Heathkit GR-53A color TV - Page 2 - Videokarma.org TV - Video

Ralph S · #16 03-18-2014, 05:04 PM

All right, it's time for another report. The set's picture and sound reproduction are working fine with the major exceptions being: The horizontal weave previously described, a tube socket which needs replacement and some buzz in the sound on certain typical over-the-air scenes. The socket change and the sound alignment will come later, but right now I've reached the end of my rope on the hum in the deflection. It shows up in the secondary windings of the yoke and convergence transformer - being a beat between the 59.97 of the vertical deflection and 60 hz, so the movement is rather slow but considerably pronounced. On the primary side there is a .390 v p-p hum at the top of the 40 mfd cap and about .185 v p-p hum on the +390 vdc feed. The hum cannot be seen at the plate of the vert. output tube and on the feed side of the primary winding. BUT get to the secondary winding feeding the vertical yoke and it's very obvious.

I've tried slapping extra 100 mfd capacitance on both the C19 cap to the primary winding and the +390 vdc feed to the green/white lead of the secondary and R42. There is no difference by either of these additions.

What's going on here? Any positive ideas would be appreciated. Check the portion of the schematic below for the area I'm talking about.

Electronic M · #17 03-18-2014, 05:18 PM

If you have a tuning eye type capacitor checker I'd recommend checking all lytic capacitors between the secondary of the power Xfmr and the vertical stage(also double check that none of the lytics are wired in backwards.). Check the B+ rectifiers for leakage if they are not tube also.
Heater-cathode shorts on tubes are also a potential source of AC leakage into the B+.

Ralph S · #18 03-18-2014, 05:33 PM

The PS doubler is working fine and all of the electrolytics along with the tubular caps are new. Before they were put in they were checked with an ESR meter and a capacitance bridge for correct and tight values. I tend to agree with you that the most suspicious site would be a heater to cathode short, but so far I haven't found it (or them). I've gone through the two major pc boards with a fine-tooth comb and haven't found anything out of the ordinary. Any other thoughts? Bear in mind that this set was assembled by a rank amateur a long time ago and I've already fixed an "arm's-full" of construction problems, but there may be more. Thanks for your comments.

old_coot88 · #19 03-18-2014, 05:46 PM

A 'hula dancer' weave sounds more like ripple on the B+ feeding the horiz sweep and/or horiz osc. areas.

DaveWM · #20 03-18-2014, 06:59 PM

wow, hula brings back fond memories of my BW magging with the loose screw on the sweep board, which was a pressure connection of the ground on the pcb to the metal chassis.

I ended up finding it by feeding DC from a battery to the various tube filaments, one by one returning to the AC supply. Triple check all chassis grounds esp if there is a common cathode/filament return to ground on the sweep boards.

old_tv_nut · #21 03-18-2014, 08:17 PM

Quote:

Originally Posted by Ralph S

All right, it's time for another report. The set's picture and sound reproduction are working fine with the major exceptions being: The horizontal weave previously described, a tube socket which needs replacement and some buzz in the sound on certain typical over-the-air scenes. The socket change and the sound alignment will come later, but right now I've reached the end of my rope on the hum in the deflection. It shows up in the secondary windings of the yoke and convergence transformer - being a beat between the 59.97 of the vertical deflection and 60 hz, so the movement is rather slow but considerably pronounced. On the primary side there is a .390 v p-p hum at the top of the 40 mfd cap and about .185 v p-p hum on the +390 vdc feed. The hum cannot be seen at the plate of the vert. output tube and on the feed side of the primary winding. BUT get to the secondary winding feeding the vertical yoke and it's very obvious.

I've tried slapping extra 100 mfd capacitance on both the C19 cap to the primary winding and the +390 vdc feed to the green/white lead of the secondary and R42. There is no difference by either of these additions.

What's going on here? Any positive ideas would be appreciated. Check the portion of the schematic below for the area I'm talking about.

Confusing!
1) you have a HORIZONTAL weave
2) you are looking for it on the vertical yoke.

a) Is the weave a deflection from side to side (that is, the left and right sides of the picture go the same direction) or is it a size change (left and right sides of picture go opposite directions)?
b) Is there any vertical motion at all?

Ralph S · #22 03-19-2014, 07:54 AM

I agree with you regarding that the idea of finding the source of the hum in the vertical side sounds silly, but I've spent days checking the horizontal side and no hum appears there, only on the vertical side. There is a very obvious, slow moving hum in the vertical side. It's counter intuitive, but true! That's why I reached out to the group to try to get some help trying to nail this fault. I' stumped. The fault displays itself as a slow weave from side to side, traveling up the screen, then repeats exactly in step with what I see on the scope. On the 21" screen, the movement is almost an inch of screen width.

old_tv_nut · #23 03-19-2014, 02:55 PM

Ok, my guess then is that the signal on the vertical is not related to the problem, except that it happens to be coming from the 60 Hz line.

I'd poke around the sync separator / amplifier (whatever's in that area) and maybe the AGC at this point. Can you post the schematic for the sync section?

DaveWM · #24 03-19-2014, 03:41 PM

I still think you should check the grounds, if there is a common ground for the deflection board (assuming it has a PCB) then a defect in the ground could see a beat freq with the vert vs AC , then share that with the horz (same ground on pcb) and get some modulation on the horz tube cathode. Power up the filaments on the deflection with a 6v battery and see if it goes away. On my hula it would take something like 10-15 seconds to work its way thru (a vert line would show a slow moving horz shift like a hum bar, but much slower).

Ralph S · #25 03-19-2014, 03:41 PM

Here's the AGC, Sync Sep and Vertical section of the Heathkit. If you need the Horizontal section, let me know. I'm going to take a look at the Horizontal section again this afternoon. If I stumble into something, I'll let you know.

Electronic M · #26 03-19-2014, 04:33 PM

A picture of the symptoms could also help...

Ralph S · #27 03-19-2014, 04:54 PM

Well, thank you to all who replied and if I had a live TV feed to videokarma, you'd see me knocking my head with my fist for not checking this first: it was the PCB grounds as Dave and others suggested. I had put a tight ground bond on the IF board several days ago and only checked the Video/Color and sound/sweep boards with an ohm meter at that time. But the moment I bonded the grounds to chassis on those two boards the problem was solved. What a relief! Now on to getting rid of the nasty cataract and getting the color setup spruced up. MANY THANKS AGAIN!!!

(PS: I'll try to get some pictures out tomorrow!)

old_tv_nut · #28 03-19-2014, 09:51 PM

Good! Onward...

Ralph S · #29 03-20-2014, 01:54 PM

As promised, here are two off-screen shots showing the present stage of the Heathkit GR-53A set. The bars are from a Sencore VG91 and the live shot is off the air from KABC news at 11:00 AM. I didn't adjust anything between the two shots. The cataract is very evident, but the picture in the center tells the story. Also, horizontal hum/weave is gone!!!

DaveWM · #30 03-20-2014, 02:18 PM

looking good