Main > Monitor/Video Forum
NeoGeo mvs-4-25 (WG K7000 compatible chassis?) w/ color separation, size issue
lilshawn:
yer fallin' apart mate!
loss of vertical deflection. issue with the vertical driver IC or power supply to it.
probably flat one attached to the straight heatsink all by itself. check for broken traces especially if you've grabbed that heatsink to pick it up or move it around...or propped it up on it (especially while doing the capacitor swaps)
Sememmon:
So, a couple questions about this. I've reheated the solder on a few things including the LA7831. With the old solder on this board.. is it better to remove/resolder? Or is just remelting the original solder ok? Also, when I took a look at the LA7831, 3 of the 10 pins are not soldered (2 on one end, 1 on the other). It looks like they're not actually used, but I can't be certain. Should I solder them? Or leave it as is? This isn't something I've touched before and it was working previously so I'm figuring it was intentional... just kinda odd as it looks like the only thing on the board that wasn't soldered.
Thanks for the help btw. I realize this thread got a bit off track from the original post, but I'm really appreciating the support.
Edit: As far as I can tell, the LA7831 looks ok. I don't see any damaged traces. I'm not sure how to test that it is getting the appropriate power...
lilshawn:
it does have a few pins that don't do anything (N/C) Vin is on pin 8. the datasheet is all in japanese, but the best i can muster is it's supposed to be anything 18 to 27 volts.
also check pin 5 and make sure there is something there. this is the voltage input used to drive the vertical deflection. probably going to be like 60 volts or something like that...as long as it's not zero or near zero, it should be okay.
best way to check these voltages is to carefully solder a small wire onto the pin you need to test (or a component pad directly attached to it.) and attach your meter to this wire. that way you can keep your mitts out of the high voltages and safely power it up.
only power it on long enough to get a reading, blasting your tube with a solid line of electrons meant to be spread out over a whole screen is not great for it.
Sememmon:
I attached a wire to pin 5 and pin 8 and got a reading from my multimeter of 28V on both of them.
So... guessing that means power to the IC is ok? But signal from the IC is not? Not sure.
What's next? Replace the IC?
Thanks again for the help! This is proving to be quite the trial for my limited electronics skill.
lilshawn:
if it worked and you farted around with it...and it now no longer works... generally something you've done has broken it. usually it's something snapped like a connection or solder joint is all. something simple. search around... wiggle anything that sticks out and see if something on the solderside is flapping in the breeze.
you seem to have voltage...so that's a good start. maybe the input is not receiving a signal. possibly another chip like the sync separator probably the dip package towards the video input connector...the LC7823. it takes the sync signal and separates the horizontal and vertical and sends them on their way....if the vertical pulse isn't extracted and sent to the driver IC, the 7831 won't drive.