Stereomour II - Issue with Shunt Regulator?
- Thread starter lskiii
- Start date
We will have to address the lower volume with just a tube in socket B only. Leave the jumper wire in that you have now between A3 and D3, then add another jumper between terminals 10 and 11. With the two jumpers in, let me know if the volume level coming out of the amp is evened out.
-PB
-PB
Well, that would have me suspecting that you have a broken wire or a bad solder joint on or around the 9 pin socket on the offending side.
So, I re-soldered pin 9 on the C socket (the left channel) and when I tested it, both the L and R channels sound the same (which is good). Thinking that the problem was solved, I removed the jumper between the 3 pins and the 10/11U and the problem came back (L channel is weak). So, I re-installed the jumpers and the problem went away again.
What should I try next?
Also - I hope this helps - I keep suspecting that there's a problem with the C socket. While music was playing just now, I touched the tube in the C socket and got a ton of crackling noises. If I do the same thing to the tube in the B socket, nothing happens. I also noticed that if I applied light pressure to the C socket that there was a large volume drop. Again, doing the same on the B socket produces no change.
To go back to the very beginning of this thread, I had suspected all along that there's something wrong w/ the C socket - it's either a bad solder joint or something with the socket itself. So, before even opening this case, I re-soldered the whole C socket. When doing that, I believe I accidentally swapped the wires going to the shunt regulator. I believe that this is why I started this thread thinking that the issue was with the shunt regulator (as it was measuring wrong).
What should I try next?
Also - I hope this helps - I keep suspecting that there's a problem with the C socket. While music was playing just now, I touched the tube in the C socket and got a ton of crackling noises. If I do the same thing to the tube in the B socket, nothing happens. I also noticed that if I applied light pressure to the C socket that there was a large volume drop. Again, doing the same on the B socket produces no change.
To go back to the very beginning of this thread, I had suspected all along that there's something wrong w/ the C socket - it's either a bad solder joint or something with the socket itself. So, before even opening this case, I re-soldered the whole C socket. When doing that, I believe I accidentally swapped the wires going to the shunt regulator. I believe that this is why I started this thread thinking that the issue was with the shunt regulator (as it was measuring wrong).
Now try just the A3/D3 jumper, then just the 10/11 jumper.
If the amp is OK with the A3/D3 jumper but not ok wit the 10/11 jumper, then you have a driver issue (9 pin socket) on that channel. Typically when your DC voltages are OK but the sound is not,, that's a soldering problem or a broken wire that's just barely making contact where it's broken. Sometimes these issues can be revealed by playing music through the amp and poking around with a wooden chopstick to see if pressing on any particular area dramatically changes the sound or causes pops. This can help focus your efforts quite a bit.
If the amp is OK with the A3/D3 jumper but not ok wit the 10/11 jumper, then you have a driver issue (9 pin socket) on that channel. Typically when your DC voltages are OK but the sound is not,, that's a soldering problem or a broken wire that's just barely making contact where it's broken. Sometimes these issues can be revealed by playing music through the amp and poking around with a wooden chopstick to see if pressing on any particular area dramatically changes the sound or causes pops. This can help focus your efforts quite a bit.
So here's what I found:
Jumper on 10/11 only - L and R sound the same
Jumper on 3/3 pins - L is weaker than R
Sounds like that narrows down the situation a bit? I've visually inspected the L channel wiring many times and reflowed anything that looks fishy to me. I'm open to any suggestions.
Thanks!
Jumper on 10/11 only - L and R sound the same
Jumper on 3/3 pins - L is weaker than R
Sounds like that narrows down the situation a bit? I've visually inspected the L channel wiring many times and reflowed anything that looks fishy to me. I'm open to any suggestions.
Thanks!
Not sure is this helps, but I also just tried it with no jumper at all.
No jumpers, Left is substantially weaker than Right. Right sounds great.
3 - 3 jumper, Left is weaker than Right but not as extreme. Also, Right sounds very bass heavy.
I tried reflowing a bunch of connections on the left channel just now. Still no change.
I guess my last hope is to tap on every connection on the left channel while the system is playing?
Thanks
No jumpers, Left is substantially weaker than Right. Right sounds great.
3 - 3 jumper, Left is weaker than Right but not as extreme. Also, Right sounds very bass heavy.
I tried reflowing a bunch of connections on the left channel just now. Still no change.
I guess my last hope is to tap on every connection on the left channel while the system is playing?
Thanks
These results now seem to contradict what you were experiencing before. If just a jumper between 10 and 11 appears to solve your problem, then you have a wiring/solder problem between the RCA jacks and the amp itself. This could be something like a loose resistor in your attenuator if you have that upgrade or a bad solder joint on one of the pots. Jumpering 10 and 11 combines L+R outputs from the input selector and attenuator.
I figured it made sense to start over a bit, so I did a full resistance and DC test and I think I might have found something.
Every test checked out except for 14. I was reading 260. I looked around at what that's connected to and it's connected to the small board. On the small board there are 2 heat sinks. The heat sink that goes to 02B was completely cold to the touch, while the other was warm.
Would this offer any clue as to where to look? I'll try re-soldering the small board right now just in case.
Thanks
Every test checked out except for 14. I was reading 260. I looked around at what that's connected to and it's connected to the small board. On the small board there are 2 heat sinks. The heat sink that goes to 02B was completely cold to the touch, while the other was warm.
Would this offer any clue as to where to look? I'll try re-soldering the small board right now just in case.
Thanks
That feeds terminal 14 then down to the 9 pin socket on that side to pin 1. If you have the 10/11 jumper, does that DC voltage change?
For you to get 260 there, here are some possibilities:
1. Bad solder joint or missing jumper between pins 4 and 5 on the 9 pin socket.
2. Loose cathode resistor going to pin 3 on the 9 pin socket.
3. Missing ground reference from attenuator issues (ruled out with the 10/11 jumper).
4. Bad solder joint on the small PC board itself, especially the center joint of the MJE5731A.
5. Broken wire getting from the "O" terminal to the 9 pin tube socket itself.
What DC voltage do you see at pin 3 on that 9 pin socket?
1. Bad solder joint or missing jumper between pins 4 and 5 on the 9 pin socket.
2. Loose cathode resistor going to pin 3 on the 9 pin socket.
3. Missing ground reference from attenuator issues (ruled out with the 10/11 jumper).
4. Bad solder joint on the small PC board itself, especially the center joint of the MJE5731A.
5. Broken wire getting from the "O" terminal to the 9 pin tube socket itself.
What DC voltage do you see at pin 3 on that 9 pin socket?
1. Bad solder joint or missing jumper between pins 4 and 5 on the 9 pin socket.
I just did a resistor test and both pins 4 and 5 go to ground, and the solder looks really solid.
2. Loose cathode resistor going to pin 3 on the 9 pin socket.
Is this the resistor from the center of the socket to pin 3? If so, I did a resistance test and it's .366
3. Missing ground reference from attenuator issues (ruled out with the 10/11 jumper).
4. Bad solder joint on the small PC board itself, especially the center joint of the MJE5731A.
I reflowed the solder, but it looks good to me. Is there a way to test the MJE5731A?
5. Broken wire getting from the "O" terminal to the 9 pin tube socket itself.
Did a resistance test between the O terminal on the small board and pin 1 and it's a good connection.
I just did a resistor test and both pins 4 and 5 go to ground, and the solder looks really solid.
2. Loose cathode resistor going to pin 3 on the 9 pin socket.
Is this the resistor from the center of the socket to pin 3? If so, I did a resistance test and it's .366
3. Missing ground reference from attenuator issues (ruled out with the 10/11 jumper).
4. Bad solder joint on the small PC board itself, especially the center joint of the MJE5731A.
I reflowed the solder, but it looks good to me. Is there a way to test the MJE5731A?
5. Broken wire getting from the "O" terminal to the 9 pin tube socket itself.
Did a resistance test between the O terminal on the small board and pin 1 and it's a good connection.
You can flip the small PC board 180 degrees and reconnect it to see if the problem is on the board or off the board.
I think we're getting there -
I flipped the board, and now 14 (OA) measures 218 and 7 measures 263.
7 is now going to OB and 14 to OA. I flipped IA and IB as well w/ 9 and 12. They measure the same - 297.
Seems like the issue followed the A side of the small board? Would replacing the small board be the thing to do?
Thanks!
I flipped the board, and now 14 (OA) measures 218 and 7 measures 263.
7 is now going to OB and 14 to OA. I flipped IA and IB as well w/ 9 and 12. They measure the same - 297.
Seems like the issue followed the A side of the small board? Would replacing the small board be the thing to do?
Thanks!
I would reflow the joints on the transistors. When you get high voltage out that is very frequently a cold joint on the center leg of the MJE5731A. As a last resort you could ask replacement parts about getting a new board, LEDs, transistors, and resistors. Just replacing the transistors on that side would also likely do the job.
I just tried reflowing and that didn't do the trick.
As a last step, I just checked the sound and the weak channel is now on the right side. So, clearly the issue is somewhere on that small board.
I'm going to just buy the parts and swap it out.
Thank you for your help and patience.
As a last step, I just checked the sound and the weak channel is now on the right side. So, clearly the issue is somewhere on that small board.
I'm going to just buy the parts and swap it out.
Thank you for your help and patience.
