KilgoreCemetery
- Apr 12, 2017
- 258
- Joined
- Apr 12, 2017
- Messages
- 258
I've been troubleshooting this one for a while. First, it has a special power supply similar to what made Carver amps famous. I don't fully understand what each part does, but I know that it chops up the line voltage using triacs, almost like a slow version of a switch mode power supply. I've checked all of the resistors and diodes on the two "Primary" boards. I was even able to pull the IC and triacs out of a working Yamaha A-760 to rule them out. At this point, I'm beginning to think that the problem is further down stream.
I did verify that the pilot light works by running about 5vdc through it with the hot side disconnected from the board. Based on what I've read, the pilot lamp is important for this model because it's wired to a couple of transistors on the main board (TR347, TR348). Honestly, I have no idea why or what those transistors are doing. Best guess is that it has something to do with voltage/current regulation.
Also, I found that both of the output transistors on one side are shorted. However, desoldering them from the board didn't seem to change anything. Driver transistors TR334 and TR332 test fine.
Can someone help me decipher what all the extra circuitry is for and maybe give me an idea of where to look next?
I did verify that the pilot light works by running about 5vdc through it with the hot side disconnected from the board. Based on what I've read, the pilot lamp is important for this model because it's wired to a couple of transistors on the main board (TR347, TR348). Honestly, I have no idea why or what those transistors are doing. Best guess is that it has something to do with voltage/current regulation.
Also, I found that both of the output transistors on one side are shorted. However, desoldering them from the board didn't seem to change anything. Driver transistors TR334 and TR332 test fine.
Can someone help me decipher what all the extra circuitry is for and maybe give me an idea of where to look next?