Soundstream 404s Preamp Issue

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scsiguy

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Joined 2013
#1
My Soundstream 404s had an intermittent channel. I tracked this down to a cracked solder joint on one of the RCA pairs. Unfortunately, in the processes of disassembly/reassembly/repair, I lost output for all channels.

Thanks to the amazing information here, I've tracked this down to a fault somewhere in the preamp section. Both regulators have the appropriate rail voltages, but the LM337T has no output (should be -16V). I tried replacing this part, but saw no change in behavior, It's still outputting 0V.

Without the schematic I feel like I'm running blind. It's been four days since I sent my schematic request to Soundstream, but no reply yet. While I continue to wait, are there other components in the preamp area that I should verify?

Thanks!
 
#3
What voltage do you have into the regulator? These regulators have input, ground or reference, and output leads. With no output I would check input and ground reference. If those are intact then lift the output lead and see if the regulator has output. if it does then its probably seeing a dead short on its load side causing it to drop out.
 
#4
On the one I took apart I made the mistake of not using the fiber covered washer on one of the regulators. If I would have read Perry's section on the 404 I would have know this. Take a look at your washers for a fiber covered one.
Take a look at the board traces to see if a regular washer could short them out.
 
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