688 problem, seeking help

[HermanLifer]

I'm experiencing a puzzling issue with this 688 midistudio. Everything seems to work fine, except an intermittent popping through channels one and two, when no inputs are used and no tape is in the deck. The sound can be heard through the monitor and the meters bounce accordingly. I've got electronic repair experience, I'm just looking for tips to speed up the troubleshooting. So far I've cleaned up all the pots, faders and connections. I've also cleaned the heads of the tape deck. I'm thinking this it's an output issue, because signals are good on their way into these channels. Any advice would be welcome. I'm new to tape machines.

 

[John Mackenzie]

This sounds like a capacitor problem, or dry joint somewhere. Could be difficult to find. I am surprised you only get this on only two channels. My 688 just recently blew up. When I switched it on, all the meters went to full red, and there was a nasty smell. Now I have no audio at all, but everything else works perfectly. Do you think this might be a power supply issue or perhaps an audio chip failure? i am waiting for the service manual to arrive from USA, to try and identify the problem. I really love this machine and am willing to spend some money on it, within reason !!

 

[rohmal]

Did Sir John, If you check your power supply. It should have on pin 1 -0V, pin 2-+10V, pin 3-negative 10V and on pin 4-+7V. If all is OK and check when a pre-recorded tape is played you have LCD meter level display on it when OUTPUT button pressed for display. If all is OK your sound output is blown. In my unit 644 the out put IC's are BA6209 ( seperate for each channel). There may be a pre-amp also. If you open the unit You can visually see any burnt part as if it diid smell before stopping.