Path: ...!2.eu.feeder.erje.net!feeder.erje.net!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail 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 Lines: 32 Message-ID: <1qqgdp3.ctwevlwal8p6N%liz@poppyrecords.invalid.invalid> References: <1qqfgdv.1y9tmdayl1lntN%liz@poppyrecords.invalid.invalid> X-Trace: individual.net UdXUxCaTqal8D88pT0ZlWguknw/18ErrMUbWn4AG2SYC48IjL5 X-Orig-Path: liz Cancel-Lock: sha1:gGrgN07JYe0aoNSp5V9wgAatPcM= sha256:/5+HXbVPpq2j6ONdKlIQGL87NzDd7DGlR3Um5mjFKl8= User-Agent: MacSOUP/2.4.6 Bytes: 2104 John Robertson 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