CNC Board Repair/ Capacitor Help

[Sierevello1]

I have an older Anilam Crusader M 3 axis mill. I have some bad caps on several of the boards that are starting to give me issues. I have attached a few pictures of the ones I need to replace. One is marked 4u7 35, which I assume means 4.7uF and 35v, and it appears to be a Tantalum cap.

The other is green with a red dot on top and is marked 103 M5 and the board is marked .01 where the cap goes. I'm not sure if this is a ceramic cap or also Tantalum.

Any help in identifying these are appreciated.

Thank You,
Steve

 

[EPAIII]

Yes, the first one is 4.7 uF at 35 V. And it does appear to be a tantalum. In my experience, those dipped tantalum caps only rarely go bad.

On the second one, the 103 marking stands for the digits 1 and 0 followed by three more 0s. And the value is in pF. So it is a 10,000 pF or a 0.01 uF (same value). It is very likely a ceramic disc, but could be any of several other types. I doubt that it is an electrolytic or a tantalum electrolytic. Again, if it is a ceramic disc, i strongly doubt that it has gone bad. I spent a 45+ year career troubleshooting electronic circuits to the component level and, in that time, I only had to replace one bad ceramic disc capacitor. Oh, the M5 marking is probably a temperature coefficient designation. If you really need to replace it, look at the highest differential supply Voltages that the PCB uses and go a bit higher than that and you will be safe. Bu the highest differential Voltage I mean the highest positive supply Voltage plus the absolute value of the greatest negative Voltage (eg: +12 V and -12 V gives you 12 V + 12 V = 24 V. The next higher available Voltage rating is probably 35 V so use that). And regardless of what type it actually is, a disc ceramic should be a safe choice. PS: the very fact that they are using a 0.01 uF strongly suggests that the actual value is not all that important. In a digital circuit, 0.01 uF caps are used by the dozen to suppress logic spikes in the power rails. You will probably find them all around the circuit board.

Actually in a digital circuit, both of these caps are likely filtering for the power supply rails.

 

[Milland]

You might want to explain how you determined the caps were bad, as well as how you diagnosed the board. If there's a misinterpretation of readings you're taking, perhaps someone like EPAIII can help you focus-in on more likely problems.

 

[markz528]

Yes, the first one is 4.7 uF at 35 V. And it does appear to be a tantalum. In my experience, those dipped tantalum caps only rarely go bad.

On the second one, the 103 marking stands for the digits 1 and 0 followed by three more 0s. And the value is in pF. So it is a 10,000 pF or a 0.01 uF (same value). It is very likely a ceramic disc, but could be any of several other types. I doubt that it is an electrolytic or a tantalum electrolytic. Again, if it is a ceramic disc, i strongly doubt that it has gone bad. I spent a 45+ year career troubleshooting electronic circuits to the component level and, in that time, I only had to replace one bad ceramic disc capacitor. Oh, the M5 marking is probably a temperature coefficient designation. If you really need to replace it, look at the highest differential supply Voltages that the PCB uses and go a bit higher than that and you will be safe. Bu the highest differential Voltage I mean the highest positive supply Voltage plus the absolute value of the greatest negative Voltage (eg: +12 V and -12 V gives you 12 V + 12 V = 24 V. The next higher available Voltage rating is probably 35 V so use that). And regardless of what type it actually is, a disc ceramic should be a safe choice. PS: the very fact that they are using a 0.01 uF strongly suggests that the actual value is not all that important. In a digital circuit, 0.01 uF caps are used by the dozen to suppress logic spikes in the power rails. You will probably find them all around the circuit board.

Actually in a digital circuit, both of these caps are likely filtering for the power supply rails.

I agree - I have never seen a tantalum or ceramic cap go bad. Its the electrolytic that go bad.

 

[JST]

Tantalum caps similar to that have definitely gone bad by the skid-load.

I have replaced potfuls of them. They are a known issue.

The 0.01 uF cap is not a likely problem, far more likely that the tantalums went bad. So the best approach is to replace any tantalum ones that seem bad, and probably the rest of any value/type that you have had to replace some of, because the rest will go bad also.

 

[jatt]

Good thing their not surface mount!!! Somewhat easier to ID the older stuff, unless of course u let the smoke out!

Having played with stuff that was subject to lots of vibration in the past - vehicle mounted equip, my first goto was checking for bad solder conns before going further. Reworking sus looking solder joints -- large elecrolytics are chronic for it, and of course can give trouble after time. Wasn't fond of the 85 deg units, favoured the 105 deg or higher.

Cleaning off missed solder flux.

Cant ID those parts any better than whats been offered up already.

Good luck with it.

 

[billmac]

Tantalum caps do fail unfortunately. They pop and make a horrible characteristic smell. You may even be able to detect the smell if the failure is recent.

 

[Larry Dickman]

Tantalum caps do fail unfortunately. They pop and make a horrible characteristic smell. You may even be able to detect the smell if the failure is recent.

especially when a numb nuts assembler puts one in backwards. They don't like that. Like was said above, tantalum and ceramic caps rarely go bad.

 

[EPAIII]

Perhaps I should have said more about tantalum capacitors and their failures. Yes, in contrast to the extremely small rate of failure in the disc ceramic ones, tantalums do go bad somewhat more than that. But they are also have a far smaller failure rate than standard electrolytic capacitors which fail all the time.

I have had to replace bad tantalum capacitors. But most of those failures were in the TUBULAR tantalums, not the dipped ones. The dipped tantalums have a far lower failure rate than the tubular ones do. Perhaps I have seen this in equipment that is built with higher quality components than some others here have seen. But that is my observation.

So if I had to rate capacitors for reliability, starting with the most reliable and working down to the least reliable, it would look something like this:

Mylar
Ceramic Disc
Dipped tantalum
Tubular tantalum
Aluminum electrolytic
Standard or older electrolytic

The Mylar and the ceramic disc types are similar in reliability and you could put either one a the top of the list while the others in the list are separated by greater amounts. As I said, I did see ONE bad disc ceramic type, but I have never had even a single bad Mylar one. And the more recent, aluminum electrolytics are said to approach the reliability of tantalums.

To be sure, there are other types of capacitors. Some have various plastic insulating layers. They are used for special reasons and are not as common as the above types so it is harder to rate then but they would be near the top of the list in reliability. Likewise for other types: I just do not have enough experience to place then on the list.

I do not know for sure, but I suspect that the difference between the tubular and dipped tantalums is due to better sealing with the dipped type.

The first, 4.7 uF capacitor that the OP showed APPEARS to be a dipped tantalum. But even that is not a certainty. A quick test would be the weight. Tantalum type capacitors are heavier than most others of the same size. But I can't tell that from a photo.

 

[JST]

Thr dipped (solid) tantalums do have a low failure rate.

But, they were often applied with low voltage margin. They do not like any voltage spike etc over their voltage rating, and will fail rapidly if that happens. The typical failure mode is a short.

So, what is the reason for replacement? If it is not a short, then replacement may not be required.