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I got Fanuc Power Supply / Amp Issues...


Hot Rolled
Feb 7, 2007
midcoast U.S.A.
Next day I threw the switch and it came up all --'s! (that's a good thing) Seems to be the opposite problem of a cracked ignition coil?

Ox, I've fixed many cracked solder joints that wouldn't make connection when cold, but would expand slightly when warmed somewhat, and work fine. So, yeah, heat may be the biggest enemy of electronics, but occasionally they fail when colder, rather than warmer. If you get some freeze spray from an industrial electronics supply, you can shoot areas of a board that you suspect to be bad, and often cause it to fail by chilling the bad joint or component, thereby identifying the guilty party.;)


Perry Harrington

Oct 7, 2006
Klamath Falls, Oregon
I'd reflow all the SMT joints on the board, chances are you have cold solder joints due to low lead solder or just due to bad thermal design of the board. A hair dryer works well for diagosing these problems as well.


Aug 27, 2002
West Unity, Ohio
I really can't believe a broken circuit. Once it is warmed/fired, it will be fine now as long as the power is kept to the case level. The lamps are not on the drives anymore. It is simply for start-up that it is an issue at all.

If it was a solder joint - I wouldn't expect two units to have the same issue, both slowly preggressing at same pace. Seems to be componant level to me. (Not that I know enything about it all.)

My techie said something about getting a new tester that should be able to read those little shiny ones better. He tried to bench test tham last week and none of his meters could get a logical reading on them.

Ox, chances are the drives are different. The base transistors (igbt's) are probably sized for a specific amperage output. You would have to see down deep in the guts of the drives to see the base transistors and other high-power components.

Now, if all the base components are similar, then the output difference would be in the circuit boards...probably just a setting or two..

Yeah - I would hafta start to really dissassmble the drives to get in to see more of the high power unit stuff. Everything that I could see all had the same values on them. That's why I kinda wonder if the D-board doesn't simply "know" to send a limited amount of juice to the smaller motors - rather than have that many more major componants to stock?

Could go either way really...


Think Snow Eh!