Amp came in with a blown power supply. I replaced all PS drivers, gate resistors, and about half the FETs. Good drive signal.
Amp draws excessive current but appears to power up. I removed ALL rectifiers and PS is working just fine. Then I put rectifiers in for the Class-AB side and amp works fine. Rectifiers installed in the Class-D side; and something is wrong. Amp is using IRF640/IRF9640 output transistors which are not measuring shorted. I removed the driver board with the F16/B52 ICs and the amp powers up just fine without excessive current draw.
Im not 100% positive what to look at next. Either I was going to remove the IRF640/9640 outputs to the troubleshoot the driver card (Type 1), or possibly try powering the amp through a current limiter.
Amp draws excessive current but appears to power up. I removed ALL rectifiers and PS is working just fine. Then I put rectifiers in for the Class-AB side and amp works fine. Rectifiers installed in the Class-D side; and something is wrong. Amp is using IRF640/IRF9640 output transistors which are not measuring shorted. I removed the driver board with the F16/B52 ICs and the amp powers up just fine without excessive current draw.
Im not 100% positive what to look at next. Either I was going to remove the IRF640/9640 outputs to the troubleshoot the driver card (Type 1), or possibly try powering the amp through a current limiter.
What does the drive look like on the gate legs of the output FETs?
What do you consider to be excessive?
What do you consider to be excessive?
I see square drive on the gates of the output FETs.
Excessive is sucking down my bench PS, drawing about 12A. The amp's PS also squeals and the PS FETs get very hot quickly.
Using a 4-ohm current limiter the amp will power and draw only 1.25A for testing.
Excessive is sucking down my bench PS, drawing about 12A. The amp's PS also squeals and the PS FETs get very hot quickly.
Using a 4-ohm current limiter the amp will power and draw only 1.25A for testing.
No sir. In fact, the amplifier will pass audio out the speaker terminals while its drawing excessively, but not under current limiting.
If the outputs are not heating up, it's hard to see how a fault in the output stage is causing the high current draw.
Are the rectifiers leaky?
Bad rail cap?
Are the rectifiers leaky?
Bad rail cap?
I dont believe those parts have failed. I can pull the Class-D driver card and the class-d side still gets good rail voltage. While card is out, I can play the amp through channels 1-4 with high load and the PS runs fine though I only pushed it out to about 15A draw. As soon as I put the Class-D driver card in the amp wants to draw about 10-12A. PS fets get very hot. The PS also sounds really weird like its struggling badly. Almost like PS drive circuitry breaks down. Voltage on TL494 Pin 4 probes unstable between 5.0 and 0vDC. Actually several pins of the 494 become unstable to probe when the amp is like this. This kicker is kicking my ***.
Pin 4 can be like that on some kicker amps. Installing a 1000pf capacitor between pins 4 and 7 will generally allow you to read the voltage.
Was the amp completely out of the heatsink (on the bench) when you tested it?
Was the amp completely out of the heatsink (on the bench) when you tested it?
Yes it’s out of the sync with ps fets clamped to some insulated aluminum stock. I also tried another bench ps and same issues. I disabled soft start and that seems to have helped elsewhere but no change to the stated problem.
Looking at the diagram, it looks like there is already a cap from pin 4 to ground, C11.
I don't see any softstart unless they're initially charging C11 through the protection circuit transistor then allowing it to discharge through R10.
Was the amp doing this when you had everything clamped to the heatsink and all grounding screws in the board tightly screwed down to the board?
I don't see any softstart unless they're initially charging C11 through the protection circuit transistor then allowing it to discharge through R10.
Was the amp doing this when you had everything clamped to the heatsink and all grounding screws in the board tightly screwed down to the board?
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There is only 1 case grounding connection for this amp. No I did not sync-mount it, but grounding that one wire did not help the issue.
Yes sir thank you for the schematic reference. This may help.
2 days ago I actually tried lifting R09 but that did not help.
2 days ago I actually tried lifting R09 but that did not help.
Does the temporary heatsink span the PS FETs and the outputs on a single bar?
Does it draw excessive current without any heatsink?
Does it draw excessive current without any heatsink?
I just had small insulated syncs on just the ps fets.
Yes it will draw excessively while totally unsynced.
Yes it will draw excessively while totally unsynced.
When it was passing audio, was it clean?
With no input, is the rail to rail square wave clean or was it noisy (jittery)?
With no input, is the rail to rail square wave clean or was it noisy (jittery)?
Audio is clean.
Back on this amp, if I power it up through a limiter, or setting my bench PS to 10vDC, it powers up just fine. As soon as I try to power it up at 14.4v, the PS in the amp freaks and draws excessively.
I thought I disabled both soft-on and soft-off, but now Im not so sure. What do I have to remove to disable soft-on exactly?
I did replace the TL494 and yes those pins are tied at the PCB.
Photo attached
Back on this amp, if I power it up through a limiter, or setting my bench PS to 10vDC, it powers up just fine. As soon as I try to power it up at 14.4v, the PS in the amp freaks and draws excessively.
I thought I disabled both soft-on and soft-off, but now Im not so sure. What do I have to remove to disable soft-on exactly?
I did replace the TL494 and yes those pins are tied at the PCB.
Photo attached
Attachments
R10 I jumped the other day. I just now removed Q04 and the amp quick-starts and stops just fine. The only issue I see if it even is any kind of issue; amp is running full tilt. No regulation. Is this OK to run like this? Seems fine to me. Amp briefly draws 6A at start and then idles at 2A. Plays.
Unless the amp is yours, you can't run it without protection (Q04).
I'd reinstall that transistor and try removing transistors that feed the protection circuit. Possibly starting with Q704.
I'd reinstall that transistor and try removing transistors that feed the protection circuit. Possibly starting with Q704.
Ok Q704 removed doesn’t solve the issue. I followed PROT on the schematic and removed one part at a time, mostly 4148 diodes all testing well, disconnecting PROT from each area of the amp, and the amp continued to draw excessively.
The furthest component I can pull, which allows the amp to power on cleanly is actually C704 which is a 4.7u cap tied to ground. If I pull that part, amp powers up fine. I replaced it and tried different values and no help. I'm tempted to leave C704 out of circuit. Thoughts?
The furthest component I can pull, which allows the amp to power on cleanly is actually C704 which is a 4.7u cap tied to ground. If I pull that part, amp powers up fine. I replaced it and tried different values and no help. I'm tempted to leave C704 out of circuit. Thoughts?