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#1
03-06-2009, 06:21 PM
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Magnavox 32" Set Question?
Its been awhile since I've posted here, as I've had to devote alot of time to things in my virtual world. Things are calming down again, so here we go.
I was given a 32" Magnavox color set model # MS3250 C321 with a chassis number 32T800 7629 installed. Its not much of a set, features wise, but it intrigues me. When you turn it on, it powers up and runs about 12 seconds. A purple picture will pop up and stay on for about 6 seconds then the set shuts down. I know the history of this set. Friend bought it new, and it failed once during the warranty. It worked fine 18 hours a day for about 3 years. Then, he noticed that the set would turn off (shut down) when there was a bright image on the screen. It started doing it more often, and over the years, he had to turn the brightness down a bit more to keep it working. ' The last time I saw it playing, it had a dark, but beautiful color picture. That was about 7 months ago. He recently told me that it was just turning on and shutting down like what I describe above. Here's what I've found so far. I found the soldering that the warranty shop did. How sloppy! I re-soldered the previous work, and generally reheated connections under the flyback, Hz drive transformer, Hz output transistor, etc. Checked the CRT board for bad connections, and slapped it back in the set. Turned it on, and the dim purple pic came on. I am using an old VCR for a signal, and I have a good clear picture, with no green. All 3 guns are lit in the CRT. When the set shuts down, the power light stays on, and the CRT filaments go dark along with everything else. I tried turning on the chassis with the CRT unplugged, but there is no difference. The chassis powers up and shuts down as always. On the CRT board, there is an IC attached to a heat sink. Is this the video drive for this chassis? Is this something that fails on newer sets? I worked on TV's for many years, but have never worked on much of anything newer than around 1987. I understand how the shut-down circuitry works on newer sets. If I can get this set working reasonably well, I'm going to give it to my 9 year old nephew so he can play his wii games in his room instead of on the living room set. His mother will appreciate it. What do you guys think? Bruce 
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#2
03-06-2009, 06:37 PM
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This sounds like a post 2000 model TV. That IC on the CRT neck board is actually the three video output transistors rolled into one package. The first thing I would do is adjust the screen (G2) control on the flyback. Some of the newer Philips/Magnavox sets have circuitry that will shut the set down if the G2 control is not set properly. Also, if you have access to a CRT tester, check the tube. If it's weak, that will be your problem. If the problem is still up in the air, you'll have to obtain a schematic and check voltages in the video output stages. Some sets have a low ohms resistor in the 200 V B+ line to the video output circuit. If this resistor opens, there will be no B+ to the video output stage and the result will be a very bright screen w/ retrace lines and then the set will usually go into overcurrent shutdown. Also, look for a high voltage electrolytic cap in this same B+ line. It can also fail and lower the B+, causing a bright screen, a smeary picture, a picture that is darker on one side, etc.
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#3
03-06-2009, 07:23 PM
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Thanks for your reply, but, wouldnt the set stay on with the CRT unplugged if the G2 was set wrong?
Like I said, the pic is dim and sharp and purple. Yep, its a 2002 model set. Bruce
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#4
03-06-2009, 07:28 PM
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Quote:
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#5
03-06-2009, 07:36 PM
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Hmmm I'll take this into consideration. When I work on it tomorrow, I will get some voltages at the IC on the CRT board.
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| Audiokarma |
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#6
03-07-2009, 03:46 PM
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Im getting 179 volts at the CRT for all three drives until the pic comes on. Then, they all drop to around 115 volts or so. I still have the purple picture. I dont own a CRT tester anymore, so I can't test the tube.
Using a junk chassis, I swapped out the diodes that were overheated and previously soldered badly hoping that this would be the problem. It isn't. The junk chassis has everything on the main board, but is cracked. Someone before me cut the CRT board at the wires and took it. I will work on it some more in the morning.
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#7
03-07-2009, 10:35 PM
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Its all over now. I waited until dark and went outside and turned on the set and looked carefully at the CRT heaters. They all 3 came on, then after a few seconds the green gun in the center goes out. Then, the set shuts down.
The CRT is an LG-Phillips. No good. Thanks for the suggestions. You were right on, RadioTVNut!
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#8
03-07-2009, 11:41 PM
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Sorry to hear that it wasn't an easy fix. Those LG-Philips tubes are really not that great. I ran into one awhile back where the red and blue were dead and the green wasn't far behind. It was in a 20" RCA flat screen. I've seen some more that were still watchable; but, were not great looking.
These newer Philips sets are really a joke as far as quality is concerned. The '90's NAP sets were pretty good. Ever since '99 or so, they have been steadily going downhill. I don't guess Philips even offers a current CRT set. I guess about the only companies that do are Orion, Funai, and whoever makes RCA.
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#9
03-08-2009, 10:30 AM
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I have been nursing a 1991 Philips (on 24/7) with a GR1CX chassis since it was new, chassis is still perfect but I am on my third CRT. First one was a NEC 31V it faded with no emission, second was a Philips 32V made in Germany, it lasted over 10 years till first the blue then green guns lost emission, even shot the tube with the Sencore but the cathodes were to far gone. The third tube is a Phillips out of the Ohio Ottowa plant, 3 years and still looking good. The Philips LG tubes were a cheep cost effective tube but not long life.
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#10
03-08-2009, 02:36 PM
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I did NAP / Phillips / Magnavox / Philco / Sylvania service in the late 70's up through the early 90's. Used to come to Knoxville for training seminars alot.
They were on the ball back then. Many of the people came from the Fort Wayne facility. I almost never had a bad kine on anything. I had no expectations for this set. Glad I didnt tell my nephew that I was working on a set for him. When I opend it up and saw the LG name on the CRT bell, I said to myself: zenith... And in the late 1980's and up, I did Zenith service. I got several 20" tubes new in box that were bad. One had a short that shut down the set when I tapped the neck of the tube! Also had Zenith tubes rebuilt by the outfit that did Sears stores rebuilds. Those tubes are still playing. Like I said before, this set looked really nice until last year. Amazing how fast it deteriorated.
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| Audiokarma |
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#11
03-08-2009, 10:50 PM
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Spent 12 years at Straw Plains, did all CRT, degaussing, and yoke approvals, spent time at Greeneville and Juarez plants, those were good years then they closed us down in 98, design went to Singapore then got moved to China a few years later.
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#12
03-08-2009, 11:15 PM
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#14
03-10-2009, 01:05 AM
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My 84 Magnavox set was still working. Had to retire it in 2004 because the crt was getting so weak. This set had tons of hours on it though, and even though the tube was getting dim the color was still good. The only repair I had to do was replace the flyback once, cost a whopping $25 dollars.
Bill R
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#15
03-10-2009, 01:10 AM
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A 32 inch Magnavox followed me home from Mobile Alabama yesterday. Don't have the numbers yet. Set was working and now just whinning from power supply, I was told. Hope it doesn't turn into a nightmare.
Bill R
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| Audiokarma |
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