View Full Version : Radio Shack Portavision (color CRT) suddenly died, dark out-of-focus image


CPQ5360
07-26-2017, 09:47 AM
I have a circa 1998 Radio Shack Portavision 5" color CRT TV I bought mint in the box a couple of years ago. A few weeks ago I finally put it into use, running a couple of hours a day.

Today I go to use it, and it seemingly died for no reason overnight. It now has a dark and completely out-of-focus image, and there's a subtle hissing/whistling sound coming from inside it. This is on both TV and monitor modes.

Any ideas as to what could have suddenly went wrong? I suppose I'll crack it open later and have a peek inside. I did test the power supply, which is supposed to be 13.5V, and it read 19V. I'm hoping that's just because I tested it with no load. I'll test it under load later.

tom.j.fla
07-26-2017, 10:09 AM
What is the catalog number? Thats' how you find data for Radio Shack electronics. With that we VK'ers might be able to offer help. All the best,Tom.J _ p.s.model number is like this:16-000.

CPQ5360
07-26-2017, 11:15 AM
Catalog number 16-125.

Findm-Keepm
07-26-2017, 12:19 PM
You'll find more info under Memorex 16-125. We apparently had one in for repair - it was a cracked board, so I can't offer up any direct suggestions.

Dark and out of focus could be just about anything in the sweep/flyback area. Common on some of the smaller sets was arcing around the base of the flyback, near the screen (G2) control and focus lead coming out of the flyback. Again, just a generality.

zeno
07-26-2017, 05:44 PM
Dark & no focus point to the HV divider which is almost always
built into the FBT ( flyback) as the focus & screen controls.
Normally I would measure the G-2 pin of CRT BUT there is
a chance of too much voltage that can wreck your meter.
Check for cold solder joints under the FBT first. Usually a pin
set apart from the rest & flat. To track down the noise you can
use a stethoscope made of an old paper towel tube. Odds are
the noise is coming from the FBT.

73 Zeno:smoke:
LFOD !

timmy
07-26-2017, 08:44 PM
Hissing sounds like hv, dust, flyback cracked from age. :scratch2:

CPQ5360
07-29-2017, 04:31 PM
I found out what's going on. I did look inside the TV - everything was factory clean, no bad solder joints or loose wires, etc.

When I powered the TV on, I saw the problem - something is arcing at the very back of the neck of the CRT, where it connects to a socket on the circuit board where the flyback runs to. It's a small purple arc, emanating from under a blob of epoxy covering part of the back of the neck of the CRT.

I attached a picture showing where I see the arcing. I can smell ozone when it's turned on. I would assume one of the leads exiting the tube is broken.

Something interesting; it turns out the CRT was actually made by Samsung. I would have expected some nameless Chinese company.

I have no knowledge or training with repairing CRT displays, so I'm comfortable with calling this unit pooched. Such a shame since it was mint in the box, and I only put a few hours on it. Thanks everyone for the help.

mstaton
07-29-2017, 06:49 PM
That blob may have turned conductive. Just a thought

WISCOJIM
07-29-2017, 07:34 PM
Looks like someone added that goop to try to stop the arcing in the connector.

.

Findm-Keepm
07-29-2017, 07:34 PM
That blob may have turned conductive. Just a thought

+1 - the focus voltage loves to find a path to ground. That goop is there to keep the CRT socket on during shipping, Carefully remove it from the socket and neck, and see if the problem disappears.

CPQ5360
07-29-2017, 07:39 PM
Thanks - I'll give it a shot. Any special precautions I need to take? I'm not at all comfortable working on a CRT - it's one of the few things I refuse to touch as an electronics hobbyist. I don't own an HV-insulated screwdriver, and I also don't know how durable the neck of the tube is, should the screwdriver I use to pry off the goop slips and strikes the neck of the tube.

CPQ5360
07-29-2017, 09:21 PM
I was able to remove the black goop - TV acts exactly the same. Arc is in same place and same size/brightness. Worth a shot though - thanks.

Findm-Keepm
07-29-2017, 10:35 PM
Sounds like your CRT socket has arced, carbonizing some of the plastic. Can you get a photo of the phenomena in a darkened room? Sure would help...

CPQ5360
07-30-2017, 01:17 AM
Here are two more photos, with and without flash. Externally linked so you get the full resolution to zoom in. You can see the corona in the photo with no flash.

http://i.imgur.com/6auxjBh.jpg

http://i.imgur.com/6p3OXVj.jpg

mrjukebox160
07-30-2017, 09:46 PM
Bad CRT. Broken pin in CRT seal.

Findm-Keepm
07-31-2017, 10:09 AM
Bad CRT. Broken pin in CRT seal.

The area looks external to the CRT - possible conductive white RTV sealant. Sony and others used it for isolation of the focus pin, but the RTV gets dirty with dust over time and the combination of HV and dust leads to problems. Sony had the tech take off the RTV coating between the plastic CRT base and the CRT, and use their part-numbered RTV sealant. We used RTV3145 or GC's Silicone Sealant for Electronics with 100% success.

http://knobsandpots.com/images/TVP0557.pdf

I'd get rid of the White and black sealant in the areas pointed at.

andy
07-31-2017, 02:23 PM
It's unlikely, but it's possible that another problem such as an internal short in the CRT, or a bad flyback could be causing excessive voltage on that CRT pin. Try running it with the CRT socket unplugged to see if it still arcs on either the socket, or the end of the CRT.

zeno
08-01-2017, 08:59 AM
It's unlikely, but it's possible that another problem such as an internal short in the CRT, or a bad flyback could be causing excessive voltage on that CRT pin. Try running it with the CRT socket unplugged to see if it still arcs on either the socket, or the end of the CRT.
Exactly..........
Could also be the spark gap in the CRT socket
All pins will have spark gaps almost always built into the socket.
Sometimes they are separate little rectangles with a slice
in them. Usually fail from too much focus voltage ( FBT ).

73 Zeno:smoke:
LFOD !

CPQ5360
08-02-2017, 09:06 PM
I removed the circuit board from the neck of the TV - no arcing on the socket. No improvement with the board re-seated (in case there was any build-up of oxidation). There is no silicone or anything there that could have become conductive.

Upon observing the CRT again, the arcing appears to be just inside the glass. But I assume that isn't possible without air in the tube, so I'm guessing that the lead has broken just outside the glass, and the CRT is a goner.

centralradio
08-02-2017, 10:43 PM
I remember back in the early 1980's I looked at my neighbors 1970's 12 inch Zenith portable was arcing inside the CRT which turned out the CRT went to air.

CPQ5360
08-02-2017, 10:44 PM
Oh interesting. And it was still showing some sort of a picture at the time?

kvflyer
08-04-2017, 06:17 AM
Oh interesting. And it was still showing some sort of a picture at the time?

Somehow, I doubt it...