Author Topic: Wells K7500 - top half is dark (Read 3971 times)

jconstanza · « **on:** December 04, 2008, 05:38:58 pm »

Working on a Wells Gardner K7500 that has the top half of the screen darker than the bottom. Tried swapping U601 (TDA1771) and U701 (LA7851), same thing. Am I looking in the right places?

grantspain · « **Reply #1 on:** December 04, 2008, 05:44:24 pm »

got a pic of the prob

jconstanza · « **Reply #2 on:** December 04, 2008, 05:53:52 pm »

Here you go

grantspain · « **Reply #3 on:** December 04, 2008, 05:57:26 pm »

whats your input source to this?

jconstanza · « **Reply #4 on:** December 04, 2008, 06:01:28 pm »

Well I have it on a wells pattern generator right now, but it came out of a Hydro Thunder

grantspain · « **Reply #5 on:** December 04, 2008, 06:20:11 pm »

the generator is giving this a 15khz signal?

SirPeale · « **Reply #6 on:** December 04, 2008, 06:22:47 pm »

That's a weird one.

Just for giggles, check R101 and see if it's open.

grantspain · « **Reply #7 on:** December 04, 2008, 06:37:42 pm »

looks like a problem with the vertical sync or a frequency issue

sarge · « **Reply #8 on:** December 04, 2008, 09:02:14 pm »

what happens when you adjust the vertical size?

Arm123 · « **Reply #9 on:** December 05, 2008, 12:35:38 am »

I had a similar problem with a K7000 that had half the screen darkened, but split vertically. Never got around to looking at it again. Interested in hearing your solution.

jconstanza · « **Reply #10 on:** December 05, 2008, 09:21:35 am »

15khz not sure? I have it set to EGA on the generator. R101 is not open. I use only my multimeter to troubleshoot. I do have an oscilliscope, but no clue on how to use it. Can I measure khz with my meter?

grantspain · « **Reply #11 on:** December 05, 2008, 09:49:26 am »

well if the generator is set to ega/24khz then the signal is fine
the vertical hold or sync is the only thing i have ever seen cause this

do you have an option for sync polarity on the generator?

SirPeale · « **Reply #12 on:** December 05, 2008, 09:49:59 am »

Quote from: Arm123 on December 05, 2008, 12:35:38 am

I had a similar problem with a K7000 that had half the screen darkened, but split vertically. Never got around to looking at it again. Interested in hearing your solution.

Smoothing cap - 47uf, 160V @ C57.

jconstanza · « **Reply #13 on:** December 05, 2008, 10:10:03 am »

No, no option for that.

jconstanza · « **Reply #14 on:** December 05, 2008, 10:17:39 am »

grantspain · « **Reply #15 on:** December 05, 2008, 01:05:29 pm »

and you have the same problem in the cab?

jconstanza · « **Reply #16 on:** December 05, 2008, 01:48:55 pm »

grantspain · « **Reply #17 on:** December 05, 2008, 02:07:30 pm »

well thats good(in a way) as it rules out frequency
have you followed the wg repair guide on this?

jconstanza · « **Reply #18 on:** December 05, 2008, 02:23:35 pm »

Ehh, not completely. It's tough cause I don't have all the parts that they are pointing out

SirPeale · « **Reply #19 on:** December 05, 2008, 02:59:09 pm »

Quote from: jconstanza on December 05, 2008, 10:17:39 am

C57?

That was a response to the guy who had the problem with his K7000.

grantspain · « **Reply #20 on:** December 05, 2008, 03:07:32 pm »

from wg guide
SCREEN BLACK ON ONE SIDE
BLACK WIRE ON FLYBACK REVERSED
C310, C812

i had a similar fault on a few polo monitor caused by a resistor on the g1 circuit.its equal on the k7500 is r545 150ohm

jconstanza · « **Reply #21 on:** December 10, 2008, 02:39:25 pm »

Wow! I feel like an idiot. I got it like this from the customer. It had the wrong controller board.

grantspain · « **Reply #22 on:** December 10, 2008, 02:49:21 pm »

qrz · « **Reply #23 on:** December 12, 2008, 07:37:38 pm »

Quote from: jconstanza on December 10, 2008, 02:39:25 pm

Wow! I feel like an idiot. I got it like this from the customer. It had the wrong controller board.

so much "fun" when someone has been in 'em.

recently had a serv call on an RCA projo. the hv splitter was arcing ( AND in the wrong place - HUH ??)
seems another "shop" had replaced the red crt , and didn't put the block back where it belonged,
misrouted ctl/spkrs lines and didn't reinstall a number of screws.

hauled the chassis back to shop to undo all the damage ....

qrz


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