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Hi (been trying to fix a sony receiver grrr)


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Hi all,

 

Pleased to be here. I've been trying to fix an old sony strdb790 receiver, bought a multimeter and everything and diagnosed an issue with a transistor but it's seems to be an odd model and there are circuit boards soldered in the way and I can't get to the screws so I can try and take out the dodgy transistor. Anyway, this isn't really an asking for help post, just my way of an introduction. I'm keen to check out this forum

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Jumping right in...

 

So you haven't removed the transistor... the question, so how did you test it/determine it was faulty, ok if it's charred but incircuit testing can be tricky. I see from hifiengine that it's an AV unit, generally these are difficult to repair. The power supplies are somewhat easier but the audio...

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18 hours ago, mbz said:

Jumping right in...

 

So you haven't removed the transistor... the question, so how did you test it/determine it was faulty, ok if it's charred but incircuit testing can be tricky. I see from hifiengine that it's an AV unit, generally these are difficult to repair. The power supplies are somewhat easier but the audio...

Hi, I used my multimeter and I found  a short in the transistor from using the diode setting. I also checked for current running through the resistor after turning the receiver on and the faulty one was a bit cooked: the other ones didn't have current running through them. The fault is that when I turn the receiver on it comes with an error message and then turns off: 'protect mode'. youtubing this shows its a very common problem -- guess it's like many things nowadays where you really have to go out of your way to get superior build quality. Perhaps it's time for a vintage japanese amp...

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Diode test is good, however check the schematic for alternate paths when in circuit testing. "Protect Mode" is a common issue, generally it may be attributed to over current, over temp, excessive DC voltage and in yamaha RX-V's missing/low DC voltage.

 

I'm into vintage, if you have basic diy skills then you could do a lot worse than picking up a vintage japanese amp. Many good amps from each of the main players Sansui, Pioneer, kenwood, marantz, yamaha,,, If you can afford to get into separates then they generally better most vintage amps.

 

If you are on a tight budget then the AVR's can sound decent

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I'm not sure I'm competent enough to be comprehend anything from checking the schematic. I was basically just following a trouble shooting youtube video on the protect mode error. However, at the moment the problem I've run into with even attempting to replace the diode is that it's a bit inaccessible: how can I remove the screw if I can't reach it because those circuit boards are soldered on top? See inserted pics.                             Seems to be a strange design choice from Sony.

IMG_0053.JPG.jpeg

IMG_0056.jpg.jpeg

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Exactly which transistor is suspect faulty, eg TRnnn, Qnnn and on which board. I will check schematic for low resistance paths that may screw up your in circuit testing.

If you are 100% sure then no other way but to unsolder the boards, need a reasonable quality solder pump/sucker. I would also melt some solder on the iron tip and then apply that melted blob to the pin to be unsoldered (distributes the heat) and use solder pump.

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Those top boards are just "mechanical stays", unsolder away. Maybe the solder joints provide easy access to some test points??? You now mention that the problem is a diode. As a punt, I hope you are not talking about either D549,D444,D699,D649 on the SP-A or SP-B boards. These are for relay flyback, they are connected across the relay. If you try and test the diode your MM will test the relay since it's an easier path and will show a low ohm/near short.

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