Ampeg BA115HP Output and crackling/static

[g1]

Reinstall C40?

No. C40 is suspect and should be thrown out and replaced. You measured a short across it (D12 diode check) that went away when it was removed. It might only fail when under voltage.
It's a very cheap part and not worth taking a chance of it failing again.
If you don't have one, you can continue testing without it until you get a new one.

[ca7922303]

No. C40 is suspect and should be thrown out and replaced. You measured a short across it (D12 diode check) that went away when it was removed. It might only fail when under voltage.
It's a very cheap part and not worth taking a chance of it failing again.
If you don't have one, you can continue testing without it until you get a new one.

Got 100uF 35v radial capacitors delivering Saturday..

[ca7922303]

No. C40 is suspect and should be thrown out and replaced. You measured a short across it (D12 diode check) that went away when it was removed. It might only fail when under voltage.
It's a very cheap part and not worth taking a chance of it failing again.
If you don't have one, you can continue testing without it until you get a new one.

Installed 100uF 35v(C40).

[ca7922303]

No. C40 is suspect and should be thrown out and replaced. You measured a short across it (D12 diode check) that went away when it was removed. It might only fail when under voltage.
It's a very cheap part and not worth taking a chance of it failing again.
If you don't have one, you can continue testing without it until you get a new one.

Rechecked voltages after C40 installed and they're back where they were with original C40 installed.

[g1]

Rechecked voltages after C40 installed and they're back where they were with original C40 installed.

So you are still missing the -16V at D12?

[ca7922303]

So you are still missing the -16V at D12?

Yes

[g1]

Now in circuit, C40 measures low resistance across it again?

[ca7922303]

Now in circuit, C40 measures low resistance across it again?

Yes

[g1]

Then it was just coincidence or measurement error when you lifted it before and D12 gave correct voltage. Something in the line supplied by the -16V must be shorted.
Try de-soldering the IC's (-) supply pins until you no longer measure the short across C40. Do them one at a time and re-check C40 resistance each time.

[x-pro]

Show a picture of the C40 from the solder side.

[ca7922303]

Then it was just coincidence or measurement error when you lifted it before and D12 gave correct voltage. Something in the line supplied by the -16V must be shorted.
Try de-soldering the IC's (-) supply pins until you no longer measure the short across C40. Do them one at a time and re-check C40 resistance each time.

It was U5. Pins 3&4 were soldered together. They are separate now. C40 is reading mega ohms now.

[g1]

Do you have output at headphones or speaker now?

[x-pro]

It was U5. Pins 3&4 were soldered together..

post 215 [With ground @ speaker output:
D12(-16/-16vdc)]


Questionable result. If there was definitely a fault there, then the absence of C40 would not help in shaping (-16V) either.

[ca7922303]

Do you have output at headphones or speaker now?

Have distorted output thru headphones only. No speaker output.

[g1]

Do you now have proper -16V across C40 ?