Main > Monitor/Video Forum
WG D9400 Red slowly got brighter, now full brightness despite red gain set to 0
yatzr:
After doing a cap kit and replacing IC801 (LM1269), I had a perfect picture and played a game for several hours with no problems. Then I switched to some other games. During one of those, I noticed a black screen was showing some red. Over the next 2 minutes or so, the red slowly got brighter and even starting showing red retrace lines. I adjusted the red gain down to 0, but the red brightness stayed.
I'm assuming I have a bad transistor in the red circuit on the neck board, but that's really just a guess (and maybe it's the reason my original LM1269's red output was busted). I tried doing a diode test on all of the transistors in the red circuit and compared them to the transistors in the blue and green circuits but didn't any inconsistencies. I'm not sure if testing without removing the transistors invalidates the test or not.
Anyone have experience with this particular problem, or have ideas of other things I could try checking? Thanks!
lilshawn:
most likely bad transistor. it's not uncommon for them to get weird once they heat up.
generally if you replace the video amp IC, you should replace the transistor too as well. it's possible for the transistor to short in a way that dumps high voltage into the IC killing the output.
luckily the transistors used are common and are cheap
yatzr:
--- Quote from: lilshawn on November 30, 2020, 01:04:09 pm ---most likely bad transistor. it's not uncommon for them to get weird once they heat up.
generally if you replace the video amp IC, you should replace the transistor too as well. it's possible for the transistor to short in a way that dumps high voltage into the IC killing the output.
luckily the transistors used are common and are cheap
--- End quote ---
Which transistor is it most likely to be? The Q812 SC2682 is the one with the big heatsink, but the Q811 ph2369 is the little guy connected to the ic output. Or maybe I should just replace both?
Also, where are some good places I should be looking to buy these? I was struggling yesterday cause the shops I normally use either had them as special request or very large minimum orders. I ended up getting the video amp ic off ebay, but there's gotta be a better option than that.
lilshawn:
in this case i'd replace the pre-driver and the driver transistor. might as well.
mouser has good onesies and twosies prices. (of course the more you order the cheaper it is.) shipping is variable depending where you are. if you need a pile of stuff (over 100 bucks) shipping is free... it would be a good time to pick up some soldering stuff or a power supply or microcontroller boards or something to pad out the order.
if you don't need anything else, even if you pay shipping, it's super fast. i get stuff in like 2 days here in canada. it's not going to be a week or anything.
yatzr:
Interesting, mouser was actually one of the first places I looked. Is there a strategy for finding newer equivalent transistors? When I search for SC2682, I only get non-stocked or obsolete results. Similar story with PH2369.