Got a Memphis SRX500D.1 amp, had blown output fets and power supply fets. Removed all the fets and went to power it up to check power supply drive wave. It still went into protect, so I checked pins 1, 2,15 and 16 on the TL494, because pin three was high (+4 volts). Found pin 16 at 4 volts with pin 15 at 2 volts, this was causing pin 3 to go high. Two things go to pin 16, from the header pins of the pwm board, pin 2 and pin 9 (going left to right). Pin 9 is the RT thermal on the side of the output filter coil, disconnected that and the amp would briefly turn on then protect. Traced out header pin 2 to transistor Q23 on the main board, removed this and amp would then produce power supply pulses. Traced Q23 back to Q86 and then Q85, tested all of them. Here is the kicker, the gate leg trace for Q85 runs under the output filter inductor and I have yet to find where it comes out (it heads to the output section). Anyone have the schematic for this amp so I can find where the trace goes without removing this giant inductor?
P.S. I have fixed over 30 amps in the last year, never had to repair the protection circuits, tonight I have 2, the kicker and this memphis, i'm going to bed LOL.
P.S. I have fixed over 30 amps in the last year, never had to repair the protection circuits, tonight I have 2, the kicker and this memphis, i'm going to bed LOL.
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Are the windings of the inductor rubbing on the transformer?
If you have the tutorial, section 44 explains why Q85 and 86 are causing the amp to shut down.
Q85 is a bipolar transistor so its control terminal is a base, not a gate.
If you have the tutorial, section 44 explains why Q85 and 86 are causing the amp to shut down.
Q85 is a bipolar transistor so its control terminal is a base, not a gate.
I will check the inductor and transformer, the windings do seem to be close or touching. Worked all weekend and was up super late, sorry about the gate - base screw up. My guide is old, and doesn't have sections labeled up to 44 or beyond. I am looking in the generic protection circuit troubleshooting and rereading that, focused on the reference, delay and muting circuit part. Got to get some rest, will hit this and the Kicker amp tomorrow after work. Thanks again for taking the time to help with this.
I think this is typically a 'type 4' amp. The circuit seems to be a mix of old and new. Q85/86 are part of a circuit that shuts down the amp if the PS FETs have drive but are not producing rail voltage. This can make it shut down the drive if the FETs or rectifiers are out of the circuit.
Q23 was used in the SLA1500 and its collector drives pin 16 of the 494. Q85/86 drive Q87 in some amps. Q87 and Q23 are basically serving the same purpose.
So, if you get the supply up and running, none of these components should cause you any problems.
Q23 was used in the SLA1500 and its collector drives pin 16 of the 494. Q85/86 drive Q87 in some amps. Q87 and Q23 are basically serving the same purpose.
So, if you get the supply up and running, none of these components should cause you any problems.
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