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If you have old Yaskawa CACR ac drives in your machine...

gregormarwick

Diamond
Joined
Feb 7, 2007
Location
Aberdeen, UK
Just got done repairing one of these in one of our old workhorses, and it led me on a wild goose chase in the process on the back of some faulty assumptions and diagnostic oversights on my behalf. Decided to post about it here in case anyone is interested, or might be helped by it.

Over an extended period of time, the machine has been intermittently but increasingly faulting out with a z axis servo alarm when enabling the servos (cold startup or releasing e-stop etc.). Reset and try again - perseverance would make it go, but required more and more of that (this is a big clue in hindsight that I overlooked). In the winter, we would point a heater at the control cabinet for a few minutes and usually that would make it go. The servo amps are in a different cabinet on the other side of the machine.

Servo amp shows no alarm - all fine, ready to go. So, I check the cable, all fine. I check all the way back to the pin in the connector on the Z axis board, signal high, all good. So, I assume that there is a fault on the board. I'm thinking that the heater pointed at the cabinet aspect suggests a dry solder joint or something on the board. Trace it back, first thing is a resistor array. Checks out fine, but I replace it anyway. No go. Next is a ILQ74 opto isolator and a latch. I think I've hit the jackpot, replace those, but again to my disappointment, no change.

After that the routing branches off in about 10 different directions, so I decide not to continue. I have a spare board, that is slightly modified for a different configuration. I re-modify it to match the problem board, swap over the proms, set the jumpers, switches, etc. and plug it in. Same result. This seems unlikely, and I'm about to throw in the towel, but it's already late and I'm not in any rush to go home, so I decide to take a closer look at the fault signal coming into the board.

I soldered a wire onto the back of the board at the connector pin to attach my scope to. For some reason I decided to try it at this point, and it fired right up! Cold solder joint at the connector? While I'm kicking myself for not checking that first, I hit estop and try it again. No dice, servo fault. Ok, just a shitty coincidence to mess with me.

I hook up the scope, and sure enough the servo fault signal is going low for a few ms and coming back again. I do the same check right at the drive, and yes, it's the same there.

Externally, it still appears that the amplifier is working fine. All the correct leds are lit, no error on the display. I dismantle the drive and look for anything obvious on the boards. Everything looks fine. All three servos on this machine are identical, so I swap the controller board between the Y and Z axis. Still faults out on the Z axis, but I notice now that the fault signal is dropping low for a much longer period, and actually the error display is blanking out for a second when I try and enable the servos. I suspect the power supplies, so I swap the power supply boards between the Y and Z axis, sure enough the fault moves to the Y axis amp.

The power supply board has lots of electrolytic caps. I look for swelling and leaks but find no evidence of any. I pull a few of them and check them out of circuit. Under two 25v 470μF caps there is actually some evidence of leakage, and one of them measures significantly low on capacitance. I happen to have a bag of these on hand from a previous unrelated repair, so I put them in, reassemble, and immediately the machine works perfectly!

A long route to a simple repair. Have ordered complete replacement cap sets for all three servos...

I guess in the wintertime with the heater, enough warm air was working it's way into the servo amp cabinet to eventually make a difference. But that led me down the wrong path for sure.
 
Great job!

I always replace the electrolytic caps on a drive/power supply that is acting up.

Older caps may not be leaking, and may show good capacitance, but their ESR (electric static resistance) will rise over time, and this can definitely effect a drive’s operation.

Nothing like the feeling of bringing one of these old electronic devices back to fully functioning!

ToolCat
 
Great, useful post!
I’m wondering if my old Mitsubishi Meldas drives/power supplies are suffering from a similar problem.
They definitely don’t like starting cold.
When the machine is cold, it takes a long warmup and a lot of hit and miss before the drives enable.
And after they enable, they will often fault out when I try jogging an axis or starting the spindle.
After the machine has warmed up for a while, it seems very reliable.
 
Great job!

I always replace the electrolytic caps on a drive/power supply that is acting up.

Older caps may not be leaking, and may show good capacitance, but their ESR (electric static resistance) will rise over time, and this can definitely effect a drive’s operation.

Nothing like the feeling of bringing one of these old electronic devices back to fully functioning!

ToolCat

It was kind of a watershed moment for me when I discovered how frequently old electrolytics are the root cause of failure in old electronics. Such an easy fix!

And this old machine - I have some kind of mental deficiency about wanting to keep it running! It still makes good parts, it wants to work! I can't quite bring myself to let it die...

Great, useful post!
I’m wondering if my old Mitsubishi Meldas drives/power supplies are suffering from a similar problem.
They definitely don’t like starting cold.
When the machine is cold, it takes a long warmup and a lot of hit and miss before the drives enable.
And after they enable, they will often fault out when I try jogging an axis or starting the spindle.
After the machine has warmed up for a while, it seems very reliable.

What you describe are pretty much textbook symptoms of failing electrolytic capacitors. If I hadn't had such tunnel vision about the fault I was diagnosing being in the control and not the drives, I would have figured that out far sooner as I had the same textbook symptoms.

Electrolytic caps have a finite operating life, and it's generally pretty short compared to the working life of a typical machine. High quality electrolytics might specify 10k hours working life. Cheaper ones can be as little as 2k hours.
 
If anyone has need

I have surplus to my needs

1) CACR-SR05-AB1BR New Old stock in original packaging with literature and connector.

1) used USAREM-07AE-2NX motor

no cables

Bought for a project years ago that did not fly..

PM and we can discuss if interested.

Cal
 
Congrats on finding the issue. I too have just replaced Caps on older power supplies on the chance it's the issue. More often then not there is no sign of failure. No leakage or swollen tops.
 
In the world of vintage audio and video devices, a 're-cap' is often step 1, without even bothering to investigate. Popular gear often has a 're-cap kit' available, with all the right values/sizes/properties available as a single order.
 








 
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