Ampeg BA115HP Loud Hum

[ca7922303]

Powers on, loud hum, no controls effect hum, even mute button, disconnected control board to main board(no change). All 10w resistors are good(resistance), all diodes are good(diode test),

[glebert]

Did you disconnect the speaker and see if the amp was sending DC to it?

If no DC, is there bass sound that comes out with the hum?

FYI, I'm pretty sure the power amp can't function without the front panel board connected. The zeners for generating the +/- 16v are located there and the power amp needs those for the bias circuit.

[ca7922303]

Did you disconnect the speaker and see if the amp was sending DC to it?

If no DC, is there bass sound that comes out with the hum?

FYI, I'm pretty sure the power amp can't function without the front panel board connected. The zeners for generating the +/- 16v are located there and the power amp needs those for the bias circuit.

Speaker disconnected and at board reading(-1.8mv/-17vdc)
No bass sound output Reinstalled control board cable previous to this.

[glebert]

Is that -17VDC at the board speaker terminal? That doesn't seem right.

Just another thing to check, it is pretty easy to get the connectors for the cables between the two boards off by one pin (ask me how I know...)

What do you get out of the headphone jack? How do the voltage rails look?

[ca7922303]

Is that -17VDC at the board speaker terminal? That doesn't seem right.

Just another thing to check, it is pretty easy to get the connectors for the cables between the two boards off by one pin (ask me how I know...)

What do you get out of the headphone jack? How do the voltage rails look?

Yes -17vdc at board speaker terminal. Will check other this evening when off work. Thanks for the help.

[glebert]

I would check all the voltage rails and the gate voltages on the FETs. Having -17V is kind of weird, not zero but not like a shorted FET either. I found getting a reliable ground reference to be a pain on these, I usually use pin 1 of the speaker out connector.

[Enzo]

17v offset suggest to me th op amp in the power amp. Either it has failed and slammed over to one rail, OR it is missing one of its supplies.

That is a 5532, so make sure it has -16v (more or less) on pin 4 and +16v on pin 8. Then look at pin 7, that SHOULD be at zero volts DC.

[ca7922303]

17v offset suggest to me th op amp in the power amp. Either it has failed and slammed over to one rail, OR it is missing one of its supplies.

That is a 5532, so make sure it has -16v (more or less) on pin 4 and +16v on pin 8. Then look at pin 7, that SHOULD be at zero volts DC.

Pins 4 & 8 are mv.

[ca7922303]

Is that -17VDC at the board speaker terminal? That doesn't seem right.

Just another thing to check, it is pretty easy to get the connectors for the cables between the two boards off by one pin (ask me how I know...)

What do you get out of the headphone jack? How do the voltage rails look?

I'll check the headphone jack after work this evening. 5532 pins 4/8 are reading mv. But I'll check again now that you've mentioned ground issue. Thanks.

[Enzo]

Pins 4 and 8 are mv??? You mean each only has a few millivolts? You need to have good clean 16vDC on each of those pins. Negative on pin 4 and positive on pin 8.

[ca7922303]

Pins 4 and 8 are mv??? You mean each only has a few millivolts? You need to have good clean 16vDC on each of those pins. Negative on pin 4 and positive on pin 8.

Yes, pin 4 & pin 8 on the ,5532 only reading a few millivolts each.

[glebert]

So did this amp work OK and just start having this problem? Did it fail during use or after long storage?

If you aren't getting +/-16V and the board cable is properly aligned at both ends either the rails are being dragged down near zero because of shorts or they are never being generated in the first place. I would disconnect the boards and test R66 and R68 to make sure they correct resistance and test D11 and D12 for shorts. If you have shorts across D11 D12 at the board then you have to start removing components (or at least lifting legs) to see what is shorted. If those aren't shorted I would probably look at C39 and C40 next.

edit: looking at first post I see you said all 10w resistors and diodes checked.

[ca7922303]

So did this amp work OK and just start having this problem? Did it fail during use or after long storage?

If you aren't getting +/-16V and the board cable is properly aligned at both ends either the rails are being dragged down near zero because of shorts or they are never being generated in the first place. I would disconnect the boards and test R66 and R68 to make sure they correct resistance and test D11 and D12 for shorts. If you have shorts across D11 D12 at the board then you have to start removing components (or at least lifting legs) to see what is shorted. If those aren't shorted I would probably look at C39 and C40 next.

edit: looking at first post I see you said all 10w resistors and diodes checked.

Got this amp not working. No knowledge about previous condition and yes, all diodes and the 10w resistors test good. I will check components you mentioned this evening when off work. Thanks.

[glebert]

Does the power LED come on? If so then 16V is working at the front board.

[ca7922303]

So did this amp work OK and just start having this problem? Did it fail during use or after long storage?

If you aren't getting +/-16V and the board cable is properly aligned at both ends either the rails are being dragged down near zero because of shorts or they are never being generated in the first place. I would disconnect the boards and test R66 and R68 to make sure they correct resistance and test D11 and D12 for shorts. If you have shorts across D11 D12 at the board then you have to start removing components (or at least lifting legs) to see what is shorted. If those aren't shorted I would probably look at C39 and C40 next.

edit: looking at first post I see you said all 10w resistors and diodes checked.

R66/R68 good D11/D12 good
no output out of headphone jack