another zenith combo - Videokarma.org TV - Video

DaveWM · #1 10-30-2010, 04:29 PM

picked this up today, owner displayed raster, has a bad case of magnatized screen, I hope the deqausser will clear it up, and its not a bend shadow mask.

The finish is in very good shape, I had planned to scrap it out and save the chsssis for a parts set (has good stereo and phono as well) but its so nice that I may end up just keeping as is.

Dan Starnes · #2 10-30-2010, 04:38 PM

Love it!!

sampson159 · #3 10-30-2010, 06:14 PM

save the cassis?save the entire set!this is a keeper and before you tear it apart,let someone take it to preserve the whole unit.if you were closer,it would be me!

DaveWM · #4 10-30-2010, 08:18 PM

its safe for now, I had hoped the finish would be bad but its in good shape.

DaveWM · #5 10-31-2010, 01:57 PM

got it out of the back of the X, only got a charlie horse in one arm.

since it had been turned on before, and from what I understand from the orig owner (granny passed away) it had been used reg up to a year ago, I skipped my normal routine (HOT/VOT out variac slowly).

color is VERY weak but working (hues good etc...) but you have to be on the ragged edge of the fine tuning to get it to come in, and the color level all the the way up.

No ghost or any other nonsence, so I will start by checking the color circuit tubes, maybe the AGC as well (contrast it all the way up).

the degausser got rid of the magnatized screen so the shadow maske was ok.

I will check the built in degusser, so far every set from that era has had a busted thermistor (down to my last CL90).

Needless to say its VERY dusty inside so I will put on my dust mask and blow it out so I can see what I am doing.

Tested the CRT tested very good, excellant tracking and good emissions even at 5v on the filaments. Of course the little CRT pin guide broke but I have a couple extra that I can put on if I can get the base off. Or I will just super glue, but its not a big deal. the pins on the crt looked pretty corroded (had some green on them) so I am pretty sure the tubes will need a good pin cleaning as well as the sockets.

Stereo works but needs some attention to the controls, Phono will need to be cycled a few times to see if the mechnicals can work them selves out, it would not turn off but that is prob just lack of use and or lube. this turntable seems to rely a lot on gravity to move all the parts into place in operation, I like the magnavox TT much better.

DaveWM · #6 10-31-2010, 05:25 PM

it had a few weak tubes, the color burst and color amp, replaced both helped some but still way too weak. Cant find my long handled flat screw driver to adj the AGC, so will hold off on anything else until I do that.

I will review the service notes, and take some voltage readings, starting with the cathode and grid voltages of the CRT.

Looks like I may need to touch up the audio quadrture coil (after I sub the
6Z10 tube) the audio is weak until you again get right at the ragged edge of the fine tuning.

I suppose it could be something amiss in the IF, although all the tubes checked fine.

but 1st thing will be that AGC, I have had enough issues with keyed agc to make sure its right 1st.

Jeffhs · #7 11-05-2010, 01:50 PM

Quote:

Originally Posted by DaveWM

picked this up today, owner displayed raster, has a bad case of magnatized screen, I hope the deqausser will clear it up, and its not a bend shadow mask.

My RCA CTC185 table TV fell off its stand a couple years ago. When I put it back and powered it up again, the picture had color splotches all over the place, as if the CRT had become magnetized. This set has an auto degausser, so I thought that should have gotten rid of the impurities; however, it didn't. What did clear up the problem was a couple of sweeps around the screen with a magnet from an old speaker in my junk box. The shadow mask in my TV's CRT may have been bent just a bit when the TV hit the carpeted floor in my apartment, and the magnet may have straightened it out; the picture was like new when I powered the set on again. I don't know why this worked so well (I thought that the speaker magnet would remagnetize the CRT and make the problem much worse than it already was), but the important thing is it did work, and well. The same trick might (I emphasize might) work on the CRT in your set if the shadow mask is bent; I'd try it first before even thinking of getting a new tube -- CRTs for these older sets may be difficult or downright impossible to find in this age of flat-panel, HD, 3D (!) TVs, unless you can find a good used tube.

DaveWM · #8 11-06-2010, 07:21 AM

crt is fine, degausser fixed it right up.

holmesuser01 · #9 11-06-2010, 11:16 AM

Unless a set has hit the floor, I've only seen one or two sets that had bent shadow masks.

I used to love hearing the description of the problem when a customer would bring in a set with a burned up degaussing circuit.

The words FIRE, and SMOKE, and STENCH were used often.

DaveWM · #10 11-11-2010, 06:21 AM

I have been fighting with some minor pic problems, tends to bloom a bit go out of focus on some scenes. check the HV again, 26kv with pic, but jumps around a lot with brightness (beam currrent on crt). when set to the setup mode the HV is 27kv and will not go lower (that is with it turned all the way down).

I have been down this road before, on my last zenith with the pulse type regulator (6HS5). That one required a new VDR and a factory mod to the HV control pot to get under control.

also while watching I noticed the reds start to fade to pink and get splothcy.

the darn purity ring assy is very loose, some how I must have moved it. I found it when I checked the setup (after checking the crt). Oh well at least I am getting a bit faster at finding the problem.

DaveWM · #11 01-17-2011, 01:34 PM

took a break from the TV for a bit to concentrate on the SS stereo. pots needed some cleaning. AM was not working right. It was very odd, would birdy and could be made to work if I turned it off and then on and carefully manipulated the selector. had some odd voltages in the AM section. Noticed I could kill it by touching the VC (the midde section for the RF tuned section, not the osc and not the main tuning from the antenna coil). it would stop and would only play if you turned it off and then on again. I finally swapped out the RF amp transistor and bingo, works fine. The RF amp transistor had leakage between the E and C and had the wrong v reading in the diode mode between one of the leads to the base. Anyway its working well now, I check the stereo separation, all good, so it will go back in now. I will be turning my attention back to the HV regulation next. I noted some odd bends in the vert color bars I was getting OTA, the right side bars were not straight. guessing someting in the horz sweep. I will check caps around there esp the coupling caps, and mess with the horz osc/horz out to see if I can get it working, but I need the get the HV regulation working 1st.

DaveWM · #12 01-17-2011, 01:42 PM

wondering about how tight the zener diode should hold the voltage, it says 11.5v on the schematic, I get 12.6 at the zener.

DaveWM · #13 01-18-2011, 09:29 PM

back to the tv, 23XC36, full raster, but the pic loses about 1 inch from the left side. Its kind of a soft black edge, I am new to this but think I read up on blanking issues. The right side is not a problem. I am going to check the two blanking diodes that connect to the grid of the vertical amp. There is also some streaking in the pic, I need to tap around there but again I am thinking the video driver transistor or more likely the vert amp tube. I am not sure how to check or even test for defective blanking if that is what this is. I dont think its horizonal centering as I assume that would effect the raster. the horz hold adj did not move it at all. I dont recall seeing this when I first got the set, but perhaps I just did not look it over close.

I still need to pull the chassis to go over the HV reg parts and will prob replace the 1kv caps (tube type).

for the streaking I was planning on putting up a test pattern and checking with a scope starting at plate of the video out tube and working my way back, looking for noise. will prob just sub in a new video out tube 1st and hope for the best.

anybody work on one with the loss of pic from the extreme left edge?

ctc17 · #14 02-06-2011, 09:06 PM

After fighting with a totally weird Zenith HV issue myself all day....all I can say about Zenith tube sets and their HV is they inspire a non stop verbal string of 4 letter profanity.

I dont know if these things ever worked right from the factory but they are so FING hard to fix! Every single one of them has some super bizarre HV issue that is so totally hard to figure out. The sets work, but the regulation is crap, the hv is way to high or fades when the set heats up. Some just annoying crap.

The only positive thing I can say about Zenith at the moment is the flybacks never seem to fail.
At one point today I had this 25mc36 up to 50kv and the stupid thing was arcing so loud it was hurting my ears, I didnt even know it was possible to get the hv that high.
GRRRRRRR

mbates14 · #15 02-06-2011, 09:13 PM

Quote:

Originally Posted by ctc17

After fighting with a totally weird Zenith HV issue myself all day....all I can say about Zenith tube sets and their HV is they inspire a non stop verbal string of 4 letter profanity.

I dont know if these things ever worked right from the factory but they are so FING hard to fix! Every single one of them has some super bizarre HV issue that is so totally hard to figure out. The sets work, but the regulation is crap, the hv is way to high or fades when the set heats up. Some just annoying crap.

The only positive thing I can say about Zenith at the moment is the flybacks never seem to fail.
At one point today I had this 25mc36 up to 50kv and the stupid thing was arcing so loud it was hurting my ears, I didnt even know it was possible to get the hv that high.
GRRRRRRR

Hey Ma, you can see a picture of my bones on the wall. XRAY :-)