Capacitor burned out on cnc control board, possible causes and identity

Thread Starter

dandy1

Joined Sep 30, 2017
91
This is a shot of my cnc control board with a capacitor burned out. Cheap Chinese stuff so I'm not surprised. It's off a 3018 machine but there are others that use the same board. Can someone help identify for replacement. The cap is across the barrel jack dc out at 24v switched by the relay to the right. Everything was running fine, tried out the spindle with a couple of cuts with no problems - until I installed limit switches. The control board has pins for 6 switches but I paired up each axis to save some time on soldering pesky little headers.

So I tried out the limit switches on the cnc with the homing command an to my amazement, first time round - worked like a charm.
Then went back to try out the spindle again but as soon as it was enabled it would trip a limit.

Now I have learned that unshielded cable on cnc acts like an antenna, so after installing some 47nF caps on the limit signals still got trips from the spindle just like before (maybe add some pull ups too). So I tried the methodical approach and removed one by one until no limits were connected.

TBH I should have known better and install a diode across the spindle but I was hoping(without checking) that it would be taken care of either within the spindle or on the control board. How wrong you can be....

Another thing I hadn't done is ground the spindle case and also the machine itself, I doubt this would have changed anything but looks like a must in such applications.

there is 105 printed underneath the cap so does that represent something?

Anyway thanks DSC_0253.JPG DSC_0255.JPG for reading.
 

ericgibbs

Joined Jan 29, 2010
10,198
hi dandy,
Looking at the Ident codes on the PCB capacitors shows they use conventional coding for Caps ie: C4, C6 etc.
The 105 coding is often used for MOV or TVS components.
I have been searching online for a match, no luck so far, so it maybe a MOV or TVS

E
 

BobaMosfet

Joined Jul 1, 2009
1,118
105 usually means it's 1uF and that looks like a tantalum cap, can you see any marking to determine if it is (it will be polarized).
 

Thread Starter

dandy1

Joined Sep 30, 2017
91
hi dandy,
Looking at the Ident codes on the PCB capacitors shows they use conventional coding for Caps ie: C4, C6 etc.
The 105 coding is often used for MOV or TVS components.
I have been searching online for a match, no luck so far, so it maybe a MOV or TVS

E
Hi Eric thanks for the reply. Here's a better shot. It's denoted C6 and measuring C5 (jut above) gives 1.2uF but switch mm probes and gives nothing?


DSC_0259.JPG
 

pmd34

Joined Feb 22, 2014
507
I'm in agreament with Bobamosfet 105 on a capacitor usually means 10 00000 pf. Tantalum capacitors are usually yellow looking like that, though if it has no polymerization I guess it could be a leaded "MLCC" ?
.
It looks like it is a simple power supply smoothing capacitor, so its either seen too high a voltage, or its been a poor quality capacitor. So I would not be too fussy with what you replace it with, so long as it has a high enough voltage rating and a value >1uF
 

Dodgydave

Joined Jun 22, 2012
9,206
Tantalum capacitors are Polarised,,, usually with a dotted + line, or inverted L..

Code 105 i would say is 1uF, 106 is 10uF..


R2620.jpg.jpeg
 

bertus

Joined Apr 5, 2008
20,568
Hello,

The shown part is likely a tantalium capacitor, as the others also mentioned.
I have seen them blown and creating a short on the powersupply.

Bertus
 

Thread Starter

dandy1

Joined Sep 30, 2017
91
Update :

DSC_0260.JPG


Didn't get to read Burtus post before I done this, put in a 3.3uF 50v electrolitic. Took about 10 secs to blow mind so stood up well. The relay that switches the power was clicking away just fine, didn't have the spindle connected because first thing was to check the flyback polarity, so for sanity sakes the band on the diode goes to +?
Anyway, it's clearly something like Burtus has predicted and need to check that out.
China China
 

Thread Starter

dandy1

Joined Sep 30, 2017
91
Think I found what I'm looking for:
12v on the base and emitter (c&r) so it looks like the relay is shot back feeding the 8550


DSC_0262.JPG
 
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