That looks like the waveforms I'm seeing. The voltage swing is only about 8 volts. Which is very close to B+ since I have to power it through a resistor.
How did those get into the amp?
If one of the rectifiers has its center leg directly connected to the negative terminal of a rail cap, that rectifier should be a negative rectifier.
If one of the rectifiers has its center leg directly connected to the negative terminal of a rail cap, that rectifier should be a negative rectifier.
I don't know. That's what was in it when I opened it up. I thought it odd that the rectifiers were the same. What should they be?
I have no information on this amp. Maybe MTX will tell you what the originals were. I'd probably use the MUR1620CT and MUR1620CTR (negative). You probably only need to replace the negative rectifier.
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.
You can look up the datasheets for the regulators to see which legs the programming resistors connect to as well as the input and output terminals. That should help to confirm which is which.
I will do that. I'm really hoping Terrence can tell me which side is positive and which is negative. I'd like to fix this thing if I can. Maybe gift it to my customer, for all the work he sends me.
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.