Blown Tantalum Capacitor Advice

[Rob Jarratt]

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of shadoooo
> Sent: 09 October 2016 18:30
> To: cctalk <cctalk at classiccmp.org>
> Subject: RE: Blown Tantalum Capacitor Advice
> 
> Hello Rob,
> I'm quite sure that the tantalum explosion has nothing to do with the spin-up
> failure.
> Indeed the RD53 (Micropolis) is infamous for a problem in the head
> positioning shock absorber.
> The head positioning system is based on a voicecoil inserted in the magnetic
> field; the angle covered by the head arm is limited by two adjustable metal
> limits originally covered with rubber.
> At startup the mechanism is moved back and forth to check the two limits,
> and exactly at the ends a special magnetic pattern is recorded on the surface
> of the disks for calibration.
> Due to age, the rubber becomes goo, so the angle limits become wider, so
> during the calibration the head falls offer the calibration area and spin-up
> fails.
> The suggestion is to choose a clean room with few dust and a good lighting,
> carefully open the top cover of the disc, and remove the goo the more as
> possible using adsorbent sticks.
> Be sure not to touch the disc surface with the goo accidentally.
> Then try to insert some small pieces of paper over one limit (if I'm not wrong
> the failing is the left) in place of the missing rubber, and try the disc, and
> continue to add thickness until it works.
> Then you are sure about the right limit to move.
> Then remove the paper, loosen a little the screw, but just a little so the limit
> will not move unless pushed with some strength and a screwdriver.
> Then move a very small amount towards the center and try, then repeat trial
> and error until the disc starts. Then tight the screw and it is over.
> Close the disc and voila.

Thanks Andrea. I have done this with other RD53s, but not gone as far as loosening the screws. Unfortunately I have failed so far with this particular disk and will try again another day. I suspect though that in this case the goo has spread more widely in the mechanism and gummed it up elsewhere, making the whole thing a bit sticky. I'd like to find a way to clean it more thoroughly.

Regards

Rob