K7100, no red anymore. Bump the machine, red comes back (briefly)

scottkeen

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K7100 red tinted background instead of black. Bump flickers normal (briefly)

In my other thread, I mentioned I was having weird color problems after I moved my arcade (it was probably a simple degaussing issue).
http://forums.arcade-museum.com/showthread.php?t=209811

But in my troubleshooting, I tweaked the Cut-Off and Drive color pots and lost my red colors for the entire screen. The crazy thing is, if I bump or bang or jolt the cabinet hard, the red colors appear for a brief moment then they're gone again.

I took the advice and heated up the following contacts with a soldering iron.

IMAG0311a.jpg


I'm very new to arcade repair, and I'm not an electronics guy. We have no arcade repair technicians on this island in Hawaii, so I can't take it somewhere.

The upsetting part is, it was working perfectly in the garage until I laid it down to put wheels on the bottom and then wheeled it to inside the house.

Please help me troubleshoot this. Thanks
 
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Check the video signal from the game to the monitor.

It could be a bad solder joint at the video input connector. It could be the wire at either end of the video signal cable. It could be the transistor on the neck board for the red gun.

Just a few things I've seen.
 
I disconnected the jamma cable edge connector, re-attached it, and my colors came back to normal (but just temporarily). I thought, "Great! I'll move the arcade to the corner of the room where it belongs".

After I moved it, plugged it in, and the reds were gone again. The degauss problem also came back.

Actually, I think the correct analysis is that it seems to be getting flooded with dark red, so that the background is dark red and anything that is red disappears into the background. Not sure how to explain this, because the background isn't exactly a bright red, but it's definitely not black. (It's black-ish with a dark red tint?)

I jiggled the machine a bit, and you could see the screen flicker and every once in a while "lock in" and it will be fine until it's just slightly bumped.

FWIW, whoever mounted this ICade board did a bad job. It was mounted with just 2 screws, and only one screw had a rubber standoff under the board.

This seems very much like a bad connection somewhere. I'll try looking at the connections mentioned above, but assuming I have a bad wiring connection somewhere, I'd like some help to troubleshoot this by process of elimination. Thanks
 
what about the header that the R,G,B,GR and synk plug on to on the monitor chassis. they have cold solder joints as well.

then verify that all the pins are making good contact in the same header.

the on and off pattern you are experiencing when banging on the cab is a cold solder joint or a loose wire.

that is if you re-flowed the pots and the 3 neck board transistors like you said you have in the pic. also hit the 3 big resisters on the neck board they get hot and get cold solder as well.

Peace
Buffett
 
I will do as you say Buffett and report back.

In the meantime, this is what I was saying about how everything has a dark red tint, even the background black is reddish, so that anything that should be red (like the girders in Donkey Kong) just blend into the background. You can still see a faint outline of the girders, but they blend into the dark red background. The background isn't a bright red, it's just a dark red instead of black.

The camera is actually making everything redder than what appears to the eye, but the effect is the same.

I'll still hit all the solder connections you've mentioned, but maybe you or someone has an idea what component, what wire, or what circuit where there would be a loose connection would produce this effect as seen in the picture. It would really help with narrowing down where I need to double-check my repairs.

IMAG0313.jpg
 
Going by the pic of the neck board, the solder pads look fine. I'd look at the connections from the logic board.....maybe even reseating the socketted chips on the board. If the jamma connection is an issue, you can clean up the edge of the board using a pencil eraser to gently clean the silver connections under the jamma connector.
 
it also appears you are missing green.

yes verify all the connectors are making good contact. and the headers get re-flowed.

and check for solder bridges. looks like a transistor is possibly on full blast all the time. that will kill a transistor and the gun if left UN-fixed.

then center all the pots again on the neck board and see what you get.

Peace
Buffett
 
If the jamma connection is an issue, you can clean up the edge of the board using a pencil eraser to gently clean the silver connections under the jamma connector.

Yep, did this on the jamma already.

I'm still suspect of the neck board. The reason is, this red coloration problem only came about when I started messing with the pots on the neck board. I didn't move anything, I didn't bump the arcade. But the moment I started turning the pots on the neck board, I got this red coloration problem.

I'd like to try wiggling the neck board while the arcade is turned on, just to see if it's some connector or cold solder on the neck board, and either narrow down or eliminate the neck board as the cause of this problem. But, before I do that, is it dangerous to mess with the neck board with the CRT on?
 
it also appears you are missing green.

yes verify all the connectors are making good contact. and the headers get re-flowed.

and check for solder bridges. looks like a transistor is possibly on full blast all the time. that will kill a transistor and the gun if left UN-fixed.

then center all the pots again on the neck board and see what you get.

Peace
Buffett

Is it green that I'm having the problem with, not red?

If a transistor is on full blast or there's some solder bridge, can you narrow it down which transistor on the neck board or the chassis board?
 
possibly both.

you may also have a broke pot. those pots can break rather easy.
inspect them to make sure. wiggle them ever so slightly to see if they are broke or the pad has been damaged

make sure nothing is bridged with solder and no traces are broke on the neck board.

after you have looked at all theses things. you could get more adventurous and swap the transistors to see if the problem moves to a different color.

Peace
Buffett
 
you may also have a broke pot. those pots can break rather easy.
inspect them to make sure. wiggle them ever so slightly to see if they are broke or the pad has been damaged

I also suspect a broken pot, since I'm reading that this is common and that this problem started when I started turning pots on the neck board.

Got 2 questions.

1) Can I wiggle the pots on the neck board with the power on, is that dangerous?

2) I have a 25K7193 monitor in another arcade, but the monitor doesn't turn on. Can I just swap out the neck board from that monitor (no guarantee it works either)? It's a different model number, K7193, whereas this one I'm working is a K7197.

3) Do you know where can I just order a complete neck board for the K7197?

Thanks
 
you can just don't get carried away.

yes the neck boards are interchangeable go for it.

but you will need to fix both to have 2 working monitors eventually for both cabs.

no need to order a new neck board. both of thoes can be fixed way cheaper. than buying a new one.

Peace
Buffett
 
This literally fell off when I pulled the neck board off the back of the neck tube to reflow the solder of the 3 big transistors.

Could this broken piece of plastic be the cause of the intermittent color problem?

Is it dangerous to use the monitor with this piece broken? It fits inside the hole on the neck board just fine and slips onto the neck tube. All that plastic around there is very brittle.

I fired up the arcade and it came up great, colors were all correct. A few seconds later, it went back to the dark red tinted background instead of black. I banged the side of the cabinet a few times and it went back to normal for a second or two, then went back to the red tinted background problem.

I reflowed the solder of the 3 big transistors on the neck tube, still the same problem.

I have to still reflow the solder of the chassis board input header.

IMAG0321.jpg
 
Well, it's premature I know, but I think I've got it fixed!!!

I reflowed the solder connections under the R/G/B input connector on the chassis board, and reflowed a couple other solder connections which looked sketchy.

Works great now!

I even wheeled the arcade around while it was on, and there was no screen flicker or color shifts (I was wheeling it around to test a degaussing problem with my Bose ceiling-mounted speakers theory -- yes, I can say with a high degree of certainty (but not 100%), the Bose Acoustimass 4" cube speakers create a tremendous amount of magnetic field, even 5' away, enough to cause a degaussing problem and wash out the colors on your CRT).

So I think it's good -- time will tell for sure. But thanks everyone, thanks esp to Buffett for sticking with me on this and pushing me to reflow solder connections on the chassis board.
 
Well, it's premature I know, but I think I've got it fixed!!!

I reflowed the solder connections under the R/G/B input connector on the chassis board, and reflowed a couple other solder connections which looked sketchy.

Works great now!


Excellent! Nice work!

So gald it was that simple.
 
your degaussing issue is probably not due to some speakers that are located 5 feet away....this is common with games being turned from north to east to south and the reason is the earths polarity.
 
your degaussing issue is probably not due to some speakers that are located 5 feet away....this is common with games being turned from north to east to south and the reason is the earths polarity.

Interesting!

OK, so it seems to be fine when facing north (screen pointing north), but when it's facing west (screen pointing west), then I get the problem.

So, will a degaussing coil, or time, fix this?
 
Well, it's premature I know, but I think I've got it fixed!!!

I reflowed the solder connections under the R/G/B input connector on the chassis board, and reflowed a couple other solder connections which looked sketchy.

Works great now!

I even wheeled the arcade around while it was on, and there was no screen flicker or color shifts (I was wheeling it around to test a degaussing problem with my Bose ceiling-mounted speakers theory -- yes, I can say with a high degree of certainty (but not 100%), the Bose Acoustimass 4" cube speakers create a tremendous amount of magnetic field, even 5' away, enough to cause a degaussing problem and wash out the colors on your CRT).

So I think it's good -- time will tell for sure. But thanks everyone, thanks esp to Buffett for sticking with me on this and pushing me to reflow solder connections on the chassis board.

i was wondering how long youd mess around before you bit the bullet and reflowed the header pins
 
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