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Sansui 2000a Dead left channel

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poppa_psychs

New Member
Hello everyone,
I want to first say how helpful this forum has been for my getting started in a restoration of an old unit.
I recently recapped the big power caps and all the electrolytics on the power amp card. Used the unit for awhile and started noticing weak bass in the left channel which turned into a completely dead left channel.
I then replaced the transistors on the power amp card hoping that would bring it back. It didn’t. Now I’m wondering where to go.
I have sprayed deoxit on the pots but haven’t done anything with the tone board itself.
If I touch the pre-main jumpers, the right one makes a buzz but the left does nothing.
Just wondering if anyone could offer any guidance.
Thanks for the help!
 
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Take out the pre main-in jumper. Connect left pre to right main in and right pre to the left main in with jumper RCA cable. If your problem switched side then the problem is in the preamp. you have to work on the pre-amp. If problems remain in the right then the main amp still has a problem.
 
Thanks for the response sanjib
If I swap the inputs and the sound comes out of the same speaker, the 1180 card is probably to blame correct? Just making sure I’m thinking about that correctly.
 
poppa_psychs said:
Thanks for the response sanjib
If I swap the inputs and the sound comes out of the same speaker, the 1180 card is probably to blame correct? Just making sure I’m thinking about that correctly.
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Not the input. The conventional jumper between Pre-out and Main-in at the back of the receiver connects left pre to left main and right pre to right main. You should take out those jumpers first and then you connect left pre to right main and right pre to left main with RCA cable.
 
Ok. I tried that the other day (left pre out to right main in and vice versa) sound was still coming from right speaker. This should eliminate the tone control board correct?
 
poppa_psychs said:
Ok. I tried that the other day (left pre out to right main in and vice versa) sound was still coming from right speaker. This should eliminate the tone control board correct?
Click to expand...
Yes. Is your left channel dead silent? Have you checked the fuse F801 and F802, particularly the one connected to left channel?
 
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Yes the left channel is dead silent. I even plugged an iPod into the main as another check left was dead then too. I checked the fuses with a meter both are good. I may have to just check all the transistors that I replaced on the 1180 card.
 
I really appreciate your guidance on this. Thanks a lot! I am going to pull those transistors and check them out. Hope to provide an update soon
 
I pulled those transistors and tested them per that post. They checked out ok. I did order some replacements. Just considered it part of the restoration. Do you think it would be worth swapping the ones from the right channel? As another check.
 
Do you have a dim bulb tester? If you measure it ok then put it back on. Can you measure the voltages at different points on amp board as it is marked in the schematic? Also, before putting the OT recheck all of your work on the board, in particular, the polarity of caps and the orientation of transistors.
 
I don’t have a dim bulb tester. Just a fluke meter. I’m still new at this and reading the schematic is a skill I’m still learning! If there is a voltage shown, and it isn’t associated with a cap, I should see that at that location? I think my capacitors are ok. I’ve used it since their replacement. Will check the transistors
 
Okay powering on check the voltages on the collectors (that is the outer case of transistors) of the terminal output transistors and next on the collectors of two middle output transistors. Have you replaced C821 and C822?
 
I guess 33VDC is in the good channel and 26VDC in the bad channel (left channel)? Check whether you can bring that voltage around 33V by rotating VR801
 
Are you getting any sound from the left channel now?
After working on the amp boards did you adjust the bias current as mentioned in SM?
First, adjust the bias current I believe it should be 10mA, then you have to balance the amp. If you follow the SM you need to have a signal generator and the oscilloscope and that the best method. But if don't have it then you make the voltages at the collectors of middle OT's equal to half of that at the terminal OTs by turning VR801 and 802.
 
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