Short Circuit between terminal 12 and 13

alepoli · 967

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Offline alepoli

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on: April 11, 2015, 07:46:20 PM
Hi,

I am new to this forum, therefore I am sorry if I am posting something that has already been posted.
I got my crack and built it up. I then checked all the resistance readings and they were all perfect. I then powered it up, and the heaters glowed perfectly. So then I went to do a voltage check. I had my brother hold the negative lead to joint number 12 and tested the rest with my right hand. My brother slipped and the probe touched the 12 and 13 terminal simultaneously, discharging the capacitor with a large spark. There is now a large silver area on the resistor between 12 and 13 (photo attached). Also the fuse is blown. What should I do (apart from get a new fuse)? Is the resistor done? After doing some resistance checks, the place where it should be 0 (grounds) were all higher than 1. Please help!

Thank you,
Alex 



Offline alepoli

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Reply #1 on: April 11, 2015, 07:58:39 PM
All the resistance readings are back to 0. That was my bad. 



Offline Grainger49

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Reply #2 on: April 12, 2015, 12:10:30 AM
That was the output of the high voltage power supply, it shorted to ground.  All the voltage stored in the three power supply caps was dumped through the resistors in the power supply.  But the resistor pictured is between T13 and T12.  It is there to bleed down the voltage when you turn it off to make it safe to work on it.

The resistors that took all the current are the two white ceramic ones.  And the fuse should have blown.  That was too much current being delivered.

But all the resistance readings should not be zero.  Verify that the resistance readings across the two RCA jacks (inputs) is about 100k Ohms.  That was not in the circuit that "popped." 

It is likely that the diodes and capacitors are bad.  But take measurements through the power supply.  Those are around the transformer.



Offline kgoss

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Reply #3 on: April 12, 2015, 06:36:26 AM
Also get some alligator clip leads for your meter.  The next time you do voltage checks use the aligatot clip lead on the ground and the probe lead to take measurements. It's a lot easier when you don't have to worry about the ground lead moving.

Ken Goss


Offline Paul Birkeland

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Reply #4 on: April 12, 2015, 06:37:00 AM
Or you can also ground the probe at the bare ground wire at the IEC inlet module.

-PB

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline alepoli

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Reply #5 on: April 12, 2015, 08:01:30 AM
Thank you all for your help!
 
I meant that the resistance reading that were supposed to be zero are. All resistance reading now check out. The RCA center pins are at 98 and 101, so they are also good.

Thank you for your help!