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Technics SU-V6 Venting PS Caps
Technics SU-V6 Venting PS Caps
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Old 20th October 2016, 07:11 PM   #1
rickcl is offline rickcl  United States
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Technics SU-V6 Venting PS Caps
Default Technics SU-V6 Venting PS Caps

Hello all. I bought a broken SU-V6 amplifier that had a bad bridge rectifier and power supply cap. I replaced all power supply caps and the offending bridge rectifier. In hindsight I should have replaced both bridge rectifiers. After powering up the amp worked for about an hour and a cap blew. I replaced the cap and bridge rectifier. I thought that should do it. Negative rail cap vents.
In order to show what I have replaced I showed the succession in the jpg attached.

Yellow first replacement
Red second replacement
Green third (the current vented - rail cap)

I hope I haven't confused everyone. I measured each rail at +-51vdc. The replacement caps are rated at 65vdc.
I dont know if the rf suppression cap could leak and cause this. I will get my scope out and look at voltage to the caps. I will attach a section of the service manual soon.
Thank you all...
Attached Images
File Type: jpg SUV6.jpg (472.1 KB, 70 views)
File Type: png SUV6 1.png (289.6 KB, 65 views)

Last edited by rickcl; 20th October 2016 at 07:22 PM. Reason: Adding attachment
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Old 21st October 2016, 03:53 PM   #2
east electronics is offline east electronics  Greece
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Location: Athens GREECE
A main filter capacitor may see even up to 30% of it's operating voltage (63V) almost with out blowing at the correct polarity ...
In reverse polarity just a few volts are enough to blow the capacitor but then the short produced is so hard that mains fuse if exist and if not cannibalized to 30A rating will blow before the capacitor ( doesn't mean that the capacitor will survive the shock)

In your case i could imagine a rectifier that is pretty messed up with 2 internal failures resulting that the capacitor is fed with AC after all ...That is a good reaason for a cap to blow but still there should be something wrong in the sound of the amplifier like noise ( cannot predict that ) and obviously plenty of distortion if the amplifier pushed above 5W.

One other option could be a fake capacitor or a defective one

In general something is missing from the picture of your description .

Farther more if a short is produced after the capacitor for example from the bypass capacitor that will be enough to blow mains fuse if exist and if not cannibalized to 30A rating Might short the rectifier but that is very remote but in no case blow the capacitor .

A multiple failure where there is a short , then the mains fuse is cannibalized to 30A rating , the bypass capacitor presents short , the rectifier fails on the first place to produce a short and in the second place goes partially open resulting feeding AC to the main capacitor has less chances than the state Lotto ....

Kind regards
Sakis
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