another maggie - Page 2 - Videokarma.org TV - Video

*zenithfan1* · #1 08-12-2009, 11:53 PM

Sounds good, looking forward to some pics. I'm glad you got 'er finished. That's a nice looking set.

DaveWM · #2 08-13-2009, 08:04 PM

been having some issues with the spot that results when you turn of the set, not sure why this one does it an my other does not, but a quick fix was to put a resistor/cap in series from the crt cathode to ground. The cap charges during normal viewing, when you turn the set off, the cap discharges into the cathode holding it positive while it cools off biasing the tube for about 15 seconds, no spot. I was worried that it could burn the CRT.

DaveWM · #3 08-14-2009, 12:21 PM

I tried sever RC combinations, 470k and 22uf seems the best for spot control with miminmal impact on time it takes for the full brightness to be achieved when the set is turned on. Again this is just a series connection from the cathode to the ground. during operation the cathode has a positive charge, when the set is turned off this charge goes away, and the spot comes on (very bright dead center of the screen). by using the RC combo the cathode maintains a positive charge long enough for it to cool down and stop emitting.

DaveWM · #4 09-19-2009, 11:38 PM

update on this set, I think I lost a lot of post but it is the one that was having the hula problem, or snaking or maybe even weaving.

bottom line is there was a low freq low amplitude wave that would work thru the screen. You could see it on vertical lines. the wave would repeat about every 15 seconds and would deflect the vertical lines (like a foot ball field) about 3/16 of an inch.

I was able to get rid of it if I powered the vert sync tubes heaters with DC.
no HK shorts (swapped tubes from a working set).

tried cleaning PCB traces along the filament trace, no help

had all new E caps (filter/decouple/doubler)

finally got it licked by adding a direct ground connection from the two vert tubes to the chassis ground.

Those two tubes use the PC traces for a heater ground return, and the PC trace is grounded via some solder fingers that press against the chassis.

I may have been able to just tighten up the screws, but I figured the direct wire to chassis was more of a sure thing. Seems kind of lame to rely on just a press contact point for a ground. The horz osc tube had its own factory ground wire, and did not rely on the pcb for a ground path on the heater.

any way it did tighten up all the pcb screws on all the boards jic.

anyway learned something new, small problems (the wave was very minor but there) often have small causes (I prob could have fixed it by just tighting up the screws).

Small causes can still be hard to find, maybe harder since they are not obvious. But anyway you can bet for now on all pcb screws will be checked 1st thing.

Charlie · #5 09-20-2009, 10:25 AM

Glad you found your problem! I've heard many guys here emphasize checking ground connections... especially between circuit board and chassis.

DaveWM · #6 09-20-2009, 11:58 AM

roger that Charlie, you can bet that is the 1st thing I will check on any set I get that has PCB's for now on

I am just glad it is working, It was really starting to bug me.

the screws were not loose, but I was able to tighten them all up about 1/4 turn. I guess with age it was just enough oxidation to cause a problem.

I have another maggie with the same chassis and you can bet I am going to check them.

DaveWM · #7 11-15-2009, 10:38 PM

Update"

Got the new CRT tester (Sencore CR-70) tube show nothing on emissons and cutoff, according the the "beam rebuilder" guide I did rejuvenate, nice little sparks fly in the CRT neck and I am think Oh fudge now what have I done. Anyway checked and solid in the good and great cut off.

I turn it on and the focus is much better and the picture looks pretty darn good. I hope this fix last.

I like the Sencore.