The 2DM860H chinese controllers vs the rest?

[Kitwn]

Neale,
When I was a lad power transistors (at least the radio frequency ones) were described to me as "the fastest fuse on three legs". In practice these things often fail as a short circuit which is what takes out the fuse to protect everything else as you say. Doddy's got an evening amusing himself with his soldering iron out of it so all's well that ends well.

Putt's Law states that technology is dominated by two types of people. Those who understand what they do not manage and those who manage what they do not understand.

[Doddy]

Neale,
Doddy's got an evening amusing himself with his soldering iron out of it so all's well that ends well.

Putt's Law states that technology is dominated by two types of people. Those who understand what they do not manage and those who manage what they do not understand.

I seem to have many things amusing myself at the moment. Ho-hum. I like Putt's Law, I need a coffee mug with that on it.

[Neale]

When I was a lad power transistors (at least the radio frequency ones) were described to me as "the fastest fuse on three legs". In practice these things often fail as a short circuit which is what takes out the fuse to protect everything else as you say.

My degree, best part of 50 years ago now, was in electronic engineering - this at a time when a quality "transistor radio" was still populated with germanium transistors. I remember the same quote! My son once borrowed my variable-voltage bench power supply to charge a car battery. Not a good idea. At least 2N3055s are big enough to get a decent size soldering iron on! 6 of them, as I recall...

[Doddy]

I cut my teeth on AC171s

Edit: my bad, AC181s.... twas 45 years ago.

[Kitwn]

50 years ago was about when I got my Philips Electronic Engineer Set for Christmas. And look where that got me!

AC181s......You were lucky! I actually preferred playing with BY1144s but that came later.

[Doddy]

I've just googled a BY1144. I don't think my pocket money would have stretched that far. Nor the incomer to the house supply.

Recap:



I'm going to replace MOSFETs marked M1 and M6. I'm going to be lazy and crop the leads from the devices to give me 3 pins soldered to the PCB, but first a sanity check that the device, removed from the board, exhibits the problems measured in circuit.



Next, with tweezers (reduce the thermal mass) remove each pin with the aid of a soldering iron from the copper side.



Next, with solder-wick and the iron, try to clean out the lead holes for the MOSFETs the best I can. In honesty I did 4 this way before falling back on a desoldering workstation - I figured I'd proven the point that this can be done cheaply... but no point labouring this point to myself - use the best tool for the job.



Next, repeat for the second device. Then clean up all the old flux with a bit of IPA and the wife's toothbrush.



Bend and crop the leads of the replacement MOSFETs, insert and solder from the copper side of the board. A quick examination of the component side confirmed no heavy current traces on that side, so no need to risk trying to solder from the component side as well (the access is inhibited with a couple of wire wound resistors).


Note, plenty of heat-sink paste applied to all components.

Next apply power (having replaced the fuse), without a motor attached to check that nothing goes pop...



80-odd milliamps - sounds about right for a microcontroller and LEDs.

Full blown test - sig-gen pulsing the STEP input to the driver. It took me five minutes of checking before first realising that 5Hz and whatever micro steps selected that the motor was actually turning, before ramping up the frequency.




So, thanks to the encouragement from Kit to not throw it away - I think I have a repaired Stepper Driver. Having compared the electronics to the replacement DM860 that I bought I'd sooner use this 2DM860 model with what appears much better (robust/specc'd) electronics.

Repair is not for everyone, but perhaps if someone is as clumsy as me you might consider this before spending on a replacement. Your results may vary!

EDIT: Eagle-eyed video viewers may notice that I'd replaced the cooling fan wiring to the board with a couple of Dupont connectors, just to allow me to separate the board from the heatsink easily, plus, the soldering job underneath the silicone was atrocious.

[JAZZCNC]

Well done that man, I've got a few dead drives I'll send you them to keep you busy in lockdown...

[Kitwn]

Super job and an excelent set of pictures and video. I'm jealous of the range of test equipment. Who'd have thought I could infulence the behaviour of someone so far away

You haven't used any tools that most builders aren't going to need anyway to fit all the plugs and sockets on a machine (I'd add a solder-sucker for clearing out the holes) and my only gripe would be the lavish amount of heatsink compound. Nice to think Dean will be sending you a pallette-load of stuff to repair.

[Doddy]

my only gripe would be the lavish amount of heatsink compound.

I agree - the problem is twofold here - there are isolating pads currently stuck (I use the term guardedly) to the heatsink - using a little bit of heatsink compound. There's no registration of the actual devices to the pads, and no mechanical means other than the PCB stand-offs (and bolts) to mechanically couple the devices to the heatsink. So, you're relying on the stand-off of the device from the board to mate with the heatsink, and/or the blob of compound to provide a conformal interface with a reasonably low thermal resistance. I've not been able to find from the data sheet if the device tab is electrically connected to the silicon, but a test of one of the fails devices suggests that it is - which warrants considerable caution with maintaining the superficial mechanical registration with the pads. The usual approach of a thin film doesn't work in this situation.

[Kitwn]

I should have known you had a god reason for it.