Bad K7000 revisited

R3LL1K

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So I have a chassis that has given me problems for almost half a year. When I first checked it out it had a blown fuse so I replaced it and it blew again. They flyback was bad so I bought Bob's deluxe kit and replaced the flyback, HOT, caps and even the voltage regulator since I had a spare. I also replaced diodes D19-D22 and C36. Popped a new fuse in and powered up the chassis and the monitor powered on for 1-2 seconds before the fuse blew.

Anyone know what I might be missing? I put the diodes in the correct way and checked all of my caps to make sure they were in the right position and they were. I got this chassis non-working in a cab I bought. I have a few other chassis to repair but would like to get this one going since I've already invested so much time in it. Any suggestions or ideas on what to check or where the problem might lie?
 
Welcome to the world of why K7000's are apparently despised. I have a paperboy med res K7000 that has defeated me. I can't even stand to look at it now.
 
You might want to take out the known good components and get rid of the chassis. I think I will be doing this shortly. At least it will keep me from putting more good parts into it. I'll focus on the 2 chassis I have that actually fire up with issues. I have 4 chassis and I need to get 3 of them going for monitors I have.

I might end up just throwing the whole lot on ebay and buying some Wei Ya chassis. :(
 
A bad D18 can cause this issue. This diode is also known to develope cold solder joints (which, can cause this issue).

Edward
 
And don't forget the C36 safety capacitor might be shorted.

Remember there are four different B+ regulators for this chassis and to replace like number for like number. Two have different pinouts than the others.

You need mica insulators & silicone heat sink grease behind the horizontal output transistor and the B+ regulator lest you short them to ground.
 
So far I've replaced everything except for the D-18 diode. I'll be picking one up at lunch and testing everything again including the C36 cap before I fire it up. I hope I can finally be done with this. If it doesn't work then this will be a nice parts donor as just about everything on it has been replaced. -__-
 
what're the mica insulators? the thin sheets of plastic-y stuff in the HOT and heat sink sandwich?
Yes. Everytime you replace a HOT or voltage regulator you should clean them off and apply new silicone compound. If the silicone is old and dry it won't conduct the heat very well to the aluminum "heatsink" and it will shorten the life of your transistor if it doesn't fry it out altogether.

c36 is my bet....

also every once in awhile i find one with a shorted (usually visible) fried vertical output ic...
Would a bad Vert IC cause the fuse to blow and the HOT to go out? Can these be tested without the monitor being on? I have only thought to test these if the image is bad. Which I obviously haven't gotten to with this chassis.

Update: I checked the D18 and it's fine. I replaced it anyway. The HOT was also blown so I replaced it again (sigh). I'm running out of new HOTs I had seven of them and now I'm down to my last 3. :(

C36 was just replaced and I tested it yesterday and there wasn't a short. I haven't tried the chassis again since I replaced D18. Here's a checklist of what I've tested and is known to be good.

D18=good
D19-D22=good
HOT= Good
Voltage regulator=good
C36=good
Flyback=good

There is an extra small board is bolted to the chassis that has a wire going to the middle leg of the HOT. I think the problem might be with one of the resistors or caps in that small "undocumented upgrade". I'll check those out this evening but if I don't find the problem there I'll probably abandon this chassis and start stripping off all of the new parts I just put in it for other chassis. This chassis has taken more of my time than any other chassis and I could have probably fixed the other three that do power up and don't blow fuses but have minor synch and vertical collapse issues.
 
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So is this medium res or standard res? I thought that little add-on board you mentioned is a medium res thing.


His add on board is a factory modification of the circuit board. It usually only has a cap, a couple of resistors, and a diode. The med res board is configured differently with an adjustment pot among the parts included.
 
D18 is a high speed diode and needs to be the EXACT type.
It is the exact same type. I also took readings from the one I pulled and the new one I put in and got the same values for each so the one I pulled was working. I don't want to try the chassis out again for exactly this reason since I don't believe D18 was the problem unfortunately.

I was hoping that D18 was the problem and I almost thought it was since when I first tried it out on the board it gave me a different reading than the other one but that was only due to the HOT being blown. :(

When I tested it using diode test I got a reading of 500+ with the positive test lead on the stripe side when I reversed the leads I got an overload or "infinte" reading. When testing it on the board with the Blown HOT I got a 500+ reading both ways. After replacing the HOT I got a reading along the same lines as the working one with 500+ on one side and overload or infinite on the other.
 
The board is labeled an "Auto Protect PC Board" and seems to be tied into the sync circuit. It (the whole board) looks to be a voltage limiter on the sync circuit.

BTW - this is NOT just a "medium-res thing". All the 25" versions of the 4900 (K5500's) have that board. And it is hooked up on both standard and medium red versions, for those who think it's not hooked up for the standard-res version.

I have a K5501 (standard-res) and it has it and it's hooked up. In fact, i looked at the 5501 and a 4901 and the only differences is that board and the parts attached near it on the left wall. Apparently that is all that is needed to boost it to a 25"....
 
BTW - this is NOT just a "medium-res thing". All the 25" versions of the 4900 (K5500's) have that board. And it is hooked up on both standard and medium red versions, for those who think it's not hooked up for the standard-res version.

I have a K5501 (standard-res) and it has it and it's hooked up. In fact, i looked at the 5501 and a 4901 and the only differences is that board and the parts attached near it on the left wall. Apparently that is all that is needed to boost it to a 25"....


Do you have a manual for the K5501? Maybe it is the adjustment of the pot on this subboard that alters the chassis to med res...
 
No, that's not it, either. The medium-res and standard-res versions use a different IC chip. I think the flyback is different, too.

And no, I haven't found a K5501 manual, but like I said, except for that little board, it's exactly like the K4901 - IC, flyback, etc. Only the 5501 uses an STR381 VR and the 4901 uses an STR380. HOT's are the same though.

There IS a K5515 manual online:

http://arcarc.xmission.com/PDF_Monitors/WG K5515_Manual.pdf

It has that board in the schematics, and seems to be tied into the horizontal drive and sync amplification circuits, but it's not listed in the documentation about adjustable controls...
 
So I have a chassis that has given me problems for almost half a year. When I first checked it out it had a blown fuse so I replaced it and it blew again. They flyback was bad so I bought Bob's deluxe kit and replaced the flyback, HOT, caps and even the voltage regulator since I had a spare. I also replaced diodes D19-D22 and C36. Popped a new fuse in and powered up the chassis and the monitor powered on for 1-2 seconds before the fuse blew.

Anyone know what I might be missing? I put the diodes in the correct way and checked all of my caps to make sure they were in the right position and they were. I got this chassis non-working in a cab I bought. I have a few other chassis to repair but would like to get this one going since I've already invested so much time in it. Any suggestions or ideas on what to check or where the problem might lie?


Check c38 .39uF@200v and c37 .15uF (and parallel diode D15 for shorts.
 
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