when i test the electrolytic caps for continuity with my dmm, it gives a short interval of beep, after which, there is no more beep sound. is this normal for caps?
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Thats normal, they draw current till their capacitance is filled. Do you have a capacitance meter?
I really hate to ask this, but remove C12P and put another cap in temporarily. Needs to be at least 160V, but can be more for testing. Does this fix the problem?
Really bad numbers. Two of these voltages should be about 45V and the other two about twice that.
Are you sure about them?
Measure the AC between the negative terminals of C8P and C9P. This should be 30VAC. If it's not then the multiplier is not getting the full transformer secondary voltage.
If it is, then I don't know. Either something is wrong on the board (open trace??) or one or more of the components in the mulitiplier section i is(are) bad. To get the readings you're getting nearly all of them have to be bad.
But for all of the capacitor voltages to be this low says that there is a global failure.
On the transformer, to create the CT you have joined together one lead that has no black dot and one lead that has a black dot?
At power input to the board it measures 15V at 15-0-15 input point. however it measures 3V between negative legs of C8P and C9P. Adding to the fact that i have been hearing occasionally cracking sound coming from the trans, i think the transformer is dead. I will replace it and i hope it should be ok after which.
IF the transformer measures 15-0-15 at the power terminal block, then it may not necessarily be bad.
Sorry for being very particular about this, but I'd like to not cause you to waste time or money.
Did you measure that AC or DC voltage between the caps? What you want to measure is AC and this should be identical to the full secondary of the transformer, or 30VAC.
If you get 30VAC at the inlet but only 3VAC between the caps then there must be an open trace between the inlet and the caps.
I will check again when i get back home. The amp was working very well for past 6 months. It just stopped working last week. Can we rule out the possibility of open trace? Could the transformer be failing such that it does not provide enough current for the devices and thus the voltage drop ? Thanks for all the help Alex. I appreciate it alot
Possible, yes. Is the transformer spec the same as in the excel BoM?? If so, it should be more than big enough to handle the amp's requirements. It is unusual for a transformer to die if it is operating within spec, hence my puzzlement. Maybe there is something else wrong that caused it to croak?
Even the transformer were too small and was just being pulled down by the current drain, it wouldn't be showing voltages that are this low. So, I am wondering what the hey is happening.