Sony STR-DE705 Receiver, Protection Error

Old 05-05-04, 09:46 AM
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Sony STR-DE705 Receiver, Protection Error

Hello, just happened upon your site while googling for some ideas on my Sony receiver issue. The following link:

is from a fellow sony owner with a similar problem to myself. Here is what I know so far:

Model: STR-DE705
Age: purchased ~1996

Recently I was hooking up the receiver at my new house, and was testing listening at around 40-50% on the dial to Pink Floyd. I have a set of Cambridge Soundworks Ensemble Series 1 speakers. These consist of two 6-ohm tweeter/midrange units and two 6-ohm 8" passive subwoofer drivers. Similar to Bose's early Acoustimass system.

My receiver has a 8ohm/4ohm setting, which I had been running at 8-ohm. (Would 4 have been better/safer)? The small satellite speakers were running on the "A" channel and the subs were on the "B" channel.

I did a stupid thing, and tried to switch between A/B/A+B while the music was playing. The receiver snapped (no smoke or bad smells) and then powered off. When I tried to turn it back on I get "PROTECTION" on the display.

I have checked the spring terminals for loose pieces of stranded copper wire, couldn't find any. I've also unplugged the receiver for a time and tried it a week later, no change.

When you power on the unit the relay will connect and I hear the audible "click" that I always get. Instead of sound, now all that follows is the protection msg.

I tried to do a visual inspection of the inside of the unit, didn't see anything burned/broken/smelly/etc.

I am asking for any suggestions on what particular components I could check with my volt/ohmmeter. My experience with electronics is above average for a layman (ie I can see the power transistors on the heatsink, but not sure how everything ties together). I don't even know what the priority to put the components in a checklist (are the power transistors the first to check, IC chip[s])? I can solder/de-solder, but don't really know where to start.

This receiver is old, but for what I used it for it was more than adequate. Even if I end up frying the rest of the components, I'd like to give fixing it a try.


Old 05-16-04, 12:49 AM
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I don't know the details of your model but unless specifically prohibited by the manual I'm surprised that switching between the modes could have caused an overload. On the other hand assuming you went from A or B to A+B would have resulted in a temporary surge which could have blown something. The normal "click" is a relay on a delay circuit to switch in your speakers once the voltage and currents have stabiized on the output transistors.

As for fixing it - unless you can see something that is visually burnt or broken you may need to get a hold of the circuit diagram and give it a go. I'm assuming you can read a circuit diagram. Even if you don't understand how the circuit works most diagrams will at least mention what the voltages should be at the different points and you should be able to use this to find the fault.

Generally it is not a good idea to switch or modify amplifier loads while it is running. Another thing not to switch is the 4 ohm/8 ohm setting while it is on. My power amplifier has a switch to convert it into "bridging" mode which turns it from a 100W stereo amp into a 200W mono amp. The idea is to be able to upgrade it to a 200W system with another power amp. However, if this were switched while it was running I suspect the ouput transistors would go pop. Although I've not looked inside or at the circuit I suspect this would connect the ouput transistor pair differentially to the output and also at the inputs.

Of course a really high end amp should have an internal fuse or breaker that can be reset if this were to happen.

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