View Full Version : Encoder Fault

06-01-2021, 09:53 PM
Hi all,

My Denford Cyclone has been out of action for a while and now I have some time to try and fix it.

It had an intermittent fault last year, (It would spin past the tool it is indexing too then do an extra rotation before stopping on it. Sometimes it would immediately move to the part other times it will wait for anything up to a minute then move and sometimes it didn't move at all. Occasionally it would just spin over and over.)
I solved this by replacing the nylon bumpers, locking proximity switch and cleaning a load of oil out of the encoder.

Now the problem has come back, any tool change apart from to tool 1, the turret just spins infinitely.

The encoder has 4 pairs of photoemitter/photodiodes inside and slots for the on and off positions. All of the bits are as they should be except bit 4 which is only meant to be high just for tool 8 but is constantly high. I have checked the others with a multimeter and they register 24v when over a slot and nothing when the beam is broken.

But the one which corresponds to bit 4 is 24v either way.

Does anyone have any idea what the problem could be?



06-01-2021, 10:21 PM
Got your PM.

I never realised these encoders were so basic.
It can ultimately only be the LED/circuit (should have a continuous voltage over the diode), the photo diode/circuit, or the output transistor/circuit.

Somebody like British Encoder (encoder.co.uk) might be able to repair it. They actually supplied the original spindle encoders for Cyclones, and they were very helpful when I needed a replacement, but I'm not sure how they'll handle a non-common encoder. Probably worth a phone call/email.

Other option would be a competent electronics repairer, but I'm not sure how you'd find one locally. If I wasn't so busy myself, I'd offer to have a look. I know one person in Brighton I would trust to have a look at it, but I'm not sure if they'd be willing to look at it, as their usual area of expertise is consumer/musical electronic repairs, but they have the kind of skillset to repair something more old school electronics like this.

I'm aware there is at least one person on here who has looked at electronics for other users before, but I've forgotten their username!

06-01-2021, 11:36 PM
Got your PM.
It can ultimately only be the LED/circuit (should have a continuous voltage over the diode), the photo diode/circuit, or the output transistor/circuit.

Generally agree, but don't ignore the oil contamination and subsequent cleaning. That might have been contributory.

OP: If you wanted a 3rd party to have a look then feel free to PM.

07-01-2021, 12:22 PM
Thanks for you replies.
I will give the encoder company a call and see what they say.
Probably a good thing that is fairly basic electronics, hopefully I can get it fixed.

One other strange thing..
In the manual for the Turret it gives the bit positions for each turret position. there is also a parity bit.


The photo diode senses the slots 24v or 0v,
But at the point where it enters the turret it is always high.
Although strangely it may not matter as it doesn't seem to go to the control. (the bit in the diagnostics is 0 and never changes.

It is wired to the fifth position from the right on the bottom and nothing is in the top. Is this the same as on your Cyclone m_c?

The Denford electrical manual doesn't to mention it either.


If it isn't used could it be used to replace the possibly faulty phot diode on bit 4?

07-01-2021, 01:55 PM
THAT'S why there's 6 transistors :) You had me wondering. It's possible to substitute the photo-diode etc, but better to replace with new (then you're not carrying a dormant fault). Discuss with the encoder company - for them it's probably easier to replace with new than juggle components.

07-01-2021, 06:03 PM
I'll be honest and say I can't remember if Parity is connected on mine or not.

I'd have to go and look, or dig out the PLC code to see if I used it or not.