tg2051
New member
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 <(*)(*)>
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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