Can I check hexfet out of circuit Xtant Amp

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#81
This was hand drawn until there was too much of a mess to be useful. Then I drew it up as seen. Many times, I draw lines from point to point on the board with a sharpie to keep track of connections when there is no diagram available. It cleans up easily with acetone. I've never drawn waveforms but I've photographed many of them for future reference.

Did you find a difference of grounds on that transformer (referenced to the main ground)?
 
#82
Nothing to chassis ground one to the main 12 volts in. transformer checks good on an ohm meter on all the winding out of circuit. all the rectifiers it supplies check good no leakage it supplies. What should the ac be coming into the primary winding voltage? and the secondary's ac or rectifiers in dc voltages off the transformer?
 
#87
Perry Babin said:
Many times, I draw lines from point to point on the board with a sharpie to keep track of connections when there is no diagram available. It cleans up easily with acetone.
Click to expand...

Just to let you know, sharpie will clean up easily with methanol as well (commonly sold as wood alcohol or wood spirits). Methanol is less harsh on plastics, rubber and things like that.

Though its good someone outside of the chemistry field about this. We mark ALL of our glassware with sharpie and then use a squirt bottle of Acetone or MeOH to erase it.
 
#92
I need maybe to find my 15 volts plus and minus if I have a proper primary voltage on the transformer and secondary side if knew their proper voltages and start tracing the voltage or and lifting components that it supplies to see if one is bleeding the 15 down plus or negative down. My kingdom for a diagram on this one or reference points and voltages...lol how many supply voltages is derived from that transformer with many windings? will it effect the supply to remove the opto coupler as I am working on this circuit as I have them socketed as don't want to damage them while looking for 15 volt supply voltages and maybe the lost signal are all related to the same component that finally totally failed. I know I am grasping at straws here. Just trying to be helpful but when your not familiar with how that circuit works you can come up with dumb ideas
 
#93
Find the 2 diodes near the yellow transformer that read ~10 ohms from pin 8 of the op-amps to their cathode (striped end).

Find the 2 diodes that read ~10 ohms from pin 4 of the op-amps to their anodes.

Find the 3 terminals of the transformer that read 0 ohms between the transformer terminals and the ends of those diodes NOT connected to the op-amps.

Of those 3 terminals on the transformer, follow the traces to see which two connect directly to the diodes. You can't do this with a meter while the transformer is in the circuit.

The remaining winding (of the 3 that were connected to those diodes) should go to ground. If it doesn't, connect it to ground. If you're unsure that you have the correct winding, insert a 1-3 amp fuse in the jumper.

Does the amp still go into protect mode?
 
#94
Traced that winding trace to the plus terminals feeding through the output choke and while was tracing it back fron the winding back it directly into the source legs on the output fets on the left bank and to the drians to the right bank. Then followed it to the + output speaker terminals on the heavy choke on the ferrite rings the one leg under the foam stip I found the original problem the owner had as one leg on that was cold soldered and hidden under the black foan cushion srip stuck to the board. 3 shops later I found the original problem as he come in because he had came in with no output to his sub he has a second one xtant running his rear speaker in an antique mustang. The rest was created from the other shops what a sin so simple turned into a disaster. Anyway being the big chicken that I am I wanted to check with you one last time with an update before I put that winding to chassis ground with a fuse in line to that winding. I still don't see how the ac is developed from for the primary winding? One leg of the winding go to + 12 volts in didn't trace the other side of that winding though. So am ready to do it if you say go ahead Perry
 
#95
If you followed what I described and found the winding that should go to ground, repair the connection. If you're concerned, do so through a 1 amp fuse to test it.

The transformer is not a push-pull like the most common power supplies. It has one winding tied to 12v and the other to the drain of an FET (on the heatsink near the rectifiers). The FET is driven by a UC3845.
 
#96
Well good news the grounding that center tap winging dropped my 15 volts supplies voltages down the one by the Jfet is now pin8 13 Volts and pin 4 -8 volts all the rest of the op amp are + 18 and - 18 volts DC big drop from what they were but not out of protection mode but were getting closer. I have to trace that circuit on that winding to ground and find out whee Trace is open to ground or component changed value, I ordered 8 new op amps just incase it is one of them killing my signal @. 95 cents each i will change them all to get my siganal back if I get my proper voltages . Can one of them or 2 op amps acting up as the one shop put that npn transistor where the jfet was damaged them. If all that is up and running properly and then install my outputs and it will work this time. Any more ideas to get the proper voltages
 
#100
Are R262 and R272 (47.5 ohm resistors) within tolerance.

What circuit does these contol as the both way off value as they must have over heated to go up in value as they did and want to check what they control for fault as not to happen again that caused them to change their values?
 
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