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One RD52-A failure mode

L

Lou - N2MIY

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Albuquerque NM / Potomac MD
I have put the RD53 that won't spin up to full speed to the side for a moment. I decided to look at an RD52-A (Quantum Q540) that quit working on me about six years ago. I never tried hard before to figure out what was wrong. On spinup, the drive would try forever to seek track 0, but never find it and go ready.

The RD52-A uses a piece of glass with small lines etched or plated on it that pass through a photointerrupter to keep count of what track the heads are over. The glass is on an arm connected to the head actuator assembly. This is similar to the glass on the head actuator assembly of an RK05. On the RD52-A, this business is "protected" inside the HDA, which breathes through a little filter to keep the insides clean.

After looking around inside the HDA, I found a film of stuff that put a haze on both sides of the glass, such that the photointerrupter did not work right. I looked at the phototransistor on the scope, and it looked weak. The haze came off with a clean q-tip with nothing else necessary. When the haze was gone, the photointerrupter worked fine, and so did the rest of the drive. It's been running ZRQA?? (disk exerciser) under XXDP for a few hours now without an error.

This drive was not used in a smoking environment. Could the film have come from decomposing/evaporating bearing grease constituents that condensed on the glass?

Hopefully this observation will be of some help to someone else.

Lou
 
Sources of haze..

All sorts environmental contaminants have shown up on such things in the past in my experience. Here are a few...


  • Maintenance deciding to sneak in one weekday night, and spray paint the acoustic ceiling tiles "in situ" so the CEO wouldn't notice their lack of maintenance of the air filtration system. Problem was, this was the ceiling in engineering - where the 11/84, RM03, and an armada of IBM PC/ATs and other small systems with items such as drive filters and "sealed" Winchester drives that never anticipated having to deal with airborne solvents. Some systems had boot floppies that were only turned off or rebooted once a year, etc... only to "fail" months later because of this.

The ultimate fallout from that makeover was probably $100k in repairs. lost time and data.



  • Insecticide [roach powder and liquids] is sprayed under pressure every 3 months onto the walls, dividers and wire ducts to prevent the little fellas from invading all the warm corners created by this powered equipment. Problem is, some of that anti-pest stuff is fine enough to get through filters over time, and coat disk platters, dissolve drive belts and turn insulation to a gooey highly viscous liquid.


  • Carpet cleaner works wonders on the intended textile, but as it evaporates it sometimes leaves that which it removes as an unintended residue. Curiously, a large component of this residue is concrete dust, a highly conductive and corrosive substance. Being a floor standing enclosure, many a MicroVAX II BA-123 succumbed to this magic cleaning event which no engineer requested or even knew about beforehand, if at all.

Back in the day, most of these devices were designed with cigarette smoke in mind, at least so they could make it through their warranty period. These other possibilities are wildcards.

It is even possible that some substance within that drive itself "outgassed" as it aged or was exposed to temperature extremes.

Did you taste or smell it, to get an idea what it was? [Beware of arsenic!]
 
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Hey, at least they actually cleaned the carpet in your engineering area!

The haze I saw was light gray. This drive was in my 11/73 that came from a university lab. It should have been a pretty clean environment.

Before it started misbehaving, this drive had always been kept in a good indoor environment (65 to 85F). It does seem to reasonable to me that the origin was from within the drive itself (as in evaporated bearing grease.)

Lou
 
Light gray... didn't happen to check it with a magnet, did you?

The only greases that evaporate to a powder (that I know of...) are Molybdenum based, unless someone was desperate enough to try Dry-Slide on it ? (Molybdenum disulfide)

Please examine the interior of the rotating assembly enclosure for evidence of erosion. This would be characterized by a change in color, patina, or texture probably in line with the plane of the platter.

What color was the oxide on the platter surface? The usual Iron red?

Yeah, I wouldn't be surprised if they gave those carpet cleaners a bonus and a medal. We used to say the company was known for "Snatching Defeat from the jaws of victory" all the time. [In reference to the ABC Wide World of Sports slogan of the day]
 
This film was so thin, there'd be no way I'd ever be able to feel if it was attracted to a magnet.

I doubt anyone tried to spray moly disulfide on the bearings of that drive. I wouldn't say that the haze was necessarily a powder either. I'd probably have to bring the q-tip to work and put it on the SEM to see what form it was. I've 86ed the q-tip by now anyway.

If I open the housing again (a pain on Q540, due to the funky grounding gasket belt that covers the seam of the HDA clamshell) I'll look for any other erosion / corrosion. I wouldn't expect to see any, as I would have thought the aluminum housing was anodized. The platters were the usual reddish brown color.

Lou
 
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