The 2DM860H chinese controllers vs the rest?

[Doddy]

Okay, so a bit of a tear-down of the 2DM860H.



Highlighted - 3 black screws that hold the board to the heatsink. 2 silver screws set into plastic top-hat isolators that secure the power electronics firmly to the heatsink.

Bottom left - 2 pin connector that is the AC/DC power input. This feeds through the fuse (normally a wire-ended... but what's there now is a bit of a hack attempt to repair. The big black circular thing is a NTC power thermistor designed to limit inrush current (it starts at high resistance but quickly drops as it warms up - likely used to allow the processor to start up and settle the power system before damaging anything.

Top left - I expect a small SMPS for the logic (untested). Left centre (left edge of board) - you can just see 4 pins for the power rectifier on the rear of the board Smoothing caps along the top and to the right of the board - all the logic. Thar be dragons.

Next pic, underside of the board, and a load of power devices...





The big thing at the top is the bridge rectifier. Four pins, which you can't see because of the thermal washer on it, but these are '-', '~', '~', '+", from left to right as orientated in the image.

The 8 TO220 packages are IRF640N N-Channel MOSFETs.

Parallel, and to the right of the top four of these are the stepper driver connections, labelled (top to bottom) "B-", "B+", "A-", "A+". If you look at the 8 MOSFETS, there's 4 pairs, vertically aligned. The left-most is driving the "B-" stepper; to the right of this drives the "B+" phase, then the "A-" and the "A+"

Each pair of MOSFETs are half-bridge configuration, and two pairs makes a standard H-Bridge for each stepper winding. The four pairs driving the 2 windings on a standard 4-wire stepper.



And a rough-order board layout...



Now, if, like me, you've blown one of the controllers up, chances are the problems are with these two H-Bridges, and the easiest method of diagnosing the problem is just measuring for shorts from pins to ground. Clearly, the bottom four MOSFETs will each have their Source terminals connected to ground (and the top fop have their Drains connected to V+)

I quickly tabulated a few measurements.

    Rg-d  Rg-s  Rg-0  Rd-0  Rs-0
    ----  ----  ----  ----  ----
M1: 1R    1R    4k    600k  2.6M
M2: 20k   20k   20k   600k  17R
M3: 2.6M  20k   3M    600k  6M
M4: 2.6M  20k   3M    600k  5M
M5: 20k   20k   20k   500k  0R
M6: 20k   2R    1R    18R   0R
M7: 2.6M  20k   20k   3.2M  0R
M8: 2.6M  20k   20k   3.2M  0R

Looking at that, I reckon MOSFETs M1 and M6 are blown. M2 is suspect, but I think the low resistance source-to-ground is via the internal short on M6 (M2 source, connected to M6 drain, which is near-short-to-ground).

The MOSFETs are through-hole devices, although I has a solder rework station I'll just crop each leg off the device, apply tension with some tweezers and heat each pin one at a time with a soldering iron to remove each pin. Solder-wick each side of the board clean, then remount and solder in from the reverse side of the board.

I do have one IRF620, but the Rds for this is too high and Id too low (5A); and a bunch of IRF3205's but the Vds for these is too low (50V). So, I'll order a pack of IRF640Ns, and replace at least M1 and M6. And report back on the robustness, or lack therein of the 2DM860H.