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Help me ID Component

M.Green

Jun 2, 2023
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Troubleshooting a power supply board from a Yamaha receive after power surge. Fuse 3701 (yellow) was blown and cap 3706 showed distress. My question is the clouded component on the drawing. Its symbol and rating indicate a resistor, but there's nothing on the board? Any idea what the drawings trying to tell me?
1685675379950.png
 

H2814D

Nov 4, 2017
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To make your life easier, and to get a better outcome here, you might want to take a very clear picture of both sides of the board with all of the components clearly visible and also supply the entire schematic. It makes it easier for the experts as well. Speaking from experience here. Oh yea..and the Receiver Model Number too. :cool:
 

Harald Kapp

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This is a bleeder resistor, used to discharge the parallel capacitor when there is no primary power. It is common to leave out components when they show not to be necessary in the final product. This missing resistor is no cause for concern but also definitely not the cause for the failure.
 

M.Green

Jun 2, 2023
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To make your life easier, and to get a better outcome here, you might want to take a very clear picture of both sides of the board with all of the components clearly visible and also supply the entire schematic. It makes it easier for the experts as well. Speaking from experience here. Oh yea..and the Receiver Model Number too. :cool:
Model is RXA-740. Here is the full schematic, A and B sides of the power board. I have replaced: R3703, TH371, C3704, C3706, C3707 and F3701 (the fuse that fails immediately upon application of line voltage). My knowledge and equipment are limited to basically component replacement and whatever testing that can be done with a multi-meter. If anyone would care to suggest a likelly next step, it would be appreciated.
 

Attachments

  • Power Supply.pdf
    255.8 KB · Views: 6
  • yamaha_rx-v677_htr-6067_rx-a740_sm p110 A Side.pdf
    308.9 KB · Views: 3
  • yamaha_rx-v677_htr-6067_rx-a740_sm p111 B Side.pdf
    264.1 KB · Views: 1

H2814D

Nov 4, 2017
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Actual pictures of the PCB and the components attached to it, front and back, is what I was talking about. Thanks for the schematic, though.

Since the fuse is in line with the mains in, and you said the problem started after a power surge, I would first check that bridge rectifier (DBL155G) and make sure it isn't shorted to ground.
 
Last edited:

kellys_eye

Jun 25, 2010
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Probably the main switching regulator device IC375 (as well as potentially the bridge rectifier as mentioned by @H2184D above).
 

M.Green

Jun 2, 2023
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Actual pictures of the PCB and the components attached to it, front and back, is what I was talking about. Thanks for the schematic, though.

Since the fuse is in line with the mains in, and you said the problem started after a power surge, I would first check that bridge rectifier (DBL155G) and make sure it isn't shorted to ground.
Photos of the board attached. Bridge rectifier tested bad. Thanks
 

Attachments

  • RX-A740 Power Board A.jpg
    RX-A740 Power Board A.jpg
    375.5 KB · Views: 4
  • RX-A740 Power Board B.jpg
    RX-A740 Power Board B.jpg
    407.8 KB · Views: 4

M.Green

Jun 2, 2023
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Probably the main switching regulator device IC375 (as well as potentially the bridge rectifier as mentioned by @H2184D above).
The bridge rectifier tested bad, I'll take a look at IC375 as well. Thanks
 

kellys_eye

Jun 25, 2010
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It's usually the IC fails first and takes the bridge rectifier out immediately. Faster than the fuse can blow! But the fuse ends up blowing anyway.
 

batdetector

Jun 4, 2023
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Hi. From the arrows, this looks like a suggested bleed resistor to connect to discharge the reservoir cap.
 
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