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View Full Version : 8" Floppy Drive Question (S-100 System Cleanup)



mkstabd
November 30th, 2009, 08:32 PM
I just completed some cleanup work on my dual floppy drive enclosure (QumeTrak 842 drives) and ran into something that confused me. Perhaps one of you has seen this before and can provide some insight.

After using my system a lot over the past week, I noticed the drive doors were starting to stick a little bit. Sometimes, the drive would open right up with no problem. Other times, it would take 4 or 5 attempts to get them to open, even when the drives were powered down. It turns out the door lock solenoid pin was sticking to the coil and not releasing because of a very sticky spacer (http://bartosh.us/s-100/IMG_0484.jpg) between the E-clip/spring, and the coil mount (http://bartosh.us/s-100/IMG_0485.jpg). This spacer is what confuses me. It seems to be made out of some kind of wax or sticky resin. I'm not sure why it's sticky like this. It's the same story on all 3 of my drives, plus another QumeTrak 842 I just bought off of eBay. The only way I could keep the solenoid working freely is to thoroughly clean all the goo off of the pin, spring, e-clip and the pin hole in the coil, position the spacer so it was centered over the hole, and then very gingerly reinsert the pin and spring without making contact with the sticky spacer. After that, plus cleaning all the mechanism parts, the drive unlatches very smoothly now 100% of the time (for now, at least.)

My question is, why is that "padded washer" (as it's called in the service manual) made of this sticky waxy substance? My theories are: 1) it was made that way originally to offer some kind of lubrication, but has essentially decomposed over the years into this sticky mess, or 2) maybe it was meant to be sticky and pliable to act as a type of noise dampening cushion for the pin, while sticking to the coil in a way that supported vertical orientation of the drive. Whatever the reason, it seems like a problem waiting to happen again. As the goo seeps around the spring, it will eventually contact the pin again and I'm right back to having to clean it off.

Can anyone help me understand what this spacer is all about?

Thanks,

Ty

PS For those interested, here's a new page on my site that shows some pics of the floppy cleanup work (http://bartosh.us/s-100/FloppyCleanup.html) (still under construction.) I'd really appreciate any feedback (especially any corrections) regarding the content of the site.

Chuck(G)
November 30th, 2009, 08:41 PM
My question is, why is that "padded washer" (as it's called in the service manual) made of this sticky waxy substance? My theories are: 1) it was made that way originally to offer some kind of lubrication, but has essentially decomposed over the years into this sticky mess, or 2) maybe it was meant to be sticky and pliable to act as a type of noise dampening cushion for the pin, while sticking to the coil in a way that supported vertical orientation of the drive. Whatever the reason, it seems like a problem waiting to happen again. As the goo seeps around the spring, it will eventually contact the pin again and I'm right back to having to clean it off..

I just remove the door-lock solenoid from my 842s. That bumper didn't start life out sticky, but has degraded to that condition with age (it also happens with old tape drive pinch rollers).

I wonder if you could contrive an adequate substitute by stacking up a few O-rings with a fairly soft durometer rating...

mkstabd
November 30th, 2009, 08:56 PM
I'm glad to hear that it didn't start out that way! I couldn't think of a reason why it should be sticky. I was thinking about fabricating some replacement collars out of some white plastic rod of the same diameter and drilling a recessed spring cradle down the middle to match the geometry of the original. Maybe I could attach one of the O-rings you describe, or even a flat rubber washer to the top of the collar.

Thanks for the confirmation!

Ty

Chuck(G)
December 1st, 2009, 11:42 AM
Plastics and rubber on old systems is generally bad news. Some of the more common problems (http://www.science.uva.nl/museum/rampspoed.html)

mkstabd
December 1st, 2009, 02:59 PM
That's a very interesting link. The capstan example seems the closest to the door lock solenoid collar problem we've noticed.

Silicon rubber may still be a suitable replacement, even if it deteriorates the same way as the previous one. However, I was reading about EPDM synthetic rubber (http://en.wikipedia.org/wiki/EPDM_rubber). It seems to be engineered to last long under harsh conditions. I know a lot of auto parts, like hoses and motor mounts, are made out of this stuff. Maybe it would be a better option. Anyone ever work with this?

Ty