How to blow up a hat diode - Videokarma.org TV - Video

blue_lateral · #1 02-03-2006, 04:29 AM

Tonight I was working on the IF alignment of my Silvertone/ctc-15 chassis. It is on the bench, as it has been quite a while now. I have the horizontal output tube and the horizontal oscillator tube removed, and a resistor loading the power supply down to simulate the current draw of the horizontal section and the CRT.

Last night I thought I heard a little snap. Not normal crackling, either. The high voltage isn't running. I couldn't find a source, so I just went on. Tonight there was another little snap. This time I saw a little spark from voltage doubler area of the low voltage power supply. I started beating on power supply parts with my alignment stick. I hit one of the power supply diodes and KA-SNAPPPPPPPPPP!!!!!!!!!!!!

. Sparks flew from the connection at one end of the diode and the circuit breaker tripped. Oops

. On closer inspection the wire running to the floating 160mfd cap was not soldered. I don't think it had ever been soldered. It wasnt even tinned.

I soldered the wire on and tried to bring it up on the variac, but no dice. I pulled the diode out. Sure enough, It's shorted. I pulled the other one, and it was ok.

I had already redone a lot of soldering in this set. The wave soldering on the boards was typically bad. I redid a lot of it. I also cleaned up several old ugly repairs under the chassis, but I missed this. It had apparently been laying there unsoldered for the last 42 years or so, and working fine.

John

jpdylon · #2 02-03-2006, 11:22 AM

Quote:

Originally Posted by blue_lateral

I started beating on power supply parts with my alignment stick. I hit one of the power supply diodes and KA-SNAPPPPPPPPPP!!!!!!!!!!!!

heh. Sounds as though your TV doesn't like abuse

Seriously that really sucks. I've run into a few sets that had been worked on by the previous owner, who didn't really re-attach a few things causing arcing and other problems. Now every new set I aquire goes through rigorous inspection. I hate that HV snap. Makes me jump every time...

frenchy · #3 02-03-2006, 02:19 PM

So what would be the effect of that cap not being connected if otherwise the set was working?

blue_lateral · #4 02-03-2006, 08:05 PM

It had to be making connection... barely. If it was disconnected half of the 405v B+ would be missing. Theres a thread somewhere here about a Zenith doing exactly that. It was dim, didnt have much deflection and had a bunch of what looked like 120 cycle ripple in the picture.

John