This amp came in in protect. Found one channel with shorted outputs. I removed them and checked to see if it would power up. Sure. But found that it had negative rail voltage on the emitters of both B688 and D718. Not sure why. Any pointers?
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You cannot use the voltage on the various components to troubleshoot when the servo/feedback loop is open (as it is with the outputs out of the circuit).
Install the output transistors, power up through a current limiter and see if there are any problems with the channel.
i get the same voltage at the speaker terminals. and if i hook up a speaker it will go into protect after a few seconds.
Remove and check the two driver transistors for that channel. Is either leaky or shorted?
While they're out, is the DC gone from the speaker terminals?
While they're out, is the DC gone from the speaker terminals?
The problem is likely farther back in the circuit. Do a quick, in-circuit check to see if you can find a defective transistor.
![20180319_201537[1].jpg](/community/data/attachments/603/603659-b3196483af376284f29d4413f93e178d.jpg?hash=sxlkg683Yo)
You may have a leaky or open transistor. Pull the drivers from the adjacent channel and (from the top of the board), compare the readings of the corresponding transistors of the two channels.
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