I checked and found 1 rectifier was connected to an output cap, that connects to an identical cap on the other side of the board. That cap is connected to the speaker negative terminal. I replaced that rectifier with a negative rectifier.
After that, it will not power up. Even through the resistor. The negative speaker terminal is now shorted to B-. I removed the 2 caps. Still doesn't power up and negative speaker terminal still shorted. I started checking for other shorts, and found both the primary and secondary sides of the power supply transformer are shorted to ground. I am lost!
After that, it will not power up. Even through the resistor. The negative speaker terminal is now shorted to B-. I removed the 2 caps. Still doesn't power up and negative speaker terminal still shorted. I started checking for other shorts, and found both the primary and secondary sides of the power supply transformer are shorted to ground. I am lost!
The shorts (as you see them with a multimeter) on the transformer are normal.
The positive terminal of the cap that has its negative terminal connected to the center leg of the negative rectifier is ground. So it the negative speaker terminal.
You'll need to post the DC voltage on all pins of the 494 if it won't power up.
The positive terminal of the cap that has its negative terminal connected to the center leg of the negative rectifier is ground. So it the negative speaker terminal.
You'll need to post the DC voltage on all pins of the 494 if it won't power up.
I went back this thing, today. Because I'm glutton for punishment...
The side that has the rectifier center leg attached to the negative side of the rail cap, is the rail that had a LM317T regulator. The rail that had the 337T, has the rectifier center leg attached to the positive side of the other cap.
I'm confused. 317 is positive, 337 is negative. What am I missing?
The side that has the rectifier center leg attached to the negative side of the rail cap, is the rail that had a LM317T regulator. The rail that had the 337T, has the rectifier center leg attached to the positive side of the other cap.
I'm confused. 317 is positive, 337 is negative. What am I missing?
I don't know. It was a trade in to a shop that I do repair work for. The board didn't have obvious signs of being repaired. What baffles me is that it came in with 2 positive rectifiers and a positive and negative voltage regulator. The 337 and it's adjacent FET were cooked. Which is why I confused it for 2 317's.
Terrence at MTX said he couldn't give me part numbers but could give values for certain locations. I've asked him for the value of both rectifiers. Maybe that will pan out.
Terrence at MTX said he couldn't give me part numbers but could give values for certain locations. I've asked him for the value of both rectifiers. Maybe that will pan out.
Terrence got back to me, today. He said the regulators are 1620ct and ctr. Go figure. According to which board locations he says are positive and negative, the voltage regulators were reversed when I got it. Along with having 2 positive rectifiers, I'm not sure how it powered up to burn the positive rail FET to begin with.
I'm going to start over with it when I get caught up. Maybe it will come together.
I'm going to start over with it when I get caught up. Maybe it will come together.
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