Sony 5.1 output transistors repair

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pentajazz

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Joined 2015
jkuetemann said:
If the amplifier has gone into protect it is likely the output devices have failed (at least one of them anyhow). The original devices are not in production anymore and user tale just got my last two pairs of my OEM devices. The voltage difference between the original and my suggested alternatives will make no difference in your amplifier, so if you can secure the current production devices I suggest you do so.
If you are not familiar with a repair such as this then please do refer yourself to a professional repair shop.
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I will certainly refer to a pro for the repair and I will refer to what has been discussed. I just wanted to get some basic info for myself in advance, and more or less, a mind therapy session for the "headstroke" I felt when this machine lost its sound.
This is a clear advice, thank you.
 
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pentajazz

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Joined 2015
nigelwright7557 said:
These protect mode failures can be hard to fix.
Output transistors rarely fail for no reason.
Simply replacing them doesn't always fix the problem.
Perhaps something else has caused them to blow.
Without fixing the root cause can see them just blow again after replacement.
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The only thing that comes in mind is to replace the UPS, I will search for other possible flows when it will be serviced, I will keep this in mind.
 
jkuetemann

jkuetemann

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Joined 2010
The Sony STR receivers were notorious for popping output devices, I was doing several a week for a while when they came out. The outputs were not adequately torqued down and local heating would kill them. Every Monday for a period of time they came in from weekend festivities having them fail. Almost never any collateral damage, just the outputs.
 
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pentajazz

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Joined 2015
9 months ago this amp played really loud for 6 to 8 hours (i assume 70 to 80% of its power capacity). The heat produced was huge. The top could burn your hand (summer ambient temperature more than 30 C) . I wish i had a cooling fan but I had not at that moment as i have never pushed it that hard. Maybe this event reduced the transistors life span. An other after effect was the intoduction of a noise hum to the transformer (mechanical one, not on speakers)
 
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s65amg

Member
Joined 2016
Welcome said:
Another common failure on these is the internal fuse inside the transformer. The display can still work because it has its own PSU, but the power amp will never play.
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i think this is the problem im facing on my a str-dh740.First problem was that it would not power on, just click (relay) and a flicking green light.I opened it up and tested the output transistors and the emitter resistors, both good.Then i got to the back side and found one of the capacitors lead had bonded with the transistor.this happened to three different transistors.So i re-worked the solder joints on all transistors and it powered on, all functions seem operatable besides no sound at all and no hdmi output what so ever.I tried all outputs, nothing.i Also tried the headphone jack, which did work when i switched to HP Direct mode but not on 2ch mode.I've looked though everything except the transformer.Since you mentioned that the receiver display powers on without the transformer, this might be the case.i also hear buzzing near the transformer which leads me to believe this.I've found no faults anywhere else. Any idea for a fix ?
 
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