SX-737 protection relay

Jaek

New Member
Hello,
I have a small collection of blue face Pioneer receivers. Recently, I acquired a 737. Right off the bat, I noticed that it differed from my two 636s and my 1010 in that the red stereo indicator would be illuminated regardless of the selected input function. Then, after using it for a week or so, the protection relay would trip after 30 minutes to an hour of use.

I'm not experienced in repairing electronics, but am handy in other areas and am not afraid to try my hand at something new.

So my two opening questions would be

1. Is the stereo indicator supposed to be illuminated when AUX or PHONO are selected?
2. Where would be the best place to start troubleshooting the protection relay?

Thanks to everyone is advance.

Jake
 
I am really new at this, but I am currently restoring a 737. I would download the service manual and check the DC neutral and idle current. You can reference this thread to guide you: http://www.audiokarma.org/forums/showpost.php?p=2408561&postcount=42 There is an error in the manual that misrepresents which pots are used for which values and that thread explains it. I would also pull the voltages on the power supply and the amp to see if they are in line. You can post those here if you like.

On the stereo indicator, I think the tuner is always powered, so yes I would assume it stays lit. I think mine is burnt out. Missed that one when I replaced the lights.
 
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You're more experienced than I am, so I'll take your advice and post back with my findings. thanks for the suggestions.
 
Hello, just from my recent experience fixing up an SX-880, you probably want to pay particular attention to the protection circuit. On mine, it was totally obvious where the problem was - one transistor had obvious heat signs around it and the board was blackened underneath. It just so happened that that particular transistor supplied 14v into the protection relay. After many years of running pretty hot, one or more of the joints had become dry so I simply reheated them with my soldering iron to reflow them. Now it runs perfectly, straight out of protection at power up and never misses a beat :)
 
Yeah I prodded around the suspect transistor with a wooden spatula and sure enough when I pressed the board the relay clicked. I knew then I had a cold joint.
 
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