General > General Technical Chat
Got shocked by a CRT
josh132:
so for all of you it was a Tektronix scope CRT i was trying to discharge to i can work around it. It was not from an old tune TV with the removable cap. The CRT used a plug for the anode and i had to use pliers for removing it. I got shocked and f##king dropped it on the board... Which killed the sweep generator. I have since visited a doctor and had no major adverse effects. Though my hand does feel a little weak. I am ok. No need to worry.
shakalnokturn:
The last time I got a HV bite was opening the connector on a Tek 22xx scope, I have plenty experience with other CRT's and haven't been caught in decades.
I consider that Tek design a wicked F'ing fail... No bleeder resistor and a connector that's just short enough to let the bloody arc reach you!
Now when I have to open those I use gloves and wrap a grounded guard ring of aluminium foil around the connectors before tugging on them.
Miyuki:
--- Quote from: james_s on January 30, 2021, 07:30:41 pm ---You're absolutely right about the power supply. People tend to fear the EHT and overlook the fact that the "low" voltage in the power supply is a lot more dangerous. One of the worst shocks I've ever had was from the bulk filter capacitor in an Electrohome G07 monitor. Those have a dangerous failure mode where a bad flyback transformer or HOT blows a fuse that is on the *output* of the B+ supply and the result is a large electrolytic capacitor charged to 170V with no load to discharge it, only the internal leakage of the capacitor itself.
--- End quote ---
Oh, that reminds me. I once grab some small adapter board with charged 400V (230V mains so something over 300V charge), just how the board nice fit to palm. And suddenly capacitor touches the skin and left two nice marks >:D |O
Oh and good old CRTs they can accumulate charge just on its own from the environment or hold charged for hours even days ::)
fordem:
--- Quote from: Miyuki on April 12, 2021, 07:35:25 am ---Oh and good old CRTs they can accumulate charge just on its own from the environment or hold charged for hours even days ::)
--- End quote ---
Back in the early '80's I worked with NCR and was sent to their training center in Dayton Ohio to learn, amongst other things to repair the CRT terminals used with the mini computers - the instructor showed us how to discharge the tube before removing it (slide a screwdriver with attached ground wire under the anode cap), and then set it aside. He did this at 5:00 pm, at the end of the day, and when class resumed at 9:00 am the following morning, before he did anything else, he discharged the tube a second time, so we could all see the charge that had accumulated overnight.
Another one of his favorite tricks was to "walk" each student one-by-one through the power supply adjustment - he'd come over to your workstation, instruct you to put one hand in your pocket, hand you a plastic screwdriver and offer to hold the meter leads on the test points while you adjusted the voltage - the adjustment potentiometer was a few inches below the anode cap on the side of the CRT, right alongside your knuckles as you held that screwdriver, almost guaranteeing that as you twisted the pot, eyes on the meter display, that the knuckle of your pinky finger would hit the anode cap where there was just enough voltage to startle you.
The lesson there was to always be aware of exactly where you were relative to the high voltage components.
Miyuki:
--- Quote from: fordem on April 30, 2021, 01:23:31 pm ---The lesson there was to always be aware of exactly where you were relative to the high voltage components.
--- End quote ---
And then you see pictures with train surfers jumping under wires with 22kV
They have no idea what they are playing with
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