Saving Circuit Board w/o Tube

[Electronic M]

Originally Posted by MadMan

You know that big cable that plugs straight onto the side of the CRT? And it has a rubber boot over the connection? Get yourself a screwdriver, wrap the bare end of a wire around the screwdriver, and connect the other end of that wire to a big chunk of metal on the tv chassis (ground). Stick the screwdriver under the rubber boot and fish around until you've touched metal. Careful not to touch the metal of the screwdriver. If it had a charge you'll hear a snap.

But as it's been several days, it's probably naturally discharged by now.

Also, don't let anyone scare you, the high voltage charge on a crt anode is not particularly dangerous. It won't even injure you. It does hurt like a mother, but it's no worse than being zapped by a car's ignition coil.

To add to this a bit if you start to do regular service work on TVs where you need to turn the set off and pull the chassis or main board quickly after power off then you want to put a 1M resistor in series with your screw driver to ground lead. If there was a lot of charge stored in the CRTs integral capacitor (which is the case imediately after power off) shorting to ground without a series resistor can cause the HV charge on the CRT to bounce back in a few moments.

Early on in my TV resto work I didn't know about that and kept getting HV bites from my Silvertone Roundy...Cussed like a pirate over it a bunch then learned about bounce back and made sure to only resistively discharge after that.(though I'll still short discharge if I'm in a situation where I don't have what I need to resistively discharge on hand)

[old_tv_nut]

Originally Posted by Electronic M

To add to this a bit if you start to do regular service work on TVs where you need to turn the set off and pull the chassis or main board quickly after power off then you want to put a 1M resistor in series with your screw driver to ground lead. If there was a lot of charge stored in the CRTs integral capacitor (which is the case imediately after power off) shorting to ground without a series resistor can cause the HV charge on the CRT to bounce back in a few moments.

Early on in my TV resto work I didn't know about that and kept getting HV bites from my Silvertone Roundy...Cussed like a pirate over it a bunch then learned about bounce back and made sure to only resistively discharge after that.(though I'll still short discharge if I'm in a situation where I don't have what I need to resistively discharge on hand)

I didn't know that using a resistive discharge would prevent the bounceback (dielectric relaxation) - interesting. I wonder if bounceback would be eliminated with a direct discharge if you just held the contact for a few seconds more?

[Electronic M]

Originally Posted by old_tv_nut

I didn't know that using a resistive discharge would prevent the bounceback (dielectric relaxation) - interesting. I wonder if bounceback would be eliminated with a direct discharge if you just held the contact for a few seconds more?

I've experienced bounce back minutes after disconnecting from IIRC over 10sec long discharge... I've also done multiple discharges and gotten multiple bounce backs on some CRTs. I either resistively discharge, leave the CRT HV connector shorted to ground, discharge immediately before contact, or regret my lapse... assuming the CRT hasn't previously been discharged beyond bounce back.

It is one of life's little annoyances.

I've always liked the SS and hybrid Zeniths that use a resistor voltage divider to obtain focus voltage from the HV since they self discharge fairly quickly.