Blast City – leak found!

So I’ve spent some significant time on this – fortunately, I didn’t get zapped along the way!

After reading the thread on Aussie Arcade – https://www.aussiearcade.com/topic/72785-sega-blast-city-abnormal-voltage-on-signal-ground-and-more/, I decided to take away my internal tx out of the picture just like the OP did. I simply tuned my 220v cab into a 100v cab and used my existing step down tx that my other blast is using – after probing, I had about 50-55V!

I probed the same areas on my other blast city and it too yielded 50-55v on the metal plate. I’ve been using that cab for almost a year and never felt a shock, so I’ve never really looked into it that much. Back to the troublesome blast…

Either way, I knew that I had a win already since I went from 172-180V down to 55V! I still didn’t have the balls to touch the metal plate yet until I got it a little lower..

Spent a good chunk of the weekend taking readings and special shout out to tiff_lee for pretty much helping with the troubleshooting

Took the following measurements – probe points are ground pin on the control panel and P1 start pin unless otherwise noted

• 56 pin (CN10) unplugged in off state (front switch) – dropped to 3v
• 56 pin (CN10) unplugged in on state (front switch) – went to 9v
• CN1 unplugged – no difference
• With CN1 and CN2 unplugged in off state (front switch) – still reading around 3.9v
• With CN1 and CN2 unplugged in on state (front switch) – went to 5.9v
• With CN1 and CN2 plugged in, probed ground and a pin in CN10 – read 60v
• Measured the pins on CN1 connector – every single pin showed 62v
• Measured the resistance of ground and the metal enclosure of the PSU – was at 0 ohms

So it was pretty clear that CN1 was the culprit, but wasn’t sure why. The next step to take was to remove the common denominator between the two cabs – the external tx!

I rigged up another tx I had and wired it up to the same place as the original tx

Upon first power up, probing the same points as I previously have been, I’m seeing with a pretty low number! YES!!!!

Did some more testing and probed the frame of the monitor which would essentially be the same as the metal plate since it gets mounted on it.. I get an 8v reading!

Looks like I can definitely close this issue off and thank f**k for that! I will try grounding the internal tx to see if it lowers the voltage even more but tiff_lee mentioned that he didn’t see a gain on his and his blast hovers in the 8-10v mark too.

The only thing left really for this blast is trying to source an original tube!

But for now, I will stick my tongue on that metal plate shock free! 😛 😛 😀