3-S Tech driver board muting transistor

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This is the input square wave on pin1 of the U1 and U2 zoomed in a little more. Scope is set at 200us probe is grounded to negative rail.

Do you think it’s safe to enable these ICs again and see what happens?

David
 

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Maybe I measured at the wrong point. I get 2.5 volts DC on pin1 of U1 and U2 measured directly at the chip. I think last night I measured pin4 and pin18 at the card header and was reading 11.89 volts DC.

As far as grounding my probe to the negative rail, where should I ground it to reference negative rail? Should I use my battery powered scope instead? I certainly don’t want to damage my scope.

David
 
The damage is likely already done and in the form of a burned ground trace to the mains. Your scope may be different but virtually every mains powered scope has the chassis ground and the scope probe grounds connected to the mains ground.

I keep stressing this because people don't know that they shouldn't do this.

A battery powered scope or a scope with an isolated ground (VDS1022I << I is critical), are safe.

The best options for mains powered scopes is to use the scope in differential mode or to use a specialized differential probe.

If you're using a single standard probe with a mains powered scope, you have to use the primary or secondary ground and just deal with the small waveform due to the rail voltage and having to use DC coupling for the waveform to be useful.
 
I had to go out of town for the weekend but I wanted to post an update on this drive issue.

I installed the board and took the jumpers off pin 2 and 3 of U1 and U2 and powered the amp up on 10 volts and limited current and the FETs switch on with no oscillation in the output section and I was reading about 70 volts DC across the speaker terminals.

I wanted to see what was going on so I connected my scope to the low side drive. I connected probe 1 to the gate leg and probe 2 to the source leg. I turned the amp on and watched the negative rail build equally on both legs until all the FETs switch on and I could see that the gate jump a few volts above negative rail on the scope screen as the FETs switch on and expected to see a small square wave rising and falling back to rail. But what I saw was a noisy looking DC line. Like it was trying to oscillate but it wasn’t pulling back down to negative rail.

I’m thinking there may still be a problem with the PWM board in the output section. Are the 4 SMD transistors toward the bottom of the board buffer transistors?

If I’m wrong about where to look for the problem, what would you suggest.

I performed this test with limited current and full current and get the same results.


David
 
There is really no way to protect the outputs with a limited 12v power source because the large bank of rail caps are charged to very near full rail voltage and if something goes wrong that causes excessive current through the outputs, they will likely be damaged (taking out the driver ICs as well).

Were both driver ICs driving the same signals to the outputs?

I'd re-short 2-3 for one IC so only one half of the amp is at risk if you're going to troubleshoot at full rail.

Drive an audio signal into the amp to see if that makes a difference in the drive at the outputs or at the driver IC.

2 of the transistors at the bottom of the board are emitter followers. The other 2 are level shifters. There is a diagram on the type 3 page if you have the tutorial.
 
Hey Perry. I finally got around to getting back on this amp. I built the low power jig and connected to the amp. Apparently I have connected something incorrectly because when I power up the amp the left light build flashes briefly and the amp goes into protection and shuts down the power supply.

Can you look over the image and left me know if you see anything wrong.

Thanks,
David.
 

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I jumped out pins 2 and 3 on the output ICs and I was still showing a short.

I disconnected my low power jig from the rectifier pads and the amp I still going into protection almost immediately. I’ve checked all of the power supply mosfets in circuit and the check good.

I’ve got to look into this further. Maybe something got into the circuit board will I had it set aside.

David
 
I can't see your entire jig. You should go from the ground on the bottom, around the transformer with about 5 turns then to the jig.

With only one set of 5 turns (perfectly fine), you would use only two diodes. The ungrounded end of the 5 turns would go to the lamp then to the center of the two diodes.

The attached photo shows using two sets of windings. The red would go to one lamp and the white to the other lamp.
 
I double checked everything with the jig. Looks to be connected properly.

I did suspect the jig at first. I disconnected it from the rectifier pads. Same issue. The I disconnected one side of my make shift transformer so it would be open and still I got the same issue.

I don’t see any foreign material or solder blobs or bridges anywhere in the power supply either.
 
I pulled the power supply FETs leaving 1 in each bank. There are 4 banks. Two for each transformer. Still the amp goes straight into protection.

I pulled all of the remaining FETs and the amp powers up with 5.95 volt square wave on the gates. All gates check identical.

I shut the amp down to do continuity checks at the FET pads. From drain to source pads I get 1.2 megohm and from gate to source I get 9.9k ohm on all of those.

It appears that some of my FETs in the power supply may be leaky since board level checks are consistent on both sides. The amp has two transformers, one for each side. If I had a bad transformer or and open ground then my readings would have been different from one side to the other. I guess I’ll be changing the power supply FETs now.

Are there some other checks I need to perform before I fit new FETs?
 
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