1998 Okuma-Howa HL-20 lathe with Fanuc 18T control. The CRT screen read out for spindle speed is fluctuating rather fast, even when spindle is stopped. The spindle encoder was replaced, due to losing the 1 position to start a threading sequence. The spindle speed was acting up (on the CRT) already, probably bout the same time. Now I have my 1 back, but the threads are outta whack, like the machine is trying to match the thread feed rate to a jumping spindle speed. Got into the diagnostics side of the controller, and there is a 417 that is fluctuating even faster than the spindle rpm on the CRT. It even shows minus figures. This has spindle amp A06B-6088-H315#H500, and I found that I could unhook JY5 (encoder cable from spindle), and the spindle speed numbers change, but still jump wildly around. The spindle 'seems' to turn the programmed speed, but a G96 (constant surface feet) doesn't work. I've looked thru 215 pages of the Fanuc thread here, and so far I've found no one else who has had this problem.....
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