Lathe RPM meter not working

https://www.amadeal.co.uk/acatalog/DRO-.html
I got this off the amadeal site and it shows the pin markings , looking at the rear of the dro the connector pins from right to left are 5v, gnd , and the two wires to the opto sensor in the link below 

https://www.amadeal.co.uk/acatalog/Sensor-Cable-for-CJ18-12A5-IC1-334.html#SID=13

I would disconnect the opto sensor as well when testing your voltages as it may have died and be pulling the 5v rail down .

Please be careful poking around in there with the power on , it only takes a slip and it can be lights out for you !

That schematic is not the official one it was drawn by a guy on another forum
https://madmodder.net/index.php?topic=6980.0

There is a link to it in the first post .

In the documentation it states that some values may not be correct so that 10K resistor could be 100R or 1k .

As Les mentioned it would be best if you can take a few pics as he may pick up on something you didn’t , maybe a bulged top on an electrolytic capacitor that will indicate a dead or leaky cap that will pull the 5v rail down . It is just a simple linear regulator and you may have troubles with a switchmode power supply like used for phone chargers or wall warts as they can be noisy and play havoc with the display .

Edited By XD 351 on 01/02/2020 01:15:53

Edited By XD 351 on 01/02/2020 01:17:53

Colin

Did you manage to sort out the problem?

I have taken the control box off my cj18 lathe to change the gears and bearings. The circuit is simpler than the one in an earlier post and is labelled with the 5v, GND and signal connections. There is no resistor in the 5v feed to the speed sensor or display. Let me know if you still need help, I can draw up the circuit diagram. 

Stuart

Edited By Stuart Smith 5 on 07/02/2020 22:42:06

Hi Guys - sorry about silence - but a few other jobs have got in the way. I tried to supply 5v to the Digital display - but without success - perhaps the digital display board itself is the culprit. In the meantime I have added a magnetic proximity unit to the gear cover with a small rare-earth magnet on one of the vanes of the rotor. This seems to work fine - although it does mean another wall plug for the supply. I will continue to investigate - but the immediate problem i.e. not having a digital RPM meter has gone away.

Stuart - one of the first jobs I did was to exchange the bearings for angular contact bearings - although I was advised (too late) to actually install taper bearings. I also did an experiment on the effect of pre-loading on the temperature increase in the bearing housing - see the following

https://www.model-engineer.co.uk/forums/postings.asp?th=130430

I've got the same lathe... and the same problem.

I've done a little fault checking and the regulator's definitely dead.

However, removing the display unit and supplying 5V to it doesn't cause it to light up and when the inputs to the display are 5V, Gnd, pulse sensor, pulse sensor I would have expected just 5V and Gnd should have resulted in a '0' display.

The capacitor across the regulator output and ground seems to be OK so I'm at a bit of a loss why the regulator died and suspect it could have been the display board (although it drew negligible current from my bench power supply).

I'll have another look tomorrow but will replace the regulator and see what happens; I don't really want to buy a new display board if I can avoid it!

An update, I replaced the regulator and it supplied a steady 5v to the display board and to the sensor. I had a look at the display board and couldn't see anything obviously wrong but without a circuit diagram etc. I'm a bit blind (and very out of practice with electronic fault-tracing).

I ended up putting my hand in my pocket for another display (£18). Fitted it this afternoon and it's working fine.

Maybe the display board died and took the regulator out? Anyway, fixed for less than 20 quid.

Thanks Stephen - you have evidently solved your problem. I just used an external RPM sensor instead - although I would like to fix mine properly. Your reply has probably prompted me to have another go. For future reference - the Amadeal CJ18a mini-lathe shares many attributes with the Grizzly-Go765 lathe and even the Warco WM180 appears to have the same control board. Some information regarding the control board can be found here: **LINK**