John's Arcade Forum - Classic Arcade and Pinball Collecting and Restoring Discussion Forum - RETRO MAME - Nintendo Vs Forum

Hello! I'm new to the forum and almost as new to arcade board repair. I recently installed a cap kit in a WG K4600 and made the rookie mistake of installing one backwards :-\ It didn't explode or anything I just simply have no image now. In troubleshooting I have on occasion got a red/orange line down the middle which I believe is evidence of a vertical collapse and it doesn't last but a few seconds before dissapearing. I have neck glow but no raster.  I'm getting 135VDC at the regulator and 160VDC at the HOT case. I have adjusted the B+ pot down and it went to 127VDC for a few seconds then climbed right back to 135VDC. The capacitor that I installed backwards was C622. I'm looking at the schismatic and it looks like it's a grounding cap but after that I don't know how to make heads or tails of what down the line to be checking. Can someone more knowledgeable than I look at the schematic and let me know what could have potentially damaged on that circuit? I'm going to reflow all the solder points on the board tonight to eliminate a cold solder joint but passed that I'm uncertain which direction to go. Any help is greatly appreciated!

http://www.arcade-museum.com/manuals-monitors/WG%20K4600_Manual.pdf

Well I'm not really any more experienced than you but to me the obvious question is... Did you replace the cap that you installed backwards or just reinstall the same cap the correct way?

Oh! Forgot to mention that, I replaced it with a fresh cap.

when you install a cap backwards it is effectively a short. therefore anything upstream of it might have been damaged.

you need to check X609
R631

and probably a few other things on the 30V line if you can read the schematic that far.

Thanks Ian! I'll check those next. Just an update, I touched up all the solder points on the main board last night and fired her up. Instead of no image I now have a proper vertical collapse. I'm certain it's not on the XY board as I've tested that board on a working chassis.

well the 30v is pretty important to the vertical so if thats now dead from that cap being backwards you wont have working vertical deflection.

ok, no 30V at test point 82. Checked X609 and I'm getting 0.46 one way and 0.0 the other. Tested R631 and am getting resistance but i tested in circuit.

Resistors have to be tested out of circuit or you will get a false value.

you will want to test 30V on the cathode side of diode X609

if you are still missing 30V, turn the monitor off and do a continuity test between Pins 4 and 6 of J607.

Ok, so I tested for 30V on the cathode side of X609 and I'm getting -.029VDC. I then tested positive for continuity between pins 4 and 6 on P607.

so without 30V you aren't going to have 15V, and that is not good. I really dont know what to say right now for what to do next. its clear you have an issue with the 30V rail. This should be fed right off the flyback so if ou have HV then you should have the 30V ac which gets rectified.

If I desoldered the line going from the flyback to the board I could verify if the flybacks actually sending 30V to that circuit yeah? And from there if it is it would just be following along the circuit checking components until I found the bad one(s) right?

you can also just unplug the board. the header is where it comes out from.  but if you rather you can just desolder the resistor R631