Main > Monitor/Video Forum
k7000 19" screwy color behavior
snappleman:
I got a broken/for parts k7000 chassis to mess around with and got it mostly rebuilt and working except this one issue:
When I got the board I noticed there had been no work done at it at all, it was all untouched. The flyback was cracked and a couple of the pots were broken off. I replaced the pots and fired it up, the red was all over the screen, focus and screen controls on flyback did nothing, brightness and contrast did nothing, red drive/cutoff took the red down some, but picture was still tinted red with retrace lines. I then tested Q201 (red transistor) and it was shorted, so I replaced the flyback, did a cap kit, replaced Q201 and reflowed the entire board.
Now everything works great except the red shows up like that pic, on one side of the screen and with retrace lines in it (no red anywhere else). When I short the Q201 heat sink to the chassis the screen goes full red so that should be fine? Every component on the red line is testing correctly, except R7. R8 and R9 are coming in at 8k rather than 33k as listed in the schematic but they're all the same and properly color coded so I assume they're fine. Tomorrow I'll swap out Q1, even though it tests fine in circuit I want to be thorough, and the drive/cutoff pots are also testing fine (but adjusting them does not affect that red blotch at all), but if swapping out Q1 doesn't fix it, does that mean IC1 could be shot?
I mean something clearly happened to this board for the pots to be broken, and for Q201 to be fried, and I'm not experienced enough to be able to tell if it's a neckboard or mainboard problem, but if everything going to IC1 looks ok, and everything on the way out from IC1 to the CRT socket looks ok, then should I order a replacement IC1 and swap it out? Or can the drive/cutoff pots be faulty even if they test well in circuit?
snappleman:
So today I went in and just shotgunned the entire red signal path, every single component replaced, the transistors, capacitors, resistors, diode and pots since I had everything on hand.
The red blotch is gone, picture looks great, but still no red at all. The screen still goes red when I short the transistor, but otherwise there is no red in the picture. With the pots doing nothing I'm thinking the signal just doesn't get past the IC. The traces/continuity past the IC all check out so at this point I think it's definitely a faulty chip. Gonna order a replacement and see if that does it.
bobbyb13:
I don't know enough about this to have any clue what is going on but I am damn curious to know what it is!
lilshawn:
more often than not, a missing color when the neckboard is not at fault is either the tube has a bad gun (but you've tested this already.) or the amplifier IC gone bad. in the k7000 this is the UPC1397C . good luck on your search, it can be very hard to come by.
i'd double check your board/game/computercable is operating properly by feeding, say the green signal, into the red on either side of the IC. if you can confirm video signal is getting in by swapping red to another color channel, the IC is bad.
snappleman:
Yeah I made sure to swap around the signals and all that to verify. Getting a upc1397c was really easy though, arcadepartsandrepair has them for $10, as does arcadecup via ebay. Also the tube is a brand new old stock TV I just got that's listed as a compatible replacement for a K7000 (which is why I got the board to try that out), so that should be fine for a while.