Safety - Videokarma.org TV - Video

ChuckA · #1 11-23-2002, 10:42 PM

Had a close call today working on a TRK-5. Most of you know this set is pre-war with a DANGEROUS 60cycle power supply.

Well I got a little careless working under the chassis. I had finished recapping the set and was trying to track down problems with video quality. I was using a scope to probe around, and decided to take a look at the B+ line for any ripple. The picture I posted here shows how close the B+ point I was looking at is to the 2500vac lead from the power transformer. Well I wasn't watching where my hand was and my middle finger came in contact with that HV lead. The energy from that voltage burned a entry hole through my fingernail and a nice exit hole through the first joint of my index finger, which was in contact with the probe ground point. My hand felt like someone hit it with a 10 pound sledge, and the smell of burning flesh (especially when it's your own) is not pleasant.

I'm just glad that my old training was second nature, always keep one hand in your pocket when working around HV, if not for that I probably wouldn't be writing this.

My point to all is don't get to complacent when you're working on one of your vintage sets, always know where your body parts are.

And no the TRK still has a lousy picture back to that tomorrow, but only after I make an insulating rubber blanket for that terminal.

Chuck

Rob · #2 11-24-2002, 12:40 AM

Chuck,

You are fortunate that you weren't more seriously hurt. Thank goodness! I like to dab clear RTV silicone sealant over any exposed HV terminals that I might accidentally get in contact with. This is an amazing HV insulator, and great at supressing corona too. It is even useful at 50 kV, employed properly.

Take care.

You don't suppose the reason the TRK-5 has a poor picture is because it is an old TV?

Man I'd love to have a TRK-9.

Rob

ChuckA · #3 11-24-2002, 07:12 AM

Rob,

I'm hoping this picture isn't all I can get out of it, the owner is going to be really dissapointed in my repair capabilities.

A TRK-9 just came out at a local auction about 2 weeks ago, a collector got it at a bargain price. A lot of people didn't see the short description in the ad, me included!!

Chuck

Rob · #4 11-24-2002, 12:15 PM

ChuckA,

I was under the impression that you were the proud, although slightly bruised owner of the TRK-5. Geeze, you took a beating fom it and it isn't even yours?! Double ouch!

Too bad the TRK-9 got away.

Rob

ChuckA · #5 11-24-2002, 01:40 PM

Rob,

I wish it was mine. I did try to buy it, but the guy had been looking for one for a long time so he isn't in the selling mode right now.

Chuck

Charlie · #6 11-24-2002, 04:49 PM

Wow Chuck... I bet that 2500 volts got your attention! Please don't do that again. I doubt anyone here would want to start an "obituaries" thread!

#7 11-24-2002, 06:39 PM

Chuck,
Thank you for sharing this experience. Your post may save someone's life!

Steve McVoy · #8 11-24-2002, 07:36 PM

The TRK-9 and 12 have 6KV AC and about 7200 VDC. Either can kill you, so I am extremely careful when I work on either of them. Chuck, the TRK-5 should give a nice but dim picture. They have absolutely no selectivity, so they need to be fed with a VCR. If you have a strong low band local channel it can cause interference with the VCR signal, so you may have to use a 10 db amplifier on the VCR output. Also, the local oscillators in the RCA prewar sets are touchy, and drift badly.

ChuckA · #9 11-24-2002, 10:07 PM

Steve,

Finished up the TRK tonight, 53 caps changed and 1 electrolytic can. Picture is pretty good, if you watch it in a dark room.

My problem with poor horizontal and vertical sync ended up with a 6N7 that developed a plate to cathode short after running in the set for an hour, pulled the plate voltage down to 16v on the sync amp. Changed the tube and locked right in.

One think I noticed, maybe you can tell me if it is common with this set, watching the video output signal from the 6V6 the video signal clips as the brightness control is turned up. This only happens on the output (plate) of the 6V6, signal on the grid is constant.

Chuck

#10 11-24-2002, 10:15 PM

Quote:

Originally posted by Steve McVoy
Also, the local oscillators in the RCA prewar sets are touchy, and drift badly.

Steve,
I read in a 1939 RCA Review article about the TRK12, that they had to make the oscillator coil out of a 1-turn loop of brass strap soldered directly to the 6J5 socket terminals, and raise the filament voltage on the 6J5 to 6.5V, just to get it to oscillate at 100 MC. I'll bet there was some tube selection going on too.

Steve McVoy · #11 11-25-2002, 06:51 AM

I'm working on a Westinghouse WRT-700 now, which uses the TT-5 chassis, and I'll check the video clipping.

Notice that the filament on the 6J5 is fed with its own 6.6 v winding from the power transformer. They must have been pushing the limits with that tube at that frequency.

#12 11-25-2002, 07:06 AM

Now I am very ignorant of TV's but I am assuming you are all following the "unplugging" rule? So these TV's can kill you when not plugged in??

#13 11-25-2002, 07:07 AM

Not to be morbid but a picture of the injury would of been neat too

Kind of like those accident pictures they showed you back in shop class.

Rob · #14 11-25-2002, 10:11 AM

Here you go Thor. This guy was trying to steal a more 'industrial looking' pro power cable for his stereo, but it was live at the time he grabbed it....to the tune of 16,000 volts.

Rob

jshorva65 · #15 11-27-2002, 09:05 AM

Chuck,

Glad to read that your injury was relatively minor. When I work on potentially dangerous circuits, I always power down before changing the test circuit connections. This prevents things like drawing an arc that can destroy a flyback, etc. I would have been more pleased to read that you had gotten the set up and running wthout incident, but your experience started a very inportant thread. Those of us who have pets and children need to be especially careful. My son is about ten years past the "toddler" phase, but toddlers need to be kept far away from workbenches. My girlfriend's cat had an unpleasant experience recently after walking under a Zenith 24MC32 that had no bottom plate. Apparently, her tail came into contact with something because she ran out from under that tv as if something had bitten her, then turned around a SNARLED at it. She wasn't seriously hurt, but she was fighting mad. Before installing my Lambda 500VDC @ 500mA power supply in my workbench's equipment rack, I made sure to have top and bottom covers made by the manufacturer who makes my reproduction tv backs.