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Main => Monitor/Video Forum => Topic started by: Cyberwhiz on January 17, 2010, 02:18:46 pm

Title: WG 27K7391 with raster but no video.
Post by: Cyberwhiz on January 17, 2010, 02:18:46 pm

Running out of ideas and really looking for some help on this monitor. Original problem was missing colors, don't remember which ones. Anyhow, after a cap kit, still had same issue so I ordered the neckboard transistors after verifying that the passive components on the neckboard were good. Once I finally got the transistors, I hooked the monitor back up to see which colors were missing and got no video at all. Went ahead and replaced the transistors (2) anyways but same issue. Turning up the screen control, I do have raster lines and the B+ is at 130v. So, following Fromm's Flowcharts, I replaced Q4 and Q7, with no effect. Reflowed the video connector and the blue/white harnesses.

When I turn up the screen control, the raster lines are there but I don't see the game playing at all. I hooked up another monitor to the test rig and it worked fine. This is the 27K7391 with the pincushion adjustment board. Board is a P538. No amount of fiddling with the screen adjustments produces an image.

Thanks in advance

Title: Re: WG 27K7391 with raster but no video.
Post by: lilshawn on January 18, 2010, 01:16:01 am

i would suspect the video amplifier chip...likely a "lm1207" but sometimes a 1205 they are interchageable

but if it's a 1203 you can switch with DBL2056, KA2139, MTV005, or TFKU2203

i'm not sure 100% the chip for the chassis

Title: Re: WG 27K7391 with raster but no video.
Post by: Cyberwhiz on January 18, 2010, 02:37:28 am

It's actually a UPS1397C on this board. Hard to find, expensive when you do, but I may have a parts board I can get it off of.

Thanks!

Title: Re: WG 27K7391 with raster but no video.
Post by: Cyberwhiz on January 20, 2010, 01:38:47 am

Replaced the IC, no change.

I can't help but think that I'm overlooking something simple. Any more ideas ?

Title: Re: WG 27K7391 with raster but no video.
Post by: Ken Layton on January 27, 2010, 10:50:40 pm

You sure that model number is right? The 7300 series is 19" and made in Wells-Gardner's Korea plant.

It must be a 7193.

Anyway, have you measured the voltages at connector P202 on the neckboard? You should read these according to the schematic:

Pin 1: + 12 volts DC
Pin 2: key
Pin 3: +130 volts DC
Pin 4: ground
Pin 5: filament (heater) volts

Transistor Q201 is for red, Q202 is for green, and Q203 is for blue.


On the main board transistor Q8 is the brightness/contrast one (check it). Be sure the black level (brightness) and contrast trimpots on the remote adjustment board are good. Check transistor Q4 too.

Non-polarized electrolytic capacitors C4, C5, and C6 (all 10 uf @ 25 volts bi-polar) couple the red-green-blue colors from color preamp transistors Q1, Q2, and Q3 to the color processing IC1 (UPC1397C)

Schematic here:

http://jstookey.com/arcade/WG_25k7191/k7191-complete_lg_.jpg (http://jstookey.com/arcade/WG_25k7191/k7191-complete_lg_.jpg)

Use K7000 manual for troubleshooting, voltage readings, and parts list.

http://jstookey.com/arcade/WG_25k7191/wg-k7000.pdf (http://jstookey.com/arcade/WG_25k7191/wg-k7000.pdf)

Title: Re: WG 27K7391 with raster but no video.
Post by: Cyberwhiz on January 30, 2010, 02:21:20 am

Ken

It's the same chassis as listed in this thread:

http://forums.arcade-museum.com/showthread.php?t=47180&highlight=27K7391 (http://forums.arcade-museum.com/showthread.php?t=47180&highlight=27K7391)

where you described it as the "rare 27" k7000 with the "pincushion" optional circuit board installed".

I'll go through it again and verify the things you listed.

Thanks again for your help !