Deep fried inductor...

Tony Duell ard at
Thu Feb 18 14:21:04 CST 2010

> I've recently been restoring an H8/H17 system.  Almost all of
> the problems involved capacitors, including a bad electrolytic
> in the H17 (diskette unit) power supply.  I repaired the H17
> supply using a dummy load but apparently the H17 was run with
> the bad supply before I got it.  I say this because some of the
> tantalum caps on the logic boards of the Wangco model 82 diskette
> drives popped and/or burned when correct power was supplied to
> them.  I've seen plenty of the "teardrop" tantalums pop, but I've
> never seen one of the "black suppository" types (used on these
> drives) go.  I believe this was the result of bad ripple in the
> supply.
> Anyway, one of the Wangcos now runs perfectly and the other runs
> fine for a while but fails after about an hour of applied power.
> The difference between the two is that, on the flaky drive, a cap
> in series with an inductor did a slow burn, resulting in the
> inductor having a "nice brown toasty" appearance and a small split
> in one side that some red resin leaked from.  By the way, the only
> way I know this is an inductor is that it is labeled "L5".  It
> looks like a large beige resistor with too many color stripes on it.
> Inductors are a weak area in my electronics knowledge.  How would
> you know for sure that one has failed?  Does it fail open?
> Other info:  When the drive fails, it can not read any data and,
> when seeks are attempted on it, it sounds "funny", not the nice
> sharp click it makes when operating correctly.  The inductor does
> not feel hot to the touch when the drive has failed.  I'm out of
> cool spray.  Tonight I will try to apply an ice cube in a plastic
> bag to it to see if that gets it out of failure mode.
> Finally, assuming it is the problem, what do I need to replace it?
> The stripes on it are:
> Wide silver (covering one end)
> Red
> Yellow
> Brown
> Gold
> Thanks,
> Bill

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