Month old Vision Pro issue - No blue!

[modessitt]

Okay now....

Installed a brand new Vision Pro from Happ into an old Sega/Gremlin Frogger about a month ago due to a WG4900 issue that would never go away.  Game looked great.  After being on location for about a month, the game went down.  Replaced some old diodes on the power supply board and game came back up, only with no blue.

First, I verified continuity from the board pad to the monitor input connector (as someone had hard-soldered the wires directly from the monitor connector to the edge connector).  Then I pulled the pin and cleaned and adjusted it.  Reflowed the connector joints.  Checked the voltages coming into the connector:

R - .12 VDC
G - .12 VDC
B - .56 VDC

I checked the Vision Pro manual and found the video input signal specs to be 0-2.4V so these should be fine.  Adjusting the brightness, contrast, and blue control pots on the neckboard do nothing.  I even hooked it up to a rejuvenator to make sure the gun was still good, and tried a rejuv and clean/balance on the tube in case that would help.  I did remove a couple K-G1 shorts, but still have no blue.  Blue gun reads just as good as the others.

In case someone's wondering if this is a board issue, I hooked it up to a WG4900 with bad Gauntlet burn-in I've got lying around, and the blue shows up fine, so the problem should definitely be with the Vision Pro.

I guess my question would be, could the diodes going bad on the power supply (they didn't burn, just got so old they cracked in half) have caused a problem with the encoder ship on the monitor?  Could I use a logic probe to check the "blue out" pin on the chip to see if it's working?  And if so, do I use the blue input signal at the connector as my red lead reference?

Any help would be appreciated.  Don't even know if this is something my boss can call Happ about and ask for an exchange at this point, even though I have attempted no repairs as of yet.

[SirPeale]

Did you check the blue drive transistor on the neckboard?

[modessitt]

As all this happened at the end of the day, I have not started repairs on the monitor yet.  I don't see why it would have failed so quickly, but that is a possibility.  Guess I'll have my boss call Happ to see if they'll exchange it before I start pulling parts.  Wouldn't want to void the warranty if he decides to try that.

[modessitt]

Well, I didn't feel like removing everything from the cab, so I tested the drive transistors on the neck board from the back of the machine.  The blue readings were off a little, but that could have been from being in circuit.  As I didn't have a replacement handy, I switched the blue transistor with the green one and powered up.  If blue was back and green was gone, then the transistor was bad.  But alas!  Green is there and still no blue!

Sigh.  Okay.  Went ahead and pulled the entire chassis from the tube and brought it to my workbench.  Started tracing the circuit from the blue input wire to the neckboard.  Found it!  Seems like the wave solder machine left a big solder bridge across a few leads on the chassis, right next to the RGB ribbon cable to the neckboard.  Cleaned it up and plugged it back in.  Blue is back!

Now what I wonder is, how did it ever work correctly in the first place?   

[WareWolF]

Maybe there was originally not a short, but some excess flux in between the traces and after being in use a while things heated up just enough to cause the soldier to flow together?

[modessitt]

Maybe, but it was quite a big blob, even more than would have been needed to do the leads there....

[StephenH]

If you have ability to swap cables, swap Blue with Red or Green and see if you get any blue.   This will tell you whether it is a monitor problem or gameboard or video card problem.

[modessitt]

um.... You mean on the video input connector to the chassis?  O guess that would work, too, though I had already determined that the monitor was at fault.  If I put the green input signal onto the blue pin and the blue input signal on the green pin, I guess it would try to draw the green items in blue and vice versa, huh?  I guess this would verify that the blue signal was working from the board, although I had already confirmed that voltage was present from the board on the blue pin, not to mention hooking it up to a known working monitor sitting nearby.

As I had a solder splash on the board at the RGB ribbon cable from the chassis to the neckboard, I still would have seen no blue and would have suspected the blue circuit - specifically the drive transistor.  I tried the fix that would let me not have to remove the chassis from the cab and just switched the drive transistors.  When that didn't work, I knew I had to pull it out and go more in depth, which finally found the solder splash.

But it is a good method to keep in mind, especially in cabs with hard-to-get-to-the-back-of monitors with color issues.