Does anyone happen to have a picture of the four SMT components near the speaker terminal and mounting hole? They are missing from my board and the component numbers were cleaned off.
I am guessing one of them to be C417.
I am guessing one of them to be C417.
Thank you Perry.
Your picture helps with two more designations. The missing one is closest to the mounting hole. I'm guessing it could be C416 or C418, so I'll look around the board to see if either of those two are used elsewhere.
Your picture helps with two more designations. The missing one is closest to the mounting hole. I'm guessing it could be C416 or C418, so I'll look around the board to see if either of those two are used elsewhere.
They were likely something like 0.1 or 0.22uf (x4) @100v. You could wire the equivalent across the positive and negative speaker terminals.
Thank you Perry.
I installed a .470uF poly cap across the output terminals while soldering the terminals back in.
This amp needs more work (and parts ordered) before I can test it.
I installed a .470uF poly cap across the output terminals while soldering the terminals back in.
This amp needs more work (and parts ordered) before I can test it.
I have this amp some what working now but it has a couple of issues.
There was some physical damage done to the input caps and little transformer. I replaced the caps and transplanted a round transformer in from another amp. I marked the orientation of the transformer before removing it from the other amp denoting which side went to the drivers and which went to the PS FETs.
With the amp powered up, I get the measurements shown below (5V/div & 5uS). First one is taken at the base of an A56 driver. The second is taken from a transformer leg driving the gate of the PS FET. Seeing half of the amplitude of the drivers at the gates I thought I made a mistake installing the transformer so I rotated it 180 degrees with exactly the same outcome.
I have ~ +/- 14.5V at the op amps and -35.5V & 33.8V (too low?) at the rectifier's and no excessive current draw at idle.
The main problem with the amp is, while it produces clean audio, it clips at ~16VAC (no load) at the speaker terminal instead of an expected ~34.65VAC. I can repeat this consistently by either sending a strong signal in or by increasing the amplifier's gain control. Right now I have the jumpers in place bypassing the preamp board and the little transformer is still installed backward from my original marking.
Is this transformer incompatible or is it defective?
The other problem is the adjustable LED lighting isn't working, which we'll tackle last.
There was some physical damage done to the input caps and little transformer. I replaced the caps and transplanted a round transformer in from another amp. I marked the orientation of the transformer before removing it from the other amp denoting which side went to the drivers and which went to the PS FETs.
With the amp powered up, I get the measurements shown below (5V/div & 5uS). First one is taken at the base of an A56 driver. The second is taken from a transformer leg driving the gate of the PS FET. Seeing half of the amplitude of the drivers at the gates I thought I made a mistake installing the transformer so I rotated it 180 degrees with exactly the same outcome.
I have ~ +/- 14.5V at the op amps and -35.5V & 33.8V (too low?) at the rectifier's and no excessive current draw at idle.
The main problem with the amp is, while it produces clean audio, it clips at ~16VAC (no load) at the speaker terminal instead of an expected ~34.65VAC. I can repeat this consistently by either sending a strong signal in or by increasing the amplifier's gain control. Right now I have the jumpers in place bypassing the preamp board and the little transformer is still installed backward from my original marking.
Is this transformer incompatible or is it defective?
The other problem is the adjustable LED lighting isn't working, which we'll tackle last.
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Why is the scope on AC coupling? With AC coupling, you omit half of what the scope could be telling you.
With ±35v rails, the best you can hope for is 24v AC at the speaker terminals.
What's the 12v DC voltage feeding the amp?
With ±35v rails, the best you can hope for is 24v AC at the speaker terminals.
What's the 12v DC voltage feeding the amp?
Switched scope back to DC coupling.
The probe placement remained the same as above but for the base of the driver, I changed the scope to 10V/Div & 5uS.
The transformer leg driving the FET is back to 5V/Div, 5uS.
I have 14.5V at the amp and I am not using a current limiter on it.
The probe placement remained the same as above but for the base of the driver, I changed the scope to 10V/Div & 5uS.
The transformer leg driving the FET is back to 5V/Div, 5uS.
I have 14.5V at the amp and I am not using a current limiter on it.
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What amp did you get the driver transformer from?
The driver transformer doesn't have enough output. The output from the PS FETs is going to be slightly less than that from the driver transformer.
You stated that you reversed it and it made no difference. Is that correct?
The driver transformer doesn't have enough output. The output from the PS FETs is going to be slightly less than that from the driver transformer.
You stated that you reversed it and it made no difference. Is that correct?
It came from a Sony xm-sd51x. It's the only parts board I had that has a transformer between the drivers and FETs.
Yes, reversing it had no impact.
Yes, reversing it had no impact.
The drive circuit is a bit different but I'd expect it to work.
What resistance (no power applied) do you read between the gate and source legs of the power supply FETs?
What resistance (no power applied) do you read between the gate and source legs of the power supply FETs?
I replaced the two 10 ohm, base to emitter resistors at the drivers.
I replaced the eight 2200uF capacitors due to physical damage.
I replaced the transformer due to physical damage.
I installed the .47uF capacitor across the output terminal.
The previous work I saw was that of the sanded area around the missing surface mount capacitors and there was another sanded area under one of the 2200uF caps.
I see non-original solder around some of the PS FETs, but they all match.
I don't see anything else.
I replaced the eight 2200uF capacitors due to physical damage.
I replaced the transformer due to physical damage.
I installed the .47uF capacitor across the output terminal.
The previous work I saw was that of the sanded area around the missing surface mount capacitors and there was another sanded area under one of the 2200uF caps.
I see non-original solder around some of the PS FETs, but they all match.
I don't see anything else.
Is the original driver transformer too badly damaged to reinstall temporarily?
Is R113 within tolerance?
Is R113 within tolerance?
Yes, there are only three visible leads on each side and those that are there are too short. I'll cut the yellow tape off it later today to see if the forth wire on each side is there.
R113 is in tolerance.
R113 is in tolerance.
The original is beyond my repair.
I removed the Sony transformer again. When I connect it to my frequency generator it's 1:1.
Wouldn't the secondary side always produce half of the primary with the pin configuration on this board using a 1:1?
The original looks like it is probably not a 1:1 but I can't know for sure.
I removed the Sony transformer again. When I connect it to my frequency generator it's 1:1.
Wouldn't the secondary side always produce half of the primary with the pin configuration on this board using a 1:1?
The original looks like it is probably not a 1:1 but I can't know for sure.
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