Magnavox TV - Colors off after hooking up DVD player

[tvwatcher]

I bought my Mom a DVD player for her birthday and when I hooked it up to the auxiliary AV inputs on the TV the picture quality was very poor. So I hooked the DVD player up to her VCR and the picture was fine so I new the new DVD player was OK. My mistake was to try it a second time on the TV – the picture was still very poor but when I disconnected the cables this time and switched the TV input back to antenna input, the colors were all screwed up. The blues are greenish, the greens are bluish, the reds are pinkist/purple, and flesh tones are a bit purple. Otherwise the picture is fine and sharp and fills the entire screen.

So I took the TV apart and noticed the ground connection on the auxiliary video input had a cracked solder joint. I resoldered the cracked joint and now get a good picture from the DVD player connected to the TV but both the antenna input and aux AV input (where I have the DVD connected) have the colors off as described above.

Where should I look next or what could have been damaged by connecting the DVD video input without the proper ground? The TV is a Magnavox Model HD2632 W103 manufactured Oct 1991. Thanks for the help. I guess no good deed goes unpunished!

[vtech]

.....Dont you hate it when that happense; >>...don't know what U did, but it wasn't doing that before? lol

Based on your description, sounds like the typical color distortion when the picture tube has been magnetized--did you by any chance move the set while it was on?
All tube tv's have a built-in deguauser which will correct this problem when you first turn on the set. BUT it only kicks in when cold--so let it cool off & try it again.

---While there is a chance that the degauser might be defective, hooking up the DVD player w/ground issue can't possibly cause the color problem as you describe

[tvwatcher]

Yes, I feel really bad and I'm sure she thinks I somehow blew up her TV with the DVD player. I didn't mention it but I did ohm out the degauser coil and it was less than 10 ohms so I figured it was OK. At first glance, I didn’t see the degauser thermistor but when I get home tonight I'll search a bit harder and check it out. The AV input is mounted on a daughter board that mounts to the main board about as far away from the degauser circuit as you can get. When I found the cracked solder joint on the AV daughter board, I just figured there must be something else wrong in the same area but I couldn’t see anything else obvious.

I didn’t move the TV while on or plug the AV cables in from the DVD player while the TV was on.

Any other thoughts? Thanks for the help.

[vtech]

K, sounds like you know about the degauser. At least you can check it's operation

On the other hand, based on your description of the colors, there is no way that hooking up a DVD can do any of that? Thought perhaps the set was moved which can mess up the colors temporarily.

Other than the tube needing degaused, just about the only other thing is the magnet ring assembly which is fixed & mounted on the neck & never messed with ---hope you did not accidently knock agaisnt it? Can you post a pix?

[Guest]

That reminds me that my Mom had the small Comcast cable box sitting on top the TV (it is a little bigger than a DSL modem). At some point while I was hooking up the cables, I moved the VCR a liitle to far and the cable box went crashing to the floor. When it slid off the top of the TV it probably hit the back of the TV's plastic case. So it didn't hit the magnetic ring assembly directly but it could have struck the outer case right in that general area. Do you think that a blow to the outer case could have nugged something out of alignment?

I looked at a bit at the degausser circuit. It looks like it uses a varistor marked DSATR and also is marked MMCC. Does anyone have the specs on this part?

Thanks for the help.

[tvwatcher]

Well additional data on the problem, the degausser circuit works fine if I disconnect the coil - I get 120VAC for about 2 or 3 seconds at the connector terminals. However, when the coil is plugged it only makes it to about 3 VAC. The coil measures about 8 ohms so it does not appear shorted. Is 8 ohms a typical value for the degausser coil? Would you agree it appears the circuit that drives the coil is the problem? Would anyone have a schematic for the degausser circuit for Magnavox model HD2632 W103? Thanks for the help.

[vtech]

As far as the cable box hitting the back on the set causing the problem? very much doubt it. you would have to physically move the magnets.
Do not have any schematic.

The degauser is very simple; All you have is a coil in series with a thermistor tied to the switched AC line. The purpose is to momentarily enrgize the coil to act like a big magnet around the picture tube for a short time to demagnetize the tube. (thermistors acts like momentary switch to reduce the AC)

Your meter readings sound correct. On some sets you can even hear a short "thump" sound coming from the coil. Better yet, start cold & try watching the picture thru a mirror as you plug the coil connector---you ought to see the effect on the picture. If you see it, it's doing it's job

similiar to this, may be not as strong for a very short time

[tvwatcher]

I do hear the thump sometimes when I turn the set on. Unfortunately I think my degausser circuit is somewhat different than you described. I believe they use this DSATR varistor from Panisonic along with a relay to control the on/off of the degauser and it times out after 3 seconds even if the coil is unplugged. I don't think I could be fast enough to plug the degausser coil connector on while hot to observe the screen for the pattern you attached. And basically it sounds like the degausser is working so now I'm back to ground zero.

If somehow the tube did get magnetized, are there times where you cannot demagnetize it with the built in degausser and need to use a hand held one?

What if I plugged the built in degausser coil directly into 120vac for say 5 or 10 seconds? Could I damage the coil? Should I put a series resistor inline to limit the current? Is it better to have the TV on or off during the degaussing process?

Thanks again for the help and sorry about all the new questions. I do have a BSEE degree and have been in the electronics field for over 25 years but I'll be the first to admit I know very little about TV's. However, I do know enough not to make the situation any worst than what it already is and keep myself from getting injured in the process!

[vtech]

Relay/varistor combination provides the same results...no way you can go the "straight to AC route" without blowing something up.

Sounds like it is working then, can you see the effect on the tube too?
Sometimes internal circuit doesn't have what it takes to demagnetize but, usually is because someone has been playing with magnets around the TV or a lightning issue which is neither in your case?. You can make your own coil but a lot safer to get a hand-held one

At this point I'm not quite sure what you have?

[tvwatcher]

What about a static electric discharge to the front of the picture tube? Could that magnetize the CRT in such a way that the built in degaussing circuit can't clear it? I had at least 2 instances where I got static shocks to the front of the tube while I was hooking up the DVD player. I have a FRYS nearby and I'll go buy a degaussing coil if we can figure out how the CRT got magnetized. Thanks again for the help.