WG6100 smoked D902 in HV cage

lmorchard

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tl;dr: My WG6100 burned D902 in the HV cage. I have a replacement (NTE558 mentioned in this guide), but don't want to just solder a new one in without knowing what might have caused it. Anyone know some common things to check first?

Some further details, because I did some work leading up to this:

I'd rebuilt this monitor 2 years ago with a kit from arcadeshop and installed an LV2000 Light. Had issues with the original Tempest board, but the monitor was fine with a replacement PCB.

Last month, video went out while playing Tempest. F700 on the deflection board was blown. Opened up the HV cage, saw C902 had popped. Tested the frame transistors - 4 of 6 were bad. (I forget which ones - maybe both the 60x and 70x)

Ordered a new rebuild kit, extra parts kit, and a flyback from arcadeshop. Spent last weekend installing all those parts. Figured I'd just replace everything I could, since I don't really understand all the electronics yet.

Then, I followed andrewb's guide to bringing up a WG6100 in sections. Had chatter from the deflection board in step 5. (I'm pretty familiar with the sound of the title screen, at this point.)

Turned everything off, hooked the HV cage back up & disconnected the game board for step 6 in andrewb's guide. I don't have an HV probe, but I figured I would at least try powering it up.

Heard a crackle, then smoke from D902. Turned it all off ASAP. Disconnected the HV cage, unsoldered the diode, and sure enough it's cracked & shorted. (It was the original diode, since none of these kits came with a replacement. Ordered an NTE558 separately to have on hand, but didn't install.)

Powered it up with the game board connected (back to andrewb's step 5), and I still get deflection chatter.

Not sure where to go from here. Hoping someone can tell me it's something simple I missed :) Thanks!
 
I would recommend going through the entire HV cage and check all values of all resistors, Check all transistors and diodes as well. That should take less than 30 minutes.
 
First thing, stop using NTE parts they are junk. Consider MUR2100 or something similar for D901/D902

Second, Turn the HV adjustment pot as far down as it will go. That diode should only fail at too high of voltage. I would be surprised if the HOT didn't go as well, possible for it not to but D902 is there to protect it. You can also get rid of D902 if you use a 8A capable HOT that has built in diode protection.
 
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