Hi Clay. Good observation. I noticed those components where bad, straight away early on with the initial check of the smps. This kind of smps requires a load be present for operation. When the output chip opened up, part of that load became imbalanced on one side, and led to the diodes opening, is my best guess. When I replaced them and brought it up slowly via variac, they failed again, just before 100 volts. That’s when I knew I needed to look further down the chain. Typically when these ic go bad, they will take other components that are more local to their own vicinity with them. In this case the design of the smps is such, that it effected the opposing side of the optocoupler chain. This was an interesting and fun one! ;).
@@rickygene774 nice job! I have the same amp on the bench with same symptoms: output transistors are blown, and turns out that same resistor and diode in the smps are bad as well. One of the 10 ohm resistor has drifted up to about 68 ohms and one of those diodes is open. I possibly would have overlooked those and just replaced the output IC’s to my detriment if I hadn’t seen this vid, so thanks!
@@claybaker9751 Glad to help! TH-cam has saved my bacon a time or two also. What a great modern time we live in where we can share information! Cheers.
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Neat, nice to hear it working!
Great vid! At what point did you discover and replace the two bad resistors and diodes? I don’t think you went over that part?
Hi Clay. Good observation. I noticed those components where bad, straight away early on with the initial check of the smps. This kind of smps requires a load be present for operation. When the output chip opened up, part of that load became imbalanced on one side, and led to the diodes opening, is my best guess. When I replaced them and brought it up slowly via variac, they failed again, just before 100 volts. That’s when I knew I needed to look further down the chain. Typically when these ic go bad, they will take other components that are more local to their own vicinity with them. In this case the design of the smps is such, that it effected the opposing side of the optocoupler chain. This was an interesting and fun one! ;).
@@rickygene774 nice job! I have the same amp on the bench with same symptoms: output transistors are blown, and turns out that same resistor and diode in the smps are bad as well. One of the 10 ohm resistor has drifted up to about 68 ohms and one of those diodes is open. I possibly would have overlooked those and just replaced the output IC’s to my detriment if I hadn’t seen this vid, so thanks!
@@claybaker9751 Glad to help! TH-cam has saved my bacon a time or two also. What a great modern time we live in where we can share information! Cheers.