My trusted old Grundig R-7500 Receiver (25 years old) suddenly started
emitting very loud rumbling noise on both channels from the speakers
(sounds like a large lorry unloading rocks and boulders). The rumbling
starts after some minutes of operation and is not affected by the
volume control. Music still can be heard behind the rumbling.

Could this be some of the electrolytic capacitor finally becoming to
old? Does anybody has an idea?

Thanks

Tolux

tolux wrote in message
ups.com...
My trusted old Grundig R-7500 Receiver (25 years old) suddenly started
emitting very loud rumbling noise on both channels from the speakers
(sounds like a large lorry unloading rocks and boulders). The rumbling
starts after some minutes of operation and is not affected by the
volume control. Music still can be heard behind the rumbling.

Could this be some of the electrolytic capacitor finally becoming to
old? Does anybody has an idea?

Thanks

Tolux


As rumbling is on both channels then very likely failing electrolytic, try
ac voltmeter on main DC rails at the caps or a crystal earpiece.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

On 3 Nov 2006 01:45:33 -0800, "tolux" wrote:

My trusted old Grundig R-7500 Receiver (25 years old) suddenly started
emitting very loud rumbling noise on both channels from the speakers
(sounds like a large lorry unloading rocks and boulders). The rumbling
starts after some minutes of operation and is not affected by the
volume control. Music still can be heard behind the rumbling.

Could this be some of the electrolytic capacitor finally becoming to
old? Does anybody has an idea?

Thanks

Tolux

Sounds to me like the filter caps in the power supply are dying. It
would sound like a 60 cycle loud hum.

schrieb:

On 3 Nov 2006 01:45:33 -0800, "tolux" wrote:

My trusted old Grundig R-7500 Receiver (25 years old) suddenly started
emitting very loud rumbling noise on both channels from the speakers
(sounds like a large lorry unloading rocks and boulders). The rumbling
starts after some minutes of operation and is not affected by the
volume control. Music still can be heard behind the rumbling.

Could this be some of the electrolytic capacitor finally becoming to
old? Does anybody has an idea?

Thanks

Tolux

Sounds to me like the filter caps in the power supply are dying. It
would sound like a 60 cycle loud hum.

No, it is not a pure 60 Hz (or 50 Hz in my part of the world ;-) sound.
It is completely random rumbling noise (like I already described, like
a lorry unloading rocks). Sounds more like someone scratching a needle
over an old LP (yes, I am that old ;-).

tolux wrote in message
ups.com...
schrieb:

On 3 Nov 2006 01:45:33 -0800, "tolux" wrote:

My trusted old Grundig R-7500 Receiver (25 years old) suddenly started
emitting very loud rumbling noise on both channels from the speakers
(sounds like a large lorry unloading rocks and boulders). The rumbling
starts after some minutes of operation and is not affected by the
volume control. Music still can be heard behind the rumbling.

Could this be some of the electrolytic capacitor finally becoming to
old? Does anybody has an idea?

Thanks

Tolux

Sounds to me like the filter caps in the power supply are dying. It
would sound like a 60 cycle loud hum.

No, it is not a pure 60 Hz (or 50 Hz in my part of the world ;-) sound.
It is completely random rumbling noise (like I already described, like
a lorry unloading rocks). Sounds more like someone scratching a needle
over an old LP (yes, I am that old ;-).


You can get that sort of noise in a failing electrolytic, i've always
assumed it is a local hotspot causing bubling in the electrolyte.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

tolux wrote:

My trusted old Grundig R-7500 Receiver (25 years old) suddenly started
emitting very loud rumbling noise on both channels from the speakers
(sounds like a large lorry unloading rocks and boulders). The rumbling
starts after some minutes of operation and is not affected by the
volume control. Music still can be heard behind the rumbling.

Could this be some of the electrolytic capacitor finally becoming to
old? Does anybody has an idea?

Thanks

Tolux

these sort of noises are usually down to a bad connection somewhere

NT

"tolux" wrote in message
ups.com...

No, it is not a pure 60 Hz (or 50 Hz in my part of the world ;-) sound.
It is completely random rumbling noise (like I already described, like
a lorry unloading rocks). Sounds more like someone scratching a needle
over an old LP (yes, I am that old ;-).

So it's solid state? Bad resistor/transistor? Signal tracer and generator
will track it down.



--
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+ damaged idiots.
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+ Server Response: '441 Posting Failed (Rejected by POST filter)', +
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++++++++++++++++++++++++++++++++++++++++++++++++++ ++

Thanks to everybody who answered.

I also suspected the electrolytic caps in the power supply, but could
not explain the funny noises. I expected humming. The explanation with
the boiling hot spots seems likely. I will replace the caps.
Furthermore I will probe the PCB to look for cracks or loose
connections.

tolux spake thus:

Thanks to everybody who answered.

I also suspected the electrolytic caps in the power supply, but could
not explain the funny noises. I expected humming. The explanation with
the boiling hot spots seems likely. I will replace the caps.
Furthermore I will probe the PCB to look for cracks or loose
connections.

You might also want to check for a noisy transistor. I had a similar
problem with a solid-state 70s-vintage receiver; turned out one
transistor was bad. I was able to easily find it since it had gone
microphonic, and tapping it produced an interesting banging noise in the
output.


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