Help with JL 500/1 2nd one

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I didn't want to stomp on the other guys post so I created my own thread.

I'm working on a 500/1. Power supply kicks on for a brief second then shuts off. It keeps trying to start the supply then dies.

I dont have a schematic for this amp.

All power supply transistors have been replaced. All Audio transistors 540s have been replaced. Light turns green and stays green. Will even play audio for a brief second but then shuts down.

Any ideas?
Will it shut down if you drive signal into it but don't have a speaker connected to it?

With a speaker connected but no signal, does it remain on?

Does it produce a pop through the speaker when it turns on?

Does the green light go off when it shuts down?

Will it come back on after it shuts down or do you have to disconnect and reconnect the remote turn-on?
Doesn't matter if a speaker is connected or not.

Power supply start up then immediately shuts down. Then starts back up again then shuts down. It just repeats this.

I have the remote tied to B+ so it just continues this cycle on its own. Audio will play for the brief second its turned on. Even without the speaker it does this.

I do have a scope so I can see whats going on. Just not sure what is shutting the supply off.

Both soft start and compensation are immediately pulled low on the PWM.

U601 gets warm to the touch and so does Q612 but without a schematic I dont know what these do.
These amps are very sensitive to low voltage. Are you sure that the supply voltage isn't dropping as the amp powers up?

U601 is the 5v regulator for the logic IC (most are between the top and bottom boards).

Q612 drives the yellow transformer which generates the low voltage for the preamp level ICs. I think it may also be used to produce drive voltage for the high-side outputs.

Neither Q612 or U601 should get hot.
I have the amp current limited to 3 amps.

Amp turns on sinks 500mA. I imagine this is before it "actually" turns on. Few seconds later the amps tries to really turn on. It then sinks the entire 3 amps and immediately shuts down.

I dont have the amp in the heat sink which is why I current limit. But I have never ran across an amp that cant turn on without a load and 3 amps of current.

I'm thinking of pulling the soft start leg up just to see what happens. If it would stay on long enough for something to get "hot" this would be easier.
The amp may not have a problem. These amps are the worst when it comes to sensitivity to voltage drop.

Let it try to power up for a minute or so. If none of the heatsink mounted devices get hot (out of the sink), I'd suggest mounting it back to the sink and removing the limiting. If you have a large supply (rated at more than 10 amps continuous), install a 10 amp fuse.

For non-class D amps, it's often OK to defeat the protection circuit but on class D amps, it can often lead to instantaneous destruction of the power semis.
There is a small driver IC that drives Q612 which drives the yellow transformer. I don't know of anything on that circuit that can shut down the amp (but that doesn't mean it's possible).

Did any of the outputs or power supply transistors get hot when you powered it up out of the sink?

If you connect your meter to the the speaker terminals (black lead on negative, red lead on positive), is there any DC voltage?

How much current did it draw when you removed the limiter?

What rev. amp do you have?

If it continues to go into protection/shutdown, pull the outputs. That will allow you to check most of the rest of the amp for proper operation.
No DC output on the output. The output seems to be ok when it is on.

The supply transistors dont even get warm. I have a really nice Tek supply PS2520G for low current but anything higher then 3 amps I have to switch to a piece of crap 25 amp switching supply so I have no way of measuring current with it. So no clue on the amount of current its pulling. But I dont think it gets a chance to pull any significant current because it powers up and shuts off instantly. Basically the instant it turn on the instant it turns off.

Do you know what type of signals I should be seeing on T601? Each side of the transformer. I'm really tempted to bypass the protection and let her rip. What's the output out of the supply?
This photo is the signal on the tab of Q612. The timebase is set to 5us. The vertical amp is set to 10v/div.


What revision is your amp? There were modifications to this drive circuit.
Ya mine looks like that. I have a rev3 board.

I was going to post the output of mine but photo bucket doesn't like the TIFF image my scope produces.
High of 28.8V
Freq 58.06 kHz

How about Q613 I am seeing this jump to 13V then drop to 0.

I also drove 30V onto the output capacitors. No current draw once the capacitors were charged. So the output is not shorted that I can find.

A schematic would make this soooo much easy. I appreciate your effort. Thank You!

Finally got it converted
It's probably not important but... the rev3 uses a UC3843 to drive the FET that drives the yellow transformer. The rev10 uses a different drive circuit.

These are the rest of the waveforms (from a rev10). Right-click to zoom in to read the timebase and vertical amp settings.

As far as I know, the schematics were never released.

Make a quick check of the output inductors and the filter caps across the outputs to make sure none have broken leads. Also, resolder all of the connections on ALL of the long buss bars. Sometimes they cause problems.

Does it stay on long enough to check the rail voltage and the ± voltage on a few of the op-amps?

What scope are you using?
opamps are +13.0v and -15v and this voltage is always on no matter what.

No supply never stays on long enough to measure the output voltage of the supply.

My rev3 is using a UC3525ADW to drive the FETs

I checked the output caps for shorts seem to be ok. Ouput inductor doesn't appear to be shorted either.

I'm using a Tek3034B

Measured the transformer and I am only noted the differences I see with what you have in the images.
Pin 6 is the same as pin 8 -> Meaning waves look the same
pins 7 flick on then shuts off.
1-4 all look like image 2. None of them bias up.
pin5 looks like the output of Q612
The 3525 drives the main supply. The UC3843 drives the yellow transformer. The UC3843 is under the preamp board.

If you run out of ideas, pull the outputs. If nothing else, it will eliminate that as a problem (if the amp still shuts down).

The legs break on the inductors and the output caps. Either one will cause the amp to shut down. There's also a large resistor next to the output inductors. I've seen a few with bad connections and that caused the amp to shut down or pull excessive current.

To do troubleshooting under the preamp board, you'll have to make a set of jumper cables. The amp will not power up with the preamp board out of the circuit.

Tek3034B:bawling: I want one.
All output caps were replace. I learned long ago that when power supplies burn up your better off buying all the parts you might think you need. The audio ouput transistors, power supply transistors, and large caps on the audio stage were replaced. 10 ohm resistor measures 10ohms.

I am only resisting pulling those transistors because my desoldering iron sucks :D

See above post for additional measurement that I edited in.

Time for bed work on it some more tomorrow. I'll think about pulling those output transistors tomorrow.

Again thanks for all the help!
You don't need a desoldering iron to remove the transistors. Apply extra solder to all 3 legs and lay your iron down so it heats all 3 pads. When all 3 heat up, the transistors will fall out (or pull out easily). Then all you need to do is remove solder bridges and power it up.

What's the voltage on pin 1 of U509? It's 5v on the one I have here. It's connected to the output of the comparator used for over-current protection.
Getting them out is the easy part getting them back in is a little bit harder without a good desolder iron.

The one I have pin1 of u509 is 5v. I pulled the output transistors.

One thing that has me wondering is the op-amp + rail its only 13.0v instead of +15V the negative rail is -15v. Could mean nothing but some of the op-amps get warm to the touch so maybe something is yanking this rail low and causeing the shutdown. Do any of yours get warm? U1,U2,U3 get warm to the touch not hot just warm.

I may need to make a cable to pull the upper board off.
Does the amp still shut down without the outputs?

Did you check pin 1 with the outputs in the circuit?

None of the op-amps are getting hot. In some of the JL amps, some op-amps run hot but these are all running cool. U1, 2 and 3 seem to run slightly warmer than the others. They are also at a lower voltage.

The regulated voltage is approximately ±14.8v on most of the op-amps.

Most of the supply voltages pass through 10 ohm resistors at various points on the board. You can measure the voltage across the resistors to determine if there is excessive current flow.

Earlier, you stated that the voltage on your amp's low voltage transformer wasn't biased high. That's because there was no rail voltage.

I used to have a desoldering station and several desoldering irons. They were all a pain. I use an Edsyn DS017 and it works very well.

Check all of the op-amps to see if any have DC on their outputs.

If you need the connector and cable part numbers for the extension cables, let me know.
Amp still shuts down without the output transistors installed.

Pulled transistors before I checked pin 1, but the amp still shuts down without them so I dont think that is the problem.

So I think what ever is driving Q613 may be my problem. Do you know what the voltages on this trasistor are supposed to be.

The gate swings to about 13V then drops back to 0. The Drain and source both stay at about 0V. I'm thinking this transistor is driving the output of the supply to 0.
There's no Q613 in the rev10 that I have here.

There should be a difference in the voltage from drain to source. Is the transistor shorted?

In most cases, the drain/source voltage will only be equal when the gate-source voltage is high (greater than ~4v). Maybe the source feeding the transistor is missing/open.

What are the other components that connect to this transistor?
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