Help Needed CNC controller PCB

Thread Starter

Badgersurfer

Joined Mar 15, 2021
4
I am new to this forum and wonder if someone could give me some advice. A long time ago I was an RAF Radar Technician so am familiar with circuits and component repair. I am currently into using CNC Lasers and Routers but I have a problem. I have a couple of German Stepcraft CNCs and for the second time in 2 years one of my controller boards have failed due to an SM14 Diode. The last time it happened I spent £150.00 on a new controller board and then found out afterwards that it was under a 2 year warranty so I sent it back and they repaired it. I kept the new one as a spare. So when the repaired one was returned I noticed that all they had done was replace a small diode marked SM14 7MY and just in front of the 7 MY was their Brand logo in the shape of an S (attached picture). So I then looked at the other PCB and it also had the same components but the diode said SM14 7KY. I figured this is simply acting as a fuse and instead of waiting weeks for repair and as I am out of warranty now probably the cost of a new board, I could repair it myself. I have found a site on eBay that sells 5 pack of these diodes for £1.25 which is more in my budget :)
I appreciate there is a reason it blew these diodes but on both occasions it was when I left the board powered over night, and literally standing idle.
It appears by looking on the Internet this problem is not uncommon with the Stepcraft PCB.
What I would like to ask the experts on this forum is in your opinion would I be able to replace my faulty diode SM14 MY with one of the standard SM14 from eBay. I figure they are the same (they physically look the same with 2 pins) but I don't know if the KY or MY chars have any importance?
 

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Thread Starter

Badgersurfer

Joined Mar 15, 2021
4
I just want to spin this by you folks. I realise this may be a bit unconventional but I decided to solder wires onto the existing diode connections. This will be easier for me to replace new diodes if needed. I hear what you folks are saying about putting in a 2amp diode but I had already ordered a bunch of new SM16s. I intend to slip a piece of heatshrink over it for insulation. I would appreciate your feedback on this idea, one thing came to my mind that if I heatshrink it is it more likely to overheat? I did it this way as I am getting old and my hands aren't as steady as they were.
 

Thread Starter

Badgersurfer

Joined Mar 15, 2021
4
I would guess that that's a bad idea.
Adding wires will add inductance. We don't know the function and circuit application of the diode.
Thank you for your feedback. I have taken your advice, removed the wires and soldered it directly to PCB. I switched it on and bingo fixed.
 
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