Magnavox Solid State Videomatic - Videokarma.org TV - Video

rangerdan86 · #1 02-04-2015, 08:20 PM

Howdy again. I am looking for help in figuring out the chances in getting this old beast fixed up.

It was working perfectly before it quit displaying video, only giving me audio. Blank screen, no flickering no nothing. It was giving me a burning smell and I believe it is a transformer of sorts. Pictures included.

In my initial diagnosis of it, I was trying to figure out what the spark gap protection was, I didn't know and in my examination of it, broke it...Fragile thing that was...

Purchased the service manual for a T995-02 from Sams Publishing, they got the the "close" T995-01 chassis service manual, but it doesn't have the matching information to installed equipment for the high volt circuits(Everything else is really close if not the same).

I believe that since it was throwing voltage through the spark gap, that i have too much high volt and that some transformer along the way needs to be replaced. I have pictures of the questionable equipment and hope that someone can throw me some advice and help. I really want this old thing to work and keep going. It means a lot to me, so thanks in advance for any help and advice.

I also need and want to figure out what to do with the old spark gap that the tv has? What have other people done with these?

If so can something this old still get parts? the vertical transformer that looks cooked(I posted a picture where I have it cut out of the tv on the desk.

If you need any other information I will try to supply it. So again thank you!

NoPegs · #2 02-04-2015, 09:53 PM

The last picture appears to be a choke of somesort. (Unless there are additional hidden wires coming out the other side.)

When you say spark-gap, can you MS-Paint an arrow to what you're referring to?

rca2000 · #3 02-04-2015, 10:00 PM

I THINK...he is referring to the big bleeder resistor in the one picture. It often goes bad and and arcs. It can be replaced by a newer style resistor. Arcing here does NOT mean the HV is excessive--it is likely 28KY or even higher anyway--which is NORMAL for this set.

WHY do you think the vertical CHOKE is bad? I have NEVER heard of a bad one in a 995 chassis. What you think is burn marks is likely just lacquer.

rangerdan86 · #4 02-05-2015, 12:40 AM

Thanks for clearing up the choke NoPegs, just this tech is so much older than even I, but a lot of fun to learn so far.

I did include a couple of pictures with what I will refer to as the "Spark Gap" because I researched for two solid weeks and couldn't get a solid answer or definitive explanation of what it was. I only found one other picture on the internet with a old tv that had something like it installed. This old monster has two HV wires coming from the top of the tube, one goes to the Glass AMP hooked in with the Flyback, the other goes to our mystery "Spark Gap".

Essentially it had a hollow ceramic core and two metal leads going on under the plastic cover.
It was scorched inside and broke the moment i touched it. From what I can tell is that it wouldn't conduct, unless voltage present at the upper end was strong enough to arc from one lead to the other, forming a low resistance path to ground once the arc had started until the breaker tripped or the over current condition passed. From what I can tell these were used as lightning protection for the CRT in some models.
This "Spark Gap was clearly conducting and for a good while cause I could hear it "whine" while it was arcing and smell the plastic burning from it.

rca2000, the choke just looked like it got hot to me. it felt like burnt paper to my hand. I just don't know. It probably isn't bad, but I was trying to cover all the bases.

And if it is just a fancy resistor that went bad I would be so pleased to know it can be replaced! Been banging my head against the wall for a while with this and really appreciate the help from both of you! Thank you. It means a lot and helps a lot to get this advice.

The pictures are of the "Spark Gap" that I know is broke and cooked real good.

Again thank you!

rca2000 · #5 02-05-2015, 12:57 AM

Pretty sure it is just a bleeder resistor. At least 200 megohms or so, possibly with a tap on it--for the focus supply and control. If there are NO other leads on it--other than the big top one going to the anode and the screw at the bottom--then it is NOT used for the focus supply...just as a bleeder--to "bleed off" the HV after turn -off of the set.

I KNOW_-that some of the newer 995 sets do NOT use this setup--there is no bleeder and the focus comes from that block behind it--known as the tripler. It does what the name suggests, triples the voltage out of the flyback, and supplies the voltage to the CRT. I have a 995 that does use the bleeder--it works ok--with a good tube too.

zeno · #6 02-05-2015, 08:03 AM

RCA2000 maybe you remember........
IIRC its just a bleeder & didnt the resistor plug in ???
Been too long. If so I myself would remove it & try it.
Looks like the focus comes off the tripler but cant be sure.
Just needs to find a one holed anode connector, not hard...
After that its just resoldering the whole thing !

73 Zeno

rca2000 · #7 02-05-2015, 08:59 AM

But will the chassis work ok without the bleeder--assuming that is all that it is?

IF it is a simple bleeder ressitor(which I THINK it is)--will the HV regulate and run ok without it there? I KNOW...the bleed off of the HV will be lost...but is that ALL that would happen? I KNOW on a projo set you do NOT want to leave the bleeder out--for fear of burning a tube--but on a DV--I do not think that would matter.

jbattles · #8 02-05-2015, 09:10 AM

If the trippler is not bad you can just unhook it and it will work. i had one in the late 80's and mom ran the hell out it from 88 - 92. Used so long cooked the pc boad around vert module. dam fine set it died just a fews after she did. i did not have the heart to fix it.

zeno · #9 02-05-2015, 01:16 PM

Quote:

Originally Posted by rca2000

But will the chassis work ok without the bleeder--assuming that is all that it is?

IF it is a simple bleeder ressitor(which I THINK it is)--will the HV regulate and run ok without it there? I KNOW...the bleed off of the HV will be lost...but is that ALL that would happen? I KNOW on a projo set you do NOT want to leave the bleeder out--for fear of burning a tube--but on a DV--I do not think that would matter.

Its got the Zenith transformer for regulation. Dont see why they would give it
a minimum load but I am not an engineer

Maybe they think we can take 25 KV but not 30KV ( not true !).
Maybe tomorrow I will pull some T995's & look.

73 Zeno

rangerdan86 · #10 02-06-2015, 12:18 AM

jbattles;
Sorry man. Somethings like that though to me are worth fixing just for the good memories they carry. I can't give up on some little things, like this tv. I have a hard time just letting it go when I have faith that it's something easy, or the fact that I stubbornly want it to work. But hey we are who we are and sorry man.

rca2000 and zeno;
As for testing the machine. I am getting some gear put together to test it with out the resistor in the circuit. Now I got to have a good day to roll it out side and test it, I think from what I am reading, that approach will tell me a bit more about the issue. I am just hoping that the bleeder was just failed and short circuiting to ground. It would make sense, it just stopped with out warning or any signs of failure...

So I remove ground from the bleeder and get it isolated, get that choke soldered back in and everything cleaned up. Should I just fire it back up. Anything exactly I should be looking for...A picture that's to bright or won't focus/track right? If it fires right up and starts working beautifully where should i start looking for a bleeder. I am not one to take the safety's off a piece of equipment haha.

The bleeder had some numbers on it, don't know if they mean anything to you but I think the picture may help i included. It was a close up of that bleeder in question.

Zeno;

Haha, yeah doesn't take much energy to kill us. When I was learning back at trade school about high volt from the power poles, they showed us a movie montage nightmare of people that got hit by fallen wires...Scary stuff, I have talked with somebody after they got blown across a room from a 3 phase panel that shorted. They were in full ppe and it was no where near 30kV. But amps are equally important for messing people up.
And Zeno, thanks for looking into other T995's. All of you thank you for your help.

Electronic M · #11 02-06-2015, 10:02 AM

If it works okay with the HV bleeder out of circuit and the HV is not above spec even with the HV regulator adjustment (if it has one) set for minimum HV, then I would not worry about it not having a bleeder. Sets less than a decade older never had those bleeders. Up until that time it was incumbent on technicians to manually discharge the HV before working on the HV, and even on sets like yours it is still good practice to manually discharge it with a HV probe.
25-30KV DC stored in the capacitance of a CRT is not the worst thing to get hit with (unless you have a heart condition). I've been bit by it a few times and am still here and just fine. It just feels like one mother of static jolt, and may trigger your reflexes (it barely triggers mine).

I've actually gotten a much worse jolt from the deflection yoke of one set....The only time my arm involuntarily retracted from a set and took out all cabling and deflection hardware in the way....I had a painful char mark on my finger for a while after that.

jbattles · #12 02-06-2015, 10:53 AM

well my point is you could unhook the bleader and use the set until you find a n.o.s part and i was stating they are very fine sets. Someone traded that set in my shop and mom was wanting a bedroom set i unhooked bleader until i could get one, but never got around to buy one. By that time the set was worn out. I did try to fix for my ant who wanted it, but the pc board where vert and horizonal modules plug were burnt to crisp and I could not get the set to work right.

old_coot88 · #13 02-06-2015, 03:44 PM

Gotta wonder what the rationale was for having a bleeder there at all.
Preemptive shock protection for some errant soul?

zeno · #14 02-06-2015, 04:24 PM

OK in Sams 1469 for T995-01
It is just a bleeder. 300 meg ohms.
OEM part # 230208-4 subs to Workman 5W-SQ-40
( which dont make sense to me )

Now it gets more interesting. The set has a 4 lead cap, its
white & looks like an American Radionics cap. So the HV
MUST be measured Calls for 25.2 - 28.6 Kv.
If it were mine I would change it. Too much HV could
have started this......

73 Zeno

old_coot88 · #15 02-06-2015, 08:43 PM

I've never run into a Maggie with the 4-legged "safety" cap (ala Zenith), but have heard of them. If it's original, and is the white tubular with axial leads, it absolutely should be replaced.
In Zeniths, when that cap fails, the HV soars to around 50KV, and often cuts the neck right offa the CRT slick as a whistle.