K7401 Pulsating

StreetzKing

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Hey guys, I picked up the game from a friend 20 minutes away. He was repair the monitor for me, Rebuilt chassis, new flyback, new HOT and all that stuff. It was on for like 2 hours, worked great had no problems turning it on and off. I brought it home (20 mins away) and it turned on great, then all of a sudden started to pulse. I talked with modessitt for a bit, I just wanted to get some other opinions. (dont mean any offense) I checked all connections. To note, I secured the connection from the flyback to the board and the game worked for like 10 minutes before the pulse came back. The majority of the time the game works for about 2 minutes before the pulse. Any thoughts?

I can get a better video if needed, this was quick.


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ALSO - good 120-122 volts from iso
 
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I'd look for cold solder all over the board but mostly in the power supply section.

Matt
 
I'd look for cold solder all over the board but mostly in the power supply section.

Matt

Yeah, I told him that - with it failing after a minute or two - it was most likely a cold solder joint or a part failing from heat...
 
Isnt there a jumper in the power supply section that has cold solder on it a lot of the time? Or am I think ing about the U5000?

OP - Take a look at the b+ pot in the power supply section too. They get cold solder joints all the time.

Matt
 
also another thing to note, not sure if it matters, That pulse in the video is very dark. Usually the screen stays bright, if I turn the game on and its working, then pulses it will stay the normal screen brightness. If I turn it on and its pulsing then its dark like the video
 
so. I turn it on to get a video of it nice then bad.. I record lke 100 times cause my camera has a 30 second limit. The one second I hit stop to start again it wigs out, when I hit play the screen stops pulsing. (pulsed for 2 seconds). go f**king figure..

Games been on for 12 minutes, no pulse other than that 2 seconds. whats the odds of this fixing it self???
 
been running since the post at 6:10, even turned off and on and been great. just that one 2 second pulse the first time, *nothing since I turned off and on
 
yea. Like I said it usually is fine for like 2 minutes, then it pulse's on top of the video

What it's doing is going into and out of shutdown extremely fast.
I had one doing that to me on location and never did completely narrow it down.
Hadn't really done it since I brought it home and put it in another machine. (maybe just lucky)

http://www.youtube.com/watch?v=Ewba47B62f8
 
Just means the B+ is spiking up and that's what is causing it to go into high voltage shutdown.

The B+ and X-Ray protection pots are notorious for going bad due to the mess of glue they put on them.

Someone had sent me a note one time about trying this, but I hadn't done it on any of mine.
R108 is a .33 ohm 2w resistor change to a .22 ohm 2w

Most likely what is causing will be over near the B+ pot.
There's a Uxxx chip if I recall, a large diode mounted on the heatsink near there, a flakey H.O.T., bunch of other "possibilities around there...... honestly I wish I had taken notes on everything I had tried on one of mine.
 
so the b+ was reading around 350 when its pulsating..

If we lower it via the pot, then it gets like 40volts then starts to fall over and over again, 40 - 0, 40 - 0 etc.

Any thoughts?
 
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