Sansui BA-2000 Heavy Distortion Left Channel No Sound Right Channel

bhuskins

bhuskins

Super Member
As the title states, no sound at all on the right channel and the left channel is heavily distorted at all volume levels but the volume of distorted sound does increase/decrease with the left gain control.

It passes a DBT and comes out of protection just fine. Here's what I've checked/tested/replaced:

-All fusible/raised resistors on F-2661, F-2630, F-2581x4, F-2631 replaced (many were way out of spec and a few open)
-All VD-1212 replaced on F-2661 and F-2630
-Pulled and Checked all Output Transistors, All Test perfectly fine.
-Pulled and tested all the Transistors on F-2661, since pulled I went ahead and replaced them but all tested fine
KSA916 for TR01 TR02
KSC1845 for TR03 TR04 TR05 TR06
KSA1381 for TR07 TR08 TR21 TR22
KSC3503 for TR09 TR10 TR11 TR12 TR13 TR14 TR19 TR20
BC337 for TR15 TR16
BC327 for TR17 TR18
MJE15030 for TR23 TR24
MJE15031 for TR25 TR26
-Pulled and tested TR607 and TR608 on F-2630 and both tested fine, went ahead and replaced with MJE15032/33
-Cleaned the Gain controls thoroughly with Deoxit
-Cleaned the Meter controls thoroughly with Deoxit
- Checked all fuses by removing and they check fine

No visible signs of any damage, overheating, leaking or swollen caps and no response from the meters either when turned on and playing the distorted sound in the left channel. Other than the dust I removed from inside it looks to be a fairly low mileage amp.

Before I go through the rest of the transistors on F-2630 I figured I should take a step back and see if anyone has an approach for me to track down the issue...I suspect it's a minor but having a big impact issue because I've been through most all of the usual suspects I've seen on this amp.

Also, before I touched anything I did power it up on DBT and it passed fine and also came out of protection. Same output situation...no sound/distorted sound.

Any help is appreciated.
 
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I would check some of the basics
Make sure that you have properly installed all of the transistors you replaced. Its very easy to reverse the pins when replacing. Verify that all B, E and C pins are in the right place. Make sure there aren't any swaps of pnp and npn small signal transistors. Make sure that all of the connections are good, and that none of the traced is damaged.

Make sure that you have the proper +55v and - 55v going to the output boards for the left and right channels. These appear to be seperate power supplies feeding the left and right channels. This same +55v should appear on pin 9 and pin 10 of the driver board, and the -55v should appear on pin 11 and pin 12.
Then check thay you have the proper +57v on pin 13 and 14, and -57v on pin 15 and pin 16 on the driver board.

If the voltages appear OK, check the DC balance and bias on both sides to see if it appears OK (0 volts on DC balance, and up to 100ma on bias measuring as per manual.

If this appears OK then use a signal tracer to see if you are getting audio to pins 1 and pin 2 on the driver board feeding in a normal input.

If you are getting audio to the input of the driver board for both channels, then your problem is on the driver board or after the driver board.
check pin 10 of the 4 output boards to see if if you get clean audio using the signal tracer. If you don't have clean audio on any of the pin 10's, then you have problems on the driver board or output issues.

If you can get clean audio on both channels then you driver and output boards are OK, and the problem is past the outputs. Check for bad relay contacts in the speaker relay, or cracked circuit traces on the protect board, or dirty or damaged speaker selector switches if any.

Good luck
 
So I finished out all the transistors on F-2661 and F-2630...I also checked all the voltages and they looked great. All of my pin outs are correct...definitely a critical part of transistor replacements and a showstopper if overlooked.

Also, music is nice and clear on the left channel now with a responsive left meter...so I start to focus on the signal for the right channel. I can get a nice loud hum on the right channel when poking around so I have a feeling the amplification is likely good to go...same hum on left channel when doing the same poking on the matching sections.

I start by tracing from the RCAs to the connections on the F-2631 Volume and Meter Board...I can swap the right input over to left and it works fine so no issues there. I can also swap the meters and either meter will work with the left channel so no issues there as well. Finally, I decide to swap the soldered signal outputs from the F-2631 and sure enough the Right channel plays just fine.

This tells me my issue is defintiely on the F-2631 Level Volume & Meter Board which should be easy enough to figure out.

I've already replaced the one and only fusible resistor on this board and I also replaced all (4) 2SC1400 with (4) KSC1845. I've checked under magnification for any circuit cracks, etc and can't find any. I'll look over the schematic and see how I should trace it but does anyone have a suggestion?

I'm definitely getting close...should be just one last thing...
 
Once I looked at the schematic I realized there's nothing on the input and output of the signal other than the gain control. Pulled them both and tested/compared them. Turns out the right one is completely bad...I had a spare 100k pot on hand and popped it in...the amp is finally working on both channels. Time to tweak it and button it up.

Thanks
 
Tom B said:
I would check some of the basics
Make sure that you have properly installed all of the transistors you replaced. Its very easy to reverse the pins when replacing. Verify that all B, E and C pins are in the right place. Make sure there aren't any swaps of pnp and npn small signal transistors. Make sure that all of the connections are good, and that none of the traced is damaged.

Make sure that you have the proper +55v and - 55v going to the output boards for the left and right channels. These appear to be seperate power supplies feeding the left and right channels. This same +55v should appear on pin 9 and pin 10 of the driver board, and the -55v should appear on pin 11 and pin 12.
Then check thay you have the proper +57v on pin 13 and 14, and -57v on pin 15 and pin 16 on the driver board.

If the voltages appear OK, check the DC balance and bias on both sides to see if it appears OK (0 volts on DC balance, and up to 100ma on bias measuring as per manual.

If this appears OK then use a signal tracer to see if you are getting audio to pins 1 and pin 2 on the driver board feeding in a normal input.

If you are getting audio to the input of the driver board for both channels, then your problem is on the driver board or after the driver board.
check pin 10 of the 4 output boards to see if if you get clean audio using the signal tracer. If you don't have clean audio on any of the pin 10's, then you have problems on the driver board or output issues.

If you can get clean audio on both channels then you driver and output boards are OK, and the problem is past the outputs. Check for bad relay contacts in the speaker relay, or cracked circuit traces on the protect board, or dirty or damaged speaker selector switches if any.

Good luck
Click to expand...
Hi @Tom B, I have a similar issue and am trying to follow your instructions above. I’m at the point where I need to check pin 10 on the four F-2581 boards. I see pin 10 on the schematic, but not on the board diagram, or the actual board. Do you happen to know where this thing is hidden? My eyes must be getting old!
 
Hunleyj said:
Hi @Tom B, I have a similar issue and am trying to follow your instructions above. I’m at the point where I need to check pin 10 on the four F-2581 boards. I see pin 10 on the schematic, but not on the board diagram, or the actual board. Do you happen to know where this thing is hidden? My eyes must be getting old!
Click to expand...
Never mind. I wasn’t thinking clearly. Just used the leg of R3. Anyway, signal is clean, so the hunt continues.
 
Hunleyj said:
Never mind. I wasn’t thinking clearly. Just used the leg of R3. Anyway, signal is clean, so the hunt continues.
Click to expand...
Yes the schematic and SM seem to have issues. While the schematic shows pin 10, the board layout for the 2581's shows as pin 9 in the very center, where the 2 emitter resistors meet.
 
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