150ish mV AC which makes no sense at all to me. Its also fluctuating and the waveform is very erratic.
How does the waveform compare to the input on the other rectifier. They should have the same input from the transformer if the rectifiers are center-tapped types.
Use the secondary ground or the negative speaker terminals (assuming that the amp isn't bridgeable) for the scope reference.
Use the secondary ground or the negative speaker terminals (assuming that the amp isn't bridgeable) for the scope reference.
Here are a couple of pics. There is only one bridge rectifier on the amp. I am probably missing something here... Ive been measuring at the output from the bridge rectifier as shown that has two wires going from it to the audio board. here are a couple pics of either side of the power supply board. The blue and red wires are the ones I am presuming are the rail voltage outputs from the rectifier. I am not certain the function of the b829s at this point.
Attachments
![DSC_1625[1].jpg](/community/data/attachments/821/821740-614307abb38b571ffc1bef7a9391f882.jpg?hash=YUMHq7OLVx)
![DSC_1626[1].jpg](/community/data/attachments/821/821765-117dcc0a851f01262fe4c47fd17be029.jpg?hash=EX3MCoUfAS)
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The 2SB829 transistors drive the primary windings of the power transformer.
Bridge rectifiers are rare nowadays. If it has negative rail but no positive rail on the terminals of the rectifier, it likely has failed internally. You can't use a standard bridge rectifier in the amp. You need a high speed rectifier. Standard bridge rectifiers will quickly overheat and fail at the higher frequencies and square wave of a switching power supply.
Bridge rectifiers are rare nowadays. If it has negative rail but no positive rail on the terminals of the rectifier, it likely has failed internally. You can't use a standard bridge rectifier in the amp. You need a high speed rectifier. Standard bridge rectifiers will quickly overheat and fail at the higher frequencies and square wave of a switching power supply.
Sorry pics were being difficult to add. They should be up now. Ive tested the rectifier outside of the circuit and it tests fine.
The connection internally could be intermittent. Did you reinstall it to see if you again had +rail?
Yup, and swapped in another bridge rectifier that I had. Same results. no more than maybe 3VDC pos on the opposite rail.
![DSC_1628[1].jpg](/community/data/attachments/821/821783-0c017a28ccb3ebc1055c5c123b36fd27.jpg?hash=DAF6KMyz68)
![DSC_1629[1].jpg](/community/data/attachments/821/821820-018bf5ec57e92b190a5166c1c63efacc.jpg?hash=AYv17FfpKx)
I don't know how the auto varies but the 97 is a 50mHz scope which is good enough.
Set the scope to 10us and 5v/div and post the waveforms on the collectors of the 2 PS transistors.
Set the scope to 10us and 5v/div and post the waveforms on the collectors of the 2 PS transistors.
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![DSC_1630[1].jpg](/community/data/attachments/821/821953-7b97cc1fce93d9147cf551fa8cd32fc7.jpg?hash=e5fMH86T2R)
The power supply isn't operating. Are you sure that you have negative rail voltage?
The supply may simply be charging the capacitor on the pulses that you see but didn't capture.
Place a meter on the negative rail and see if it remains constant or changes slightly corresponding with the pulses.
Do the same with the positive rail.
The supply may simply be charging the capacitor on the pulses that you see but didn't capture.
Place a meter on the negative rail and see if it remains constant or changes slightly corresponding with the pulses.
Do the same with the positive rail.
Unless I am testing it wrong. There is a cap on each leg that both join to one pad on the board. I am using this as reference. So, neg lead on the common pad where both caps are soldered and pos lead on one side and its a steady 33v. No fluctuation. Scope shows a little noise on it though. On the other side, its all over the place, but never goes about 8v or so.
Are you measuring on the terminals of C806 and C807 (referenced to the PS5 diagram) with the black scope probe on the circuit common to both of those capacitors (inverted triangle ground symbol)?
Do you have any spare electrolytic capacitors rated for 50v?
Do you have any spare electrolytic capacitors rated for 50v?
Yes, those are the test points I am using and black lead on common connection for the caps.
I just looked and no spares. I would probably steal them out of the other amp, but I think if you are suggesting that I swap them out, I should just probably buy a few of them just to have in my stash of parts. Does that sound like a logical approach?
I just looked and no spares. I would probably steal them out of the other amp, but I think if you are suggesting that I swap them out, I should just probably buy a few of them just to have in my stash of parts. Does that sound like a logical approach?
Try connecting it across the cap with 33v. Power up and watch the current draw from the 12v supply. Does it increase with the lamp connected?
What is the voltage across that cap with the lamp connected?
Do this with the PS transistors tightly clamped to the heatsink.
Switch the amp on only long enough to answer the questions.
What is the voltage across that cap with the lamp connected?
Do this with the PS transistors tightly clamped to the heatsink.
Switch the amp on only long enough to answer the questions.
Ok, just so I am getting this right. Connect it in parallel across both sides of the cap that has -33vdc, observe action on meter on power supply, and check voltage on the same points I have been checking to obtain the -33vdc?