Once again, i do everything i was taught on how t ok fix these amplifiers. Yet despite changing all of it i have no suppl uh voltage at the tl494? O, 4.7R resistors are good, zd1 good. The three transistors in the startup curcuit all check ok. So that leaves me with the driver card?
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Q5- MPSA06 or Q9- 2N4401 have failed. Most likely Q5 is shorted B-E. Check all transistors on the driver card.
Also ZD1-5.1 volt zener has a habit of cracking and will check OK with an ohmmeter/diode checker. The best way to determine if it is good is with a voltmeter with amp powered on or pulling it out of the board. The fixative and the placement up against the driver card probably causes this. The fixative was changed to prevent this in mid production, but with limited success.
Also ZD1-5.1 volt zener has a habit of cracking and will check OK with an ohmmeter/diode checker. The best way to determine if it is good is with a voltmeter with amp powered on or pulling it out of the board. The fixative and the placement up against the driver card probably causes this. The fixative was changed to prevent this in mid production, but with limited success.
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