With a voltage drop of ~29v across R5, you have about 2.9mA current flow which is above the 0.5mA required to unmute the amp (assuming the 10k was used as current limiting resistor).
You are reading -1.9 on P4 (V-) which should be -31. Check your U4 connector is made properly and has -31v there.
Make sure that you have continuity between each component leg and the next component on the schematic, to ensure good soldering.
When I solder PTH (Plated Through Hole) boards, I will flow enough solder from the back to make sure that the upper surface pad has a good joint too. I've had cheap boards in the past that have not had continuity from one side to the other, so it pays to check the upper surface joints and retouch those as required.
Thank you avtech, those are valuable points and I will get to them as soon as my wife turns me loose.
Interesting about soldering PTH, I had wondered about that.
Ok back at it.
I desoldered all the components and restuffed a new board.
It's running now but the readings are odd when I compare it to the other board.
The output varies like this. -2.0, -3.4, -4.n, -5.n, then back to -2 again.
l seem to remember that any DC at the output is bad, so how can I get rid of it ?
The other board has about .02 V at the output.
Thanks
I desoldered all the components and restuffed a new board.
It's running now but the readings are odd when I compare it to the other board.
The output varies like this. -2.0, -3.4, -4.n, -5.n, then back to -2 again.
l seem to remember that any DC at the output is bad, so how can I get rid of it ?
The other board has about .02 V at the output.
Thanks
It works !
And thanks to all for the help. After swapping out all the components into a new board,
I think it was a cold or faulty solder joint.
How I found it was by comparing continuity readings to the working board, and reading them from the backside. Between pin 9 and R3, the continuity varied between nil and 45,0,.45,.7. Etc. All over the range. I guess that would the account for the variable readings from the output.
Hallelujah!
So now onward to fit these into the case.
Of note is how darn hot the LM3886 gets. Burned my thumb a few times. While I was testing, I kept a sponge soaked in water and would press it against the chip. It would sizzle and I read a temp of 140c. Wow ! And it got hot in a hurry,
Ok, thanks again for the marvelous learning experience.
And thanks to all for the help. After swapping out all the components into a new board,
I think it was a cold or faulty solder joint.
How I found it was by comparing continuity readings to the working board, and reading them from the backside. Between pin 9 and R3, the continuity varied between nil and 45,0,.45,.7. Etc. All over the range. I guess that would the account for the variable readings from the output.
Hallelujah!
So now onward to fit these into the case.
Of note is how darn hot the LM3886 gets. Burned my thumb a few times. While I was testing, I kept a sponge soaked in water and would press it against the chip. It would sizzle and I read a temp of 140c. Wow ! And it got hot in a hurry,
Ok, thanks again for the marvelous learning experience.
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