M-X920 tape/amplifier? issue

[Dbzerk]

Hey all. Been working on restoring a M-X920. I have gotten this bbx to the stage where everything is working exactly as it should be... all but this one issue.
When i select tape source and press play on a cassette, after half a second or so the volume attenuates.
The tuner and line in sources work perfectly and has very clear sound.. but while in either tuner or line in source and i press play on the cassette player it will also attenuate the selected source..
Im a little confused as to where to begin to trouble shoot this one..
I have had the whole thing apart and have cleaned all the pots and record bar.
Any advice would be greatly appreciated

 

[baddboybill]

You should post video of sounds it’s making

 

[Dbzerk]

Hi mate.

This is it here..
No unusual sounds..

The first source selection is tape then I switch to tuner (MJ playing) then back to tape...

 

[TW5]

Might be in the power supply
put the tuner on and press rew or ff
see if the sound goes down ?

 

[baddboybill]

That is strange don’t think I’ve ever heard that before

 

[Dbzerk]

Might be in the power supply
put the tuner on and press rew or ff
see if the sound goes down ?

Yup.. same thing happens on ffw and rew.....
Voltage on the supply board doesn't dropped down significantly.

 

[fyj2972]

Muted, I think its circuit problem. Not Power supply issue.

 

[TW5]

It might have a voltage regulator transistor problem.
The motor power might be pulling the volage down at some place.
not that the motor is the prolem

 

[Dbzerk]

Humm I thought so also but the motor is still spinning when tape is paused..

 

[TW5]

Does the volume go low on AM as well?

 

[Dbzerk]

Didnt check that initially.. i just quickly went back out to the work bench and had another look, yes.. same fault on any band of radio also phono and line in.....

 

[docs]

Muted, I think its circuit problem. Not Power supply issue.

I'd agree with this, chase down the muting function associated to the deck being activated.

 

[Dbzerk]

Ill look into that and let you know how I go. Thanks gents.. fingers crossed

 

[Dbzerk]

Well. Its solved..
After going through and tracing out block and circuit diagrams and verifying that everything was working as it should, I realised that the tape counter has a magnetic sensor behind that without this turning mutes the amplifier.

Embarrassed...
But I have a perfectly working M-X920k now..

I hope this helps anyone who comes across this while working on this one.

Thank you all for your help

 

[docs]

Oh sugar yeh, I totally forgot about that sensor! Sorry but glad you have sorted it.

 

[baddboybill]

Awesome!!!