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Fixing flaky Panasonic 5.25" disk drives

H

hjalfi

Experienced Member
Joined
Feb 11, 2017
Messages
265
Location
Zürich, Switzerland
I have two, and only two, Panasonic JU-475-4AKO 5.25" disk drives --- generic PC 1200kB jobs. Both have failed in exactly the same way: the head does not appear to reliably step forwards and backwards, sometimes missing tracks. Large head movements usually end up on the wrong track. If I make it step one track at a time I can see the head twitch but it doesn't always actually step. It uses a rotating lead screw attached to the stepper motor with the head clamped to the screw.

I'm out looking for another drive but 5.25" drives are getting harder to find, so I should probably have a go at repairing these. I've cleaned and relubricated and replaced some of the more relevant-looking capacitors but that hasn't helped. Given that both drives have failed in exactly the same way, this sounds like a systemic problem with these Panasonic drives. Does this sound familiar to anyone? Possibilities include stepper motor failure, stepper driver failure, something wrong with the bearings... anything else?
 
I've used the JU-475 drives and found them to be very reliable. Are you certain that you're getting into the deep grooves in the leadscrew? This still sounds like a dirty drive.
 
It's possible --- I can certainly have another try. What's recommended for lubricating the screw with? I have silicone, light lubricating oil, and teflon lubricant. No white grease, unfortunately, as I haven't been able to find any in Zurich.
 
I'd start with the silicone--too viscous a lubricant can be problematic. You really need to deep-clean those leadscrew threads--use solvent and a toothbrush if you can. (Solvent = white spirit/mineral spirit/paint thinner).
 
Yep, I've run across this as well. Even after thinking I cleaned the lead screw thoroughly I still find that it wasn't enough. Like Chuck stated, a toothbrush and paint thinner seems to work best for me. Afterwards I use white lithium grease to lube everything. 80% of "bad" 5.25" drives I've fixed were nothing more than a good cleaning needed.
 
D'oh. Turns out that the lead screw was fine, but there was another rail the head slid along that I had someone completely failed to notice even after disassembling and recapping part of the board. Lubricating that solved the problem. I cleaned the screw anyway so it should be fine for a while. Video forthcoming.
 
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