Wells Gardner K4713 -- No grays or browns -- cap kit or ??

[hexcavator]

Hi all,

First post here, so I'll try to keep it short. Thanks so much for this incredible resource! Will preface the below by saying I'm relatively handy and repaired mobile electronics professionally for a couple of years, but am very new to high-voltage / mains current stuff, so very cautious approaching this project.

I recently curb-shopped a bootleg Puck-Man (that's what it says on the PCB) cocktail cabinet. Many of the components, including the WG K4713 monitor, appear to be from a Defender machine. The game board has some bad RAM (I think), so I've set it aside and decided to do a Raspberry Pi MAME setup for now. If at all possible, I want to keep using the monitor.

I've done a load of reading on this forum and others, and managed to do some preliminary use-case tests. I recreated the wiring that was in the cabinet on my work table, built a GERT VGA 666 adapter kit for the the Rpi (it's a model 3 B+), spent hours messing with the hdmi_timings, and got a picture that more or less fills the screen. Whites are nice and bright, the picture seems fairly stable, etc. I had to flip the image in software because the monitor's yoke cables are inverted (possibly because it was vertically oriented in the cabinet?) and I don't want to go prodding the internals just yet.

The biggest problem so far is, from what I can tell, I'm getting red, green, and blue in the 64-odd gradations the GERT 666 offers, but anywhere there should be grey or brown some other dark/neutral tone, I only see black. For instance, here's my Gauntlet II title screen:



And here's how it SHOULD look:



The high score screen also suggests I'm getting at least some amount of each primary color.



I tried the obvious fixes: hooking up my adapter to VGA LCD monitor to ensure I didn't do a bad job building the kit. I even bought another pre-built GERT board just to be sure. Both give the same result (normal color spectrum on the LCD, no greys on the WG). Today I breadboarded a VGA signal amplifier per these instructions: http://members.optusnet.com.au/eviltim/vga2arc/vga2arc.htm. It helped stabilize the image a bit, but had no effect on the color issue.

My completely unprofessional sense from reading the FAQ is that a cap kit may be my next recourse, but I haven't been able to find any threads addressing my specific issue (no greys vs. missing R, G, or B), so I thought I'd post here before tackling the whole CRT discharge/disassembly bit. Other things I haven't tried are adjusting the black pot -- the manual for my model says it's "factory pre-adjusted" and shouldn't need tweaking, and all the warnings around here about ruining convergence by tweaking pots on the board have stayed my grubby little fingers.

Anyhow, deeply grateful for any advice/redirection/cautionary critique y'all can offer.

Thanks much,

bryan
 

[buttersoft]

...from what I can tell, I'm getting red, green, and blue in the 64-odd gradations the GERT 666 offers...

You don't seem to be getting any low tones at all though, right? The top of the green gauntlet logo looks black to me. This could be a cutoff issue. To calibrate, use the brightness control on the chassis first. Then if no dice, unless the chassis is ancient or weird, the flyback will have two pots on it. One is focus, the other is called screen. Remember that you're doing this live, so be careful. Start by turning the screen pot up until you can see the image starting to turn grey - get close to an area on the screen that's meant to be black, and watch for the slightest sign of the phosphors lighting up, and stop there. Any the colours any better at that point? You can turn down the contrast if things smear at all. Your chassis may not have a single control for contrast. On an arcade chassis brightness for each colour is called bias or background of bkg, and contrast is gain or drive or drv.

EDIT: the above really does feel too simple, and i presume you've already tried it, but you did say you were new to the game

After that, the chassis might not be able to compensate for the signal level, maybe. I'm reluctant to recommend a cap kit because i know nothing about that chassis and what might be causing unbalanced levels.

Oh, and you can flip the yoke cable if you need to. You often find them broken in half for this reason, each half can normally be flipped. Just don't mix the horizontal and vertical coils and you'll be fine.

[hexcavator]

Hey,

Thanks so much for the reply. No suggestion is too simple given my newness to the game, and I haven't yet touched any of the adjustment pots. Will have a go at what you suggested this weekend and report back. I'd love if all I had to do here was tweak some knobs (leaving aside the whole deadly high voltages component).

My cursory memory is that my flyback only has one pot for focus, but I could easily be misremembering. Anyhow, will confirm soon.

Really appreciate the guidance!

b

[buttersoft]

There will be a screen adjustment. If the flyback only has one pot, that will be focus, and the screen pot might be on the neckboard. After that i'll admit i'm not really sure where it might be. This will have about 600V DC across it, so be careful!

[Az]

I had the same exact problem on the same monitor happen to me last week. Mine came in an extremely crappy cabinet that had been outfitted with a Konami Ajax PCB. Whoever wired it up knew just enough to be dangerous; no isolation transformer, AC wire to the monitor looked like they'd lopped the ends off a lamp cord, 1p and 2p controls wired together since it was an alternating 2p game and the control panel just had enough holes drilled for 1p.

When I first got it the monitor did power on but displayed a overtly bright picture with nothing but whites and light blues. I jerked it out, replaced it with a cheap VGA monitor, and the original monitor sat on a shelf for a year or two until finally got around to fiddling with it last week. All three RGB pots on the neckboard had completely rotted off. I replaced them and ended up with the exact same problem you have now. Strange, since prior to replacing them the picture was way too bright, now it's way too dark. After coming across this thread I got it back out to make sure I didn't look over something as simple as a black level or contrast pot. Although it's in poor shape mine still has all the original warning & instruction stickers on it, including the label where all the adjustment knobs are located.

Now here's where the fun part starts. There's a pot sandwiched on the side of the PCB that the RGB harness connects to that is not labeled. I assumed that must be it, so I cranked it up about 4/5ths of the way and turned it on. Instantly I got a super bright black screen with a green tinge (since I had the green level pot maxed out). After that, a loud crack and a puff of black smoke from inbetween the two PCB's where that pot is. I flipped the power off, checked my connections, and since the house hadn't burnt down yet powered it back on. The screen again was super bright, too bright, and due to where it's located there's no way at all to adjust the pot with the power on.

Turned it off, adjusted it, powered on, and then... nothing. I had blown a fuse in the cab. Replaced that and also found I had burnt up my J-Pac, complete with exploded traces coming off the RGB pins and burnt resistors.

In no way am I saying this would happen to you because there was obviously some issues going on with my particular setup. I'd say that's probably the pot you need to adjust, but just be careful in doing so, and unlike most monitors do not attempt to adjust it with the power on. If it's compatible I may in the future just end up getting a generic replacement chassis since this tube isn't too bad for a 40 year old set. It's got some burn in from the Ajax logo and from the cities in Missle Command, but I've got other monitors I use that are in a lot worse shape.

[hexcavator]

Happy to report that, per buttersoft's instructions, I have resolved (or at least made serious headway toward resolving!) the issue. Made sure to work extra carefully around the powered tube. I have some burly plastic pliers (rated for 1000v) that made live tweaking much easier.

Turns out the drive control (which is, as suspected, on the neck board on this model) was turned way down. I slowly increased it until my blacks started to glow slightly, then backed it off a bit. This brightened the image considerably AND revealed some really weird color balance issues -- not enough red, way too much blue. I've been messing with the RGB drive/bias adjustments in tiny increments since, trying to eke out a good image with the minimum amount of knob cranking. Weirdly, I can't find a bias pot for B, only R and G, but I'm not missing it too much so far.

Will post a screenshot when I can, but for now I'd say this a huge step in the right direction, and spares me the formidable task of recapping.

Az - Sorry to hear about your nightmare with the pots on your board! I'm really grateful that the mutant/hybrid stuff in my cab doesn't seem to extend beyond high-level part swapping. Whoever took out out the Defender guts didn't get down to the level of "repairing" the PCBs. Though I did discover a pretty hilarious inline sync-splitter IC taped up in the PUCK-MAN harness.

Many thanks again for all the advice!

[buttersoft]

Turns out the drive control (which is, as suspected, on the neck board on this model) was turned way down. I slowly increased it until my blacks started to glow slightly, then backed it off a bit.

FYI I think what you've turned on is called the Screen adjustment. Drive is like contrast, how powerful the bright parts of an image/colour get. Bias or background is the low light for black level. Brightness is the background level for all three colours at once, and the Screen pot is technically it's own adjustment but works as a master brightness control to set things up right.

I'm being pedantic, but most of us doing this are now DIY'ers and i find using the right terms makes everything easier to understand

I'm glad to hear it worked though, or enough to get you started Arcade boards didn't really have set video levels, so most chassis will need tweaking when you change the board.

[hexcavator]

Not pedantic at all; thanks for correcting me. I'm still getting used to the terminology, clearly!

I've got it fairly well internalized that "focus" and "screen" are sort of "master controls" vs. the individual color drive and bias pots. Now just have to get my brain to remember the right words for the adjustments.

My next obstacle is dealing with the damn hdmi_timings on the Rpi. I can see clear, even light across the whole tube when the monitor turns on/off, but I'm getting some jags and weird letterboxing that I'm fairly sure come down to the sync settings I'm sending over the VGA adapter.

Will see what I can come up with, then move onto the arcade controls.

Thanks again!