"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.