WG K4500 No Picture

[bstnguy]

Checked all the usual places and forums, not a ton out there. And couldn't find a flowchart.

Converted Galaxian to a Bootleg Galaga, game plays blind. Monitor has neck glow and screen is black.

Checked the wiring, and looks to be correct for the k4500 pinout.

Tried to get a signal from a TPG, nada.

Pulled the interface board, worked the Brightness pot, reflowed connectors. Nada.

Tried flipping the Service switch, no change. Tried the other switch on one of the daughter boards, no change.

I do plan on pulling it and reflowing all the headers, but didnt' know if there was something else to try before that.

Thanks

 

[bstnguy]

Got the chassis out and there is a burn hole between where R778 and J28 is.

What I can't tell as too much of the PCB is gone is if they are supposed to be tied together or not.

Anyone have a close up picture of that area? Attached is what mine looks like.

Thanks

 

[Tr3vor42532]

By looking at the video I did for my 4500, R778 is unpopulated so I can't find where that connects to on the schematic. is it possible to follow the trace that's connected to J28 back to the next component? That could identify what that's supposed to hook up to.

 

[mecha]

major problems here. they're numbered to make the procedure easier... with the cards installed (so the header pins don't move) add solder to all card header pins, remove all solder from odd pins, solder, then do even pins. your resistor explosion I advise obtaining a rotary tool and wire brush to clean up. do the same on any solder points that look like concrete, same thing then, add solder, remove, lay new solder. unfortunately I don't have a K4500 available to look at. but the trace connected to pin 12 looks like it goes to that scorched mound. may have happened cause of the solder breakdown to the header pins. all of that may be connected. see what's attached to the pin 12 in schematics and follow from there.

 

[bstnguy]

Hey, Thanks both for the input. Yes, Ill be reflowing all of those headers (and on rest of board) and cleanup too.

R778 isn't populated and saw the video hoping to see a shot of the Solder Side.

Ive seen before where a low resistance short causes heat build-up and eventually burn through, and your point about a not good header causing overheating of the copper foil.

Just not sure if those points were connected or not.

I did a quick schematic check, will do a closer look again.

 

[Tr3vor42532]

Hey, Thanks both for the input. Yes, Ill be reflowing all of those headers (and on rest of board) and cleanup too.

R778 isn't populated and saw the video hoping to see a shot of the Solder Side.

Ive seen before where a low resistance short causes heat build-up and eventually burn through, and your point about a not good header causing overheating of the copper foil.

Just not sure if those points were connected or not.

I did a quick schematic check, will do a closer look again.

Yeah if you follow that jumper next to the burn back to the closes part and identify that in circuit, you should be able to tell where it goes. Pin 12 on that connector appears to be ground, so if whatever is behind j28 goes to ground, it'll be an easy fix.

 

[bstnguy]

Did a little pecking at lunch and followed one side of the J28 back to the Red and Green pots (VR705 and VR706), and the other ended up at R730 which is on a 900V line on the other side. R778 pad at the hole is tied to ground.

I'd say its safe to say at this point they werent tied together.

 

[bstnguy]

Made some progress today. got some of the TPG test screen to at least be visible on part of the screen.

Not seeing any other colors but when I wiggle something, I see the shots of white and other color, so I think I need to pull the chassis again and give the header pins another good cleaning.

And reflow the neckboard headers and socket. Forgot about that.

I did check the tube on a BK470, and it checks out good.

Went through Tr3vors video again, and what did you use for Sync from the TPG? And you also refered to a "synch adjustment" but couldnt' quite see where that was?

 

[Tr3vor42532]

Made some progress today. got some of the TPG test screen to at least be visible on part of the screen.

Not seeing any other colors but when I wiggle something, I see the shots of white and other color, so I think I need to pull the chassis again and give the header pins another good cleaning.

And reflow the neckboard headers and socket. Forgot about that.

I did check the tube on a BK470, and it checks out good.

Went through Tr3vors video again, and what did you use for Sync from the TPG? And you also refered to a "synch adjustment" but couldnt' quite see where that was?

I never bothered getting it to actually sync to the TPG, after I saw it displaying an image, I threw galaxian on it. It might need negative sync, but I never tried it.

 

[bstnguy]

That's surprising. I thought the input pinout on the k4500 was different than newer monitors.

for giggles, ill pin the connector back to standard and see what it Does.

 

[Tr3vor42532]

That's surprising. I thought the input pinout on the k4500 was different than newer monitors.

for giggles, ill pin the connector back to standard and see what it Does.

oh yeah, the pinout is different. due to that I had a couple colors swapped when I was running galaxian on an external lcd for testing. the schematic should show what it should be

 

[mecha]

it might actually need that G02 adapter. but I don't know for exact certain. I never bothered digging deeper into K4500.

 

[bstnguy]

I did rearrange the connector to match the schematic, but again, the sync line is one I'm not sure.