25K7000 with interesting red issue

[SirPeale]

Recently got a Rev-X back off location.  When I fired it up I noted it had a very red picture.

Thinking perhaps the red transistor on the neckboard was going bad, I replaced it.  Nope.  I metered the one I pulled...it read good.  I put it back.

Pulled the whole monitor and brought it to the test bench.

After some testing, it *appears* to be a heater-to-cathode short.  I removed the red transistor altogether and it's STILL red.

According to Randy Fromm, I can take some wire, wrap it around the flyback ferrite 2 1/2 times, cut the traces leading to the heater on the tube, and solder these wires to the heater pins on the neckboard.  In theory, this should isolate the heater circuit so red doesn't fire off all the time.

Like I said...in theory.  The heater works  - no doubt there.  But it's still red!  But not right away.  It's a beautiful picture for the first ten-fifteen seconds or so.  Then red starts seeping in until everything has this massive red wash.

I have my theories as to why this is happening, but I'd like to hear from other monitor techs as to why this is going on.

[Ken Layton]

I've done this trick several times and it's worked every time.

[Kevin Mullins]

Do you think it would be worth trying a rejuvenator on it ?

[Ken Layton]

It never hurts to try a rejuvenator.

[SirPeale]

I've done this trick several times and it's worked every time.

Oh, I've already done it.  It didn't work.  I'm wondering why.

We have a rejuvinator but it didn't work, so we sent it to B & K for service.  Hopefully it'll be back soon.

[worm]

Check the votage on the neck board H H or the smaller transitor that corspond with the red transitor.

[grantspain]

if its a gun fault then sometimes some gentle tapping of the neck can sort things when you place the tube on its face

[SirPeale]

if its a gun fault then sometimes some gentle tapping of the neck can sort things when you place the tube on its face

That was the first thing we tried.  No go.

[Q*Bert_OP]

I've done this trick several times and it's worked every time.

I 've only done it once, but it worked for me...

[Kevin Mullins]

if its a gun fault then sometimes some gentle tapping of the neck can sort things when you place the tube on its face

That was the first thing we tried.  No go.

Did you try it while it was warm? (with heater voltage on)

The slow gradual part of the problem you mentioned in the original post has me wondering a bit now about caps. Seems like anytime a problem is slow or progressive, I start to think about caps. Not neccissarily electrolytic either, maybe a mylar cap to ground on the neckboard or something. (I'm just fishing for ideas now)

What's the monitor model?

[grantspain]

it gonna be interesting to find out what it turns out to be,please let us know

[SirPeale]

if its a gun fault then sometimes some gentle tapping of the neck can sort things when you place the tube on its face

That was the first thing we tried.  No go.

Did you try it while it was warm? (with heater voltage on)

The slow gradual part of the problem you mentioned in the original post has me wondering a bit now about caps. Seems like anytime a problem is slow or progressive, I start to think about caps. Not neccissarily electrolytic either, maybe a mylar cap to ground on the neckboard or something. (I'm just fishing for ideas now)

What's the monitor model?

Tried it warm, tried it cold.

I forget the exact model, 25K719X.

Oh, definitely not caps.  Tried two other known working chassis on it with the same red wash. They work fine with other tubes.

[Brunnen-G]

I had a similar issue with a K7000 series monitor in a Gauntlet machine I bought.  Turned out to be the red gun in that one as well.  Confirmed it by connecting a known working spare chassis and had the same result. 

Hooked up a Sencore CR70 and it wouldn't restore it one bit.  Finally just tossed it and ordered a new tube.

[SirPeale]

Theoretically isolating the heater should eliminate the heater to ground short.  Don't know why it didn't work.  Haven't revisited this one yet.  Our rejuvinator is being fixed right now, hopefully when it comes back we'll have more answers.