Safety tip of the day

[Eric H]

Before you power up that Isolation Transformer and turn on the power strip. Before you stick your fingers under the chassis and start to unsolder that Filter Cap, be sure the set is turned off and unplugged!

I know for a fact this is good advice, don't ask me how I know but I KNOW!

[Findm-Keepm]

Let me add that I've done the same many, many times, and that before I replace a filter cap, I ensure the set is unplugged and the filter cap has been thoroughly discharged. They can still bite even after unplugging.

DAMHIK

Cheers,

[brokenbroken]

About ten years ago I was working on a 13" RCA set with a filter cap that kept shocking me. I got frustrated with it and was just about to discharge it with a screwdriver when I noticed it was still plugged in. Good thing I noticed that especially since the boss was only a few feet from me. Even though he probably woulda just laughed and would still be ripping on me for it to this day.

[mbates14]

I worked on an old sony projection unit and forgot it was still plugged in, had the board out, replaced convergence output ICs, and put the board back in and went to reach back to plug it in, it was already plugged in. OH SHIT... lol. it powered on and worked though. hah

[radiotvnut]

Originally Posted by brokenbroken

About ten years ago I was working on a 13" RCA set with a filter cap that kept shocking me. I got frustrated with it and was just about to discharge it with a screwdriver when I noticed it was still plugged in. Good thing I noticed that especially since the boss was only a few feet from me. Even though he probably woulda just laughed and would still be ripping on me for it to this day.

If it was one of those TX81 or 82 chassis sets, the main filter cap in those will hold the full charge for a very long time even if the set is unplugged. Don't ask how I know!

[electronjohn]

I have a broadcast engineering acquaintance who intimately knows what an undischarged filter's capable of. He was working on a balky 20kW FM transmitter...it was the middle of the night & he'd been at it for hours. His most recent attempt at getting it back on the air failed, he got VERY pizzed and flung a wrench in his hands into the transmitter's guts. As bad luck would have it, it landed RIGHT ACROSS the terminals of a big filter (maybe 20uF @ 15kV). The big cap blew the wrench out like it was shot from a gun...hit him in the face, breaking his jaw & taking out 8-9 teeth. It was a Collins like I'm familiar with, so prolly ran about 8,200V @ 3A or so. Owie.

Myself? Only been zapped once...an old Gates 1kW AM got me w/about 3500V @ 500mils. Knocked me right into the wall 3' behind the transmitter. I quit bypassing interlocks that day. Oh...when I was a kid I let a color TV snap an arc right thru my fingernail. Left a cute little hole. Owie.

[drh4683]

Originally Posted by electronjohn

I have a broadcast engineering acquaintance who intimately knows what an undischarged filter's capable of. He was working on a balky 20kW FM transmitter...it was the middle of the night & he'd been at it for hours. His most recent attempt at getting it back on the air failed, he got VERY pizzed and flung a wrench in his hands into the transmitter's guts. As bad luck would have it, it landed RIGHT ACROSS the terminals of a big filter (maybe 20uF @ 15kV). The big cap blew the wrench out like it was shot from a gun...hit him in the face, breaking his jaw & taking out 8-9 teeth. It was a Collins like I'm familiar with, so prolly ran about 8,200V @ 3A or so. Owie.

Myself? Only been zapped once...an old Gates 1kW AM got me w/about 3500V @ 500mils. Knocked me right into the wall 3' behind the transmitter. I quit bypassing interlocks that day. Oh...when I was a kid I let a color TV snap an arc right thru my fingernail. Left a cute little hole. Owie.

ouch. Sorry I couldn't help but to laugh while reading that as I can picture that happening.
I've made some bad moves too and sometimes, Im amazed that I didn't get zapped when soldering/servicing under a chassis not realizing that the set was still plugged in, especially if I was working in the power supply!!!!

[marty59]

Back in my teens a good friend of mine (also into electronics) and I were changing out a CRT in an early 25" Zenith color. So here we are with the face down on a throw rug working on the (tiled) basement floor with just socks on our feet. Next thing I remember we were about ten feet away from that set laying next to each other and saying "No, I thought "You" discharged the CRT"!!

[Tubejunke]

Many of those lage capacitors can hold enough current to stop a heart for quite a while. Be careful!

[jshorva65]

My worst-yet experience with a filter cap was while I was repairing an old Harman-Kardon CA-100 PA / Paging amp (100W RMS, P-P 8417's running 645V B+ and 325V G2 from a full-wave doubler circuit) and preparing to add a custom-designed Guitar Preamp sub-chassis (minibox with two tubes, five pots, and appropriate connectors to draw power from a 5-pin socket H-K provided for a two-channel Mic Preamp for optional Mic 3 and Mic 4 and feed the Line Out signal into the RCA jack that H-K provided for the same Preamp accessory). The original problem was that the amp's output would intermittently go dead, which I traced to intermittent loss of G2 supply to the 8147's. Unplugged AC power, flipped the chassis, noticed a cold-solder joint where the G2 lead was supposed to connect to the junction of the two (about 100uF/450V) filter caps and power transformer secondary. I was about 12 years old at the time, and thought "looks like an easy fix" as I picked up the solder and soldering gun. Next thing I remember was picking myself up off the floor, fetching the spool of solder from the other side of the room, and gluing the broken case of my Weller D550 back together from where it had hit the floor and cracked like an egg. Definitely learned my lesson about remembering to discharge electrolytics!!!