drive works well which, I hope, indicates that the FDC is not the culprit, is that a correct assumption?
- I swapped the top boards between the two drives and it fixes the issue on the defective drive, the problem is therefore "somewhere" on the top board.
- I have tested the defective drive with Greaseweazle and it can do a "clean" and an "rpm" check without issue.
- Track 0 position is properly detected on the defective drive (checked at TP)
- When I boot from the defective drive, the head steps back to track 0 and the signal goes LOW, as expected

I am not quite sure where to go from here. What does that "seek error" indicate? Is that primarily an issue with the "read" circuitry?
 
Last edited:
SOLVED, using the scope I found that the amplifier NE592N in position U1 was bad! I harvested another one from a donor drive and "voila" the drive boots and works correctly.
 
SOLVED, using the scope I found that the amplifier NE592N in position U1 was bad! I harvested another one from a donor drive and "voila" the drive boots and works correctly.
Dang, good to know. Mine is consistently throwing that error with a TM-50-2. Two of them, actually, if I remember correctly (been months since I touched that machine).
 
Would be interested in hearing more about your process debugging this and what you observed that let you know the chip was bad. I have a TM-50 giving me the same trouble. Using a Greaseweazle to debug a little, I've pinned down that head 1 isn't getting any information, while head 0 is fine, which could certainly be the case if one of the two chips were wonky (though I'm sure it could be a thousand other things too). I -have- a scope, but using it correctly is just at the edge of my skill set and comfort level, so any guidance you could give would be very appreciated.
 
(I have just finally put together that these are model TM-50-1, there isn't a second head in the first place, and Greaseweazle is correctly reporting that. Still, I'm getting seek errors on now both of these TM-50 drives, so guidance is still welcome.)
 
Thanks for posting your trouble and what you did to resolve it. It helped me to repair a spare drive I had.
 
Back
Top