WG K7193 (Zenith version) with No Red picture. Worth repairing?

[Naukuga]

So, as the title says ive got a K7193 with no red displaying on the monitor. The problem im having is trying to figure out if the problem is with the tube its self, or if its a Chasis/Neckboard problem (Cracked solder joint, bad drive transistor)

A few months back i purchased a Marvel Vs Capcom cab from my local arcade. I was converting it to a MAME cab but having some weird issues with the picture on the monitor. It turns out that the JAMMA harness it was using wasnt wired entirely correctly. The Video Ground wasn't actually run back to the PCB, it was run to one of the grounds coming from the PSU. The result was a clear picture with the MvC board and PSU plugged in, and some sync issues with just the Jamma Harness.

Basically i was unknowingly running the monitor with no video ground.

While trying to figure out what was wrong, a friend of mine decided the pots on the neck board must be able to fix it. (zZzzzz). He was turning pots on the back of the neckboard and i was trying to adjust the resoultion (via quickres) when both the green and the red went out on the monitor. After unplugging and replugging it in the green came back, but the red was still gone.

Is it possible that running the monitor with no ground (for very short periods of time, <5 minutes each time) would have caused the tube to burn out in some way? or is this strictly a case of something being knocked loose on the neck board that just needs to be resoldered?

If its a tube problem, can i swap out my 25" Zenith tube for another brand? Where would i find a tube?

If its a board problem its likely to be solder joints? drive transistors? Loose wire connections?

Is it just easier to fork out the 400$ and buy one of the new Makvision monitors from happ?


edit:

Also, there is some guy offering Chasis/neckbaord repair for 75$ on ebay. Scam or worthwhile?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=250770682752&ssPageName=STRK:MEWAX:IT

[mrk8814]

Most likely the color amp or pots/solder joints just reflow the solder

If not measure ohm across the green drive pot, if ok then check voltage @ green drive transistor collector and compare with the red and blue collector voltages

Finally, if you feel comfortable sending your chassis to me just pm...I will fix it for the same price (parts not included unless I already have it as a spare)

[Naukuga]

Most likely the color amp or pots/solder joints just reflow the solder

If not measure ohm across the green drive pot, if ok then check voltage @ green drive transistor collector and compare with the red and blue collector voltages

Finally, if you feel comfortable sending your chassis to me just pm...I will fix it for the same price (parts not included unless I already have it as a spare)

So you dont think its the tube?

What exactly is the color amp?

[mrk8814]

No, I dont suspect the tube

The color amp is Q201 (red), check voltage (around 130v) @ the collector vs Q201 & Q203 collector voltages

*remember to check value of VR202*

And just for the hell of it reflow all neck board solder joints!

[Naukuga]

No, I dont suspect the tube

The color amp is Q201 (red), check voltage (around 130v) @ the collector vs Q201 & Q203 collector voltages

*remember to check value of VR202*

And just for the hell of it reflow all neck board solder joints!

What tools does one need to check the voltage? Are there any vids of this i can look at?

I assume this needs to be done while the monitor is on, is that dangerous?

[mrk8814]

tools preferred are plastic screwdrivers and a multimeter, but you can get away with a small metal screwdriver if you are VERY careful

and Yes, the monitor must be on to test the voltages and it can be very dangerous if you dont know what you are doing

There are videos on youtube im sure

But im still leaning towards the solder joints because you said your friend was tinkering with the pots on the neckboard and probably knocked the solder completely loose

If you are uncertain of checking voltages and yes it can be dangerous, then I personally suggest leaving it to someone who knows what they are doing

[Naukuga]

Ill check the solder joints for any obvious cracks when i pull the board.

I think ill hold of on voltage testing.


Ill post an update when im done

Thanks for the info.

[Naukuga]

So here's what i found.....

When i pulled the Neck board a small piece of plastic fell into my hands. Its appears to be some sort of plastic cover for the glass end of the tube. Is this critical? it was cracked and there is no way to re attach it, am i going to damage my tube if it runs without this?

Second, I couldnt find anything wrong with the neck board. No bad solder joints, no obviously blown transistors/caps/pots. So i checked the main board. It appears there is a scorch mark where the red yolk wire attaches to the main board. My assumption is that because the monitor wasnt properly grounded that it eventually built up enough of a charge to arc to the frame. Looking at the frame beneath the board you can see a small scorch mark. The bottom of the board where the red yolk wire attaches is also schorched. It looks like the arc melted most of the solder that was here. Im 100% sure its not making a connection anymore.

If i were to add the solder that melted away back would this fix my problem? is the board just completely broken at this point? what are my options?

Any input would be greatly appreciated.

[Naukuga]

So here's what i found.....

When i pulled the Neck board a small piece of plastic fell into my hands. Its appears to be some sort of plastic cover for the glass end of the tube. Is this critical? it was cracked and there is no way to re attach it, am i going to damage my tube if it runs without this?

Second, I couldnt find anything wrong with the neck board. No bad solder joints, no obviously blown transistors/caps/pots. So i checked the main board. It appears there is a scorch mark where the red yolk wire attaches to the main board. My assumption is that because the monitor wasnt properly grounded that it eventually built up enough of a charge to arc to the frame. Looking at the frame beneath the board you can see a small scorch mark. The bottom of the board where the red yolk wire attaches is also schorched. It looks like the arc melted most of the solder that was here. Im 100% sure its not making a connection anymore.

If i were to add the solder that melted away back would this fix my problem? is the board just completely broken at this point? what are my options?

Any input would be greatly appreciated.

[qrz]

the plastic is the neck guide . helps position the neck board

the diode NEEDS to be resoldered . 1st, scrape off the carbon . u may need to scrape the pins for solder to adhere

the no red condition will either be a drive problem somewhere from game to crt , or a bad red cathode ( tube)

the actual cause to be determined by testing - if the green and blue are working , compare readings . the circuitry is identical

pm if u wish a step by step 

[Naukuga]

the plastic is the neck guide . helps position the neck board

the diode NEEDS to be resoldered . 1st, scrape off the carbon . u may need to scrape the pins for solder to adhere

the no red condition will either be a drive problem somewhere from game to crt , or a bad red cathode ( tube)

the actual cause to be determined by testing - if the green and blue are working , compare readings . the circuitry is identical

pm if u wish a step by step 

Are you saying that the scorched diode isnt the cause of the no red?