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    Mackie SRM450 v1 - No audio output

    These are in the signal path. I'll get clarification from my friend as to what the exact symptoms are with this speaker.
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    Mackie SRM450v1 - Loud pop at turn on, followed by loud 120Hz Hum and no sound.

    I got a similar thread going here; mine powers on but has no output. I have made some discoveries which could be helpful. Good luck!
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    Mackie SRM450 v1 - No audio output

    I may have found something. There are approximately 12 electrolytic capacitors marked 47µf 25v which have an ESR of 2.2 Ohms which is too high. Tested a few others I had laying around and they are reading 0.2 which is night and day difference. Kind of odd that all would go bad at the same time...
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    Mackie SRM450 v1 - No audio output

    Here is an update. Tested all opamps (close to 20) and they are all getting the +/- 15 volts: NJM4560M & NJM2068. Same goes for both LM339 & SSM2164. All measurements were done with reference to ground. Next, I'll try to understand how to feed a test signal and follow the path. Thank you all for...
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    Mackie SRM450 v1 - No audio output

    Thank you so much for your suggestion. I do see approximately 20 small chips; will look at their respective datasheets to figure out which pins to probe. Will come back here with an update if any relevant discoveries are found. Again, your help is much appreciated.
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    Mackie SRM450 v1 - No audio output

    Appreciate the suggestion. To be honest, that's where I run into trouble due to lack of proper knowledge. I understand the hot/cold side of the PCB; no problem. The issue for me is not knowing much about the different stages which you mentioned as well as which components to probe and where. Can...
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    Mackie SRM450 v1 - No audio output

    I got a Fluke 117 and AC Volts resolution is as follows: 6.000 V / 0.001 V 60.00 V / 0.01 V 600.0 V / 0.1 V
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    Mackie SRM450 v1 - No audio output

    LTig, thank you for taking the time to go over the schematics and pointing me to the proper voltages. Pardon my ignorance, had never heard about power amps and muting. How would someone troubleshoot to confirm that to be the problem? Looking at the board, I see 1 or maybe 2 components...
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    Mackie SRM450 v1 - No audio output

    Hello everyone, I'm troubleshooting a friend's speaker which no longer produces sound. Already checked/confirmed/ruled out: The speaker itself has been tested and works. There are no shorts (that I could spot with a DMM & thermal camera) on the board. Please see attached schematics for...
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    JBL VRX932LAP Amp - Power flickering on and off in rapid succession

    Good news, the amp is back online after replacing the shorted Mosfets. FQP30N06 is still available on Digikey. FQP17P06 is no longer produced so used SPP18P06PHXKSA1 in its place with good results. Just documenting it here for future reference. Thanks again for all your help.
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    JBL VRX932LAP Amp - Power flickering on and off in rapid succession

    Glad to see you back. I should have tested all of these components before and not wasted so much time but that's how I learn; the hard way! I'll definitely inspect all the other components around those 2 Mosfets including the path back to Q266/267 as suggested to see if there is any damage...
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    JBL VRX932LAP Amp - Power flickering on and off in rapid succession

    More info after going over our previous discussions: With C600 out, D607 has 13~14 volts across. With Q611 out, D606 has 15~16 volts across. Both diodes have been replaced: D606&D607. Did more prodding and on the "cold" side there are 2 shorted Mosfets. Q272 & Q273 which are parallel to each...
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    JBL VRX932LAP Amp - Power flickering on and off in rapid succession

    Happy new year @AnalogSteph This is what I PM'd you about. Can you kindly check on this and let me know where I should focus, please? Abnormal Voltage Readings: Between SMPSREF & R642 - 12~14 on one side and 12~15 on the other. Between SMPSREF & Q610 (facing flat side): Each leg measures...
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    JBL VRX932LAP Amp - Power flickering on and off in rapid succession

    Okay, I figured out what the issue was. One or more of the 4 high voltage transistors labelled MPSW42 (Q607-610) were shorted; after replacing all 4 the amp now works like a champ. @AnalogSteph, I will always be indebted to you for your time, sharing knowledge, and for helping me understand...
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    JBL VRX932LAP Amp - Power flickering on and off in rapid succession

    Here are some new details as requested. First of all, the amp is not actually clicking on and off like the first one (where it was obvious that the relay was making the clicking sound) but rather the power indicator is pulsating/flickering on/off but the amp does not restart or power off while...
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    JBL VRX932LAP Amp - Power flickering on and off in rapid succession

    I do have it hooked up (the oscilloscope that is) to an isolation transformer so it should be safe. The amp is still connected to the current limiter light bulb fixture. Should be safe, right?
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    JBL VRX932LAP Amp - Power flickering on and off in rapid succession

    Thanks for the detailed explanation. I don't have an analog meter but do own an oscilloscope if that's an option here. Will do the measurements and report back with the findings.
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    JBL VRX932LAP Amp - Power flickering on and off in rapid succession

    Yes, the label on the resistors should be read as "10X' instead and they are definitely 10 Ohms. I'll replace them again today with the proper ones and see if that makes any difference. At this point everything is installed including TL494 & FAN7380MX. Will use a thermal camera and see if...
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    JBL VRX932LAP Amp - Power flickering on and off in rapid succession

    Okay, feels like I'm having a conversation with myself but here is the latest update. R637/638/639 which have a marking of "X10" on them were reading extremely high resistance (0.5MΩ). On the working boards, these measure 10 Ohms but different calculators and websites come back with a value of...
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