AXBB charge pump fault

[john swift]

Charlie
have you had a quote from CNCdrive what they charge for the repair of the AXBB controller ?
John

[CharlieRam]

I have been in contact with Balazs from CNCDrive and unfortunately it seems it won't be covered...

No, this kind of problem is not covered by warranty, because the transistor can be damaged only with overstressing the output e.g. with misconnecting the output, e.g. connecting a low resistance like a direct connection to the +24Volts.
Or if the issue is something else like a soldering error then we repair in warranty for 12months from purchase (shipping) date.

I haven't asked for a cost of repair but I did ask for the data sheet for the mosfet....

The transistor this one: https://www.digikey.com/products/en?keywords=NTR5198NL
It is not hard to remove and replace this kind of component, I mean it looks harder than it actually is.
You just need a tweezers and a soldering iron.

I haven't had chance to try another output as the charge pump yet but I'll try later. The Relay switches on and off fine when I connect it up to 24v.

I will also check the voltages as suggested but my local electronics shop may still be cheaper than shipping to Hungary and back. I am wondering though what could of caused it and will it happen again

Sent from my SM-G920F using Tapatalk

[john swift]

knowing the part number is a great help

( the Vishay Si2306DS from post 30 looks similar )



if you melt the solder on all 3 legs by adding fresh solder

a Desoldering Pump may well pick it up as well as the solder !

https://uk.farnell.com/duratool/908-...tic/dp/3125646



once repaired I would be inclined to use a relay with its own driver !

John

PS
Farnell have the NTR5198NLT1G FET

https://uk.farnell.com/on-semiconduc...ngdom%2Fsearch

[Doddy]

<deleted - just really agreeing with John>

[john swift]

Hi Doddy

I see you changed your mind
dont worry
your original reply just pointed out we use the technique that we are happy with

I have to admit unless I am under instructions to maintain a lead free status
I use 60/40 solder and add some rework flux

If lead tin solder is good enough for use in pacemakers and other mission-critical equipment
its good enough for me

John

[Doddy]

If lead tin solder is good enough for use in pacemakers and other mission-critical equipment
its good enough for me

John

Similarly, gifted with an industry that embraces the old 60/40.

Right, just tried a quick experiment - I have some 2N7002's in the shed so hooked one up to a signal generator set to 1Hz (though I ramped up to 35Hz out of boredom).


Basic circuit...



...using a practice board for SMDs as a breadboard...



So, this ran for 5 minutes without fail.

I then cut the diode (observed in image) to see if the back EMF would pop the transistor. I ran that for 5 minutes at upto 35Hz, with no failure.

Out of interest, I wet my fingers and placed across the relay coil - this calibrated method of measuring EMF confirmed that there was OUCH! volts of back-emf. Recovering the diode did quench the back emf, as expected.

I had expected the 2n7002 to fail due to the excessive VDS, but for the duration that I ran this it did not. The OUCH! test did confirm the expected high EMF present on the drain of the transistor.

So, CharlieRAM - you asked what could cause this to happen again... although inconclusive I'd recommend placing a diode, e.g. 1n4004 across the relay coil, cathode to +24V, anode to the AXBB board output. If you want a couple of diodes and a couple of 2n7002s thrown into the post let me know.

I'd recommend this for any output driving a relay or other inductive load.

[CharlieRam]

I think I have some of those diodes lying around from a previous project, I'm all for belt and braces approach I've contacted my local shop regarding the repair so I'll wait for a response.

Just a thought....my machine is in a log cabin at the bottom of the garden connected by an RCD in the house so if I leave anything on in there and then decide not to go back down I just trip the RCD. Would that likely cause an issue? It's just easier than going back down to turn it all off!

Sent from my SM-G920F using Tapatalk

[Doddy]

if I leave anything on in there and then decide not to go back down I just trip the RCD. Would that likely cause an issue? It's just easier than going back down to turn it all off!

I don't see anything wrong with that approach.

[john swift]

The belt and braces approach of adding a diode across the relay coil works for me
( As long as you have it the correct way round )



I would look for a wiring problem that could of shorted the +24V to the AXBB output

As semiconductors fuse faster than expensive fuses thats supposed to protect them
you could try adding a 22 ohm 1/4W resistor in series with the relay coil
( the resistor should only fail if the relay coil is shorted )

The only issue I would expect with tripping the RCD will be corrupting the PC hard drive
If you have not shut the PC down

John

[john swift]

Another diagram to expand on the one in post 39



John