Multibus ST-506/QIC-02 (was: Re: SGI IRIS 1400 ...)

From: Tothwolf <>
Date: Wed Jul 24 21:10:09 2002

On Wed, 24 Jul 2002, Tony Duell wrote:

> > The 8 pin chips are marked 4558. They probably are op-amps, but I haven't
> The 4558 is a very common dual op-amp.

Thats good news I guess.

> > I don't have a really nice transistor checker yet, but I do have a couple
> > of pocket types that work well. I desoldered and tested all 4 1N4001s and
> > all 4 transistors. I checked all of them with a one of the small testers,
> > and then checked them all again manually with my DMM. None of those 8
> > parts appear to be bad.
> Pity. So the fault is elsewhere. Alas the rest of the circuitry is
> sufficiently different in layout that I probably can't help you. I could
> tell you that there are interesting signals on the outputs of op-amps,
> but you'd never find them on your board.

If the 4558 is common, why would I not find them?

> But if you can get a 'scope, try looking at the signals on the 2 pin
> servo input connector (preferably use a 'scope with differential -- A-B
> -- mode). It would at least tell you if the servo head is reading
> anything.

I actually have a lead on some P6120 probes for my Tek 2213 scopes now, so
maybe I'll be able to use them in a few weeks. Now if only I could find
the Operator and Service manuals...

> > I certainly don't hear the heads moving, but I'm not sure how noisy these
> > drives are anyway.
> Try holding the drive in your hand as it spins up (you only need to have
> the power cable connected, of course). You can normally feel the heads
> moving.

Of course, I'll have to reassemble the unit again. I'm afraid I'm gonna
wear the connectors out taking the boards off so much. Maybe I should
build some cable extenders to help while troubleshooting...

Received on Wed Jul 24 2002 - 21:10:09 BST

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