9090db post successfull recap issue

I would disconnect the left VU meter before powering up again if it is pegging. You have a left channel issue and no need to damage the meter before troubleshooting the issue.
 
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Overundr1 said:
What is measured resistance on the left vrs right bias trimmer and what value trimmer did you use
Click to expand...
They are both measuring 95ish ohms. They haven't been set up since I switched them out.
Important note the ebay vender accidentally sent me 1k trimmers for the older style board. I reused the originals while the new ones came in. The left trimmer fried in the initial incident.
 
By the way we may start measuring supply voltages to the left channel from under the power supply and comparing them to the right channel to ensure the fault is on the driver card
 
Check the outputs and replace them. Pull the fuses for both channels. Set up to measure bias in ma on left channel and if you have a second meter set it to measure mv of offset at the speaker terminals on left channel. Ask if unsure please.
Also before you power things up please put up a picture of how the outputs are installed
 
Overundr1 said:
What is measured resistance on the left vrs right bias trimmer and what value trimmer did you use
Click to expand...
I used 100ohm. I'm not familiar with the brand
Overundr1 said:
Check the outputs and replace them. Pull the fuses for both channels. Set up to measure bias in ma on left channel and if you have a second meter set it to measure mv of offset at the speaker terminals on left channel. Ask if unsure please.
Also before you power things up please put up a picture of how the outputs are installed
Click to expand...
I have 2 good pairs that I'm using for testing on the left side. I have 2 new pair once I've got this under control.
 

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Update:
I followed instruction as best I could.
-DBT trouble shooting with out speakers and pre amp jumpers removed. VUs disconnected for testing
-set bias and dc offset while on dbt (with original tested and sacrificial Output transistors in left side. Dbt=good.
- full 120v power up came out of protect
-reconnected VU meters
-test listen sounded great. After 10 minutes the left channel flickering CAME BACK. It started subtly then left meter went full. Possibly something warming up and presenting?
This is the same symptom that presented at the intial failure.
I think I shut it down earlier this time.
Testing
-dbt glowed brightly
-dbt was good with the driver out.
-tested old out puts and they have good hfe
-Nothing visually obvious on the driver. Mirror image references between left and right aren't showing anything with a quick skim.

Was ready to set off set and bias at 120v until this.


Not sure the next move.
I can think of a few things that once warmed up become problems in guitar amps. I'm not sure the first place to go here would be?
I did have an issue that resolved with cleaning at the protect board? I'm looking into this...
Possibly helpful note: I reconnected the vu meters once bias and offset were set and stable on dbt. Left meter would jump up at start up and quickly settled and responded correctly after a second or two of pushing the power button.
I can't explain how helpful the generous minds have been. I am learning. Thank you
 
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Testing outputs?
Are you checking all values for leakage (six way test)?
In other words post the results for each output with test meter set to diode function, we need to rule out any sneaky failure mode going on here.
Test both sets of NPN and PNP outputs please
B-E
B-C
E-B
E-C
C-B
C-E

Then you need to carefully inspect the bottom of the driver card for any breaks in the traces between the card edge connector and the next trace in line. Note that some have reported trace breaks UNDER the connector that require its removal to find. I use probes and apply slight pressure to the card edge while using the continuity setting listening for any break in connectivity.

And as long as you are checking things flip the receiver up on its side and with power off inspect all the solder points on the underside of the power supply where the card connector plugs in. A cold solder joint looks like it has a small ring around the solder point, will post up a picture of this in a minute once I find one.

Thermally induced problems are a real rabbit hole to sort out so be prepared for lots of seemingly strange things to look over
1716127768209.jpeg

Those are examples of cold solder joints

:)
 
Overundr1 said:
Testing outputs?
Are you checking all values for leakage (six way test)?
In other words post the results for each output with test meter set to diode function, we need to rule out any sneaky failure mode going on here.
Test both sets of NPN and PNP outputs please
B-E
B-C
E-B
E-C
C-B
C-E

Then you need to carefully inspect the bottom of the driver card for any breaks in the traces between the card edge connector and the next trace in line. Note that some have reported trace breaks UNDER the connector that require its removal to find. I use probes and apply slight pressure to the card edge while using the continuity setting listening for any break in connectivity.

And as long as you are checking things flip the receiver up on its side and with power off inspect all the solder points on the underside of the power supply where the card connector plugs in. A cold solder joint looks like it has a small ring around the solder point, will post up a picture of this in a minute once I find one.

Thermally induced problems are a real rabbit hole to sort out so be prepared for lots of seemingly strange things to look over
View attachment 3205154

Those are examples of cold solder joints

:)
Click to expand...
2sb554

B-E 0. 0
B-C 0. 0
E-B .540 .538
E-C 0. 0
C-B .526 .524
C-E 0. 0


2sd 424

B-E .534 .533
B-C .512 .512
E-B 0 0
E-C 0 0
C-B 0 0
C-E 0 0

currently hunting cold solder joints and other suspect connections...
 
Telefaster said:
2sb554

B-E 0. 0
B-C 0. 0
E-B .540 .538
E-C 0. 0
C-B .526 .524
C-E 0. 0


2sd 424

B-E .534 .533
B-C .512 .512
E-B 0 0
E-C 0 0
C-B 0 0
C-E 0 0

currently hunting cold solder joints and other suspect connections...
Click to expand...
Unfortunately continuity tests at the driver were all good from the socket to the underside of the board and beyond all while applying some flex to the connector. The PS board looked fine. I re flowed a few things but I don't think any were issues. I looked at the protect board and nothing looked out of the ordinary there. I did as many spot checks for breaks in continuity and found nothing.

I am tempted to reinstall the left out puts and test again "cold" to see if something went or is fine and goes bad with some heat?
 
Well done. Outputs look good. As a side note did you change out the R13 and R14 fusible resistors on the protection board F-2657?
As I recall there were two different values used so mind the color code on the bands, either 4.7ohm or 10 ohm. Also the board may be labeled incorrectly so put up a picture if needed.
We also need to consider what is causing the oscillation so - - -
C17 0.047uf
C19 0.001uf
C21 0.001uf capacitors may need to be changed out as they prevent the circuit from oscillating which would cause the fluttering and bias issues. If you have a scope and a signal generator we can actually (see) the oscillation as it happens,
Finally, does the receiver start to mis-behave after a bit if the pre main couplers are left off?
 
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