need help with 25k7191 monitor with no blue


Timid Neo Newbie
Oct 17, 2017
Ok.. recently purchased a Neo Geo MVS 1-slot arcade machine not working.. I already pulled the neo geo board and cleaned it up.. removed the leaking battery which appeared to be only leaking on the top of the battery no acid got on the board.. i replaced the missing power supply and it boots up and plays fine.. however.. the screen doesnt look right.. kinda dark.. so i went to the test screen and the blue square is missing.. i tried to adjust the pots for the blue gun and nothing happened.. so after researching i am checking the transistors on the neck board.. this looks to have been an issue before because you can tell someone replaced the 2sc3229 transistor before and also fixed the trace for that same transistor on the circuit board.. i need help knowing how to test the tube before i pull this neck board and try to fix it.. the neck board is marked P448.. there could be another trace broken on the board as the transistor moves and you can see it pulling the trace on both legs from the board.. any help greatly appreciated.. pics to follow... also if i cannot fix this issue with the neck board.. is there a replacement neck board available for a 25k7191 (k7000) or is the P448 or equivalent available..

thanks in advance..


Last edited:


Camel Slug
Feb 3, 2006
yup your blue driver is fried.
this is a really dangerous repair - are you using proper safety measures?

you need to measure the B input before the transistor. If it measures that same voltage or approx as the rest in test mode, then you know its your driver transistor.
sounds like someone did a sloppy repair and it should be resoldered with a new chip.