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Home hifi ampli fixing problem

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Zeno

New Member
Hi all! I'm from Italy.
I'm trying to fix an old ampli wich was used with a record player.
It is not broken, because when plugged it sounds. But it doesn't sound very well.
When i turn it off for the time that remains on, it sounds very well.
I thought that it may be a capacitor or a power section problem but i don't know where to start to test it.
It doesn't seems to have any sign of broken components in a first sight.
Do you know what can be the problem? Which components may i have to test if are properly working?
Thanks for your time.
Greetings,
Francesco.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Hi Francesco,

You don't repair things by testing components, you need to fault find the entire circuit.

First thing, you don't give any details on the item at all - a schematic would be best, make and model would help, and even a picture of the board would give us somewhere to start.
 

Tony Stewart

Well-Known Member
Most Helpful Member
power supplies with bridge rectifiers only pump current for a short time to keep the voltage up between peaks. If the capacitor has low dissipation factor, the voltage will integrate up and sag down with a skewed triangle wave at twice the line frequency with a few harmonics. But if the big caps dry out and develop a high series resistance, the pumped current adds a stepped pulse which contains a lot more the harmonics like a buzz instead of a hum. So replace all the big old electrolytic caps is a good practise.
 
If this record player amplifier is old, I would highly recommend replacing any electrolytic filter capacitors, which are part of the power supply circuit. Whenever repairing old audio equipment, that is a very good rule of thumb since over time they dry out and become 'leaky' and will cause distortion to the sound or you may not hear anything at all except a 'humming' sound.. Good luck ! Let me know if I can offer any further assistance.. Mark..
 
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