Stereomour II - Issue with Shunt Regulator?

lskiii · 10130

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Offline Paul Birkeland

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Reply #15 on: April 25, 2021, 04:57:04 AM
Yes, you may need to shrink the photos a little.

Paul "PB" Birkeland

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Offline lskiii

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Reply #16 on: April 25, 2021, 10:35:32 AM
Image 1 of 3


Offline lskiii

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Reply #17 on: April 25, 2021, 10:37:10 AM
Image 2 of 3


Offline Paul Birkeland

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Reply #18 on: April 25, 2021, 11:55:18 AM
It would be a good idea to remove enough wires from the SR PC board to be able to photograph the bottom of it as well.

Paul "PB" Birkeland

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Offline lskiii

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Reply #19 on: April 25, 2021, 01:35:08 PM
Close ups of the 2 boards.


Offline lskiii

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Reply #20 on: April 25, 2021, 01:36:33 PM
2 of 4


Offline lskiii

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Reply #21 on: April 25, 2021, 01:37:25 PM
3 of 4


Offline lskiii

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Reply #22 on: April 25, 2021, 01:37:49 PM
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Offline Paul Birkeland

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Reply #23 on: April 25, 2021, 03:15:28 PM
I would go ahead and replace the TL431 on the offending side and see if that helps the situation.

Paul "PB" Birkeland

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Offline lskiii

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Reply #24 on: April 25, 2021, 07:01:29 PM
I may be out of my depth here, but from the manual, I believe you're referring to the LM431A regulator?  I'm not sure how exactly I would go about replacing that.  i.e. Where would I get the part?   



Offline Paul Birkeland

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Reply #25 on: April 25, 2021, 07:05:45 PM
You can grab one from Mouser or e-mail replacementparts(at)bottlehead(dot)com about getting a new one.  The one we use is the LM431ACZ. 

Paul "PB" Birkeland

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Offline lskiii

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Reply #26 on: April 25, 2021, 08:12:46 PM
Sounds good - I purchased on mouser and will respond back once done.  Thanks. Louis


Offline lskiii

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Reply #27 on: May 06, 2021, 03:17:37 PM
Hello - so I finally got around to trying to replace the LM431.  Sadly, I believe I trashed the PC board in the process...  I removed the old LM431 but in trying to clean out the old solder to install the new, I must have used too much heat because one of the leads to the whole came loose from the board. 

Is it possible for me to purchase a replacement big board and parts or do I need to purchase a whole new upgrade kit?    Based on my skills, it's much easier for me to populate a PC board than it is to remove/replace old components - esp. one that has 3 prongs that are close together - so just a new board wouldn't work.  I would need the new large board + components...

Thanks.


Offline Paul Birkeland

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Reply #28 on: May 07, 2021, 05:54:54 AM
Yes, you would just need to e-mail replacementparts(at)bottlehead(dot)com.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline lskiii

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Reply #29 on: May 13, 2021, 05:57:45 PM
Hello

So, today I got the replacement shunt regulator and installed it.

The good news is that the new measurements are all correct - the bad news is that the problem hasn't gone away.


OB 298
OA 298
IB. 392
IA. 392

KREG A 4.0
KREG B 3.7

When I was reassembling the shunt regulator I followed every step and I noticed a problem - I had incorrectly switched the white wire going to C8 and the red wire going to C6.  So, correcting that I now I have the white wire from KREG A going to C8.  I believe that I messed this up when I was re-soldering all the leads going to "C".  I was doing that because I thought that my problem (very weak signal in the left channel) might have been due to an issue there.

So, I suspect that in trying to trouble shoot my issue with the left channel is when I accidentally swapped those 2 wires which led to the messed up shunt regulator readings.

Regardless, I'm kind of back to the original issue.  Right channel sounds great.  Left channel is weak, has some distortion and gets louder when I power off (and then it fades).  I've swapped tubes, source, etc.

Any suggestions?

Thanks,
Louis


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