Fanuc A06B-6058-H221 Servo Amp HC Relay Problems

Ive got a Mitsui surface grinder with a Fanuc A06B-6058-H221 Servo Amp for X and Y. Fanuc OM controller. It has sometimes had a minor problem starting the amp for years. Sometimes the large 3 phase relay on the amplifier transistor board will drop out on start up (HC high current alarm). Often only in X, sometimes in X and Y. After a restart it used to go away. Does not alarm out when in use (after it starts).

This has gotten worse recently. Now it takes several restarts (or flipping the breaker on the amp) to get it going. Still stays on after a successful start, at least for several hours at a time that Ive used it lately. I do have a service manual, see some reference to setting the parameters to reduce the inrush current. Are these settable from the control? I looked at the parameters in the control but didnt see anything corresponding to the numbers given in the manual.

Maybe the amp is just going bad?

Ive been running the machine on 240 for years but tried going through a 220volt stepdown transformer today that puts the voltage right at the 220 on the nameplate. Still takes a few restarts to get the amp going. Anyone ever repair these?

Seems like maybe some of the caps are going bad. Im not thinking that any diagnostics in the manual will be very helpful as the amp always does run fine after it actually starts which leads me to think its right on the edge of working correctly.

is either the X or Y servo motor exposed to coolant? If so, coolant in a motor power connector can cause trouble like you describe.

No they are in a protected area under the machine that cant be exposed to coolant on this grinder.

Then the next step would be to look for any damaged insulation on the power cables. If those check out then I think you'll be looking to replace the amp.

I installed a replacement A06B-6058-H221 amp. The machine still does not start at first, but now if left powered on for 30 min. It will start and run normally. Thats closer to the original behavior over the years Ive owned it. When powered up the amp is errored out but still has power to it, which should indicate no voltage going to the servo motors. Wondering what is warming up in that 30min period that would cause the system to start working. Wondering if the control parameters are not set correctly for this drive. The machine did lose parameters before I purchased and they were reloaded, (not by me).

I double checked the parameter list with the factory original printout and it matches. This machine does have glass scales and is a 5 decimal place machine. Wondering if the scales being dirty could cause a servo error?

Its giving the usual 401 vready, 414 424 errors. It seems like the machine was set correctly when new and now that its 27 years old, it needs some parameter set to a more relaxed tolerance.

One other thing I noticed is that if you boot the control with the XY servo amp off, then flip the relay and reset, it takes fewer restarts to get it going. So there seems to be some voltage surge sense related issue there as well.

Have you replaced the relay? Maybe one of the contactors wont connect everytime and you are missing a phase on startup.

Marko

Think I figured it out. This machine has several modules that are connected by numerous mil connectors. The japanese mil connectors use silver, not gold like the american ones. I removed them and sprayed with de-ox. Then when getting access to the Y axis servo on top, I noticed that the gearbox was nearly empty, there's a drain tube that looks like it moved lower than the box and drained the oil. I refilled and de-oxed the connectors (and wire tied the hose in place). Now it starts normally. At least several times in a row. Maybe just oxidized connectors all along.