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Sansui 7070

Before taking everything apart, and just changing parts, why don't you TROUBLESHOOT by making some voltage measurements around TR602, to see if the issue is indeed a muting issue. My schematic does not have readable voltages on it (they are all black), but you can tell if TR602 is turning the muting on by comparing the voltages on terminal 28 and 29 of the F2620 board, or better yet by checking the voltage at the collector of TR602. If there is more than a few milivolts on the collector of TR602, or if terminal 29 is more than a volt or so lower than terminal 28, then TR602 is conducting, sending positive voltage to the base of TR603 and TR604 and the muting is turned on. It is controlled by the mode switch, the phono 1-2 switch and the protect relay normally closed contacts (the ones connected with the relay off).
 
Last edited:
AE Bob said:
Before taking everything apart, and just changing parts, why don't you TROUBLESHOOT by making some voltage measurements around TR602, to see if the issue is indeed a muting issue. My schematic does not have readable voltages on it (they are all black), but you can tell if TR602 is turning the muting on by comparing the voltages on terminal 28 and 29 of the F2620 board, or better yet by checking the voltage at the collector of TR602. If there is more than a few milivolts on the collector of TR602, or if terminal 29 is more than a volt or so lower than terminal 28, then TR602 is conducting, sending positive voltage to the base of TR603 and TR604 and the muting is turned on. It is controlled by the mode switch, the phono 1-2 switch and the protect relay normally closed contacts (the ones connected with the relay off).
Click to expand...
Can you just pull TR602 and eliminate the Muting altogether? I realize there could and/or would be "pops" when changing sources.
 
.It shouldn't be that hard to properly repair the unit. You could disconnect the collector of TR602 as a test to see if the sound comes back. BE SURE to clean both the input selector switch, AND THE PHONO 1-2 SWITCH I spent a great deal of time trying to figure out an issue just like yours, and it turned out to be just a dirty contact in the phono 1-2 switch.
 
Hi Bob, hi Sky!
I fixed the problem. The Reciver works normal. Thanks Bob for your suggestion. I changed the faulty transistor T602 (A726) on F-2620. I had one, other wiring, B in the centre. But no problem to install, Dismanteling F-2620 is not such a problem. The chassis had to be unscrewed (4 screws).
Thanks very much for the support, I would never figured it out.
Regards, Dusan.
 
Dusan Bozic said:
Hi Bob, hi Sky!
I fixed the problem. The Reciver works normal. Thanks Bob for your suggestion. I changed the faulty transistor T602 (A726) on F-2620. I had one, other wiring, B in the centre. But no problem to install, Dismanteling F-2620 is not such a problem. The chassis had to be unscrewed (4 screws).
Thanks very much for the support, I would never figured it out.
Regards, Dusan.
Click to expand...
:beerchug::rockon:
 
Dusan Bozic said:
Hi Bob, hi Sky!
I fixed the problem. The Reciver works normal. Thanks Bob for your suggestion. I changed the faulty transistor T602 (A726) on F-2620. I had one, other wiring, B in the centre. But no problem to install, Dismanteling F-2620 is not such a problem. The chassis had to be unscrewed (4 screws).
Thanks very much for the support, I would never figured it out.
Regards, Dusan.
Click to expand...
Hi Dusan, when you said "The chassis had to be unscrewed (4 screws)", is this to detach the front portion (faceplate side) of the chassis? Would this cause a problem with loosening the tuner string?

I'm also looking for tips to get access to this F-2620 board so I can replace its components.
 
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