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Akai GX-747 Channel Imbalance when monitoring source

goldswimmerb

goldswimmerb

Failed out of engineering, but look at me now!
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Hoping anyone with a bit more knowledge of this deck's signal path can possibly help, I have a GX-747 here that is nice and balanced when playing back tapes, everything makes sense with my test tape.

The issue I am seeing is that when set to "source" with a tone coming in there is a noticeable difference between the L and R channel (shows about 2dB on the meter), this also comes across when recording. Given that the issue is present in "source" mode am I on the right track assuming that my issue is in the Mic/Line in board (the vertical mounted one with the level pots)? I believe that is the only board that is present in both record/tape monitor and in source mode, but the schematic is a bit difficult to follow.
 
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You might, if you have not already done so, use Fader Lube on the level pots and some Deoxit on the source/tape switches.
 
I had a similar problem with the GX747. The problem lies in the 2sc1312s transistors (TR2, TR2b Mic/Line pcb). Replace with 2SC1845.
 
clauelf said:
I had a similar problem with the GX747. The problem lies in the 2sc1312s transistors (TR2, TR2b Mic/Line pcb). Replace with 2SC1845.
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Was able to trace it down to the level pots on the line in board, both have around 15% to 20% difference between the gangs.
 
Can I ask - how did you access the Mic/Line pots to shoot them with DeOxit/Faderlube? I took the side panel off but don't see anyway to get to them.
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you remove the entire metal side panel as well
 
Esses botões grandes têm um clipe, é fácil removê-los?
 

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I said you need to remove the SIDE PANEL (metal one) to clean the pots. You don't need to remove the knobs. Why are you asking me how to remove the knobs?
 
Retirei as duas tampas laterais do gravador, limpei e o problema persiste, um canal funciona e o outro fica muito baixo, e os marcadores (vu) funcionam normalmente
 
Is the "channel out" problem in play or record?

Is the problem in forward play or reverse play?

Clean the three head switches on the bottom circuit board with D5. They switch between forward and reverse heads.
 
o problema está na reprodução para frente e para trás, os marcadores (vu's) funcionam normalmente
 
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