k7000 has HV but no neck glow, tube good

Vectorman

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I'm going into hour 7 working on this ONE k7000 chassis. It had HV shutdown, then blew fuses, then shutdown....won't bore you. Finally got all that working...

But now it powers up, has HV (about 19kv steady) but the neck never glows. hence no picture.

I thought maybe the tube was bad, but put it on the BK tester and the tube is perfect and glows beautifully for the tester.

Thought maybe the fly was bad, but put (another ) brand new flyback on it and same results.

Any ideas?

any help greatly appreciated.

John
 
Yeah, check R213 on the neckboard, and make sure the wires to the neckboard (and from the flyback) are good. Check for cold solder around the G2 connection...
 
All the resistors are good on neckboard. Seems to have good continuity all over it. Connectors are all plugged in and making good connection.

I have trouble understanding the schematic around the tube / neckboard. Where is the heater voltage supposed to go into the tube? What voltage is it supposed to be? I could back-trace it and find the faulty component perhaps?

The red wire from the flyback to the neckboard is showing about 90vdc. One side of R213 (where it comes from the main board) on the neckboard shows about 7.5VAC, the other side (where it connects to the tube) shows near almost 0VAC and 0VDC. I tried replacing R213, but it checks out good and has the same voltages on both side after replacement.

Thanks for your help...
 
Is this an 8-pin or 10-pin socket? The heater voltage is usually 6.3v and will come in on pin 5 of P202. It comes straight from the flyback to the neckboard, thru R213, and into the tube on pin 4 (of the 8-pin) or pin 10 (of the 10-pin)...
 
It's a 10 pin socket - 25" tube. Ok, perfect continuity between pin 9 of flyback and one side of R213. And under power, this shows about 7-7.5VAC...

Then there is perfect continuity between the other side of R213 and pin 4 of the socket - but under power this shows 0V.

And the resistor tests 6.8k ohm. And I've swapped it and still the same. What is happening to that 7vac?

John

Is this an 8-pin or 10-pin socket? The heater voltage is usually 6.3v and will come in on pin 5 of P202. It comes straight from the flyback to the neckboard, thru R213, and into the tube on pin 4 (of the 8-pin) or pin 10 (of the 10-pin)...
 
And the resistor tests 6.8k ohm. And I've swapped it and still the same. What is happening to that 7vac?

John

R213 is supposed to be a 0.68 ohm 2 Watt resistor. And when you measure the voltage at one side, do you just move the test lead at R213 to the other side, or test it differently?
 
Last edited:
THANK YOU!

I had a 6.8k resistor there...off by several orders of magnitude. The other 2W resistors on the neck board are 6.8k, and I got confused. Plus my original schematic doesn't have the decimal. Now it's working! Thanks!

ONE MORE QUICK QUESTION: Is it safe to replace an STR30130 (IC4) with an STR30123?

Thanks again.
John
 
No. The 123 and the 130 are rated differently. I asked in a separate thread and found out...
 
No. The 123 and the 130 are rated differently. I asked in a separate thread and found out...

Yup, not a good idea.....Throughout the K7000 series, there's like....what, four different STRXXXX regulators used. I've swapped a few, just to see what would happen.....The end result was poor regulation with various symptoms....hula, dim screen, bright screen, unabiltiy to properly adjust B+, etc.

Edward
 
My understanding is the "123" and "130" is the output voltage of the regulator, so obviously if you change that it would affect everything else down the line.

Then there is the differences between say a 30130 and a 3130, etc....which require jumper re-arrangements and such.

I just stick with what comes out of them, much easier on the brain.

Same goes for the vertical IC's.
 
Ah...very interesting. Makes sense. I agree - in a perfect world I wouldn't dream of substituting components. But when it's 3am and I've been working on the stupid thing for hours I don't want to wait for an order to come in.

But I will....

Thanks very much guys. I am learning to hate 7000s. If only they all used the same parts and the parts weren't so (relatively) expensive, I'd just order a pile of them and shotgun every single 7000 chassis I looked at with FB, HOT, VR, Vertical chip, Critical caps, other caps, etc, etc....and just be done. I may end up having to do that anyway, as I currently spend hours chasing problems around one component at a time.

What do you guys do? Do you just shotgun them or are you good / experienced enough to know where to go right away?

John
 
Yup, not a good idea.....Throughout the K7000 series, there's like....what, four different STRXXXX regulators used. I've swapped a few, just to see what would happen.....The end result was poor regulation with various symptoms....hula, dim screen, bright screen, unabiltiy to properly adjust B+, etc.

Edward

When you mean bright screen, would that be bleeding too? Seems I've run into that a lot with my 25" and it was rebuilt with a Bob roberts kit (including Flyback) but not sure if the VR was part of that.
 
When you mean bright screen, would that be bleeding too? Seems I've run into that a lot with my 25" and it was rebuilt with a Bob roberts kit (including Flyback) but not sure if the VR was part of that.

Whenever I see bleeding on a monitor, it almost always is due to one (or more) of the colors being overdriven, and can be adjusted out using the pots on the neck board.

John
 
Whenever I see bleeding on a monitor, it almost always is due to one (or more) of the colors being overdriven, and can be adjusted out using the pots on the neck board.

John

Yep, I agree.....or (especially with 25"ers) the tube is starting to die and needs to be zapped.

Edward
 
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