K7000 died after cap kit, new flyback, HOT and Regulator replaced

Black Matrix

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K7000 died after cap kit, new flyback, HOT and Regulator replaced

Its been a while since I started this, but I had a K7000 25" monitor that I think was working but dim. So I thought I would rebuild it. Replaced the normal things: flyback, caps, hot and voltage regulator. Upon the repair job, the fuse blew. Replaced it and then the Critical cap looks like it blew out and again the monitor died. So I just got around to pulling the hot(2SD1398) and the Regulator(STR3130). Can someone tell me if they are blown.
1. Hot: middle pin 2 shows continuity with the metal frame. It shows 500 ohms resistance between 1 and 2. It shows 532 ohms between pins 3 and 2.

2. The Regulator: Pin 1 and 4 shows continuity with the metal backing. It shows 2.89 ohm resistance between pins 1 and 2 when the meter is set at 20K. It shows 63.5 ohm resistance between 3 and 4 when the meter is set at 200k. It shows 66.4 ohm between pins 3 and 4 when the meter is set to 200K.

So is my HOT blown. Is my Regulator Blown. And, is it normal for the critical cap to blow after the repairs I have made or is this an indicator of a mistake I might have made.

Lastly, this board has a 1600V critical cap. It also had what I assumed was a cap to expand the width to match the monitor size. But upon inspection. The board was P538 which should be an original 25" monitor pcb. The cap that was soldered onto the bottom of the board was soldered across the connections for the critical cap and was also 1.6KV (1600V). So my question is does anyone have any idea why a second critical cap would be soldered across the original's solder traces. Was this to expand the size or a half assed attempt at some previous repair.

I know something weird is going on with this monitor, but I just don't know what. Any advice would be appreciated.
 
Horizontal output transistor and the voltage regulator must have a mica insulator between them and the metal frame. Plus they need to have a light film of silicone heat sink grease applied to both sides of the insulator.

If you don't have the insulator installed or the existing insulator has a tear or hole in it, the transistor or regulator or both will be immediately destroyed upon power up which will then blow the fuse.
 
I reused the old mica insulators. I washed them and then reapplied with fresh thermal paste. The fuse blew immediately upon power up. And once the fuse was replaced, the critical cap immediately blew. The insulators looked to be in good condition. Its possible they were shorted, but I don't think that was the problem. And I am still wondering why it essentially had two critical caps installed. Do you have a good source for the two sizes of mica insulators that the k7000 uses. Its like 2 different oversized (T0-3 I think) insulators and Bob Roberts doesn't have them. He sends very large bottle cap insulators and your supposed to cut them down. I thought the originals would be better than the new cut down ones.
 
And the regulator was replaced with the EXACT same number as the one originally in it?

Is the critical safety cap shorted?
 
The cap that was soldered onto the bottom of the board was soldered across the connections for the critical cap and was also 1.6KV (1600V). So my question is does anyone have any idea why a second critical cap would be soldered across the original's solder traces. Was this to expand the size or a half assed attempt at some previous repair.
I've never seen the critical cap soldered through the bottom of the board. You should pull the critical cap (C36) and test to see if it's shorted. Replace it if it's bad. You also want to check C37 and C38 .

Also like Ken said make sure the parts you are putting in are the same values and have the same part numbers as the ones you took out.
 
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C36 was one of those 4 pin blue jobs that they used to put on K7000s . I had to cut the leads to get it off, but from the looks of it, the cap doesnt read a short across the cap. But the hole in the side makes me think it definitely blew. As for the cap on the bottom. Its an additional 1.6KV cap that was soldered into the circuit with the original.

I checked the C38 and it did not show continuity so I don't think its shorted. As for C37, it was a jumper wire across the two spots and it looks factory.

The board is pretty battle worn from years of service.

As for the parts being the same, I got these parts from Bob Roberts and their the ones he lists on his website to replace them. Its been so long since I replaced them, I don't have the old ones to compare it with.
 
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I would say at least 50% if not more of the 25" K7000's I get in to repair have a 1.6KV cap soldered to the bottom. Yes, your voltage regulator is shot. Should only have continuity on the last pin (4). I bet your HOT is toast as well. Google how to check a transistor and it will show you how with your DMM. Randy Fromm does a good job of explaining as well.
 
OK Guys,
Heres what I know. After reading up some on testing transistors and testing with the replacements, heres the results.
1. The Regulator is shorted (pins 1 & 4)
2. The HOT is shorted (pins 1 & 3 or B & E)
3. The original C36 retrace cap looks to be open
4. The second 1.6KV cap on the bottom of the board appears to charge up in both directions.

I haven't checked all the caps that I installed yet to see if they are all in correctly. I will do that shortly.

Questions:
1. Is it possible that the bad critical cap was my problem all along.
2. Should I pull the second 1.6KV cap from the bottom and just put 1 new one back in the top or should I install the new one in addition to the one still on the bottom.
3. Can anyone think of anywhere else to check for something that could cause these failures. I once heard something about one of the pots failing and sending the HOT through the roof. Ring any bells.

Also, I finally remember the details of this monitors failure after thinking about it for a while. The game was working up at my cousins house. One day when he powered up, it was just dead. Brought it home & pulled the chassis, and did the compete rebuild(cap, HOT, Regulator, and Flyback). Powered up, and the original fuse popped. Replaced the fuse thinking it had gotten weak from the failure. Powered up again and the original C36 lit up.

I'm about ready to tackle it again and want to make sure my chances of success are good. So any further advice is appreciated. Thanks.
 
A good HOT will read as shorted across the outside legs because they are bridged by a very-low value part and a transformer. Take it out to verify. I believe out it will measure low (like.086 or something) but that's still good....
 
I had already ordered a new hot, and regulator. I had also already pulled them both so the board would be ready when they arrived. As for the HOT being good, I measured it at 20K with the DMM. It messured .05 when the + probe was on the base and the - was on the emitter. I swapped the probes and got the same results. Tested the new one and got 1.83 and 5.57 respectively. I assumed that since the old HOT measured the same both ways that it was shorted.
 
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