Hi, as the titel says iam actually working on a Yamaha vsx-r775 power supply.
When i received the receiver it was completly dead. So after a visiual inspection and starting meassurments, i quickly found out that the 5V supply voltage is missing. My futher investigations lead me to the IC STR-Y6753, because the VCC was just add 2V instead of 16V. After that i`ve checked every component from the VCC circut but couldnt found any faulty components. So i concluded that the startup circut from the chip itself is broken and should be replacet first.
After searching on the Internet for a replacement, i found out that the STR-Y6766 version(which i already had) could be an equivalent for the 6753. I`ve checked the datasheeds and couldnt find any problems to just give it a try.
So i replaced the 6753 and things did not go as planned. Ad startup VCC is present for about 3 sec., then the IC is shutting down and ideling ad 11.3V. According to the datasheet, this should mean that the bias assist prevent a startup failure(protection / stand-by on the fb pin=0.8V).
i thought meassuring the fb pin on startup should be the next step. On startup its about 4V for 3sec., after that it goes high to 6.96V(datasheet= OLP threshhold). I checkd the transformer and parts around on the output side but couldnt find any thing. Thats the point where im struggeling at the moment and i hope sompebody got a suggestion of what to do next.
KR
When i received the receiver it was completly dead. So after a visiual inspection and starting meassurments, i quickly found out that the 5V supply voltage is missing. My futher investigations lead me to the IC STR-Y6753, because the VCC was just add 2V instead of 16V. After that i`ve checked every component from the VCC circut but couldnt found any faulty components. So i concluded that the startup circut from the chip itself is broken and should be replacet first.
After searching on the Internet for a replacement, i found out that the STR-Y6766 version(which i already had) could be an equivalent for the 6753. I`ve checked the datasheeds and couldnt find any problems to just give it a try.
So i replaced the 6753 and things did not go as planned. Ad startup VCC is present for about 3 sec., then the IC is shutting down and ideling ad 11.3V. According to the datasheet, this should mean that the bias assist prevent a startup failure(protection / stand-by on the fb pin=0.8V).
i thought meassuring the fb pin on startup should be the next step. On startup its about 4V for 3sec., after that it goes high to 6.96V(datasheet= OLP threshhold). I checkd the transformer and parts around on the output side but couldnt find any thing. Thats the point where im struggeling at the moment and i hope sompebody got a suggestion of what to do next.
KR
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