Hello folks, working on this amplifier which blew one side of the P/S FETs (Q53,Q54,Q55). I replaced them along with burnt gate resistors. The replacements are getting hot very quickly so I suspect a bad PNP driver transistor. I’m having a problem locating that transistor and was hoping a schematic could help be locate it’s designation (Q01, Q02, Q21…).
I found some schematics online for other Focal amps, but none appear similar to this one.
Thanks in advance to anyone who can provide me with a scematic.
I found some schematics online for other Focal amps, but none appear similar to this one.
Thanks in advance to anyone who can provide me with a scematic.
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Are you sure that it uses driver transistors?
What's the resistance from the outputs of the 3525 to the non-FET side of the gate resistors?
What's the resistance from the outputs of the 3525 to the non-FET side of the gate resistors?
Pardon my ignorance, I got lost when you mentioned 3525. Are you referring to the P/S FETs? The ones on the amp are RFP50N06s…. If yes, which pin would be the output? Thank you in advance.
BTW, I’ve gone over the power supply section in the tutorial several times and I was under the impression that on all power supplies that use the TL494 IC, pins 9 and 10 drive emitter-follower pairs of transistors.
In this amp, pin 10 goes to the base of A1266 which is a PNP device. The emitter goes to the gate resistors of the P/S FETs.
And the collector seems to go to the emitter of A1023 which also seems to be a PNP device. My assumption is that A1266 should connect to an NPN device. This is where I hit a dead end….☹️
BTW, I’ve gone over the power supply section in the tutorial several times and I was under the impression that on all power supplies that use the TL494 IC, pins 9 and 10 drive emitter-follower pairs of transistors.
In this amp, pin 10 goes to the base of A1266 which is a PNP device. The emitter goes to the gate resistors of the P/S FETs.
And the collector seems to go to the emitter of A1023 which also seems to be a PNP device. My assumption is that A1266 should connect to an NPN device. This is where I hit a dead end….☹️
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You didn't provide much information and I was going by what I've seen and all of the Focal amps I saw (not many) used the 3525 driver IC.
Not all (but most) amps that use the TLx94 type IC use pins 9 and 10 for the drive. The MTX Power Supplies vs Other Amplifiers page shows the other types that use pins 8 and 11 for the output.
It looks like this amp uses the 494 and you've found one of the driver transistors. The other is directly across the 494 driver IC.
There is no emitter follower. It uses only a diode and a PNP pulldown transistor.
On the PSTS (in the quick links) page, look at item #4. Then at item #33, example 3 and pull up the OV_SCH diagram and you'll see something like the drive circuit your amp is using.
Not all (but most) amps that use the TLx94 type IC use pins 9 and 10 for the drive. The MTX Power Supplies vs Other Amplifiers page shows the other types that use pins 8 and 11 for the output.
It looks like this amp uses the 494 and you've found one of the driver transistors. The other is directly across the 494 driver IC.
There is no emitter follower. It uses only a diode and a PNP pulldown transistor.
On the PSTS (in the quick links) page, look at item #4. Then at item #33, example 3 and pull up the OV_SCH diagram and you'll see something like the drive circuit your amp is using.
Thank you for your time. Yes, the OV_SCH is almost identical to this Focal amp. I’ll use an oscilloscope and compare voltages and waveforms on various components to the good side of the P/S. Hopefully I can track down the problem.
