GF-767Z Noisy Tape Mode

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ElectroKid

Member (SA)
Jun 7, 2015
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Hi all,

Please take a look in the video I made of the issue:
I was working on the tape mech replacing rubbers and now it's running nice.
While working on it something has gone bad with the tape audio, I mean tapes play but along with an 'helicopter' oscillating sound...
When I turn balance all way right this noise gone, but the VU meter still shaking and obviously the noise is just muted but still there...
Radio and Line-in are OK.
Any suggestions what happened here? (Service Manual attached)

Thanks
 

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ElectroKid

Member (SA)
Jun 7, 2015
55
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baddboybill said:
Could be bad ground to deck or loose head wires.


Bad Boy Bill
I've checked again but did not found loose wiring.
Also checked GND continuity to main board and measured good.
Finally I tried to touch the tape audio signal amp section and see if any change in that sound,
The noise was higher when I touched the coupling capacitor 4.7uF/6V which feeds to the Q101 pre-amp transistor
The interesting thing is when I replaced that tantalum cap with a same one no change.. still noise on that one side.
I tried to change it to 47uF/25V electrolytic cap but noise is still there.
but when changed it to 330uF/63V I have around, the noise got silenced and the audio is now good!

I should notice that now there's a very small volume difference in the earphones as that re-worked channel has slightly lower volume (so it seems to me). I dont have a replacement for Q101 so maybe it will stay like that.
I don't know why it's working like that.
Maybe Q101 is faulty? though voltages tested good as in schematic attached.

What do you think?
 

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ElectroKid

Member (SA)
Jun 7, 2015
55
5
8
baddboybill said:
Try cleaning the record bar with deoxit or contact cleaner and work switch 20 times or so.


Bad Boy Bill
Do you mean the big sliding potentiometer with many pins?
Yep already did that at the beginning... I drenched it with Servisol, it breaks the audio sound when pushed inside.
I have not tested the record function yet... I'll try it later as well.
 
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