Author Topic: Wells Gardner Wg k7500 no color (Read 6365 times)

Low80elco · « **on:** February 23, 2016, 01:02:19 am »

First off thank you to this forum! Because of the great write ups and follow up of the members I have learned to do things I never thought possible (solder a pcb namely). I can't express enough what this forum has taught me in my years of lurking.

Onto the issue. I have what I was hoping was an R811 issue on a Wg 7500. Bright monitor with no colors. R811 was open however after a replacement still no change. I have not checked the value of the resistor yet to see if it burned up, but I didn't smell anything or see smoke on power up. Color pots can be cranked to fill the screen with r, g and b. Brightness works. Just no color or contrast.

If it matters it's a 25" golden tee.

Any ideas of what to check next?

lilshawn · « **Reply #1 on:** February 23, 2016, 10:25:53 am »

could be a bad amp maybe? I'm not really sure what you mean by "no colors".

either you have some form of video image or you don't so i'm not sure what you are meaning.

maybe post a picture?

Low80elco · « **Reply #2 on:** February 23, 2016, 10:32:09 am »

Oh man I'm sorry. It does have video. Just no color to it. Almost black and white. I can play the game and see everything on the monitor. Just no color and the contrast adjustment does nothing.

ed12 · « **Reply #3 on:** February 23, 2016, 10:36:54 am »

the golden tee's
have a wonderful little self test program in them
open coin door
find test or service button
press once
follow screen prompt's
(in this case monitor color test)
go to through trackball up or down
press select..if no color suppect video card of the game

ed

Low80elco · « **Reply #4 on:** February 23, 2016, 10:40:30 am »

I should have elaborated further. I have pulled the board and video card and tested in a working machine. It had all colors.

Thanks for the replies so far! I really appreciate you guys taking the time to help me track this down.

Low80elco · « **Reply #5 on:** February 23, 2016, 10:44:26 am »

I bought this one broken. It was resetting and the screen was blue. Reset was a cranked 5v. I'm not sure if the blue was a product of the previous owner attempting an adjustment or if it happened due to whatever is going on with it.

lilshawn · « **Reply #6 on:** February 23, 2016, 10:46:03 am »

R811 is part of the B+ and also feeds into the ABL circuit. if it's gone open excess voltage may have been pushed into the ABL circuit.

check
R613
C805
C803
D807
D811
Q800
R837

as for what's blown out the resistor in the first place...not really sure.

maybe
Q803
Q803

Low80elco · « **Reply #7 on:** February 23, 2016, 10:49:49 am »

Thank you!! I will start checking each of these components

Low80elco · « **Reply #8 on:** February 23, 2016, 11:16:38 am »

Here is what it's doing. Screen pots can adjust screen color to fill with color, but nothing changes for the game.

lilshawn · « **Reply #9 on:** February 23, 2016, 11:30:57 am »

wierd. never seen anything like that. first for everything i guess

i suspect a diode problem. they can fail shorted closed instead of having their voltage.

most should be about 0.5 volts (no power on) when measured with the diode test function of a multimeter. some of the glass type diodes (reddish color) are around 0.6 or higher. you may have to lift one side of the diode out of circuit to properly test them. other components in the circuit attached to the diode can throw off the test.

basically it shouldn't read 0.0 or OL which is shorted and open respectively.

ed12 · « **Reply #10 on:** February 23, 2016, 11:32:51 am »

ya scratching to
abl autmoatic brightness limter
not corma ?

ed

ed12 · « **Reply #11 on:** February 23, 2016, 12:14:17 pm »

if u had 1 ?
i would think swapping the neck board

ed

Low80elco · « **Reply #12 on:** February 23, 2016, 07:11:09 pm »

I don't have one, but I'd be happy to try that before I start replacing a bunch of components!

ed12 · « **Reply #13 on:** February 23, 2016, 09:10:05 pm »

a scope would go along way here also

ed

Low80elco · « **Reply #14 on:** February 24, 2016, 12:54:52 am »

Before I start spending money on replacements I thought I would post a few pics of my boards just to see if anything looks out of whack to you guys. I did see some spots that are getting hot. Wasn't sure if that's normal or not. Thanks for the help thus far!

Low80elco · « **Reply #15 on:** February 24, 2016, 12:59:37 am »

Pic 2

Low80elco · « **Reply #16 on:** February 24, 2016, 01:10:50 am »

What do you think about u500? In the trouble shooting guide from WG it shows that as the only issue in common that could affect all 3 colors.

Low80elco · « **Reply #17 on:** February 24, 2016, 02:37:43 am »

Just to clarify u500 is the lm1203n chip

lilshawn · « **Reply #18 on:** February 24, 2016, 08:19:49 am »

It's highly unlikely but I certainly wouldn't rule it out.

Something is shorted that made that initial resistor blow out and go open. You need to find that component first. I still think something in the ABL circuit is faulty.

Low80elco · « **Reply #19 on:** February 24, 2016, 10:17:39 am »

I pulled one leg of the resistor out and checked it after having it back in the game. It was reading within spec.

Low80elco · « **Reply #20 on:** February 26, 2016, 10:31:57 pm »

U500 was not the problem. Still stumped

ed12 · « **Reply #21 on:** February 27, 2016, 12:22:52 am »

then i would look closer into the abl
as shawn did point out........
a simple 4148 diode will pull it down enough
it >the abl< is a clamp circuit right....

ed

Low80elco · « **Reply #22 on:** February 28, 2016, 03:32:18 pm »

Good to know. I will start testing components in this circuit. Thanks for the help so far!

Low80elco · « **Reply #23 on:** February 28, 2016, 03:55:15 pm »

Reading the manual sure helped me understand the all circuit. Hoping one of the diodes I'm looking at on my iPad are bad when I get back home!

Low80elco · « **Reply #24 on:** February 28, 2016, 09:32:13 pm »

Diodes were good. Problem persists.

ed12 · « **Reply #25 on:** February 28, 2016, 10:36:24 pm »

ok
what happens when u turn the contrast control up or down ?

ed

Low80elco · « **Reply #26 on:** February 29, 2016, 12:43:15 pm »

Nothing

Low80elco · « **Reply #27 on:** February 29, 2016, 12:45:12 pm »

I did pull r811 and it was down to 62k. Replaced and retested after a few power ups. Sitting in spec at 74.5. Is there something that could cause it to slowly go open?

ed12 · « **Reply #28 on:** February 29, 2016, 12:52:48 pm »

z804 leaking (under-load)
q803 leaking (under-load)
or some thing down stream of r811
etc

ed

Low80elco · « **Reply #29 on:** February 29, 2016, 11:13:33 pm »

Still very new to this so sorry for the basic question. When I hook z804 to the multimeter on the diode function it reads .117 regardless of orientation of the leads. Does this mean it's bad?

ed12 · « **Reply #30 on:** February 29, 2016, 11:39:54 pm »

with out knowing the zener specs
i would say yes,and replace it anyway
and btw so far your doing just fine

ed

Low80elco · « **Reply #31 on:** February 29, 2016, 11:42:19 pm »

Thanks Ed! Looks like an eBay wait. Not seeing anything local.

Low80elco · « **Reply #32 on:** February 29, 2016, 11:52:57 pm »

Here is the data sheet. Last part number in the picture 39B

ed12 · « **Reply #33 on:** March 01, 2016, 12:08:42 am »

9v 1w zener
or 1/2w
ya better wait if u do not have anything local ?
and strong words of advice get more then 1 of them until u work out the down stream problem....
this week some time i will be doing wg's for ---steaming pile of meadow muffin---'s and giggle's
i could start with a 26"

ed

Low80elco · « **Reply #34 on:** March 01, 2016, 12:56:45 am »

Yeah it's 1/2 watt. I just ordered 10.

grantspain · « **Reply #35 on:** March 01, 2016, 01:24:12 am »

you should desolder one leg of the diode and then read

Low80elco · « **Reply #36 on:** March 01, 2016, 11:43:42 am »

I did and that was the reading I got.

Bimmy · « **Reply #37 on:** March 19, 2016, 09:36:21 pm »

I just finished a cap kit and this is exactly the same problem I have. Black & White monitor. Everything else looks great. Before I did the cap kit, Contrast needed to be MAX to get color. If turned down at all, it would go B&W. Now max contrast doesn't help. So it tells me that something was failing before the kit, and the new caps did it in.

I did NOT change C734 or C811 because they weren't included in the kit (I have a 7502).

But just to make sure -- would mixing up the yoke wires cause the problem? I didn't note the orientation before I pulled the chassis. Currently the yoke wires are oriented as follows, if looking at the chassis from the back of the cabinet:

B
R GY

Electronic Federation · « **Reply #38 on:** March 24, 2016, 11:21:10 pm »

The issue your having is the color driver transistors on the neckboard. you can see where they get super hot. pull them and replace them. Check for DC voltage on the collectors, or the base? and compare that to the other 2.

These are the most likely culprits, very common.


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