1979 Magnavox Question - Videokarma.org TV - Video

jstout66 · #1 04-13-2012, 03:26 PM

This is going to be general question, as this set is not at my house, so I'm unsure of chassis/model number.
I do know it's a 1979 Magnavox (color console)
I've also never seen this symptom in a set.
After the set is running awhile, the brightness changes. It will get SUPER BRIGHT, and then go back to normal. Of course it's intermittant, but does seem to do it worse after the set has been on awhile. Also.. if this makes a differance, it doesn't matter if the auto color is on or not. (that set has an electronic eye that is activated when "videomatic" is pressed)
Otherwise.. the set has a FANTASTIC picture. It rivals my Chromacolor, which is unusual for a Magnavox set.
What should I be looking at?

***Eric H*** · #2 04-13-2012, 05:09 PM

Are there retrace lines on the screen when it goes bright?
Possibly a CRT starting to short out.

Sometimes a little gentle tapping on the CRT neck with a plastic screwdriver handle will cause it to show up.

Another possibility is a bad solder connection on the video board, tapping on that will also help isolate it.

jstout66 · #3 04-13-2012, 10:06 PM

No retrace lines. It literally looks like someone is slowly turning the brightness up and then back down.

Electronic M · #4 04-13-2012, 11:04 PM

If the brightness knob turns on it's own, then it's time to breakout the holy water.

dieseljeep · #5 04-14-2012, 09:38 AM

Quote:

Originally Posted by jstout66

No retrace lines. It literally looks like someone is slowly turning the brightness up and then back down.

If that set has the T995 chassis or simular, check for loose connections on the large mother board. It's a large board that has a lot of flex.

dieseljeep · #6 04-14-2012, 09:49 AM

Quote:

Originally Posted by Electronic M

If the brightness knob turns on it's own, then it's time to breakout the holy water.

That statement isn't that far fetched. A good friend of mine bought a home, where the former owner passed away in the basement office. They had a lot of strange problems in that house. She would sprinkle holy water regularly.

Electronic M · #7 04-16-2012, 03:04 PM

Quote:

Originally Posted by dieseljeep

That statement isn't that far fetched. A good friend of mine bought a home, where the former owner passed away in the basement office. They had a lot of strange problems in that house. She would sprinkle holy water regularly.

I personally have experienced the hall light switch in a previous home turn it's self off twice....didn't see it, but I could clearly hear the "click". A little prayer (my family is christian) fixed that.

There is a story about an ancestor on my mom's side who would routinely sprinkle holy water on her bed to stop it from levitating!

There are some bad things out there to be wary of, and to try to avoid.

jstout66 · #8 04-16-2012, 03:22 PM

No.. the knob doesn't turn on it's own.. but.. it looks like someone is adjusting the brightness. It doesn't instantly get bright, it's like it maxes out, than goes to the normal level. This is a set I gave a buddy who loves console TV's. This I think is the 4th set he's gone thru since 2005. I told him NO MORE consoles. He lives in a 2nd story apartment, and if I remember right.. that Maggie weighs a TON. They go out I think because they are always on when he's home, and.. he's a heavy smoker, so I'd hate to see what the chassis look like. If I remember.. he's had
1) A late 80's Zenith.. on that one, after being on awhile, there would be pink splotches on the screen.

2) A late 80's 27" Colortrack. That one would turn itself off and on all the time until one day.. it wouldn't turn on

3) One of those HORRID 26" Sony Consoles. Picture tube was soft, and the set had crappy sound.

4) The above mentioned 1979 Magnavox. At least this one has seen 3 years of hard use, before screwing up........

Firebird · #9 04-16-2012, 05:23 PM

I have a 1981 Magnavox tv. Model number RA5054. It has a t815-09 chassis. It has not worked for a while but somehow i have convinced my mother not to throw it away. I was there when she bought it in january 1981. It has stereo speakers and separate 10watt amps to simulate stereo. It gave a little trouble when it was new, the crt module was replaced and an ic was replaced on the power module. When you turn it on the channel number displays, no picture, no sound, The picture tube gun lights but after 20 or so seconds the reset button kicks out. After reading some of your post i ordered a horizontal output transistor, installed and resoldered pins on the retrace module. It still does the same thing. I have had some repair training but would like the advice of an expert.

holmesuser01 · #10 04-18-2012, 08:33 PM

Quote:

Originally Posted by dieseljeep

If that set has the T995 chassis or simular, check for loose connections on the large mother board. It's a large board that has a lot of flex.

I've soldered many of these sets. Lots of ground connections and all the little stakes that the modules plug onto. Also, check the connections on the actual modules. They like to crack.

Best of luck for you getting this one fixed.

radiotvnut · #11 05-01-2012, 04:15 PM

Quote:

Originally Posted by holmesuser01

I've soldered many of these sets. Lots of ground connections and all the little stakes that the modules plug onto. Also, check the connections on the actual modules. They like to crack.

Best of luck for you getting this one fixed.

I've seen this alot on T991/T995/T809/T815. I've even seen quite a few of the newer C1/C2 chassis TV's that had loose connections on the electronic tuner modules; so, Magnavox had a little problem with loose connections during the '70's and early '80's.

holmesuser01 · #12 05-01-2012, 07:00 PM

If I'm not mistaken, the T995 had issues with the power supply regulator module. I seem to remember a kit that was available for them. The big transistor, a couple of smaller ones, and a resistor or two. Have you tried starting it up with a variac?

jstout66 · #13 05-01-2012, 07:26 PM

If you were asking about the 79 Magnavox, no.. I don't have a variac. This set is still in heavy use, and still doing it. I just haven't had time to look at it. I was over there briefly and it only did it once.... the time before, like 8 times during a 2 hour time span. I was kind of thinking voltage issues as well, because IIRC.. that T-991 chassis was plagued with them. Just hope some cap doesn't blow the neck off the tube before I look at it.. LOL!

radiotvnut · #14 05-01-2012, 08:18 PM

The only cap you need to worry about in regards to blowing the neck off the CRT is that 4-lead safety cap in the horizontal output collector circuit. If that cap opens and the internal interlock of the cap does not break, the HV will skyrocket and you will lose a CRT. In later years, I've replaced that cap with a modern HV orange drop cap.