hello All
My old faithful 80's Proton AI3000 All in One Home AudioAmp/Cassette/CD Player has broken..left channel started to Pop/surge..then no sound out of the left channel at all...regardless of input selected.
However I was surprised to find the Headphones still work ?! (both channels fine)...
Anyone say what could be going on.
Looking at the amp circuit .. the 'line out' goes via the headphones jack sockets then onto the speaker terminal circuit board...which has upon it a cap/resistor in line with the L/R Speaker Output Terminals.
One thing I have tested so far with a meter is the resistance to ground (black negative) speaker terminal to the amps metal chassis...I was surprised to measure 4.5ohms...should it be nearer zero ?!..if so..could I just connect it the negative terminals to the chassis 'to make sure' ?
Any thoughts about what has been said ..and what I should check...many thanks in advance for responders.
My old faithful 80's Proton AI3000 All in One Home AudioAmp/Cassette/CD Player has broken..left channel started to Pop/surge..then no sound out of the left channel at all...regardless of input selected.
However I was surprised to find the Headphones still work ?! (both channels fine)...
Anyone say what could be going on.
Looking at the amp circuit .. the 'line out' goes via the headphones jack sockets then onto the speaker terminal circuit board...which has upon it a cap/resistor in line with the L/R Speaker Output Terminals.
One thing I have tested so far with a meter is the resistance to ground (black negative) speaker terminal to the amps metal chassis...I was surprised to measure 4.5ohms...should it be nearer zero ?!..if so..could I just connect it the negative terminals to the chassis 'to make sure' ?
Any thoughts about what has been said ..and what I should check...many thanks in advance for responders.
.....first i would clean the headphone jack with a cleaning spray or so what.........to be shure there is no contact failure.
The high resistance may be completely normal, I would not alter anything there.
Its impossible to advise without seeing all the circuit details but my advise would be to locate the output stages (are they chip or discrete ?) and do some basic DC voltage checks of the operating conditions.
Its impossible to advise without seeing all the circuit details but my advise would be to locate the output stages (are they chip or discrete ?) and do some basic DC voltage checks of the operating conditions.
Thanks for replies mjf, Mooly
Im going to check the headphone jack socket contacts!
Ive Attached most of the circuit in question...if anything more of the Units circuit may be of use let me know and I will post it.
Mooly,,so happens I have another unit the same for spares..which works except for a faulty cd player control board...I checked its negative speaker terminal to chassis ground resistance...its 0.5ohm! so of course thinking something not quite right...but Im not sure where in the circuitry the connection to the metal chassis is made...so not sure ..still searching.
Im going to check the headphone jack socket contacts!
Ive Attached most of the circuit in question...if anything more of the Units circuit may be of use let me know and I will post it.
Mooly,,so happens I have another unit the same for spares..which works except for a faulty cd player control board...I checked its negative speaker terminal to chassis ground resistance...its 0.5ohm! so of course thinking something not quite right...but Im not sure where in the circuitry the connection to the metal chassis is made...so not sure ..still searching.
Attachments
Seeing the circuit, and knowing it works OK on headphones then I would go along with mjf's suggestion of carefully checking the headphone socket and also the soldering of the socket and all connections to and from that small sub board.
You could also check the DC voltage across each speaker terminal (with no speakers attached). There should be less than 100 millivolts DC present.
You could also check the DC voltage across each speaker terminal (with no speakers attached). There should be less than 100 millivolts DC present.
Mooly Thanks again...and thanks to mjf's suggestion...cant be sure but after a good spray with cleaner/lube spray into the headphone socket and working a jack plug in-out more than a few times..in addition to finding a power supply socket lifting a track (resoldered) its working again !!! 
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