Zenith Console combo - Page 6 - Videokarma.org TV - Video

DaveWM · #76 09-03-2010, 06:55 PM

another problem, the CRT was blooming so I checked the HV, with brighness turned all the way down its about 24kv, but with brightness up enough to get a decent pic its only about 14kv.

I checked the CRT and it was fine back when I 1st got the set.

I replaced the regulator tube. I have not checked the B+ to see how its holding up. I replaced the HV rectifier (3A3).

I will prob start by checking around there.

DaveWM · #77 09-03-2010, 07:36 PM

not so fast big boy...

I was over my metered variac, so I got my big boy variac out, adj line voltage to 117 and HV returned to normal, well regulated etc...

even got good color bars from the B&K and I did confirm the output settings by checking against a good set.

So... it seems like its just the tuner. I will sub tubes on last time from a known working tuner, my tube testers can't check them (HK 533 and Bk600) so I cant be 100% sure I have good tubes in there. My guess is the osc must be ok since it was working, but I will sub them both anyway.

I have heard of lightning strikes messing up tuners, not sure what gets fried but I will check. I am hoping its just dirty contacts.

DaveWM · #78 09-03-2010, 07:37 PM

I must admit I am tempted to just run a composite signal to the test point just after the video detector.

DaveWM · #79 09-03-2010, 07:43 PM

think I will check the tuner AGC voltage before I go too far

DaveWM · #80 09-03-2010, 08:08 PM

tried a new 6BA11 (agc keying/syc sep/noise cancel), no joy, need to find the tuner AFC source lug and see what its reading. Or just try adj the agc pot. Getting late tomorrow morn looks good to continue.

DaveWM · #81 09-03-2010, 08:47 PM

agc voltage with no signal is 4.7v (sams say 4v) with signal its about .150-.300.

I get a better pic with my BK1076 on a modulated output, perhaps I am just putting out more than the DVD or converter box is able to.

I am getting a wierd interference lines in the pic, more that than snow, but not with the B&K.

I may just hook up a pair of rabbit ears to it and broadcast a short distance with my agile Modulator, just to make sure its not some oddness due to the connections.

The BK test pattern looked good as did the color bars.

DaveWM · #82 09-04-2010, 02:38 PM

well did not do any of the above yet, but did connect the IF out from the video modulator to the IF in of the set, perfect pic, so it has to be the tuner.

the modulator was broadcasting fine to another set so I know the RF out is good.

I did notice that on this set the antenna did not help the reception at all, its like it was not even connected. This is when I had the modulator broadcasting the RF. So I assume there is some kind of issue with the connection from the antenna term board to the tuner.

Guess I am going to have to pull that tuner after all.

DaveWM · #83 09-05-2010, 06:07 PM

getting better now, see the thread on the tuner.

next up I need to fix up the channel indicator (cracked) super glue and nylon tread should fix the cracked shafte housing.

the CRT brightness changes from top to bottom, dark at top brighter at bottom. I notice it the most in letter box format.

its as if the video signal is losing contrast as it nears the end of the vert sweep.

I have not checked any tube other than the IF and RF, and this happens regardless of the video source from the tuner or the direct IF feed.

Its like the vert blanking resets the tube.

DaveWM · #84 09-05-2010, 10:16 PM

Since I have a very another tube chassis zenith (20yc130) which is nearly the same, I decided to scope the video signal at the video amp transistor collector and the grid of the video output tube. Just to see how it should look when there is a signal. I prob should have check the videok cathode follower (6KT8) but its getting late so need ot knock off and resume tomorrow.

I also checked the agc on the working zenith so see how much hash is ok on the AGC line. Should be very little and it was. This set (the 20x, not the 20y) is VERY sensitive on the AGC setting from blank to loss of sync in only a few degrees of rotaion of the pot. I have a feeling the AGC is still not right. I dont think it should be that critical.

there are a couple 6KT8's so I wil be checking subing etc... the other is for the syn amp.

DaveWM · #85 09-06-2010, 04:05 PM

so anybody run into the screen that loses contrast toward the bottom of the screen (a progressive loss from top to bottom).

just hoping to get some pointers..

DaveWM · #86 09-06-2010, 04:45 PM

went out to hook up the scope and start trouble shooting the pic issue, power up, PERFECT pic.

the only thing I did was attach a lead to pin two of the video amp.

So I will clean up the garage, button up the back and get a pic.

Not sure why but I aint complaining.

the vert is a tiny bit jumpy, not as bad as my other zenith 20y chassis.

So now I will need to decide if I should pull the chassis or not.

the only issue I have is I know about those old paper caps HV hard shell tube caps. I am tempted to leave well enough alone as I know there is always a risk when disconnecting old plugs etc.. that something could break.

So I will button it up, get some pics, see if the picture contrast at the bottom of the tube returns and see if the vert jump settles down.

The picture color and focus is excellant. Needs a slight dynamic convergence adj. I may replace the diode pack on the board just because its old and I assume the Se's are getting leaky.

one of the reasons I want to pull the chassis is its just so damn dirty, WAF comes into play (if she happens to catch me with the back off, and its in the house).

DaveWM · #87 09-06-2010, 04:54 PM

disconnect lead get ready for pics, turn on set, contrast problem has returned.

turns out the video amp tube must have a dirty socket issue, wiggle that vert amp tube and all good again. I guess I was on the right track to check there 1st

Just another reason to pull the chassis and do a though cleaning, including the sockets.

DaveWM · #88 09-06-2010, 05:35 PM

the AGC seems to have a bit too much AC ripple in it, no hash but ripple.

Not sure if that could account for the overly sensitive AGC adj. Anyway I will end up pulling the chassis and checking all the filter caps. No audio hum and no hum bars in the pic. I should check the B+ for ripple before I pull it out, IIRC there is a big power resistor that sits on top of the chassis, one side of which connects to the choke and is where they sams show the ripple (2v).

DaveWM · #89 09-06-2010, 08:41 PM

some pics, the last two show the need for a lin adj and the pie crust effect that happens when the yoke is squealing, only last for a few seconds. I need to check purity so when I do that I will make sure the screws on tight that holds the yoke in place.

the pie crust is on the last shot of the womens face

DaveWM · #90 09-07-2010, 02:53 PM

micro panic time...

I am cleaning up the contacts, including the CRT cathode plug in connections.

Of course I put the red gun to the wrong post. After futzing with if for 30 min I realize my error, put it back all fine now, except for my messing up all the screen drives and controls trying to get the red to work.

I checked the CRT no damage, excellent tracking and good emissons, so at least I did not hurt anything but my wits.

Oh well it needed a good setup anyway, now I have a reason to do from scratch.

still has that annoying high pitched un even noise at start up, I cant be sure where its coming from. I tried touching the fly and the yoke with a wood stick to see if I could affect it, but no joy. I wonder if it could be coming from the pin cushion? the thing is its also gets some noise into the pic (the streaks). I will keep running it and see if it improves. Its not a big deal since it always stops and does not come back after the inital warm up.