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stereo reciever static

For a few years now my grandmother's stereo receiver has had intermittent static in the output. As I recall this is a Wards model Fifty Five which is a reasonably well made unit dating to probably the early 70s.

The static sounds much like brushing a microphone on carpet, it is in both channels, all inputs, is not affected by the volume control or any of the switches and seems to get worse (more frequent/consistent but not louder) once the unit warms up. Sometimes shutting off the power for a few seconds will make the static go away for a couple minutes but it comes back. Years ago I opened it up and touched up some of the soldering but as I recall that didn't make much difference. Suggestions on this? I'll try to pick it up this weekend and take a look at it but I've never encountered this problem in an amplifier before.

Reply to
James Sweet
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Divide and conquer. You need a signal tracer or scope to find out where it begins in the circuit.

Reply to
Homer J Simpson

If it is independent of the volume control and in both channels, it must be somewhere in the power supply.

H. R.(Bob) Hofmann

Reply to
hrhofmann

On Sat, 03 Feb 2007 01:12:07 +0000, James Sweet Has Frothed:

Well then you've not worked on many amplifiers :)

Take a wooden dowel and tap on some components and the pc board. You might find something that reacts to it. Could be a bad elect cap somewhere. Or a transistor that gets noisy when it warms and might quiet if sprayed with a drop of freeze mist. Would help you narrow it down if you had some test equipment like a scope and either a decent knowledge in the component layout or a schematic.

--
Pierre Salinger Memorial Hook, Line & Sinker, June 2004

COOSN-266-06-25794
Reply to
Meat Plow

I've worked on a few amps, probably a dozen or so, but usually the failures I come across are blown output devices.

I like the freeze spray idea, I'm not sure why that escaped me, I even have a can of the stuff. I have a scope too so I can poke around and see what I find. No schematic unfortunately but I suppose the circuit is pretty similar to other receivers of the era.

Reply to
James Sweet

Sounds like a power supply issue. Replace electrolytic capacitors and reflow the solder joints. Use heat gun and freeze spray to isolate it. Can you poke around with an oscilloscope to see what the static looks like on the power supply rails?

Reply to
Matt J. McCullar

Some of the other suggestions were good, power supply, intermittent connections etc, but how about this - maybe the power switch arcing internally? A quick test for this would be to run a transistor AM radio nearby and see if it picks up the static from the switch radiating. Or, using an AC voltmeter across the switch terminals of course would read zero while the unit is turned on. If voltage appears across the power switch when the problem occurs, the switch is bad.

Mark Z.

Reply to
Mark D. Zacharias

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