The 2DM860H chinese controllers vs the rest?

[Kitwn]

Doddy,
That's a brilliant job, thank you!

I know most people want to just plug-and-play with modules but when you see how simple it is to fix some of the faults for yourself and realise how cheap some of the components are it saddens me to see people just give up and trash expensive modules that can be repaired for very little. Most faults with this kind of device will be in the power supply or output devices, all of which tend to be the large components that cost very little and are easy to replace as you've demonstrated. RS components will send you a bag of 5 new transistors for less than the cost of a pint, including postage!

[Doddy]

A little unfair there - there's a long way to go before this works again, and I'm carrying cost and risk in repairing it - for some the downtime wouldn't warrant the cost of replacing with new. Also, to be absolutely honest, I don't think it's cost-effective for me to have spent trying to clear some form of metal debris from the fan supply solder pads for the last hour (finally resolved with a 0.4mm drill - which I managed to snap in the hole) - it was clear on inspection that the fan wiring was a bodge job with the assembler unable to poke the wire through the hole - silicone hides a whole multitude of sins on PCB assembly in china.

If it wasn't for this damned lock-down I'd throw the controller in the bin and be done with it, but being forced to spend time either with the wife or with a soldering iron, there's some curiosity value for trying to repair. But I do have some rather expensive tools to support that curiosity. Also for many in this game there's a lifetime of experience of feed rates and chip loadings that I just don't claim to understand, but then I wouldn't expect them to understand the behaviour of a h-bridge and failure modes of a MOSFET.

Horses for courses.

(but I'm determined now to get this sucker working again)

[Kitwn]

My apologies if I've sent you down a rabbit hole you were not intending to follow! On the other hand I think it's worth pointing out that many equipment faults can be repaired with a few tools which, once bought, will last for many years. There are more choices available than bin-and-replace for those willing to learn a new trick and I suspect you, like me, have reincarnated more than one piece of expensive electronics by knowing how to recognise and replace a faulty power supply capacitor costing mere pence.

If it were me I'd be bringing the soldering iron onto the dining table which is surprisingly close to my wife's weaving looms so I don't have to make your difficult domestic choice

[Neale]

The obvious question to ask is why, if there was a fuse, it was not accessible from the outside for replacement purposes? The answer, I think, is for the same reason that I don't stick fuses everywhere in my own control box. The fuse in this case did not protect the mosfets - it protected the rest of the upstream wiring and power supply from a potentially dangerous overcurrent situation causing a fire. Pound to a penny that the mosfets popped first, then the fuse blew to protect the rest of the system. The manufacturer knew this - no point in a replaceable fuse if the driver is dead anyway. Fuses are very important and shouldl not be forgotten - but just remember what they actually achieve and use them accordingly.

On a more positive note it's interesting to see that these drivers use well-marked and easily available replacement mosfets, although I would be a bit hesitant about working on through-hole boards - haven't had to do that myself.

[Doddy]

MOSFETs due in tomorrow from Farnell... along with some other goodies. Neale - that's pretty much the purpose of a fuse - and anyone relying on one to protect semiconductors has a lot more optimism than me. The more I look at these drivers the more I like about the design - the accountants haven't got too close to these, just close enough to the training of the assembly workers :)

[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.