Can not find it for the life of me 🙁
But, if I measure between R11, and R32, I am getting 0.4ohm
(TB101 is between those I believe…)
But, if I measure between R11, and R32, I am getting 0.4ohm
(TB101 is between those I believe…)
Ok, found it! I think…
It’s just over 1/2” in diameter. Between the PC and the heat sink.
Feeling pretty dumb right now. Not sure how I could have overlooked that…
It’s measuring 0.4ohm across the two leads
It’s just over 1/2” in diameter. Between the PC and the heat sink.
Feeling pretty dumb right now. Not sure how I could have overlooked that…
It’s measuring 0.4ohm across the two leads
Do you also see another one for the other channel? Measure it also at the board like the first one.
Can you post a good photo of the one you found?
Can you post a good photo of the one you found?
The problem is definitely related to this circuit, whether the thermal switch or something else.
Maybe there's a part of the schematic missing with protection circuitry.
There's an old saying.
Maybe there's a part of the schematic missing with protection circuitry.
There's an old saying.
“The more you look, the more you see.”
― Pirsig, Robert M., Zen and the Art of Motorcycle Maintenance
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I'm sure that someone who has worked on these amps knows the problem.
But it likely has something to do with the front end current sources shutting down.
But it likely has something to do with the front end current sources shutting down.
Quick update…
While testing P1 from the +73 input on the amp board, and trying to find a point check, I ended up using R14 to check continuity
On the left channel im seeing 1.16K on R14 (which makes sense as P1, R14 and R13 are all in parallel I think?) R13 is measuring as 7.48K
On the right channel however, I am getting 0.3ohm on R14, and 7.48K on R13.
Something is not right in the P1 area…
Any thoughts would be greatly appreciated!
Thanks!
While testing P1 from the +73 input on the amp board, and trying to find a point check, I ended up using R14 to check continuity
On the left channel im seeing 1.16K on R14 (which makes sense as P1, R14 and R13 are all in parallel I think?) R13 is measuring as 7.48K
On the right channel however, I am getting 0.3ohm on R14, and 7.48K on R13.
Something is not right in the P1 area…
Any thoughts would be greatly appreciated!
Thanks!
Adjusting P1 has zero effect on the resistance.
I guess either R14, or P1 is shorted?
Need to pull them to test.
Which brings me back to the removal of the boards from the heatsink 🙂
I guess either R14, or P1 is shorted?
Need to pull them to test.
Which brings me back to the removal of the boards from the heatsink 🙂
R14 measures fine
P1 is 5.37K between pin 1&3(outside pins) and when I started measuring it was zero between 1&2. And it was 5.37K between pin 2&3
Turned the screw back and forth and then screwed it waaaaaay in and it’s now approx. 2.5K between 1&2 as well as between 2&3.
Could it be that someone had adjusted it that far out? I tried turning it while in circuit, but made no difference…
P1 is 5.37K between pin 1&3(outside pins) and when I started measuring it was zero between 1&2. And it was 5.37K between pin 2&3
Turned the screw back and forth and then screwed it waaaaaay in and it’s now approx. 2.5K between 1&2 as well as between 2&3.
Could it be that someone had adjusted it that far out? I tried turning it while in circuit, but made no difference…
Just finished attaching the board to the heatsink.
Will get it back together shortly and see what we get!
Will get it back together shortly and see what we get!
No change 🙁
-81.0vdc on the right output.
+80.6vdc on the left output.
That’s all I’m doing for tonight. Too tired, and mistakes will happen 🙂
-81.0vdc on the right output.
+80.6vdc on the left output.
That’s all I’m doing for tonight. Too tired, and mistakes will happen 🙂
I was thinking I should replace both P1 and P2 on both L&R channels.
At least I know those are ok 🙂
At least I know those are ok 🙂
Use only high quality pots with the same footprint.
Check the setting of the left channel pot and set its new pot to the same value.
Might as well set the right pot to somewhere in the middle of its range to start with.
P1 trims the output DC offset voltage. That the right channel pot was turned
to one extreme seems like someone tried to trim out the high output DC voltage,
unsuccessfully of course.
The P2 sets the output stage DC bias current. Be sure to set the new P2 pots
to the same setting as the old ones before applying power.
Or else turn them both to minimum.
Check the setting of the left channel pot and set its new pot to the same value.
Might as well set the right pot to somewhere in the middle of its range to start with.
P1 trims the output DC offset voltage. That the right channel pot was turned
to one extreme seems like someone tried to trim out the high output DC voltage,
unsuccessfully of course.
The P2 sets the output stage DC bias current. Be sure to set the new P2 pots
to the same setting as the old ones before applying power.
Or else turn them both to minimum.