yes .ooov at 2n6491 on both channels and -.534 volts on 2n6488 on both channels. this measurement is done with power connected, limiter inline but no remote turn on. I do have one emitter resistor that measures -.534volt on one leg and -.461v on the other leg.this voltage drop is not evident when amp has no remote, but is when power up. Just throwin that out there
i am taking a voltage reading on my fluke at dc test with neg probe at ground input of amp and positive probe testing both sides of each resistor. When i have the amp powered up with remote all emitter resistors read -.540volts with the exception of one resistor that has -.540v on one side and -.440v on the other. that resistor belongs to a 2n6491. its location is in order of: fep16ct, 2n6488 x3, then the suspect 2n6491
removed. i now read .032 volts on the the three output 2n6488's and now .047volt on the trailing 2n6491's following the resistor i removed. they previously read .000volts. The last 2 6491 resistor voltage changed. the larger blue resistors(similar to green emmiter but slightly smaller) on the positive rail side used to measure voltage but now are .000volts thank you.
i thank you for your help, im checkin out for tonight. have to go. Dad duty calls. if you can tell me how to accuratly check them for leakage i will pull them tomarrow. as far as their junctions, i assume connections to the circuit board. these 4 fets i have not pulled off the board, so i would think that they are solid. factory solder.
The outputs are not FETs. They're BJTs.
The junctions are the PN junctions (base to emitter and base to collector) inside the transistor. They should read approximately 0.6v when probed one way and open when probed the other way. They should read completely open collector to emitter, no matter the probe orientation. You have to remove them to test for leakage.
Before you remove all of them, remove the two that have their emitters (leg one) connected to the 2.7 ohm resistors that are connected to the base of the output transistors. Does that eliminate the voltage across all of the 0.1 ohm emitter resistors?
The junctions are the PN junctions (base to emitter and base to collector) inside the transistor. They should read approximately 0.6v when probed one way and open when probed the other way. They should read completely open collector to emitter, no matter the probe orientation. You have to remove them to test for leakage.
Before you remove all of them, remove the two that have their emitters (leg one) connected to the 2.7 ohm resistors that are connected to the base of the output transistors. Does that eliminate the voltage across all of the 0.1 ohm emitter resistors?
since i last posted i have removed all of the output transistors and found one 6491 bad. currently the amp only has the last 6491 and 6488 on both sides installed. the amp powers up without blowing the fuse. Dc voltage across emittor resistors is .0000 v However i now have a new resistor burning. this resistor is directly above the one that i replaced from my first post. Was that initial resistor burning because of the failed mpsa056? the replaced resistor measures 4 volts across legs, while the burning measures 15 volts.
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