K7000s - kicking my butt!

Peale

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Working on two K7000s - a 19" and a 25"

Instead of blowing fuses, I've been using a "lightbulb fuse" - eg if the 100W lightbulb comes on bright, there's a dead short and shut it down before it toasts something.

The 19" was working but had a blown tube. Replaced the tube, it fired right up. After I capped it I got C57 backward, and of course it smoked. Replaced it and the fuse was blown. Replaced that and it blew right away.

Testing revealed that the HOT was blown and C38. Replaced both...nope. Still a dead short somewhere. Solder work appears to be clean. Did find one resistor that the solder had puled away from the pad (the pad was fine). Resoldered it with no change.

The 25" had a blown fly. Replaced that, fully capped it, replaced HOT...blew fuse. Replaced fuse, HOT, and tested around until I found that C38 was also bad. Replaced it, fired it up...no, still has a dead short somewhere.

Both monitors appear to have an interesting issue with R98 and R99. They're both 2.2K resistors, but both are reading a dead short. Of course when resistors die, they go open. But I'm having a heck of a time finding the cause of these two.

Ideas?
 
Both monitors appear to have an interesting issue with R98 and R99. They're both 2.2K resistors, but both are reading a dead short. Of course when resistors die, they go open. But I'm having a heck of a time finding the cause of these two.

Are they reading shorted out of circuit ?
 
Nope. Out of circuit they read 2.2K. Something is "bridging the gap" so to speak.

Both the width coil and the...gah, name escapes me at the moment...the other coil right by it - how can you test them? Or are they supposed to read shorted no matter what?
 
The width coil and linearity coil will read as shorted with a regular DMM. You would need a ring tester to check them properly. I doubt either are causing your issue unless they look burnt or broken.

If C38 was bad, then you should be checking C36, D18, D13, D14, R91, R92, IC4, R103, R89, R101, and all those diodes around the filter cap....
 
also chec the vr when the hots go thr vr usually does too.. hope to hell thats all it is. i have a evil one here now i gotta send to mid to figure out. ive done it all on that damn pos
 
also chec the vr when the hots go thr vr usually does too.. hope to hell thats all it is. i have a evil one here now i gotta send to mid to figure out. ive done it all on that damn pos

There's that damn "mid" again.

and I mentioned the VR in my post - IC4...
 
7000

Sounds like you have a shorted mylar cap or a shorted diode on the left side of chassis.
I hope you dont have a bad yoke that started this.
 
I'm sure it's not a shorted yoke.

I swear I've been over every part in the power supply circuit. I've also got a chassis that's working, so when I find a reading I think is odd I've been going over that one to see if the reading matches.

The VR (30123) on the 19" reads fine. I replaced the 30130 on the 25 regardless. How do you test the 30130?
 
The width coil and linearity coil will read as shorted with a regular DMM. You would need a ring tester to check them properly. I doubt either are causing your issue unless they look burnt or broken.

If C38 was bad, then you should be checking C36, D18, D13, D14, R91, R92, IC4, R103, R89, R101, and all those diodes around the filter cap....

I'm going to have to unsolder the diodes to check, but everything else in that list checks okay, with the exception of R89. It's marked as 3.9K, but reads as 5K.
 
Bah...spent at least another hour on the 19" last night - touching up solder joints, looking for bridges, testing components...nada.

I did discover that the 25" has a blown HOT - again, and will replace that later tonight.
 
How do you test the 30130?

Pins -
1. Common (ground)
2. Base
3. Input
4. Output (where the B+ is derived from)

A short between the Input and Output is obviously bad.
A dead short between ground and any pin is bad.
Output should be right at 130V.
Input voltage I believe is right up around 160V.

Don't confuse this with the STR3130. (different pinout) So maybe verify the right VR is in there for the chassis jumper layout. (info can be found on the schematic notes)
 
I soldered one in a couple days ago - not cut off.

Either way, tested each pin against all the others, nothing shorted.
 
You're right on the pin count... I had to go dig out some chassis to double check myself.
But if you look at the 5th pin solder pad on the STR30130 version, it goes nowhere, so only the four pins are actually being used.
The STR3130 uses the same number of pins, but is a totally different pinout.

And if you found no shorts on the VR then keep moving right along, your short is still elsewhere.
 

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I got the 25" to fire up! I've been using the lightbulb trick in place of a fuse so I stop blowing them. I went to take some voltage readings (B+) so I was keeping it on only briefly. I fired it up, light was very bright. Suddenly it went dim - and it fired up. B+ is low, but I suspect I can figure that out. Also had vertical collapse, but I suspect the yoke wires weren't tight enough.

I'm guessing the main filter cap may need replacing (hence the slow startup time and the large current draw at the beginning) and I'll tackle that when I'm next able to work on it. Any other insight?
 
What did you do to get it to fire? I am having similar trouble with a 25".
 
After checking everything in the power supply circuit and not finding anything else shorted I thought I'd try other things. What's why I'm guessing the main filter cap is bad/dying - it would have much more draw when it was cold and when it warmed up allow to operate "normally".

If you're not using one of those Bob Robert fuse circuit breakers I'd recommend the lightbulb trick.
 
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