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Old 24th November 2006, 02:50 PM   #1
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Default Testing a fried Marantz SR50 - any tips?

I have a Marantz SR50 I got for free. It's toast, but I think I can fix it, and the output FETs are about 3$ each, anyway.

The diode rectifier bridge was blown (I replaced it with a RadioShack bridge), and while the control section seems OK, one of the channels (if used) instantly engages the protection relay.

Now, for a dumb question - what's the best way to test the individual transistors? Do you think an output transistor is blown (an easy fix), or one of the preamp transistors is blown (a hard fix)?
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Old 24th November 2006, 05:00 PM   #2
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I would tend to be suspect of the output devices on the channel that triggers the protect circuit . Check out this site.for troubleshooting tips.
http://sound.westhost.com/troubleshooting.htm
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Old 24th November 2006, 05:08 PM   #3
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Hmm...

I'll check the output MOSFETs. Any tips for doing so, or should I just blow 6$ and hope it works?

Finally, will my amp go "boom" if I remove the output transistors and try the headphone jack?
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Old 24th November 2006, 05:16 PM   #4
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what is the part # on the fets? Chances are slim that you will do anymore damage with outputs removed provided you make sure that you don't leave any solder bridges ie. shorted traces after removal.
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Old 24th November 2006, 05:28 PM   #5
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The numbers were:
A1263
C3180

Look like the A1263 is a Toshiba transistor - and hence, liable to be a fake.
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Old 24th November 2006, 06:00 PM   #6
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Those are audio transistors not mosfets. If you have a dmm 1.)remove the transistors from the circuit . 2.)measure from base to emitter and from base to collector and from emitter to collector .3.) now reverse the test leads and make the same measurements they should measure similar to a diode. High resistance one way and low resistance with the leads reversed. If any combination reveils a zero ohms "bingo" LOL
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Old 24th November 2006, 06:20 PM   #7
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Quote:
Originally posted by XEAGLEKEEPER
Those are audio transistors not mosfets. If you have a dmm 1.)remove the transistors from the circuit . 2.)measure from base to emitter and from base to collector and from emitter to collector .3.) now reverse the test leads and make the same measurements they should measure similar to a diode. High resistance one way and low resistance with the leads reversed. If any combination reveils a zero ohms "bingo" LOL

D'oh!

Will do. Anyone know where I can find replacements?
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Old 24th November 2006, 06:23 PM   #8
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You asked .
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Old 24th November 2006, 06:45 PM   #9
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http://www.newark.com/
Newark lists them bit doesn't have them in stock. Try a search on the net.
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Old 25th November 2006, 10:14 AM   #10
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Digikey sells Toshiba 2SA1962 and 2SC5242 that will work fine. Overkill for your amp, but they'll be tougher to blow up.
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