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I need some clarification on CRT discharging    
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Telefunken U47



Joined: 09 Mar 2018
Posts: 2

PostPosted: Fri Mar 09, 2018 8:39 pm    Post subject: I need some clarification on CRT discharging Reply with quote

I once had a Daewoo television that needed some work. I discharged the anode cap (Using the classic screwdriver + Wire) to the braided wire that wraps around the tube. Heard the pop, assumed everything was good and I poked around the board, reflowed a couple things, took some parts out of circuit to measure them, etc. When I tried turning it on, it was 100% dead. (Whereas it wasn't before)

Inside the casing, it had warnings about X-radiation, tube implosion, etc. and also a warning "CAUTION: SHORT ANODE LEAD TO CHASSIS ONLY." I've always heard you should only short to the CRT ground, like the lugs in the corners or the wire around the tube, because shorting to the board may damage parts. So, I suspect that discharging to the wire on the tube is what killed it. I suppose I could have killed it while messing with the board, but I didn't really do very much to it.


So, now I have another Daewoo TV (just a little project) with the same warning, and I'm not sure how I should discharge it- the conventional method says short to the tube grounds because shorting to the chassis ground may damage parts, and the warning in the case says I should only short to the chassis ground. This TV has a tuner shield and a couple of heatsinks (I think one is the HOT) I can clip to.

I see in kuhurdler's article he used to discharge to the tuner or heatsink, but was corrected and now grounds to the spring on the CRT. Which seems to be the opposite of what the warning tells me.

Here's a link to the service manual-

https://www.manual.guru/download-manual-10/458914/not-specified-daewoo-crt-television-dtq-14v1fc20v1fc.html?download#.WqHfMXzavyM

It doesn't even mention discharging the CRT at all.

What should I do here?
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JTS1957



Joined: 21 Jan 2009
Posts: 2388
Location: Far, Far Away

PostPosted: Sat Mar 10, 2018 1:04 am    Post subject: Reply with quote

http://www.riddledtv.com/journal/DischargeCRT/
Telefunken U47



Joined: 09 Mar 2018
Posts: 2

PostPosted: Sat Mar 10, 2018 7:14 pm    Post subject: Reply with quote

JTS1957 wrote:
http://www.riddledtv.com/journal/DischargeCRT/


I mentioned this article in my first post, of course I read it. The problem is the warning on the TV case seems to contradict the conclusion of the article, and I was hoping someone with more experience could help me out.
kuhurdler



Joined: 28 Dec 2006
Posts: 2877
Location: Overland Park, KS

PostPosted: Sun Mar 11, 2018 7:48 am    Post subject: Reply with quote

In your instance, I would interpret "Chassis" to mean the metal frame of the CRT, sort of like a car chassis... and not the circuitboard ground.

The metal frame should already be electrically connected to the aquadag.

In most instances all of those things are electrically bonded together, but it's considered safer to discharge it furthest from the circuitboard PCB.

It's probably also less likely to damage any components if you also use a resistor so that there are no sudden discharge sparks.

At least that is my interpretation.
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