SL-3B DC. Tacho. Generator problem - spindle drive

[nlh]

Hi,

I'm looking for some advice on a problem that just recently popped up on our 1980 SL-3B (yasnac 2000G universal display).

To make a long story short the lathe needed to be disconnected from the main panel, when it was rehooked, the "wild" leg (use phase converters) was mistakenly put on the wrong leg as well as the ground lead being hooked to the wrong bus in the breaker panel.
At first I didn't realize any of this until I tried to turn on the spindle(rest of machine came up no "ready" fine). When I pressed the spindle "forward button" the chuck started dancing back and forth very rapidly (if it was an AC motor I would say it was single phasing) and then the machine shut down. Turned power back on and the machine came back up with an alarm 28 (machine not ready). Went around to the back to look at the spindle drive (DC Varispeed 505 MT) and the light for "FU" (fuse) was lit. Turns out 1 of 3 fast blow fuses inside the drive was blown.
Replaced this, turned machine back on, come up on ready with no alarms etc. So I try to turn on the spindle again (bear in mind at this point I found the hookup problem and had that remedied) and the control immediately goes into another alarm 28. Nothing from the spindle at all. The light on the spindle drive at this point is "TG" (tachometer generator). According to my manual for 505 MT drives, this means the tachometer is shorted or disconnected. I pull the cover off the spindle motor and the tach and brushes were all gunked up. With these cleaned up, unstuck, and reinstalled....still nothing, same problem. Swap this out for another spare unit I have and the same thing. Do some checking with my meter and there is 12-13 ohms (depending on armature position) across the tach, the spare unit was 15 - 16 ohms. I compared this against my SL-1 which turned out to be around 120-130 ohms. Also, I checked the spindle drive itself for blown diodes, transistors, SCR's, etc. All appears to be normal on the drive, also can not find any short circuits in the wiring connecting the tach to the drive.
I should also mention, with the spindle turned on with either the forward or reverse buttons and the speed selector knob turned all the way down (off), if I grab the chuck with my hand and spin it, it will instantly go into the alarm 28condition with the "TG" light. Thought this might be a tidbit of good information but maybe not.

I apologize if this comes across in a rambling fashion but it is pretty much the way it happened from the end of last week to now. Have any of you experienced Mori guys on here ever had anything for a problem like this? I am in desperate need to get this fixed. Unfortunately we are NOT a big shop and funds are always tight so I am usually forced to diagnose and fix the problem myself, this results in a lot of late late nights and lost time. If it is an expensive problem to fix I will need to junk the lathe as I just won't be able to afford it. The trick, as always, is to find out exactly what the problem is. I appreciate any help or insight I can get.

Thanks

[Al_The_Man]

A tach is fairly easy to check with a voltmeter, it is likely 7v/1000 or 20v/1000 rpm.
The polarity will change with direction, if you get someone to manually spin the sp motor as fast as possible and check the voltage out, I assume the connection have not been reversed?
Al.

[nlh]

Thanks Al,

I do not believe the connections have been reversed. I made sure to put them back in the correct places. I have the SL-1 that I can refer to if in doubt, also have a wiring diagram for the SL-3 which covers that. I will try to get someone to rotate the chuck today while I check voltage. I'm quite sure this is a 7V/1000RPM unit. At least that's what the yaskawa manual for the drive says.

Nate

[Al_The_Man]

Best to monitor the voltage right at the drive input terminals also.
Al.

[nlh]

Checked the voltage at the input terminals. With the machine in low gear and someone rotating as fast as they could I could come up with ~1.25 volts. Just couldn't spin it any faster. So I'm guessing this is a good sign although without devising a test rig I have no way of knowing what the voltage at 1000rpm is. I'm off to recheck the SCR's, diodes, etc, all over again.

Thanks