K7000 Diode Question

Torin

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On a K7000 Medium Res I'm working on, D19-22 all pass current in both directions in-circuit but test good out of circuit.

Is this normal or does it mean I have a short somewhere?
 
do you mean by pass current in both direction as they show up with a voltage in both directions? if so thats kind of expected since you are measuring basically all 4 at the same time.

edit: if you are getting a short on any one of them in circuit its worth looking deeper but if they test fine out of circuit then the diodes themselves are fine.
 
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Ok, thanks. I think they are all testing as they should be. I just wanted to clarify how they test in-circuit.

I'm just fighting this HV shutdown issue where no fuses are blowing.
 
have you tried running it with an end of D10 pulled out? this will disable the HV shutdown; entirely theoretically, if it runs with D10 out you most likely would have a bad voltage regulator. I have had some chassis I never finished fixing that even with new voltage regulators, the B+ would be pegged. which at that point I would guess there's some bad major resistors.

if you have D10 pulled and it still doesn't work however, you're looking at a bad HOT.
 
have you tried running it with an end of D10 pulled out? this will disable the HV shutdown; entirely theoretically, if it runs with D10 out you most likely would have a bad voltage regulator. I have had some chassis I never finished fixing that even with new voltage regulators, the B+ would be pegged. which at that point I would guess there's some bad major resistors.

if you have D10 pulled and it still doesn't work however, you're looking at a bad HOT.

I have pulled D10 and it still doesn't work but HOT tests good in and out of circuit. Waiting on a new flyback and a replacement R101 to get here. I will also replace the HOT, VR and shutdown pot. I've replaced R89 already, which was way out of spec
 
I have pulled D10 and it still doesn't work but HOT tests good in and out of circuit. Waiting on a new flyback and a replacement R101 to get here. I will also replace the HOT, VR and shutdown pot. I've replaced R89 already, which was way out of spec

yeah, all those valuable resistors I mention a lot are subjected to a lot of heat which is why a) they fail and b) the solder pads usually disintegrate. if you lose the right ones in the circuit there, you'll have what you're experiencing. in other instances it'll put you in a fuse blowing nightmare; I'm guessing this is caused by the concentration of power that has nowhere to go, so it gets stuck on the diode bridge side and pops the fuse.

R101 could be at fault, so you're stuck until that arrives. there's a goofy little transistor at Q10, and the transformer at T2. I don't really know how to test T2 except swap with a known good one maybe -- I've personally never found a bad one. lastly, there's IC2, which if I recall is the smaller of the 2 chips. that has some kind of power drive control; I think if you desolder pin 16 on it and go to measure a bad R101, it'll actually reach the full 6.8k ohm reading (from my travels)

lastly, there's C36. if that doesn't work then you won't have horizontal deflection either. I read in a thread earlier you can do a continuity test between the 2 halves and if it shows a short then it's bad. never tried this myself.
 
Awesome, thanks for the help Mecha, you rock. I already replaced IC2 but won't be able to test it until the flyback, R101 and the shutdown pot get here.

I went to a local operator yesterday and bought a cheap, nice looking k7000 parts chassis. This should help with odd parts like the T2 etc. I guess its just a waiting game now for parts. I'll report back after I get em.


yeah, all those valuable resistors I mention a lot are subjected to a lot of heat which is why a) they fail and b) the solder pads usually disintegrate. if you lose the right ones in the circuit there, you'll have what you're experiencing. in other instances it'll put you in a fuse blowing nightmare; I'm guessing this is caused by the concentration of power that has nowhere to go, so it gets stuck on the diode bridge side and pops the fuse.

R101 could be at fault, so you're stuck until that arrives. there's a goofy little transistor at Q10, and the transformer at T2. I don't really know how to test T2 except swap with a known good one maybe -- I've personally never found a bad one. lastly, there's IC2, which if I recall is the smaller of the 2 chips. that has some kind of power drive control; I think if you desolder pin 16 on it and go to measure a bad R101, it'll actually reach the full 6.8k ohm reading (from my travels)

lastly, there's C36. if that doesn't work then you won't have horizontal deflection either. I read in a thread earlier you can do a continuity test between the 2 halves and if it shows a short then it's bad. never tried this myself.
 
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From personal experience, if C36 is out of whack it will start blowing fuses. In my K7000 I accidentally got C36 and C38 switched when doing a width cap adjustment and kept blowing the fuse on the chassis. Once I corrected my dumbass mistake, the HV shutdown ceased and the fuse quit blowing.

Since the OP here indicated that no fuse blew, I would believe that C36 is functional and within specs.
 
From personal experience, if C36 is out of whack it will start blowing fuses. In my K7000 I accidentally got C36 and C38 switched when doing a width cap adjustment and kept blowing the fuse on the chassis. Once I corrected my dumbass mistake, the HV shutdown ceased and the fuse quit blowing.

Since the OP here indicated that no fuse blew, I would believe that C36 is functional and within specs.

Yes, when I test C36, it seems fine and fuses are not currently blowing.
 
If you are still in HV shutdown after lifting on end of D10 and not blowing fuse then you have a horizontal deflection problem.

Have you measured the voltage at the metal tab of Q11 (HOT)? Also look for any lifted or broken pads on the legs of Q11. Any break in a trace or lifted pad will put you in shutdown.

I'll bet you will have 0 volts there. If so start looking for a break, lifted pad, or cold solder joint. I just fixed a K4900 that had a pad burnt loose from the trace where the collector lead on the HOT soldered to.

Also have you checked Q10. It is your horizontal drive transistor. If bad that will put you in shutdown also.

Ed
 
Thanks Ed. When I had the monitor powered, I measured the middle leg of the HOT and it was at 160vdc. Is that the same measurement as the metal tab?

I tested Q10 in circuit and it measured good with my Leader transistor checker. I'll pull it and see what I get.


If you are still in HV shutdown after lifting on end of D10 and not blowing fuse then you have a horizontal deflection problem.

Have you measured the voltage at the metal tab of Q11 (HOT)? Also look for any lifted or broken pads on the legs of Q11. Any break in a trace or lifted pad will put you in shutdown.

I'll bet you will have 0 volts there. If so start looking for a break, lifted pad, or cold solder joint. I just fixed a K4900 that had a pad burnt loose from the trace where the collector lead on the HOT soldered to.

Also have you checked Q10. It is your horizontal drive transistor. If bad that will put you in shutdown also.

Ed
 
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I measured 0vdc at the shiny metal tab near the HOT. I measured 153vdc at the center leg of the HOT. Q10 tests good out of circuit.

I replaced R101 and the shutdown pot and no change. Still in shutdown.

I have looked all over for any kind of broken trace or lifted pad. Everything that has been suspect, I've bridged with a trace repair from old capacitor legs.

This is so frustrating.
 
I hear ya. I have a K7000A chassis that I brought back from the dead, but it has horrific horizontal banding around the center of the screen. Haven't really touched that monitor in a while since my K7000 is now fully working.

Keep at it though. Eventually, you'll figure out what the problem is and be excited that you went through the effort to fix it.......... then you'll neck the tube while moving the now functional monitor around. :p
 
I "think"I found it but I can't test it until tomorrow. Stay tuned!
 
Well, this one is fixed. I found another broken pad at C40. Changed the flyback, HOT and VR and she fired up.

In addition to the above, I replaced R89, R101 and VR8 and reflowed most of the chassis.

Picture looks great! Thanks for your help guys.
 
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