Haas VF-8 Tripping CB3 after Cabinet Fan Short

Hi everyone,

Today, I opened up the rear cabinet of my VF-8, and when I closed it the cabinet fan cable got pinched in the door and shorted out and tripped the breaker. I fixed the fan cable, but the short is still persisting even with the fan totally unplugged. I called my local Haas outlet, and tech support thought it might be a short on the main I/O board. I took off the board and looked at it front and back and it's fine.

It keeps tripping the CB2 breaker on the power supply board every time I power on, which is the 120 volt one on the far right side. It seems to be the only one tripping.

The machine is from 1997, if that helps.

edit: changed CB3 to CB2

I'm no sparky, but it seems with the machine fully powered off and that breaker open, you should see continuity across its terminals due to the other short(s). If you can trace back from its wiring you may find your problem.

Electrical issues suck, I'd much rather fix things like the broken gearbox pump coupling that I did today.

Agreed. I heard a pop and smelled some magic smoke, but I'm sure it wasn't from the I\O board. I thought it might've been from the fan cable that shorted but I'm not sure. My next thing to check is the circuit board power supply where the tripped breaker is. Also, the low voltage power supply has been going bad for awhile on that machine so I wonder if something in it shorted out and is taking the rest of the board with it.

The manual for Service will have good diagrams in there. CB2 controls the 3-phase 115volt distribution.
It can be tripped only if there is a short in the control cables or on the IOPCB in pinching the fan, you shorted 110V of one phase to the cabinet. The path for that to ground is usually pretty instant. On the PDU board, it takes the phases and splits them out for 110Vac (hence AC distribution). That board will then route the AC along breakers and fuses and traces to various parts of the system. CB2, then is something you can check with an Ohm meter. Unplug the cord. turn the CB1 breaker to off. Using the ohm meter w/ black on ground, (may need to find something on that board to use if isolated. I do not know. Poke around.
With the RED, check for ohms value on the 3 lines into the PDU distribution board. I think you'll find 2 of the AC lines (usuall a red wire set that goes into the PDU board as "ac in" in a set of 3. one for each phase. Somewhere in there I think you'll find one of them shorted to ground or very near it. The I.O board has a lot of 110AV on it. You could start unplugging those connectors one by one while watching the meter. Something like a wire or two might have melted to a case or post or wire too, causing the near short. Just my thoughts... chased a few of these in my day.

Page 345 of this guide shows the line flow.

Thanks!

That's pretty much what Haas tech support told me. The likely cause of the tripping breaker is a remaining short on the 115v section of connection on the upper right side of the I\O board. They just recommended unplugging each 115v connector one at a time until the machine stops tripping the CB2 on power up. I guess I'll find out what else is cooked when I get the board back in the machine on Monday...