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

[retrobecanes]

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?

 

[retrobecanes]

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.

 

[oktology]

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).

 

[emersonrp]

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.

 

[emersonrp]

(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.)

 

[CHO]

Thanks for posting your trouble and what you did to resolve it. It helped me to repair a spare drive I had.