No screen voltage

**moeee** · 02-10-08, 10:17 PM

When i remove the neck board the screen voltage measured is 320 Volts.
When i plug it back on the tube, there is zero again.
There don't seem to be any shorts on the pins of the tube.

The symptom is a dull green light emitted from the screen.
The TV is a DEC 29 inch thing.
Chinese I guess with a samsung flatscreen tube.

Anyone have a clue as to my next test or a cure.

**Fernbay** · 02-10-08, 10:18 PM

Get the desolder wick & isolate

**best4less** · 02-10-08, 10:20 PM

Have you taken the HV lead off to see if there is any burning,arcing or tracking to the earth paint on the tube ???

But sure sounds like a shorted tube to me

Or you could try floating the tube

**iwacelect** · 03-10-08, 09:10 AM

Quote:

Originally Posted by best4less

Have you taken the HV lead off to see if there is any burning,arcing or tracking to the earth paint on the tube ???

But sure sounds like a shorted tube to me

Or you could try floating the tube

floating will work if it's a heater short, he still need to get out the wick and isolate!

**moeee** · 03-10-08, 10:01 AM

Obviously there must be HV present because I have a display.
Also I'm familiar with a heater short and the symptom doesn't correspond so I don't Have that.All my Kathodes read around 180 Volts or so.

This isolate thing?
Do I need to dewick what?..the screen pin on the neck board?
Wouldn't removing the neck board off the tube be doing the same thing?

I have a couple of similar TV's out the back and I might try a substitute tube to see if it comes up.
Trouble with that is the tubes could be all different and the amount of time spent would be not worth the price the job is worth.
Educational purposes only.
But then again, I ain't in the business no more, but the trouble is, ny old customers don't seem to believe me

**Studio1** · 03-10-08, 05:02 PM

Suck the solder off the screen pin on the rear of the CRT base. If the voltage comes up, you got a dud tube or a short in the CRT socket. Also check the plastic insulator on the base of the tube - they can arc up in there and cause carbon shorts to other pins.

As you say tho, bloody chinese junk - not worth the time p*ssing around with it.

Educational, yes. And it has just made me realise that new techs starting in the TV repair field will soon only know how to repair flat panel TVs, CRT will be foreign to them and the only ones who will know will be us old farts who have worked on them for years.
Are they even teaching valve/CRT techniques in the technical institutes these days?

**moeee** · 04-10-08, 09:33 AM

Tried another tube without the yoke connected to it.
Then swapped yokes.
Picture came up but wasn't happy with the convergence and size.
Checked the faulty tube closer and found some resistance between the screen pin and the G1 pin.
Tried grounding the G1 pin with neck board removed and taking the focus voltage and applying it to the screen pin hoping it might zap the problem.

Didn't work

**rievax** · 04-10-08, 10:22 AM

I have occasionally found pin to pin leakage under the key base. Fixed by carefully removing it, scraping everything clean then sticking it back on with silastic. Its also possible to do a test run whiile the key base is removed.

**Studio1** · 04-10-08, 11:23 AM

Quote:

Originally Posted by moeee

Tried another tube without the yoke connected to it.
Then swapped yokes.
Picture came up but wasn't happy with the convergence and size.
Checked the faulty tube closer and found some resistance between the screen pin and the G1 pin.
Tried grounding the G1 pin with neck board removed and taking the focus voltage and applying it to the screen pin hoping it might zap the problem.

Didn't work

Looks like you might have a couple of dud tubes. How sure are you that they are genuine Samsung tubes?
Wouldn't put it past those slippery sods to produce their own crap tubes and put someone else's name on them.
They did it with the first lot of TVs that were sold at The Warehouse (Red Shed) here - Panasonic badge on the front but the rest of the set was anything but.

**moeee** · 04-10-08, 01:12 PM

Nah the other tube wasn't a Samsung.
That why it didn't come up as perfect as I would like.
I just tried it to verify that the original tube was stuffed.

KEY BASE?
Is that the ceramic or plastic thing glued to the glass and pins?
I'm bit scared to try removing that.
Might smash the neck.
I'll give it a small try.
Don't really wanna smash the blokes tube even though it is stuffed.

02-10-08, 10:17 PM	#1 (permalink)
moeee Senior Member iTrader: (0) Join Date: Jan 2008 Posts: 124 Spent time on board: 1 Day and 13:17:35	No screen voltage When i remove the neck board the screen voltage measured is 320 Volts. When i plug it back on the tube, there is zero again. There don't seem to be any shorts on the pins of the tube. The symptom is a dull green light emitted from the screen. The TV is a DEC 29 inch thing. Chinese I guess with a samsung flatscreen tube. Anyone have a clue as to my next test or a cure.

02-10-08, 10:18 PM	#2 (permalink)
Fernbay Super Moderator iTrader: (30) Join Date: Jan 2008 Location: Newcastle Posts: 873 Spent time on board: 1 Month, 2 Weeks, 5 Days and 3:47:23	Get the desolder wick & isolate __________________ FS:- DM7020 - $525 DM500S $170 , DM500 2A PSU, $25ea... DM500 mobo - $130 - Free domestic express post PM for details

02-10-08, 10:20 PM	#3 (permalink)
best4less I'am Not a Bloody Joke iTrader: (10) Join Date: Jan 2008 Location: Australia Posts: 2,617 Spent time on board: 1 Month, 4 Weeks, 0 Days and 10:39:18	Have you taken the HV lead off to see if there is any burning,arcing or tracking to the earth paint on the tube ??? But sure sounds like a shorted tube to me Or you could try floating the tube __________________ Please wipe your feet before walking all over me

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03-10-08, 10:01 AM	#5 (permalink)
moeee Senior Member iTrader: (0) Join Date: Jan 2008 Posts: 124 Spent time on board: 1 Day and 13:17:35	Obviously there must be HV present because I have a display. Also I'm familiar with a heater short and the symptom doesn't correspond so I don't Have that.All my Kathodes read around 180 Volts or so. This isolate thing? Do I need to dewick what?..the screen pin on the neck board? Wouldn't removing the neck board off the tube be doing the same thing? I have a couple of similar TV's out the back and I might try a substitute tube to see if it comes up. Trouble with that is the tubes could be all different and the amount of time spent would be not worth the price the job is worth. Educational purposes only. But then again, I ain't in the business no more, but the trouble is, ny old customers don't seem to believe me

03-10-08, 05:02 PM	#6 (permalink)
Studio1 Senior Member iTrader: (0) Join Date: Jan 2008 Location: Inside the toaster Posts: 484 Spent time on board: 3 Days and 11:13:34	Suck the solder off the screen pin on the rear of the CRT base. If the voltage comes up, you got a dud tube or a short in the CRT socket. Also check the plastic insulator on the base of the tube - they can arc up in there and cause carbon shorts to other pins. As you say tho, bloody chinese junk - not worth the time p*ssing around with it. Educational, yes. And it has just made me realise that new techs starting in the TV repair field will soon only know how to repair flat panel TVs, CRT will be foreign to them and the only ones who will know will be us old farts who have worked on them for years. Are they even teaching valve/CRT techniques in the technical institutes these days?

04-10-08, 09:33 AM	#7 (permalink)
moeee Senior Member iTrader: (0) Join Date: Jan 2008 Posts: 124 Spent time on board: 1 Day and 13:17:35	Tried another tube without the yoke connected to it. Then swapped yokes. Picture came up but wasn't happy with the convergence and size. Checked the faulty tube closer and found some resistance between the screen pin and the G1 pin. Tried grounding the G1 pin with neck board removed and taking the focus voltage and applying it to the screen pin hoping it might zap the problem. Didn't work

04-10-08, 10:22 AM	#8 (permalink)
rievax Premium Member iTrader: (1) Join Date: Mar 2008 Posts: 35	I have occasionally found pin to pin leakage under the key base. Fixed by carefully removing it, scraping everything clean then sticking it back on with silastic. Its also possible to do a test run whiile the key base is removed.

04-10-08, 01:12 PM	#10 (permalink)
moeee Senior Member iTrader: (0) Join Date: Jan 2008 Posts: 124 Spent time on board: 1 Day and 13:17:35	Nah the other tube wasn't a Samsung. That why it didn't come up as perfect as I would like. I just tried it to verify that the original tube was stuffed. KEY BASE? Is that the ceramic or plastic thing glued to the glass and pins? I'm bit scared to try removing that. Might smash the neck. I'll give it a small try. Don't really wanna smash the blokes tube even though it is stuffed.

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