Need pointers on 65 zenith color roundie 25mc33
 

So its still original I never could tune in a picture just snow and audio.

I'm thinking now to recap it before doing anything else. At least all can caps and if there is wax paper which I have no clue if it does.

I've had this a few years now finally getting to try fix it. It seem the build quality is way better than my 63 roundie Magnavox with pcb boards. However the Maggie works great go figure.

So does anyone have schematics for this set?

Also what the best approach to getting this working properly again? You know the do's and dont's

I've fixed a few TVs trolling this VK site I'm still somewhat a newbie to TV repair. I'm good with building and modifying tube Amps and tuners just to give you some background.

are you sure its snow and audio or blank raster and audio?

Unlikely to need a recap of any kind, if the HV is working the B+ is prob ok at least enough to trouble shoot the video.

could be tuner, try a new RF tube, make sure balun is not blown, get a video if possible makes it much easier to understand the issue

Time for screen shot. If you have good audio but "true"
snow it dont make sense. What it might be is the fine tuning
is off & the fine tune gears are no longer working. Set has a
super gold video guard tuner ( SGVG ) best anyone built.
You can pull it, take the cover off & be sure the screws on
the channel strips are being moved in & out. There is a gear
on the FT shaft that moves & engages the screws. This one
probably has the diaper pin style, a common fail.
Good luck

73 Zeno:smoke:

I have one about the same, but most of my problems were related to the horizontal efficiency coil going floppy and high horizontal output tube cathode current which can fry the flyback. I also had to replace the 3AT2 HV rectifier socket and bypass the resistor underneath. On these topics since you wanted pointers; my studies on old color sets in general is that the current I mentioned should be observed on a meter in series with the cathode (all current is measured in series). Some people place a .47mfd 600VDC cap in parallel (across the two meter leads) when making this measurement I believe to filter out unwanted AC and get a true reading. I'm not the best at explaining that. I have done it with and without the cap and got the same results.

I personally would run the set on a Variac or some variable AC line source at a reduced voltage. Since you have already been powering the set, you wont have to start at really low voltages working your way up. The old electrolytics in the power supply and other places along with paper or film caps have already proven that they can take the punishment of full line voltage. Feel the filter cans and/or carefully feel the smaller caps. They should all be cool to the touch. The set produces heat of course so I don't mean cold, just not hot. If one is suspect, look and see if it is positioned right near a tube. That may be the reason it is hot.

We all need a good tube tester, so look on Ebay for a decent tube tester that can test the compactron style tubes in there. Don't buy just a basic emissions tester if you are really interested in this realm of electronics. Clean your tube sockets and pins. Trust me on that one. You have the best old color TV type that you could get as far as build quality and flybacks that last IMO and that of many others. Good luck and post those screen shots so some of these real wizards can put you in the right direction!

Bear in mind that you'll need preferably a 10 amp variac. A 5 amp won't handle the load of a color set really well.

I'll have to do this when we get home from work. I do have it on a 10amp variac at 115vac I know for accurate measurements I should be at 117vac.

What voltage should I run it at?

My tube tester is a seco 107 I'm not sure if its good enough. I know there is way better though. What is a really good tube tester for TV repair?

I have a current checker that's for tubes using pin #8 and it can check current on tubes using pin #3 I believe it goes to 200ma it that enough?

I also have a bias probe I made to plug in to my meter.

Cool! This is the closest thing to a picture I've ever got.

It's not color, its on ch2

However I see those clusters of red, green, blue so I'm sure the guns are working.

Is this more a Tuner issue?

Haha, those guys. There's a 90s throwback.

I like using cartoons for checking since I know how it should look. Yep thats beavis and butthead

Is there a remote for this TV? If so which one would I need?

http://www.videokarma.org/attachment...1&d=1435414703

"Huh huh huh, hey Beavis, we're like, on a really old TV."

"Whoa! Check it out Butthead the screens all like, weirdly shaped and stuff!"

"Huh huh huh yeah, they like, didn't know how to make TV screens back then."

is the RF output on channel 2? generally its either 3 or 4 if you have a DVD or video tape player as the source.

lack of color could be as simple as miss adjusted fine tuning.

It was on ch2, I'll change it to 3 and see if I can tune it in. My other roundie TV worked that way so I didn't think much of it.

I'm using a older Sony DVD player with the rf output.

MRX37 that's hilarious! They would see old musicans singing and make comments.

Oh yeah I know all about Beavis and Butthead.

Seriously though your TV looks like it's 90% working. your color guns are definitely working and working in good balance, because you have good grayscale with no tinting that I can see. (Red, green and blue combine to make white in a color set)

Also your convergence looks pretty good.

About the only issues I see are the lack of color, and it looks like your vertical is shrinking. You might want to start troubleshooting capacitors.

First off the set is NOT a remote.
Looks like the CRT is still pretty good, good grey scale.

The no color may be just fine tuning or the DVD channel is 3 or 4
as mentioned.
As you FT you will start with no sound & poor B&W pix. As
you turn it ( usually CW) the pix improves & the sound comes in.
Go a little farther & the color pops in JUST BEFORE the pix gets "wormy".
Keep on going & the pix goes away but you still get sound.
If the set has AFT aka AFC turn it off til your done then put it on.
Almost all sets 1960+ had an adjustment for each VHF channel.
You can usually tune adjacent channels also, like on the #4 you
can FT down to #3 or up to #5

The vert problem on Zeniths is usually the vert intigrators.
Thats the next thing. After you evaluate the overall set to be
sure its fixable, good CRT etc always make the set as good a B&W as you can then do any color problems.

73 Zeno:smoke:

I'm on ch 3 now.

I notice color level must be all the way CW and a slight jiggle to get any color

Peak pix has no influence on the picture.

Brightness is all the way up

Contrast is all the way CW

looks like a snowy pic

do you have a matching transformer on the ant? 300 ohm to 75 ohm.

dark pic is often a case of weak video out tube OR just not setup right (screen drives).

You should see if there is a service switch and go thru the setup procedure.

I assume you have checked the CRT and it test ok?

Brightness is best checked by confirming as follows:

Test CRT for emissions and cut off
check HV (25kv)
check voltage at CRT pins

if the above check out the CRT pretty much has to produce a decently bright pic. the CRT pin voltages will isolate where to look.

example, if the cathode pins on the CRT are too high a voltage (results in a dark pic), then you can go right to the video out tube. A weak video out tube (or a defect in the circuit making it not draw plate current) will result in too high a plate voltage at that tube. Since the set uses directly coupled cathodes (tied directly to the plate lead of the video out) the resulting high plate voltage at the video out is coupled to the CRT. The high CRT cathodes will essentially cut off the CRT (bias it off) making it too dark.

One more thing, this is the case, but if all looks good and you have a completely dark CRT then you need to check the focus voltage. if you lose focus voltage the CRT will be completely cut off. Focus voltage should be around 4.5-5.5 kv, best tested with a HV prob.

The only crt tester I have is for B&W TVs. And I'm not convinced it even works right since it told me a tube i had was bad but it had a great picture.

I tried a different matching transformer it was only slightly better.

What's a good crt tester to get for these color roundies?

http://www.videokarma.org/attachment...8&d=1435525011

"Hey Beavis, if we had a TV like this, we could like, pick up chicks. Lets take it home with us."

"Unhhhh ahhhh Butthead It's too heavy to lift!"

"Beavis you wuss. Here, let me do it. Unhhhh... Uh... This TV sucks. Let's go get some nachos."

"Yeah! Nachos! Nachos!"

Like Todd's girlfriend lol.

1st of all you have a vertical sweep problem. There is no better way to troubleshoot than to have the schematic and the proper test equipment, otherwise it's like throwing darts to find out what's wrong, depending on where you live, your public library might have the Sams Photofacts on file, they do here in South bend. As I always taught apprentices, check the basics first and then move on.

Could vertical shrink be that 50 mf cathode bypass cap on the 6HE5?

BTW, I have a 25MC33 and two more Zeniths of a similar vintage so Im paying close attention here. Right now Im just too busy fixing stuff for others...and here I go again.

Still need a schematic? PM me

check fine tuning belt.zenith has a small rubber belt on the fine tuning assembly.

I don't know how many times you are going to have to ask about the equipment you need. Cartoons won't fix it! LOL! Anyway, I found this thread right here at VK: http://www.videokarma.org/showthread.php?t=261808

It has a few good brands and types. Personally, my cheapest emissions only tube tester is the only thing I have with crt adapters. It's an Accurate Instruments tester, but it tells me enough. I would like to have one of the nice Beltron or B&K jobs mentioned in the thread above. Also, you have been asking about a tube tester. I am a big Hickok fan of test equipment in general, but they can be pretty pricey. However, it will be about the best built unit money can buy short of ultra high end jobs I have seen in the $Ks. With old test equipment you may find yourself UN-wantingly getting into restoration of that, so don't go on Ebay and find just any tester with a sweet buy it now price. Find one that has a seller who knows (or seems to) his equipment and can verify any claims of repair and/or calibration. Make sure the model you choose will test the types of tubes that you are interested in. One from the 50s isn't going to do your Zenith.

I ran across a B&K Precision 747B that I think would be a relatively modern, solid state tester that covers a LOT of tube ground. I got lucky and found mine owned by someone who thought that tubes no longer existed, thus a tester was worthless. WRONG! This tester will cost you a C or two, but supposedly worth it. Simple to use and is Mutual Conductance and measures in (GM) micromhos. A story within it's self, but it's how good testers test.

Oddly I bought the same crt tester yesterday that's in that link. It's a sencore CR168 big mack.

I don't mind buying a good tube tester here soon. My seco tube tester has been fine for amplifier tubes. I rarely use it though. I've bounced between Hickok, B&K and sencore. There is so many models of each brand.

I'd like to get something thats cheap in price but does a OK job. If I can't find that then I want a really good one which I'd hope to get under $500.00 or about. I hate buying something then regretting I didn't spend X more for better.

Also for this chassis what are typical tubes that go bad? I'd like to buy extras for a rainy day.

I'm a Magnavox nut for thier console stereos. I have a nice stash to keep them going after in gone. I'm 32 by the way. I'm always trying to get younger people in to vinyl. So anything I learn during this process I plan to pass on.

Is there any good tech books I should read?

The Tab Book in the center of this goldmine http://www.ebay.com/itm/HUGE-LOT-80-...item28026c3ab7
is the "Zenith Color TV Service Manual - Volume 1" by Robert L Goodman, it has most of the schematics and lots of service notes and information based on factory info.
This W A S my go-to book back when I started messing with color sets in 8th grade.

Well looked like a lot of good info in there. So I bit the bullet and bought the lot. I'll probably cherry pick it then sell off the rest.

Thanks!

Congratulations! That looked like the A-list of Sams Photofacts. Those 1975 and 1976 Sams master index are pretty useful.

If you want to sell off the rest, PM me. I like the antenna stuff, to the point of distraction. :sigh:
When DTV broadcast was piloted here, about 5 years before analog shutdown, I bought a Samsung STB and started acquiring all manner of unused antennas to experiment.:D

I sent a email. I'll go through the lot and see what I'm keeping.

So I have a crt tester and a supposed good tube tester coming in the mail.

I have the Sams in PDF.
Send me a PM.
Phil

I agree with Zeno. Replace K1 and K2 vertical integrators. VERY common problem.
Changed a ton of them.
Phil

So I got some working test equipment finally.

I found a pin on the crt that was very corroded. I cleaned it up.

Crt tester showed a weak gun so I followed the rejuvenation instructions and all 3 are now in the good range. No shorts either.

The color is better but I'm not sure what my issue is so here's a short video. I'll find something else to play later on.

65 zenith color roundie troubleshooting: https://youtu.be/iFTNy6VR-AY

The Color bar generator was fun to mess with.

So now I can test tubes and do a little more now.

Try a blanking tube. There is both vert retrace & a white line
going down the left side.
Also be sure you can turn the brightness down. If
not it may need a set-up by the book, no big deal.
This set should come out quite nice. Keep in mind
even when new they are not bright sets, use in subdued lighting.

BTW the volume knob will have the Zenith color triad on it.
Tons around I am sure.

73 Zeno:smoke:

looks like some fold over on the left, maybe need the horz setup procedure. ( oops forgot zeniths dont really have a setup procedure other than adj the hold control for good lock, you could try just adj the horz hold of tube swaps below do not help)

Anytime I have issues like this I start with new horz out and damper tube, and horz osc.

also agree with zeno, you have to not drive sets too bright, esp if the CRT is not great on cutoff, or you get the vert retrace.

Test pattern generators are often not the best signal source. Be sure to test them on a known working set to make sure they are not the problem.

on vert size, 1st suspect would be the cathode bypass cap on the vert out (100uf), next I would go a head and replace the .1 1KV boost filter cap on the vert size pot. Any leakage there would drag down the voltage supplied to drive the vert osc. you could confirm this by checking voltages of the plate of the vert multiplier. I routinely change out those since I can't test for leakage at 1kv. Be sure to try a new tube 1st both the vert multivibrator and the vert output. Never assume tubes are ok, and you cant test them as you need to sub those.

This is the best pic I could get. It's actually pretty good.

Turning brightness down helped. I finally felt like the controls made adjustments. Where before it didn't do much at all.

I'm really thinking to recap all the can caps at a minimum. Or should I do all electrolytics?

I really feel like the Tuner it dirty is there a test point on the chassis I can inject a composit signal? Also any tips on cleaning it?

My 1963 B&W Magnavox has a perfect working tuner that keeps stations locked in very well.

I'll buy the new tubes for it that you mentioned Dave thanks.

Dont forget to order a blanking tube !

You can usually inject 1V P-P composite at the 1st video amp.

For tuner pull the cover. Hold a big eraser against the strips
& turn. Work your way down the tuner. Best to pull it
out so you can see what you are doing. Things get delicate there.
Can also check your FT mech at same time.

73 Zeno:smoke:

Where is the blanking tube located? I can't find it on either schematic that I have. I'm not sure what one is or does.

TV repair makes amplifier repair look easy.