tube tester dual focus DEAD (Attempting ZOMBIE) nope still dead

[lilshawn]

i have a tube on a Makvision M2929 that I suspect has a bum red gun. I have a B&k 470 tester and I would like to confirm that the issue is actually the tube... but the tube has a dual focus, and i don't have an adapter to fit it, nor can i find any info on which socket would fit it. or even if i could test it with the 470.

the tube number is M68QDY259X

[qrz]

Sencore used a "universal adapter" for their units . consisting of a tester compatable socket terminated with mini-clips.
it reduced the number of sockets needed .
focus leads shouldn't be needed for testing anyway .
doesn't one of your sockets have a keygap wide enough to fit ?

[lilshawn]

unfortunately no... the tester was purchased from a government auction a number of years ago. It only came with 1 socket (odd ball CR-6 socket of course), all the rest from the kit got lost along the way someplace.  so a colleague had to scab together a socket and make a #23.

i think your right about the focus, i don't see it being used even in the universal adapter. i might just make something up.

[lilshawn]

well i made myself up a cable and wired up the tester. chopped up the (thus far) unused CR-6 socket and attached a cable to the receptacle. I then un-solderd the CRT socket and attached my wires to the legs. the focus lead gets attached to the G3/G4 lead anyways, so i just inserted a wire pigtail into each focus lead hole and tied them both to the G3/G4

for future reference when facing the CRT socket the pins clockwise from bottom focus are as follows:

Focus Red (Right side) Focus White (Left Side)
N/C
N/C
Red Cathode
Heater
Heater/Ground
Green Cathode
G2
Blue Cathode
G1
N/C


I believe the colors listed are right... the schematic for the M2929 neckboard (first series) is wrong. it shows the inputs and outputs of IC102 (TDA9535) incorectly

GREEN out is actually BLUE based on input from pin 9.
BLUE out is actually RED based on input from pin 3.
RED out is actually GREEN based on input from pin 7.

unless something else is messed... personally I don't care anymore. In fact i can't even remember what color doesn't work anymore... this schematic has me all screwed up. i was checking one circuit, then the chip inputs and outputs didn't mesh with whats on the schematic... so i was checking all the wrong stuff...  


Seems there is a short between the cathode and the heater. the problem gets exasperated when I knock on the neck. It's not fixable, but I tried a few short removals and rejuvenates to see if it could get cleared out. No joy.

makes sense, the emissions from the gun are getting sucked up and grounded by the heater.

[MonMotha]

Have you tried using an isolated supply (e.g. a few turns around the flyback) for the heater supply to remove the ground path?

[lilshawn]

Have you tried using an isolated supply (e.g. a few turns around the flyback) for the heater supply to remove the ground path?

I haven't, but I just might. I read some stuff in the B&K manual regarding the use of a 1:1 transformer. I've tried to source 1:1 transformers locally for use in ground loop isolators to no avail. but your suggestion just now jogged my memory about something else i read a while back about using the flyback as a power supply to increase the voltage to the heater to fix low emissions... 


I'll have to see if there is room to get a wire through the core... there should be. I'll have to check tomorrow. (it's at the shop)

Otherwise the tube is good. the gun still emits, in fact it's slightly better than the other two.

any recommendations on how many core turns I might need to get around 6 volts? I guess I could start with 1 and work my way up... maybe i'll just wrap as much wire as it will hold and see what happens 

[MonMotha]

There was a link floating around at one point, but I can't find it.  I seem to recall 2-3 gets it about right.  Remember that you'll need a true RMS meter if you want to measure it.  I know qrz has commented on this process before; you might ping him.

[lilshawn]

There was a link floating around at one point, but I can't find it.  I seem to recall 2-3 gets it about right.  Remember that you'll need a true RMS meter if you want to measure it.  I know qrz has commented on this process before; you might ping him.

'sall good. I have a Fluke 87 series V.  it's almost bullet proof.  Someone once said that you could put it into Ohms range and plug the leads into a wall socket, but I don't want to try it.

[MonMotha]

I once ground looped the AC from my bench via an oscilloscope.  Had the scope ground lead on the primary DC- side of a SMPS design and totally forgot about it when I went from a 24V (isolating) transformer to straight 120V (no iso) input for testing.  Made a nice pop before the fuse on the DUT (thankfully) blew.  Scope shut off.  I was afraid I'd broken the thing.  Cycled the power switch, and it came right back up good as new.  All the self tests and calibration checked out.  Thank you Tektronix.

[lilshawn]

Well I did as you suggested and put 2 turns on the flyback. Test...10.06 volts... Alright take off a turn... 6.96... close enough

Sigh... Still no color though.

I'm going to try some Frankenstein stuff... Gonna jump a working color CRT socket pin to the non-working one. BRB

Nothing still. Double sigh. It looks like the color I jumped it with is dragged way down to near nothing. Something is defiantly FUBAR.