SX-1250 New Issues

mdemott

Member
Hello:

Several months ago I did a full recap, etc... of this receiver replacing all parts shown in the main sx-1250 restoration thread. The receiver played wonderfully for 3-4 months....probably 10 hours of playing. Then it blew fuses 1 and 2 on the AWR-107 Board. Replacing fuses and powering on from DBT indicated a short. I had suspected issues with the Stabilizer Board so I obtained one, rebuilt it and turned on with DBT and no more short. Went to adjust voltages on stabilizer board and was able to get 65 volts on pin 17. Pin 16 wouldn't move beyond 3V +-. Voltages on pins 9 10 and 8 on that board all check out fine.

Looking further I noticed I didn't hear the relay click on. I also found +1.3V at PIN 14 on the stabilizer board which also impacted reading on pin 2 of the flat amp board and 3 of the protection board. I wonder if the previous short caused an issue on one of these boards.

I might be asking this the wrong way but should the -25V that I should be seeing originate from the protection board? I'm trying to figure out why I'm not getting voltage there and then proceed.

Any thoughts would be greatly appreciated. Thanks.
 
Zener's tested OK but replaced with new anyway.

Also notice both pins 2 and 5 on flat amp see +1.3V and should be -25V.

I can confirm this issue was not there before the fuse blowing situation happened. I kept a record of all voltages measured after the initial rebuild.
 
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Replace C3 and C4 on the Stabiliser, I had C3 partially shorted on the one I restored a few months ago.
It basically was pulling the +65VDC down to about 18V, and I could not adjust it any more than that.
I used some stacked film caps 100pf the originals are 82pf but its not an issue to go up to 100pf.
If you have to order, then get the right value.
 
Thanks for clarifying. I did not replace those so I will check them out. Only replaced electrolytics.
Yeah this is what I saying, its not just the electrolytic caps causing issues these days, other types of caps are starting to fail now as these units get older...
 
I replaced the two caps as suggested and yes I got stabilizer voltages as I should and everything seemed to be working. Unit started up with DBT and after a while of running it with DBT I went without. Played music fine and stabilizer board voltages were holding. Then after about an hour fuses 1 and 2 blew. Same issue that was there before I rebuilt the stabilizer board so I'm missing something. Any thoughts on what else could cause those two specific fuses to blow?
 
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