[howd]

1998 Okuma-Howa HL-20 lathe with Fanuc 18T controls. When the machine powers up, the spindle speed readout is all over the place, at a very fast pace. Even when in Estop. Several posts in the Fanuc Forum lead to no responses. I went thru all 318 pages of posts, no one else seems to have ever posted on this. (I think it was 318, cudda been more). Anyway, I went thru the 78 in the Okuma Forum, same thing. The spindle position encoder had failed (lost the Z1 for threading), so that was replaced. I do believe that the spindle speed was acting up before the encoder was replaced. The neat thing is, for a mere $4800 dollars, you get every part of the encoder assembly!! The NOT neat part is, the machine isn't fixed. I do have my Z1 back, as I did TRY some threading, and it does 'know' when and where to start. But the federate for the threading cycle (G76), seems to be trying to keep up with the wild readings for the spindle. A feed of .0555 measured .312, and even varied. Can't decide if this is on the Fanuc side, or the Okuma! I did read in the Okuma forum at one post, that the 'tach' could be off because of a bad battery. There is a battery on the main board that has never been replaced, at least not since I've owned it, since 2007. The batteries on the servo amp boards have been replaced numerous times. Course, I can't see how a weak or dead battery could give such wild variations to a spindle speed readout, specially when the spindle is stopped. In the diagnostic screen, there is a 417 that shows the spindle speed (even changing faster than the crt readout), and it even shows - readings. Ideas?

[Algirdas]

1.

There is a battery on the main board that has never been replaced, at least not since I've owned it, since 2007

replace the battery
2. check how bits of encoder data changes while rotating slowly. Maybe there is one or two lines jumping random.
3. check the cable and connections from encoder to control input

[howd]

Hey Algirdas; Thanks for a reply. I forgot to mention that even with the cable disconnected from the spindle amp (J5-S), the spindle speed on the crt still wildly fluctuates. It does change some, but still wild, and never 0. With the cable from the encoder hooked to the spindle amp, slowly rotating the spindle has no effect on crt readout.

[Algirdas]

check cable and connectors if there is no difference if cable is connected or not. check consistency of the lines from encoder to input port.