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From: liz@poppyrecords.invalid.invalid (Liz Tuddenham)
Newsgroups: sci.electronics.repair
Subject: Re: Is it a capacitor, is it a resistor?
Date: Fri, 15 Mar 2024 08:56:19 +0000
Organization: Poppy Records
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John Robertson <jrr@flippers.com> wrote:

> On 2024/03/14 1:56 p.m., Liz Tuddenham wrote:
> > I was asked to repair a Pioneer QX-949 quadraphonic tuner/amplifier.  It
> > is a complex beast and one channel had gone down to almost nothing.
> > Luckily the service sheet was available and I traced the fault to the
> > board which houses the tone controls and filters.
> > 
> > The gain is in two stages with the tone controls around the second
> > stage.  On one of the channels, the voltages on the single transistor
> > for that stage were all wrong.  After lifting the transistor off the
> > board, it became apparent that the base bias was far too high and the
> > finger of suspicion pointed to the inter-stage coupling capacitor
> > feeding in leakage current from the preceding stage.
> > 
> > I tested the capacitor, which was marked "4.7".  It read exactly 4.7k in
> > both directions on an ohm-meter !!!
> > 
> 
> Can digital ohm-meters be fooled by ESR?

Possibly, but not to that extent.  The meter was a Philip PM2518, which
I believe uses DC for the ohms measurement.

A new capacitor solved the problem and saved a rather expensive and
special piece of kit from being consigned to the scrap heap.


-- 
~ Liz Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk