KT 2725 Help needed

[CRTonFire]

First post !

I have a monitor I'm trying to get working and have had no luck in finding any information about it. I guess that could mean it's either 'usually' rock solid reliable and doesn't need repairs, or it's a piece of junk and no one in their right minds uses them.

I'm completely new to the arcade scene so if something I say sounds wrong, it likely is. Here is a pic of the chassis



IDENTIFICATION
There is only a small ID and serial number on the solder side of the chassis PCB and neck board PCB. I couldn't see anything that wasn't a plug or component name on the silk screened top side of the board.


Typing 'KT 2725' into google brings up a couple of related hits for people asking for cap kits, but some say they have a 'Kortek KT 2725' while others say they have a 'Sharp Image KT 2725'. Is there a difference between these? or are they both speaking of the same unit?

ISSUES/OBSERVATIONS
1. When I got the arcade machine this monitor was installed in, the game did display on the monitor. The image was a bit green and had small white lines running horizontally the whole way up the screen. Each line was about 25mm above the one below it.
2. For what ever reason, I decided turning the 'X-RAY' pot would yield results. It did. The monitor went dark. I returned the pot to where it was but the monitor stayed dark.
3. I started the monitor up twice after it went dark, both times the screen would show some light but shut off immediately. Each time it shut off, a reasonably loud pop could be heard.
4. After the shutdown and pop, the neck of the tube still looked to be glowing.
5. After deciding to do some homework before 'fixing' anything else, I discharged the tube and removed the chassis and neck board for inspection.
6. There is a damaged component which from what I've read may be the H WIDTH adjustment coil. I think it is supposed to have a ferrite core which looks to be missing and there is a fair amount of heat damage. Next to this part is a blown small electrolytic cap.


7. Some of the poly caps show signs of heat stress


8. There is a cable that runs from the chassis to the neck board with three pins, I can only make out 'HB' before the connector plug covers the writing. One of the wires from this plug has been cut on the neck board and a separate voltage fed in to the neck board via a small transformer mounted off board. The PCB trace has been cut and a small capacitor added as part of this modification.


9. The 'B+ADJ' pot has a glob of silicon stopping any adjustment from being made.
10. The picture tube model is GA63ADG25X
REQUESTS
1. Can anyone provide a link to a service manual for this monitor?
2. Does anyone know why adjusting the xray pot had the effect it did?
3. Is there anyone who knows this chassis or similar that could help me get it running again?

I can solder and have no problem in replacing damaged components

[grantspain]

i think you have a sharp image version of a kortek ktm chassis
fundamental mistake to touch the x-ray protection pot as badly adjusted will put the chassis into shutdown

your original issues could have been resolved by adjusting the screen volts pot on the flyback(below the focus) and adjustment of the green cut off pot on the neck card-or green gain pot on the main chassis

i do not think the horizontal coil is damaged,it looks like a fixed value coil

you should not touch the b+ pot unless you are using a multimeter to set it correctly and know the correct level to set it

the cut wire is for the tube heaters,someone must have modified this chassis to run on that particular tube

the chassis looks to be a high impedance type chassis as the vertical deflection appears to controllers by two transistors,you can read the vertical winding of the deflection yoke to prove this-30 to 50 ohms is high impedance

[CRTonFire]

That is great information, thanks grantspain!

fundamental mistake to touch the x-ray protection pot as badly adjusted will put the chassis into shutdown

So.. my list of things to do comes down to adjusting the xray pot and replacing the blown cap next the H coil.

The XRAY pot
Not knowing what this even does exactly, what are my options here?

Find someone with the same chassis and ask nicely if they could measure the voltage on the pot and replicate that? or do they vary wildly from chassis to chassis?

Is there a good procedure to run through if the setting is unknown?

Is it the chassis going into HV shutdown the cause of the pop?

The capacitor
This one is easy and the board looks like it has had a cap kit done previously (you can see the rosin flux around the joints that have been hand soldered) so this cap may have been put in backwards and failed right away as they don't usually pop that badly...

your original issues could have been resolved by adjusting the screen volts pot on the flyback(below the focus) and adjustment of the green cut off pot on the neck card-or green gain pot on the main chassis

Yes the screen voltage pot is what I was actually looking for but didn't find until I took the chassis out, it wasn't visable/accessable where it was mounted in the cab. It is good to hear that it may be a minor thing to fix it if I can get the thing to stop shutting down.

i do not think the horizontal coil is damaged,it looks like a fixed value coil

Well this is good news then!

you should not touch the b+ pot unless you are using a multimeter to set it correctly and know the correct level to set it

In light of my earlier exploits, great advice!

the cut wire is for the tube heaters,someone must have modified this chassis to run on that particular tube

That's interesting, are the heaters the things that make the neck glow?

the chassis looks to be a high impedance type chassis as the vertical deflection appears to controllers by two transistors,you can read the vertical winding of the deflection yoke to prove this-30 to 50 ohms is high impedance

In keeping with the 'check first' approach, how do I identify the vertical winding? does this have an impact on the xray setting? or just a curiosity?

[grantspain]

a few kortek chassis were marked incorrectly for polarity of caps,if unsure then use a non polarised cap

once you have checked bad solder joints and replaced that cap then turn the x-ray pot a 1/8th turn each time and try to power on,you should leave it off for at least 30 secs before trying to repower each time

yes tube heater is the orange glow you can see in the neck

to read vertical deflection winding just set you meter to ohms and read the yellow and green wires of the deflection yoke,horizontal will be blue and red wires

[CRTonFire]

So, I changed the capacitor out for a non polarised electrolytic 4.7uF, checked for broken tracks and dry looking or cracked joints and re assembled the monitor. I followed your advice regarding the x-ray pot and managed to get the display to fire up!

So now that the problem I created is close to being fixed, it's time to look at the original issues with the displayed image.

THIN WHITE HORIZONTAL LINES



This was flagged as the screen voltage being too high in one of your earlier posts. I adjusted the screen volts on the flyback transformer and the lines do fade, however just as it appears that the lines have faded to the point they will disappear, the display shuts off and I need to dial the voltage back up a bit and restart to get an image to display again. The lines are faint when an adjustment has been made, but they are still visable when darker images are being shown. The photos tend to make it look worse than it is but it at least shows a picture of what I'm talking about.

SCREEN SIZE



The screen over all seems too large in the horizontal. None of the horizontal adjustments on the remote board would allow me to bring the screen size in enough to stop it cutting off the edges. In the vertical, it seems possible to get it right with some fine adjustment although it is very touchy.


SCREEN INSTABILITY (see above picture)

This thing has it all doesn't it? No matter the adjustments I made, I couldn't eliminate a 'wobbling' (for want of a better term) on the left and right quarters of the screen. The above picture shows the regions of the distortion but only shows distortion on the RHS of the character select boxes. I may need to grab a video to better illustrate what is happening.

I adjusted the image to as good as I can get it, but if I then switch off the cabinet and restart, the display briefly lights up then shuts off giving this pattern. If I shut the machine off and adjust the H-HOLD pot a little (1/8th turn), then re apply power, it works again but of course now the image is not in a stable state.

COLOUR ISSUE



As mentioned in the first post, there is some discolouration on the screen which I've included a picture of above. It seems the left hand side (as viewed by a player) is the most affected. I checked locations of magnets but didn't see anything on the left of the screen (the speakers for the machine are located at the top of the screen). I did try adjusting the RGB pots on the board (gain) and the neck (bias) but did not find it reduced the discolouration. Does the screen require degaussing? I tried the degaussing button on the isolation transformer and while I assume this is functioning (the screen gets a little distorted when the button is pressed), again it does not improve the discolouration.

[grantspain]

screen discolouration is degauss not working,you may need a manual degauss

screen wobble is most likley unstable power supply,normally it is caused by a regulator or capacitor fault-other things that cause wobble are proximity to electromagnetic fields,for example transformers and light ballasts.A faulty degauss ptc component will also cause wobble

horizontal size issue could be down to capacitor as well but i think there is also a width jumper on that chassis that may pull the picture in

those white lines are because the brightness/screen volts is too high-use the colour control pots to improve the picture

[CRTonFire]

Hmm, might have to look into a degaussing coil. I was pressing the degaussing button and the releasing it fairly quickly, is this how it's intended to be used or are you meant to hold it down for a time?

When you say an unstable power supply, are you referring to the section of the monitor chassis with the rectifier diodes and big filter cap? I'm fairly sure there isn't any wiring or magnetic devices running beside the display. The ballast and starter for the marquee fluoro is mounted on the floor of the cab. The only thing that comes to mind is the external transformer added for the tube heater. This transformer shares a mounting bolt with the monitor chassis so I will insulate the two from each other and see if it makes a difference.

As far as the faulty degauss PTC component you mentioned, what is this? (push to close switch? positive temperature coefficient poly fuse?) and would popping the fuse (F601 as pictured in the overall photo in the first post) out disable this part of the circuit and confirm/rule this out (assuming the 'D-COIL' notation on the board refers to the degaussing coil)?

Could you give me some more information on where the h width jumper may be? Is it something that should be on the chassis PCB or is it related to the remote board?

Thanks again for your continued advice!

[grantspain]

strange it has a manual degauss but you hold on the switch until the screen clears-a quick press will actually make a screen worse

the horizontal width jumper is a red wire terminating in a grey connector-the chassis connection points are marked N and W(narrow and wide)
i have marked them

[CRTonFire]

Aha! I was wondering what that pin labelled 'N' was for, I'll give it a go. I'll also try using the degaussing coil correctly this time.

Also simply out of curiosity, why does this board appear to have two deflection yoke connectors (labelled 'A' and 'B') ? Is this for low and high impedance monitors? most chassis I see just have the one.

[ed12]

reverse and normal

>Also simply out of curiosity, why does this board appear to have two deflection yoke connectors (labelled 'A' and 'B') ? Is this for low and high impedance monitors? most chassis I see just have the one.<

ed

[epicfatigue]

reverse and normal

>Also simply out of curiosity, why does this board appear to have two deflection yoke connectors (labelled 'A' and 'B') ? Is this for low and high impedance monitors? most chassis I see just have the one.<

ed

Sorry to bring back an old thread but ill do it for two reasons,

Hey Ed , Thats for if you want to flip the image without snapping the conector in half, most monitors in australia i see have this.

Also to the poster, if you are still having issues and need part information let me know, i just repaired one of these and have it fully working so PM me if you need something should have it here for another week. 

[jcapone]

Did anyone ever find the manual for this screen? I just picked a dual cab Crusin USA and this was the screen in it.. Currently it doesn't light up at all.

[epicfatigue]

check r610 if its open

[jcapone]

Where is r610? I am trying to find it above..

[epicfatigue]

big one in with the flyback

[jcapone]

Ok, so I got the monitor to start up. I bought new fuses and that seemed to do the job.
I do think there is an issue with some of the wiring.

1) First Picture has a wire coming from the "Yoke" of the monitor. I would assume this goes to the monitor board, but don't see where this would go.. Anyone have an idea?

2) The wire with a circle comes from the power supply.. Where does this attach to? I am assuming that it isn't a ground.

3) The chassis it self wasn't bolted down. Do you have to have spacers like a computer motherboard between this and the monitor frame? Also, all the metal you can see right here is electrified. I was shocked  :angry:a couple times trying to figure this one out.

Any help would be greatly appreciated.

[jcapone]

Additional pictures.. Wouldn't let me post all in one respond.