25" K7000 Black Screen, Low voltage at R301

[whoamonga]

Well, maybe this is where the monitor is deemed deceased... I removed the neckboard and checked for continuity between the top 2 "H" pins sticking out of the tube and nope... no continuity...

It stand to reason that if the two pins are normally connected, I'd also get continuity between the two solder points on the neckboard. No again, no continuity.

Perhaps an internal element was the "POP!" I heard before. Maybe if it's supposed to receive 5-7vac, but received 75vac, it did some damage... pretty lame.

So is that it? Is this thing just toast?

 

[KevinMullins]

And you're absolutely sure the meter was set correctly and you were measuring the correct two pins on the tube ?

I just gotta ask....hate to condemn a tube without being ABSOLUTELY sure since I'm not there myself.

Got a crt tester/rejuvinator handy ?
(for testing purposes, won't fix it if the heater element is actually blown)

 

[whoamonga]

dude, i tried all the top pins in varying combinations, no continuity... i could put the two leads together and get the beep, but not on those two pins...

So is the yoke worth selling?

 

[whoamonga]

or is a tube swap worth a try? Odds probably aren't good that I'll find a matching tube out there though..

 

[KevinMullins]

A tube swap is possible. You can still find tubes that will work in these from older TV's and whatnot.

I was hoping to get a second opinion to chime in here and see if there might be something else missed, or to check first.

 

[modessitt]

I was hoping to get a second opinion to chime in here and see if there might be something else missed, or to check first.

I'd prefer it be checked with a rejuvenator before giving it up. Possible that the heater pins still aren't being checked properly...

 

[whoamonga]

k. I'll check the Houston area and see if someone can lend a hand. If not the heating element, anything else that could explain this?

 

[KevinMullins]

The only thing throwing me off is that these should have measured the same.
The "Earth ground and top of R213" is close to what we're looking for. (good)
The "Earth ground and P202" (pin 5) should have measured exactly the same.

Earth ground and P202 measured 76vac.

Earth ground and top of R213: 11.8

Same thing here. The bottom of R213 is what feeds the heater voltage, so it should measure the same as what you get across the two H pins. The right H pin and the bottom leg of R213 are one and the same, so the measurement should have been the same.

75.8vac across the two heater pins

Earth ground and bottom of R213: 8.6

 

[whoamonga]

The only thing throwing me off is that these should have measured the same.
The "Earth ground and top of R213" is close to what we're looking for. (good)
The "Earth ground and P202" (pin 5) should have measured exactly the same.



Same thing here. The bottom of R213 is what feeds the heater voltage, so it should measure the same as what you get across the two H pins. The right H pin and the bottom leg of R213 are one and the same, so the measurement should have been the same.

Well, with the bottom of R213, I put the black lead on the Earth ground, and with the two heater pins, black lead went on one heater pin, red on the other. Black lead wasn't in the same location on both measurements.. should it still have been the same?

 

[KevinMullins]

Well, with the bottom of R213, I put the black lead on the Earth ground, and with the two heater pins, black lead went on one heater pin, red on the other. Black lead wasn't in the same location on both measurements.. should it still have been the same?

The left heater pin and earth ground ARE THE SAME THING.
The right heater pin and the bottom of R213 ARE THE SAME THING.
Pin 5 of P202 and the top of R213 ARE THE SAME THING.

Follow the traces and you'll see what I mean.
Hence why they should have had the same AC measurement.
ie. - Can't have 76vAC between the two heater pins .... and 11.8vAC between the earth ground and the bottom of R213. Should be the SAME THING.

Did you Ohm R213?

 

[whoamonga]

they're completely different. gotcha.

yeah, that doesn't make sense. Maybe I'll test with another multimeter and see what's up.

I didn't desolder a leg of R213 to take Ohm reading because there was no continuity between the heater pins. I'll give it a shot tonight though.

 

[whoamonga]

I'm sorry dude, I deserve a bonehead of the year award...

I must have been using chassis ground with R213 to get those low voltage readings... cause anytime I use earth ground at R213, or the Heater pins, or P202 (since there are connections) I get 76vac. Earth ground to top, AND BOTTOM of R213 is 76vac...

attempting to desolder and Ohm read R213... perhaps there's hope?

 

[whoamonga]

also, with the monitor turned on I get continuity between the 2 heater pins. Turned off though, still nothing.

Side note, R207, R208, and R209 were all really hot. R213 wasn't even warm.

Also, disconnected R213 and took an Ohm reading from the two legs. I'm not sure I'm doing this right... I set it to the Omega sign and let is stay on AUTO. It displayed 1.2 on the 400 setting, but would still bounce around a little.

But if I manually set it to 4, 40, or 400 (either with the M or the K to the side) it showed 0.000. So I'm not really sure what to make of this...