WG K7501 horizontal hold / sync issue

tg2051

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Anyone have a suggestion on what to look for when a K7500 chassis displays signs of horizontal hold / sync issues but only when the video signal is applied at the same time as power is applied to the monitor, but the monitor works perfectly any time power to monitor is applied AFTER the video signal is applied to said monitor? If I turn the game pcb (GT) on and allow the monitor to be powered on at the same time I get a scrambled image... however, if I turn the game PCB on first, then apply power to the monitor after the game signal is running, the monitor displays perfectly, every time.

This issue happens consistently... I can get the image/monitor to display fine as long as I wait to apply power to the monitor after the game pcb has power applied to it first. The delay does not need to be long, a few seconds is all it takes.

If power is applied to both the game pcb and the monitor at the same time and I leave it running for extended length of time, the scrambled image does NOT go away (but if I unplug the monitor and plug it right back in, a perfect image appears.... it matters not how long I let it run scrambled, once I bump power to monitor the image appears fine). I believe this rules out any issues caused by heat stressed components... I also believe this would indicate no cold solder joints since it will 100% consistently fire up with a clear stable image as long as power to monitor is applied a second or two (or minutes, hours, days) after a video signal is reaching said monitor.

I tried putting in an isolation transformer... did nothing, same exact behavior.

Other information... monitor was recapped, but not 100% of the caps... I think all but 2-3 were replaced.

I checked for cold solder joints and re-flowed the flyback joints.

I also replaced the LM1203N video processor on the neckboard... still does the exact same thing.

I guess I could install a temp. switch on the cab to bump the power to the monitor just after I turn the cab's on/off switch on, but that would be ghetto deluxe.
Any suggestions would be helpful and appreciated <(*)(*)>
 
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You gave no mention of trying to adjust the Vertical or Horizontal Holds a bit. (or adjusting anything else for that matter)
Sounds like things are just a hair off which could cause the sync issues. Most likely horizontal.
 
Kevin, thanks but your suggestion falls short...

Of course I tried adjusting... and since it works 100% of the time (if power is applied after signal) that would indicate it is not a simple adjustment of the pots.
 
So if you adjust the Horizontal Hold one way until it rolls or goes out of sunc, then adjust it the opposite direction until it does the same, then find the happy middle...... it still does the same thing on power up?

How is your sync wire connected ?

PS - I was referring to the adjustments on the main chassis itself, NOT the remote board. (just to clarify)
 
there should be no H-Hold on the remote board. the K7500 has it on the deflection board. at least on my 7500s that pot is empty on the remotes.

are you sure you're not running a standard resolution game on this as well?

like an idiot, I had a Blitz 2000 boardset that I kept as a test board (for the monitor patterns/colors, for white balancing in particular) and I had it running in standard res and I hooked it up to another Blitz cab with a 7500 and started tinkering with the H-Hold pot without thinking it was running the wrong resolution to boot. :)

medium res on a standard res monitor yields a triple image, standard res on a medium res monitor... I don't know.
 
Guys, I think your missing one key point... the game/monitor runs perfectly when power is applied to the monitor after the PCB signal is already reaching the monitor... so OF COURSE I know I am running the correct resolution (i.e. medium res... GT 2005! FORE!), otherwise it would NEVER work.

I will try the horizontal hold pot on the deflection board, that may be a reasonable suggestion, but it seems if the horizontal hold pot was not quite where it needs to be that I would be getting a scrambled screen at least 1 in 100 tries when I apply power after the game signal has been applied... again, applying power to the monitor chassis after the game signal has already been applied results in a 100% everything works perfect state, every time.
 
Check TP202 for proper B+ when the sync is off (130vdc). If it appears to be off a bit, do your power trick and then check it again. If the B+ is off a bit, it can cause weird hold issues...
 
If you haven't resolved this issue yet, I looked at a game (med-res) with either a K7500 or U5000 in it that has a similar issue. When the game is turned on, the monitor gets power but no neck glow or image. Unplug the power connector for a few seconds and reconnect it and the picture comes up just fine. But after about 10 minutes the picture starts flickering to black again.

I'm pretty sure the problem is related to caps or cold solder. I'll be fixing it in the next week or two if you still need a resolution...
 
Anyone have a suggestion on what to look for when a K7500 chassis displays signs of horizontal hold / sync issues but only when the video signal is applied at the same time as power is applied to the monitor, but the monitor works perfectly any time power to monitor is applied AFTER the video signal is applied to said monitor? If I turn the game pcb (GT) on and allow the monitor to be powered on at the same time I get a scrambled image... however, if I turn the game PCB on first, then apply power to the monitor after the game signal is running, the monitor displays perfectly, every time.

This issue happens consistently... I can get the image/monitor to display fine as long as I wait to apply power to the monitor after the game pcb has power applied to it first. The delay does not need to be long, a few seconds is all it takes.

If power is applied to both the game pcb and the monitor at the same time and I leave it running for extended length of time, the scrambled image does NOT go away (but if I unplug the monitor and plug it right back in, a perfect image appears.... it matters not how long I let it run scrambled, once I bump power to monitor the image appears fine). I believe this rules out any issues caused by heat stressed components... I also believe this would indicate no cold solder joints since it will 100% consistently fire up with a clear stable image as long as power to monitor is applied a second or two (or minutes, hours, days) after a video signal is reaching said monitor.

I tried putting in an isolation transformer... did nothing, same exact behavior.

Other information... monitor was recapped, but not 100% of the caps... I think all but 2-3 were replaced.

I checked for cold solder joints and re-flowed the flyback joints.

I also replaced the LM1203N video processor on the neckboard... still does the exact same thing.

I guess I could install a temp. switch on the cab to bump the power to the monitor just after I turn the cab's on/off switch on, but that would be ghetto deluxe.
Any suggestions would be helpful and appreciated <(*)(*)>
Did you ever find out what is wrong with your chassis? I have the same problem with my WG-7550 chassis as well and I'm trying to find the repair.
 
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