Musical Fidelity preamp channel down on phono input - diyAudio
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Old 22nd April 2010, 03:19 PM   #1
mr-br is offline mr-br  United Kingdom
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Default Musical Fidelity preamp channel down on phono input

Hi

I have a Musical Fidelity F25 preamp with a problem with the phono stage - the right channel is down on the MM input. If I try my TT into the MC input instead, the left channel is missing, with the right channel much quieter and muffled which seems rather odd! If I plug my TT into one of the line level inputs, both channels are present but much quieter and tinny sounding, as expected.

I looked at the PCB and found a slightly crusty ecap (Jamicon 16v 1000uF) near the phono stage which I replaced but it made no difference. The input selector is a multiple button microswitch strip so there's no rotary selector to suspect.

My only diagnostic tool is a multimeter - does anyone have any suggestions on how to trace the fault or what to suspect? I'm not experienced at repairs although I can solder and do have a basic understanding of electronics, but my knowledge on how to trace faults is minimal.
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Old 22nd April 2010, 05:29 PM   #2
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You need more equipment to do the job effectively. An oscilloscope and of course get the diagram so you know what the parts do. Otherwise you will be spinning your wheels and are more likely to cause problems than solve them.

Do you have the diagram? If so, post it so we can try to guide you.
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Old 22nd April 2010, 09:20 PM   #3
mr-br is offline mr-br  United Kingdom
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Unfortunately I don't have a schematic, nor a scope, so I guess it looks like it'll have to go off to a repair shop.
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Old 22nd April 2010, 10:19 PM   #4
Westley is offline Westley  United States
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I suggest contacting John Sampson at JS Audio Repair in London. He is very good and knowledgable on MF products.
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Old 23rd April 2010, 08:47 AM   #5
mr-br is offline mr-br  United Kingdom
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Thanks for the tip.
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