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-   -   sugden a28b (http://www.diyaudio.com/forums/solid-state/134003-sugden-a28b.html)

Sjaak 29th November 2008 08:07 PM

sugden a28b
 
Hello DIY'ers,

Can someone tell me what could be wrong with my sugden A28B?
There is noise in the left channel when the volume control is operated. I replaced the potentiometer (ALPS) but the problem is still there. I have no schematic so it is difficult to find the problem.
Thank you for any advice!
Sjaak

Rikard Nilsson 29th November 2008 09:59 PM

Noise from a potentiometer can origin from DC voltage across it. That in turn may be the result of a shorted electrolytic cap, or an DC operating point way off.

But a schematic would help a lot.

Sjaak 30th November 2008 01:11 PM

Thank you Rikard,
So if DC is over the potentiometer I have to search for a short capacitor in the pre amp stage only?

Rikard Nilsson 30th November 2008 02:58 PM

I think so, or something else that might cause a stage to operate at the wrong DC level. I cant imagine there should be any DC voltage across the pot. You could always measure the working channel to see if there is any DC.

If there are tantal caps these are the ones to check. They are known to short.

andreabwv988 5th November 2014 01:28 PM

Sugden a28b
 
2 Attachment(s)
Hello everybody. I'm a new memberer and owner of a Sugden A28B. I looking for help because from one channel exits only noise. I took some pictures inside:
Attachment 446921
Attachment 446922

I would be very pleased if someone could help me.
Thanks


dragonweed 5th November 2014 04:09 PM

Those charred resistors do not look too promising on the pc board... First you will need a schematic to find out where they are in the circuit, and why they might burned.

andreabwv988 24th November 2014 01:12 PM

sugden a28b
 
Thank you Dragonweed.
I found only a user manual. Sincerely about schematics i'm little more than a beginner. But i'm able to replace electronic components.
I might begin to find the component responsible of those charred resistors, maybe beginning from a capacitor nearby...


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