Help with troubleshooting a monitor problem

twistedsymphony

Well-known member

Donor 2013
Joined
Feb 7, 2013
Messages
2,023
Reaction score
79
I have a Double Dragon machine I think it has a K7000 monitor but I'm not very good with identification so here are some pics:

double_dragon_01

double_dragon_02

double_dragon_03

double_dragon_04


The picture on this monitor is perfect, it's bright crisp, has great colors....

the problem is after an hour to hour and a half the screen goes completely blank. If I turn it off and leave it off for a few minutes it will work again when I turn it back on.... so I'm assuming that something is overheating...

I decided the other day I was going to try to watch and catch it in the act, unfortunately I had to step out of the room and missed it :( but I did notice that at one point during that hour the screen rolled vertically once and at another point the screen collapsed into a single vertical bar for a split second and then fixed itself.... I'm not sure if these two one time occurrence/split-second oddities are related to the monitor shutting off.

So anyone have any ideas as to what could be causing this problem?
 
Yup, you've got a K7000 with what looks to be factory caps or old caps. Could also be cold solder but it wouldn't hurt to cap the board while you have it out.
 
yup guaranteed you will need new caps and a fly and a good re-flow.
that chassis is old and needs a tune up.

and it is a K7000.

if you need any parts let me know or if you need it repaired i can do it for you.

Peace
Buffett
 
Thanks for the quick replies, I'll be ordering up a cap kit and new flyback and see how it goes. :cool:
 
Most likely you have a solder joint failing on one of the larger resistors, (2w or 3w).

Although you do need a cap kit and new fly, they may not fix your problem. Reflowing the larger resistors on the other hand should fix your problem.
 
Most likely you have a solder joint failing on one of the larger resistors, (2w or 3w).

Although you do need a cap kit and new fly, they may not fix your problem. Reflowing the larger resistors on the other hand should fix your problem.

that actually makes sense. as the other components generally reach temperature rather quickly a larger resistor will take a while to heat up.

I've got a whole rebuild kit coming for this monitor later this week (caps, flyback, and a few other parts), I figure if I'm going to go through the hassle of pulling it out I might as well take care of everything.
 
So over the weekend I finally had some time to pull the chassis and do some work.

I had bought a rebuild kit from Bob Robers (included caps, flyback, HOT and a new fuse).

Pulled the chassis installed all the new stuff and I re-flowed all of the big resistor points as well as a few other spots that looked like they could use some work.

When I went to pull the fuse out of the holder one of the prongs that holds the fuse broke off.

Also the kit included two 470uF 16V caps but my chassis had 470uF 35V caps installed in those spots... since I had to order a new fuse holder I bought two new 470uF 35V caps to install here just to be on the safe side.

-----------------

The flyback, hot and caps all installed without incident. I re-installed the board and powered up the cab... I saw the PCB get power for 2-3 seconds then one of main fuses in the cab blew... the monitor never made any noise or light. Around the back of the cab I could smell a slight scent of burning electrons from the monitor :(

I double checked all of the plugs everything was hooked up correctly, the flyback was wired in correctly, nothing on the bottom of the chassis was grounding out anywhere.

My Initial inspection didn't reveal any burn marks or apparent damage... that chassis fuse didn't even blow. So aside from just giving it a closer inspection is there anything I should be looking for in particular? I wont be able to test again until I find an pickup some new fuses for the chassis.
 
There are other caps on that board that internally short. They are the big fat redish-orange/blue/green caps behind the flyback. You can test them in circuit using your ohms meter but it might be best to pull them out (one at a time) and test them. they should read into the millions of ohns of they are good. If any of them are shorted then most likely your new HOT is also bad.

Also, did you put the mica insulator behind the new HOT? If not that needs to be corrected. The tab on the HOT should not be shorted to the chassis.
 
Disconnect the monitor completely, (both power and video) replace the cab fuse, and power the game up. Does the game play and stay on playing blind?
 
This capacitor may have shorted:

http://homearcade.org/BBBB/csc.html

If you replaced the horizontal output transistor, did you remember to reinstall the mica insulator between the transistor and metal frame? Also, this transistor needs silicone heat sink grease applied to it and the insulator.

There is a possibility that your B+ voltage regulator could be shorted.
 
Last edited:
There are other caps on that board that internally short. They are the big fat redish-orange/blue/green caps behind the flyback. You can test them in circuit using your ohms meter but it might be best to pull them out (one at a time) and test them. they should read into the millions of ohns of they are good. If any of them are shorted then most likely your new HOT is also bad.

Also, did you put the mica insulator behind the new HOT? If not that needs to be corrected. The tab on the HOT should not be shorted to the chassis.
yup I installed the new HOT with fresh silicone and the mica insulator

I'll check out those caps, thanks

Disconnect the monitor completely, (both power and video) replace the cab fuse, and power the game up. Does the game play and stay on playing blind?

everything worked (monitor included) before I removed the chassis, I actually played it an hour before the chassis was pulled. I suppose I can check again to see if it plays blind.


This capacitor may have shorted:

http://homearcade.org/BBBB/csc.html

If you replaced the horizontal output transistor, did you remember to reinstall the mica insulator between the transistor and metal frame? Also, this transistor needs silicone heat sink grease applied to it and the insulator.

There is a possibility that your B+ voltage regulator could be shorted.

yup I installed the new HOT with fresh silicone and the mica insulator

I'll check out that cap and the B+ regulator, thanks.
 
Last edited:
People never seem to realize that when you replace all of the 30 year old electrolytic caps, you have just created a new weak point in the system. It is for this reason GO7's will blow the flyback if you only do a cap kit. K7000's are no different, they like to blow the critical safety cap, reg, and / or HOT.
 
People never seem to realize that when you replace all of the 30 year old electrolytic caps, you have just created a new weak point in the system. It is for this reason GO7's will blow the flyback if you only do a cap kit. K7000's are no different, they like to blow the critical safety cap, reg, and / or HOT.

I thought I'd be safe replacing the flyback and HOT at the same time as the cap kit.. :-/
 
big red cap behind flyback read several M ohms for a split second and then registered as no connection
big blue cap behind flyback (I believe this is the critical safety cap) reads 244ohms (in circuit)... testing it out of circuit I get no connection.

I pulled the HOT and checked it against the old HOT, it tested similarly.. no conection between the center pin and either of the side pins.

I'm not sure which chip is the voltage regulator or how to test it... that seem the next best place to check since, unless I'm misinterpreting things, everything else check out ok so far.
 
With the flyback closest to you on your left, the reg is in the back left corner and is labelled STR31XXX
Dok

Thanks, is there any way to test it or do you just replace it and hope for the best?

So despite the fact the HOT and the two caps behind it tested well I was figuring I'd replace those as well as the voltage regulator... just to be on the safe side. Is there anything else I should be testing and or replacing?

------
One other question that has bothered me. what keeps the bolt holding these chips against the heat sync from shorting out where it passes through? obviously the nut makes a solid connection against the heat sync but if the screw is pushed slightly to one side it has the chance to short on the back of the chip... why wouldn't they just use nylon hardware to be safe?
 
Last edited:
here is a video that i made on how to test the VR.
you can do it in circuit or out of circuit.

if you get a short in circuit remove it and re-test it out of circuit.



Peace
Buffett
 
here is a video that i made on how to test the VR.
you can do it in circuit or out of circuit.

if you get a short in circuit remove it and re-test it out of circuit.



Peace
Buffett

thank you for that... my voltage regulator tested good, and I retested the hot again following the video and it tests good too, though I don't get continuity when touching the two outer pins together, I don't know if that's normal or not.
 
i have not seen a chassis that does not have continuity between the legs.
but there are so many revisions of the K7000 that it may be possible.

check over your work for any solder splashes or bridges.

check all the caps for proper orientation and value.

are you still blowing fuses.

if you are not blowing fuses.
just for a test pull one leg of D10 and see if the chassis works.

Peace
Buffett
 
Back
Top Bottom