Monitor convergence problem? help!

PsHayes

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I don't have much knowledge about these arcade monitors. I just got a 2nd cab this last weekend, a Gauntlet Legends. It has a 27" monitor in it. The tube says Zenith, but the chassis has a sticker saying it must be replaced only by WG K7500.

When I power on the game the bootup red text is all blurred and unreadable. If I go into the test menu and look at the monitor tests here is what I see:

The color bar test seems to look ok to me but the shape is pincushioned. Is that normal:

http://img23.imageshack.us/img23/2486/img3595r.jpg

The white convergence test shows violet squares shifted when the game manual says everything should be even squares:

http://img196.imageshack.us/img196/7272/img3585q.jpg

The violet convergence test shows blurry image in all 4 corners, worst in the bottom two:

http://img190.imageshack.us/img190/5527/img3587e.jpg

I was told the convergence on this monitor is on the stem with 3 plastic tabs. They are glued and probably were from factory. There are some voltage warning labels in that area. I haven't messed with it yet.

I was told the monitor is medium resolution only. I was hoping it would support standard as well.

Is there anything I can do to fix these image issues? They do affect gameplay because some of the messages as you pick things up are blurred on the bottom of the screen or offset making them difficult to read.

I can link more pictures too if you think that would help. The focus was adjusted as I picked up the cab so I could read the test menu text. Maybe this made the game image worse?
 
try the cap kit , but I have a 4900 doing the same thing, bad tube. swapped a G07 chassis in (known working perfectly ) convergence issue as well. tried to converge, tried restetting the deflection angle and distance in case I buggered up putting the yoke on , no avail , same crap. I can get the convergence to move but by all accounts they line up when I put them back

edit, tried a couple different sets of rings as well , no change, swapped the G07 back to its tube, perfect picture
 
After reading the links it does sound like that could explain the poor image in the corners. Where on the monitor/chassis is this pincushion board? How difficult is it to replace? Any idea on cost?
 
You should roll through all the caps first (aforementioned Cap Kit) to level the playing field, freshen up the chassis, and to eliminate what is, basically, "consumable" parts.

There is a fair chance, like very fair, that once all the old, well worn, caps are replaced your problems will go away since the various circuits will be back in designed specs.

A kit is like 5-10 bucks for most common monitors. If you can solder then labor is just your time.

Most of us will shotgun all the caps right out of the gate rule to them out when we trouble shoot a monitor. If problems still exist then its a deeper dive in.
 
Here's the excert from the K7500 manual. I've attached the picture of the circuit.

There are quite a few caps in that circuit. Not sure if any get replaced with a normal cap kit or not. But if you have a bad cap, and you aren't getting correct voltage, or any voltage to the pin cushion circiut that would be a problem.

If a cap kit doesn't help you will need to check those transistors in the pin cushion circuit.

It's also possible, that someone jacked with VR770 and it may just need adjusting.

I've never worked on a 7500, so I'm only going on what the manual states.

The pin cushion circuit receives the output from vertical transistor Q602 at pin 8 of the pin cushion board. this is ac coupled to the base of amplifier q770. In addition, the output of the vertical correction network is connected through pin 7 to the TRAP variable resistor VR771. The buffer output is applied through PIN variable resistor VR770 to a capacitance voltage divider consisting of C772 and C773. The parabolic correction voltage developed across C773 is applied out through pin 3 to the base of transistor Q709, then coupled wto the horizontal sweep circuit by transistor q710. The correction signal causes the horizontal yoke sweep speed to be varied depending on the position of the verticle sweep. Adjusting VR770 determines the amount of correction and is set for the most linear display.
 

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Recap it first, then connect the picture tube to a rejuvenator to test it. I think your red gun is weak.

Don't even touch the convergence rings. They are not the cause of the problem. The yoke is probably ok so don't touch that either.
 
I just took out the bad monitor today and dropped in a used Nanao MS9-29SU 27" monitor that I was able to get from a local tech. It looks so much better. I need to degauss part of the screen and do a horizontal adjustment yet on screen position but the colors and sharpness are way better than the wg 27". Is Nanao a good monitor?
 
You probably would have been better off doing a cap kit on the original monitor.
 
You probably would have been better off doing a cap kit on the original monitor.

eh, I have the same situation with one of my Polos. gonna grab a U5000 to replace it until I get around to tinkering with it.

my belief is that you can never have too many monitors. :)
 
I just took out the bad monitor today and dropped in a used Nanao MS9-29SU 27" monitor that I was able to get from a local tech. It looks so much better. I need to degauss part of the screen and do a horizontal adjustment yet on screen position but the colors and sharpness are way better than the wg 27". Is Nanao a good monitor?

Let's see some similar convergence pictures on your new monitor. I want to compare it to mine. :)
 
Let me degauss it first then I'll put up some pics so you can see the improvement. My only knock is a bit of screen burn where I can see SEGA on certain backgrounds in the monitor tests. I have not been able to see this with the game on though.
 
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