The Emperor is full of hacks (25MC46Z) - Videokarma.org TV - Video

Carmine · #1 12-28-2010, 01:08 AM

We all like to find that unmolested old set that grandpa kept in the living room, serviced by a friend who did honest skilled work... Well I did pick up one of those sets over Christmas, but this ain't it! (I'll post the other pics soon)

Do keep in mind that before dis-assembly, this TV did produce a reasonable picture, and was operated for an hour... here and there. The CRT was OK, so long as you weren't big on the color blue.

So I've embarked upon fixing this thing while I have the time off work, or at least making it better.

Here are some of the hacks I'm hoping someone here might be able to help me with (I'll attack the stereo section again tomorrow).

Below is a bulging 100 mfd/450v cap that was soldered between the chassis and one of the test points on top of the chassis (actually one terminal to the right of the arrow). I don't know what function it serves because I don't have a schematic, but I've pointed it out in the picture below. There is a silicon rectifier in this same area, if that helps. I rather wonder if this thing was even connected near the end, given the very bad solder job... it just fell off under the weight of the cap itself.

Next photo is below the chassis. Some kind of disc cap with most of the exterior coating flaked off (thus I can't read it's electrical rating). I have a feeling this is not an original part either, because if you look where the arrow is pointing, there is a broken-off spade connector loaded with solder that's just floating off in space.

The next items are not critical (for now)...

Something with red wires has been cut off from this part of the space-command circuitry...?

Nice way to wire-in a replacement tuner motor... I've already fixed this one.

And my own temp-hack repair, a cut-off rubber thumb replacing the fine-tuning belt. Looks like it was just about to break. Since replaced with a neoprene o-ring.

ctc17 · #2 12-28-2010, 01:32 AM

One of the power supply filter caps must be dead so someone bridged it with that hacked in cap that fell off.

The thing you are calling a disk cap looks like the degaussing thermistor to me. It looks like on of the leads separated? they do exactly that when they fail. The set will usually work without that but the purity will never be right. Those are an easy find from Moyers.

I would replace that filter with another 100 at 450 in the same fashion if it were my set. The thing was working so no reason to risk screwing it up.

On second look it looks like the old thermistor fell apart and they soldered another one in. If the degaussing is working I would leave that thing alone. You may destroy it trying to desolder it and clean up the tacked in repairs. Those things are like little charcoal briquettes with wires cemented on the sides, touching it wrong will turn it to ash.

Carmine · #3 12-28-2010, 01:43 AM

Quote:

Originally Posted by ctc17

One of the power supply filter caps must be dead so someone bridged it with that hacked in cap that fell off.

The thing you are calling a disk cap looks like the degaussing thermistor to me. It looks like on of the leads separated? they do exactly that when they fail. The set will usually work without that but the purity will never be right. Those are an easy find from Moyers.

I would replace that filter with another 100 at 450 in the same fashion if it were my set. The thing was working so no reason to risk screwing it up.

Power supply filter caps... Not the same as electrolytic cans, right? I'd rather not replace it like that, and wire it under the chassis. (it's already out, lol) The other end of the cap is soldered to the terminal strip that has RGB wires running to the CRT. The particular terminal simply connects to the chassis through a soldered rivet.

I have a pretty good local electronic supplier... I could ask for the thermistor if you can tell me an electrical rating...?

DaveWM · #4 12-28-2010, 08:17 AM

agree with CTC17, the 100uf 450v is a replacement for an open section of one of the filter cans, the other is a Thermistor. Those zenith chasssis that use that style of term strip make for convienent test points, and in this case a quick fix from the top of the chassis (the orig service guy prob did not want to pull the chassis, and since its a combo, did not want to flip it over to get at the service saver plate on the bottom).

since the orig prob was the blue gun, you should test the CRT, then check the voltages at the CRT pins, wiggle some of the demodulator tubes. Scope the grid of the Blue gun at the crt and see if anything is going on. Looks at the screen voltages of the CRT with a vtvm compare the blue to the other two guns.

Careful handing the zenith chassis with it out of the cabinet, there are a lot of parts leads that can short if a part is moved around by handling. I set a chassis down on some soft padding for transport, the padding pushed up, came into contact with a large disc cap, moved a lead into something it should not have been, ended up with a difficult to find hum bar.

Carmine · #5 12-28-2010, 12:02 PM

No luck getting a cap that big from my local parts house (but they do have thermistors.. I just need to know the specs).

So I went to a local TV shop that has a LOT of flat screens on the bench, and asked if they would just sell me a cap. They offered a 150mfd @ 450 cap that looks like it was removed from a power supply board. They said it would be close enough? What say you all? I took a shot of it on the chassis which I carted up in the trunk of my car. They didn't know what size thermistor I'd need... Do any of you? I had some Zenith schematics for this set, but can't find them.

Hopefully this pic works (posting from phone again)

ctc17 · #6 12-28-2010, 12:23 PM

You can use a 150 at 450 but i would just order a 100 at 450 with axial leads and solder it in the bottom. You need a soldering iron that puts out enough volume of heat to get a good solder to the heavy metal. One of those 25watt jobs wont cut it.

Leave the thermistor alone. It looks like they all do.

Carmine · #7 12-28-2010, 12:29 PM

But I've always had purity problems???? Shouldn't it be fixed?

freakaftr8 · #8 12-28-2010, 02:08 PM

If so then I would say that thermistor is faulty and/or the degausing field. Now if there is a short in the daugausing field maybe it could cause the thermistor to blow? Without that thermistor operational you will have no degausing causing purity problems. Best way to tell if you have power to the degausing field is test for voltage at connection. should be 110v I believe. Had this happen to a Zenith of mine before. Also test the leads of the thermistoer for continuity. See if you get a reading (in ohms).

bgk283 · #9 12-28-2010, 03:34 PM

try the part number Zenith 63-10710, i know that they have them at Talon electronics. Also ,and i know this is hack like, but on an old mc30 i used to have, i disconnected the deguassing ring and used a jump wire between the contacts as a short term fix, good luck. Bruce

bgk283 · #10 12-28-2010, 04:11 PM

sorry, i wrote before i checked my records, disregard that part number i gave you. Hopefully someone will have the correct value of the part you need. The info i had is from a different chassis.

freakaftr8 · #11 12-28-2010, 04:49 PM

I have that chassis. Lemmie take a gander and see what I come up with.

ctc17 · #12 12-28-2010, 06:49 PM

Does this set have the thermistor in series with the b+ and a big vdr in series with the degaussing coil paralleled across the thermistor? If so the set would be dead if the thermistor was open.

freakaftr8 · #13 12-28-2010, 08:17 PM

For s&g's can you just wire a slo blo fuse across thermistor leads to see if it works. Of course its not a permanent thing

Carmine · #14 12-29-2010, 09:15 PM

This has got to be one of the most hacked-up TVs I've ever dealt with. No wonder the prior owner was glad to dump it. (Although I paid nothing for it, and am still happy to have it

) Adding to it is a stereo that's just as bad, lol.

So I get the chassis on my workbench, even plug-in my soldering iron to install the new cap... Then I notice that I never wiped down the HV lead and it's covered with filth. After a wipe down, I notice a smallish crack in the insulation. Immediately I start thinking of which BPC set I'm going to steal the HV wire from, but I need to get at the HV cup. This leads to my opening up the HV compartment to find a massive wad of electrical tape!

It is then that I notice the HV cup is secured with just one screw, so the rectifier is hanging down on the flyback doughnut. No worries, just add more electrical tape!

The cup is melted so bad that I have to add to the cracked/missing area in order to bust the tube socket out of it.

The low-res of my cell phone camera really does no justice to this 3rd-grade level soldering job. At this point, I think I may have to just turn to another less-desirable set to get this thing back on its feet.

This poor sucker has been hiding in a deep corner of my basement for years. I haven't moved it out yet (it's late as I type this) but off hand, I think these may have the same chassis... Age looks about right, and both have the same "hi-fi" sound controls. I think the only difference might be the remote tuner on the Emperor, and I can hope that's a plug & play?

Last time I used it, this set did work...

ctc17 · #15 12-29-2010, 09:55 PM

wow that had a few house calls in its day. Factory fly but the focus and centering pot look replaced.
You should be able to find the rectifier cup. The crack in the red is most likely not a big issue as that is just a dust shield, the real insulation is the clear under it. Used crt computer monitors are a great source of that wire.
If you were to replace the fly and that rectifier socket you would have everything new in there.
Someone really got their moneys worth out of this set.