Kortek KT-2914 top foldover

[lilshawn]

got a Kortek KT-2914F, the top was folded over about an inch to an inch and a half. The image was a little dark despite the brightness turned up to 100. Pulled the machine back to the shop for some work.

power it up and display a crosshatch pattern on the screen. horizontal looks good but the vertical size is sort of jittering a bit while it warms up. okay no big deal.

go searching for a schematic in the manual folder can't find one. in the 10 minutes it took me to search through the folder the screen has squashed down to about 6 inches, top still folded over. image is in the bottom 1/2 of the monitor. TDA8172 vertical oscillator IC chip is hot hot hot. Great.

grabbed a schematic off of one of the other threads here (http://forum.arcadecontrols.com/index.php?action=dlattach;topic=112506.0;attach=168301) and pulled the chassis.

So, now I'm in the process of replacing some of the caps in the vertical section. we will see if the TDA8172 is still good after.

[grantspain]

common problem with these chassis
there are a few caps and a couple of resistors around that tda chip that need checking,most i change the tda anyway

access the extended menu to get better brightness,contrast etc

[lilshawn]

well i got it back running again.

replaced c201 c203 c204 c205 c206

checked all the resistors in the 200 section and q201... still good.

decided to just go ahead and replace IC201. no sense chancing having it break again for the sake of a $5 part.

funny thing, q201 had a weird silicone tube over the chip, then was clamped to the heat sink... okay. uhh, the tab on the TDA8172 is connected to ground... Why do we even need isolation? besides, the heat sink is isolated too, so even if the tab was energized, it wouldn't matter anyways. so i rip off the old one and use some good heat sink grease on the new chip and screw it down. that TDA should run plenty cooler now without that stupid silicone tube deal on there.

[grantspain]

have you ever come across one these chassis when the switching fet's catch fire-pretty common problem
never got one going after that happened-most of the pcb around those fet's burns out completely

anyway if you ever get stuck with one of these that you can't repair due to the above issue you can install a rodotron 666a chassis-it will run raw thrills stuff like fnf and bbh

[MonMotha]

You mean the main SMPS FET (which IIRC also has an integrated control circuit)?  I've not seen that happen...  Are you running these off 120V or 240V?  IIRC they're marked universal input, but I somehow doubt they really got much testing at 240V.  Even the Andamiro PIU cabs that run everything internally at 240 seem to run the monitor straight off the (120V) AC input on the US builds.

[grantspain]

You mean the main SMPS FET (which IIRC also has an integrated control circuit)?  I've not seen that happen...  Are you running these off 120V or 240V?  IIRC they're marked universal input, but I somehow doubt they really got much testing at 240V.  Even the Andamiro PIU cabs that run everything internally at 240 seem to run the monitor straight off the (120V) AC input on the US builds.

nah,the frequency switching fet's for each resolution-they actually catch fire
these are running on 230vac u.k voltage btw

[MonMotha]

Oh yeah, I've had lots of problems with those, though I've never had them catch fire.  I usually just see them fail open and take out lots of other stuff because they're not engaging the right correction caps.  I agree, these seem to be the most common failure on these things.

Have you seen this on the "F", "DF", or both?

Glad there's a suitable replacement chassis, btw.  I'll remember that if one dies on me in a way I can't get fixed.

[grantspain]

only seen it on the "f" chassis as that seems to be the only version imported into the u.k-they were in early fast and furious