Another K7000 blown fuse cap repair help thread

neopolss

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The purpose of this topic is to find out everything I need so that I can order it all at the same time. Here's the story. I have a K7000 19" that upon receiving it had a blown fuse. I replaced the caps, flyback, HOT, IC4, the diodes by the filter cap, and a few various resistors that had some levels of corrosion (was sitting in florida weather for awhile). I did NOT change the crit cap or the big resistor R103 (?) by the pack of 4 diodes on the chassis. I reinstalled the chassis, and to my delight, it fired up! For all of one minute. It had no picture, and when I adjusted the screen brightness to check for raster, the fuse blew moments later. I put another fuse in, and now it blows right away (as it was doing before the repair). One thing comes to mind - the large resistor. After a few minutes of being off, it was still extremely hot while everything else had cooled. I plan to replace it, but since it is now blowing fuses again, what other parts should I be checking again? Will I need to get another HOT and diodes? Thanks for any help.
 
you need to check your parts so there is no guessing.

check your H.O.T VR C36,37,38

filter cap for a short. (note that sometimes if your H.O.T or VR are shorted it will cause the filter cap to show a false reading) take it out to test it.

if the resister measures correct after it cools i would not replace it.

all your diodes D13-24.

check to see if all the caps are in the correct locations and installed the correct way.

check for solder bridges anywhere on thew chassis and any parts that are bent over causing a short.

this is where i would start.

i stock all the parts i talked about and more if you need any of them.

Peace
Buffett
 
I've bought new flybacks that were bad. If you have an old flyback which still works use that one while troubleshooting/repairing so you can rule that out.
 
I got 2.8 across the resistor. Diodes I show shorts on all of them except D17. HOT shows as shorted. Haven't tested the VR but assume it's gonna be bad too. The caps show okay, haven't tested the filter cap yet. Will test it out of circuit later tonight.
 
Here's the readings I got:

D19 .530/.520
D20 .530/.530
D21 .530/.530
D22 .530/.530
D23 .450/NL
D24 .450/NL
D16 .435/.900
D17 .460/NL
D13 .439/.989
D14 .204/NL
D15 .432/.453
C36 0/0 (meter jumps around a little)
C37 .452/.433
C38 .858/0
R103 2.7
HOT 1.3/1.2

Can anyone make sense of some of this? It's seeming like many of the diodes are bad, the resistor at r103 good, HOT is good? When I recapped everything, I put new diodes in at D21-D24 but didn't check the ones at 13, 14 or 15.
 
Here's what happened. You've got some sort of marginally bad part in there, if I was going to guess it's C36 the critical safety cap. You put all the new shit in (except C36) and it worked fine until C36 or whatever's marginal decided to shit the bed. When it did shit the bed, it shorted your HOT. Now since the HOT is bad (and whatever blew the hot is still bad) you're blowing fuses immediately.

There are only a handful of things that will blow the fuse. Bad resistors won't blow the fuse because they open instead of short when they go bad. The end result of that, is it raises your B+ so high that the monitor goes into shutdown.

So, if you have a fuse blowing, it's either in the section before the voltage regulator (which would be the rectifying diodes by the filter cap, or the filter cap shorted (rare). OR, it's in the section just after the voltage regulator... so it would be the voltage regulator itself, the HOT, C36 or the other two or three large mylar caps in that area... D19 which is right by the Yoke connector, or the flyback.

Since you replaced the flyback, the HOT, and the voltage regulator the first go around... you've probably got a bad mylar cap around that area.

You need at least a HOT, I dont know what your reading of 1.2 is but the way you check a HOT is you put one lead on the center leg and one lead on the ground of the chassis (the plate behind it). If you get a low reading (like 1.2!) it's shorted and useless. If it's shorted (like it seems it is) it will blow the fuse every single time you turn it on.

So you need to unsolder that bad HOT, and then check the mylar caps. The one that's parallel to the back heat sink will always test shorted in circuit, you need to remove them and check it out. When you find the bad one, replace it, and replace your HOT, and you should be good (if it didn't blow your voltage regulator as well)
 
after you remove the H.O.T. retest C36. even replace it if you think it could be the problem.

i had one just recently that C36 was half dead and it smoked several H.O.T.'s before it finally went totally bad.

i replaced it and the chassis ran fine for hours on the test bench.

after you get the H.O.T. out retest all the parts to see if a short remains.

to test the H.O.T.
black lead on the center leg of the H.O.T. and red to both outside legs.

The one that's parallel to the back heat sink will always test shorted in circuit, you need to remove them and check it out

this is not entirely true.

on C37 the one that parallels the heat sink if the chassis is working correctly.
you will see the diode drop one way. and the way other it will climb to infinity.
it will read shorted for a split second as your meter passes the zero reading.

Peace
Buffett
 
Good information right there. I will probably need to order some parts for this. Buffet, you have all of tis in stock? Ill put together a list after testing some more
 
I know I need HOT and C36, maybe a few diodes to be safe. What should I be reading for the other caps C38?
 
pull all your parts off the chassis and retest them.

9/10 times when C36 tests shorted in circuit, it is because the H.O.T. is bad.

i have had this happen on the last few repairs. and C36 was just fine after the H.O.T. was removed.

there is no reason to replace a good part.
but if you want it anyway i have them.


Peace
Buffett
 
Ok, so these readings are with the HOT pulled from the chassis

HOT pulled out measures .066/.000 (black lead on center, measuring outer leads)
C38 .857 (continuity reading)
C36 .804
C37 .426
R87 - no reading (very corroded)
D13 .426/ no read
D14 .205 / no read
D15 .426 / no read
D16 .434/.885
D17 .446/ no reading
D19 - D22 .519/ no read
D23 & D24 .447/no read
R103 2.8

Any other readings I should be taking? The only thing I can gather from this is that I need to replace R87 for sure, and I'd feel more comfortable replacing C36 anyway, simply because they do tend to fail.
 
all of those readings look ok.

C36 does not fail much from my experience.

you will need a H.O.T. flyback and cap kit from what i can tell.

i do not have the resister you will have to source that.

if you want parts let me know what you want.

shoot me a PM.

Peace
Buffett
 
Re-install the old flyback

Don't forget what an earlier dude said: "I've had new flybacks that were bad."
I too have had a couple k7000 brand new flybacks that were DOA.. Spent a ton of wasted time re-checking my work and pulling parts to test.. When the whole time it was the new fly that was shit.. Happened to me during a red tent chassis repair (2 of them). Both new flys were bad, reinstalled the old ones and almost crapped myself.. Wasted hours
 
when was this that batch should be almost gone.

i have never seen a bad fly.

i have seen faulty anode wires that needed to be re-crimped and that was why the fly was not working.

if he has done all that and it is still pooping the H.O.T. and the fuse, then he need to check all of his work and look to see if any caps are in backwards.
if they were they need replacing not just re-installed the rite way.

C36 could be half faulty but without the proper meters it is hard to test.

he could replace it and see if his problem goes away.

but if it does not then it is going to be a head scratcher for sure.

Peace
Buffett
 
There was a bad batch a couple years ago, which I bought a few.. Within the last 5 months I've had (2) DOA or blew up within an hour k7000 flybacks. One bought at bob's and another purchased from Arcadeshop via a customer. I prolly still have one of the DOA ones and I'll send it to you Buffet as proof :) heh
Both blew small holes out of the fly.

The two DOA red tent flys were bought from Chad, whom quickly refunded me.
These looked fine, but once installed I got a vertical line in both chassis.

Maybe its just bad luck, or maybe I'm just lucky and win the bad flybacks..


when was this that batch should be almost gone.

i have never seen a bad fly.

i have seen faulty anode wires that needed to be re-crimped and that was why the fly was not working.

if he has done all that and it is still pooping the H.O.T. and the fuse, then he need to check all of his work and look to see if any caps are in backwards.
if they were they need replacing not just re-installed the rite way.

C36 could be half faulty but without the proper meters it is hard to test.

he could replace it and see if his problem goes away.

but if it does not then it is going to be a head scratcher for sure.

Peace
Buffett
 
Please remember that i already recapped the chassis, and installed a new flyback and hot. The chassis then worked for a few minutes before again blowing the fuse and not working. Now it continuos,y just blows fuses. I do have a spare flyback to try, but i saw no sparking or smoke from the one installed.
 
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