Troubleshooting Sony STR-DH750 RECIEVER

Thread Starter

J Rowe

Joined Apr 16, 2022
3
Hello everyone. I recently blew my Sony STR-DH750 receiver and could use some help from people smarter then me. Main issue occurred when I was listening to music loudly when it shut off. I tried to power back on. Red standby led changes to green but display is no longer working. After about 20 seconds the led changes back to red.. I opened and did find a blown 8A 125V 5mx20m fuse. I feel like there may be more then that wrong.. Waiting to recieve new fuses by friday.
 

Thread Starter

J Rowe

Joined Apr 16, 2022
3
Hello everyone. I recently blew my Sony STR-DH750 receiver and could use some help from people smarter then me. Main issue occurred when I was listening to music loudly when it shut off. I tried to power back on. Red standby led changes to green but display is no longer working. After about 20 seconds the led changes back to red.. I opened and did find a blown 8A 125V 5mx20m fuse. I feel like there may be more then that wrong.. Waiting to recieve new fuses by friday.
5mmx20mm... Im hoping someone could help me troubleshoot and teach me a thing or two. please and ty.i.a
 

rsjsouza

Joined Apr 21, 2014
350
Indeed. It is rare that a fuse itself is the root cause of a problem - it is usually a symptom of another malfunction. Of course, despite the receiver be able to reach almost 1kW.
 

MrSalts

Joined Apr 2, 2020
1,762
I had a few Sony AV Receivers similar to this one. They tended to blow their power transistors (Darlingtons on the 300 and 500 series - I'd assume your 700-series is the same layout, just more doodads. The other common failure is a 7800-series voltage regulator. One 7815 for the 15-volt line and one for a weird 7808 8-volt line on the older one.


Getting to all the output transistor pairs (triplets actually because there is a bias transistor mounted to the same heat sink as each output pair (NPN + PNP) can be a challenge as there is a mezzanine board and heat sink for two to four channels and then three more channels on the main board (the one you can see from the bottom of the unit). It's a few hours to disassemble alone snd document all of the number ribbon connectors.

They usually start sounding like crap as the PNP fails and then a few hours to days later the NPN channel fails.

They have a memory of the last startup failing. You have to completely disconnect mains power to clear that (connect to a power strip and toggle the switch for 30-sec or so to clear.

These units have an output relay that checks for a short circuit speaker and then connects to the power transistors. Try disconnecting all the speakers and see if it starts up. Then try connecting one at a time to check if one of your output channels has failed short.

If it doesn't startup when all speakers are disconnected, you'll have to dig a lot deeper.
 

Thread Starter

J Rowe

Joined Apr 16, 2022
3
After realizing the Display didn't work and it goes back to standby. I tried the reset but and unplugged for 24hrs. same results after. Pulled unit and disconnected all speakers and other connections. same results. I do believe I may have fried the 14 transistors... i could be looking at a $100 cost repair IF that is the only issue..
 
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