Jet 3520B Speed Display Faulty

[Duncan A]

The digital display on my 3520B lathe has suddenly started displaying "0" regardless of actual speed or direction of rotation.
The speed is sensed by a proximity sensor (proxy) picking up the four lobes of a rotor as it passes the proxy.

I have checked the air gap between the proxy and lobes; about 1mm, unchanged from previous.
There is no dirt on the lobes or proxy.
There is no visible damage to the proxy or associated electronics.
A red LED on the proxy remains lit whenever the lathe is powered up whether the lathe is rotating or not.

Speed control is unaffected, and speed display is not really needed anyway, but it's annoying me so I want to fix it. The proxy is probably an inductive device, which are known to fail occasionally, but I'd be grateful for any suggestions as to the likely cause or fixes.

Duncan

 

[gregmcateer]

At about £3,000 my suggestion would be a conversation with the supplier!

 

[sunnybob]

follow the sensor lead from the pick up to the display. if it has any bad looking areas at all change it. the wires inside are so tiny they can snap if you just look at them sideways.

 

[RogerBoyle]

At about £3,000 my suggestion would be a conversation with the supplier!

Agreed

 

[Alpha-Dave]

2 years ago my Jet 3520b had a similar fault; one segment of the display never lit. This was when it was brand new, as-received. I phoned the dealer I bought it from (G&S Specialist timber in Cumbria), they immediately contacted jet UK who said they had to check local stock, and sent out a new display unit to me the following day. It took 5 min to fit, no issues since.

 

[Duncan A]

Thanks for the comments gents.
Greg, Roger - I shall be contacting Axminster in the coming week if I don't find a solution myself, but very often electronics queries are met with the response "replace the board/module/everything" which is a bit of a blunderbuss approach - and expensive, hence asking to see if anyone else has had the same problem before contacting them.
SunnyBob - the wires look good, although they are not individually visible along their full length. I may see if I can disconnect them and test them for continuity. There is a rather poorly designed PCB box entry and also a very sharp bend which would be my favourite candidates for failure, but no amount of wiggling in those areas has caused a display segment to flash on/off so I think they're OK at this point.
Alpha-Dave - the lathe is 4 or 5 years old and well out of warranty so I don't reckon I'll get any free replacements. I don't think it's the display as the displayed "0" would change as the lathe changes speed but I'm not ruling anything out at this stage.

I'll keep you posted as to progress.
Duncan

 

[Duncan A]

I fitted a new proxy and the speed now reads correctly, but members may find some more detail useful:.

I checked the voltage to the speed sensor board - 220Vac as it should be.
Next I checked the voltage to the speed pickup itself - about 16Vdc which is within the working range of the device, but I don't know whether that is the correct voltage for this setup.
With the device powered up, the on-board LED should be off when no metal is within the sensing range, on when it detects the presence of metal. It actually stays on regardless of the presence of metal and, since this is the normal failure mode of these devices, I have taken the view that it is the pickup that is faulty, not the associated PCB.
Perhaps foolishly, I didn't ask Axi for advice, just price and availability of a new pickup.

For the record, the original is a BAKS DA1805NO which I have identified as being NPN type, NO contacts, 10 - 30V, 600Hz switching frequency, 150mA max, 0 - 4mm operating range, size 18 x 18 x 36mm.
These all seem to be fairly standard specs so I fitted a £5 cheapo speed sensor from eBay - but that didn't work although the specs seemed OK.
On 10th July, I ordered the genuine item from Axminster, £35.
24 hours later I received it, so a pat on the back for both Axminster and Royal Mail for excellent service.

The proxy works perfectly. I tested it before fitting and the LED remained off when the lathe was powered up and the proxy held in air, turned on when a screwdriver was placed close to the face - as I had hoped for. Once fitted, a run to full speed gave the correct readings of about 3200 rpm.
My cheapo proxy is obviously duff as it failed the screwdriver test, not sure it's worth claiming £4 back though.

I'm happy now!
Duncan

 

[J-G]

My cheapo proxy is obviously duff as it failed the screwdriver test, not sure it's worth claiming £4 back though.

YES IT IS - - - even if you have to spend some time making a claim. If you don't, the supplier will continue to supply duff product simply taking the possible hit of negative feedback - I assume you have already left some!

It's a bit like ignoring poor use of English - if you don't correct, you accept.

I'm happy now!

You'll be happier still when you receive the refund!

 

[Duncan A]

J-G, you're probably right, but I never even thought of the feedback route. If I do that I'll have to ask for my money back first, purely to be fair to the retailer of course and give them a chance to respond.
As for ignoring poor use of English, I usually just fume! BBC among the worst offenders - and doubly annoying because I'm paying for them.
Better go now before I get on my high horse!
Duncan