Can someone please help me with my Definitive Tech PF15TL? There is no sound but it powers up. Changed the resistor that was blown (19.1 kohms) and STK4050V but still no sound. A schematic was shared in March 2007 and I'm using this as a guide. I'll appreciate all the help. Thanks.
at1receptor
at1receptor
The MPSA92 is working. Tested it out of circuit. Diodes and resistors in the "Trip Point" circuit are also good. Wondering if IC U1 (LM324-but in my circuit it was replaced by LF347N, don't know why) can be defective? I don't know how to test I.C.'s in circuit. I replaced the U3 (MC14011B) - that is defective 'cause now the unit when plugged is not powered-on, only when signal comes in does it power up. Then it shuts down when signal is down so U5 (MC14541B) is working. Appreciate any recommendations (except to throw away my amplifier). Thanks.
Cause of meltdown: friends were doin karaoke. Probably, too loud, don't know. Left them alone singing. Following day, subwoofer pilot light was lit but only crackling sound came. That's it. Called Def. Tech. but I'm out of warranty. Since I can remove amplifier they said they'll replace it for $225.00 to $250.00 but have to send the old, damaged one to them since the manufacturer of ampli stopped production & they're repairing and selling them back as refurbished. That started my journey. Presumed the STK4050V was busted since it is the output stage. Changed it. Meticulously soldered connections (pcb is double sided). Still no sound but power on. Was able to read a thread in diyaudio with identical problem. Changed the 19.1 k ohms resistor connected to pin 4 of the STK (yes the resistor is fried) with 10 K and 9.1 K in seires (1watt) but still no sound. And now power is on always even without signal. P12 and P24 are present. No, I don't know what you mean by DMM, sorry. Changed the MC14011B which looks like it functions as "gate keeper." The power turned off and now switches on when signal present. Sorry for the long response. Really appreciate your help.
Thank you for your answers but the unit switches on and off now when an audio signal is detected because I replaced the MC14011B. I also checked the resistors in the output stage (from the input to the speaker)- none are shorted or opened (except the R89 which is the 19.1 k ohms- by the way, can't find the exact value anywhere). I tried it again tonight, still no sound but unit switched off 15 minutes later (which is what the use manual stated). I'll appreciate any recommendations.
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