[tech] Status of snack machine

[Harry]

So Nick, Cameron, and Harry braved the snack machine internals on Friday
evening and found:

1. Checked PSU through up to motor driver ICs. PSU all looks ok.

2. Measured 24v high-side motor driver (UCN5890A) and found
three stuck at 24V; pins 9, 10, and 12(?). No stuck pins of low-side
driver (UCN5841A).

3. Disconnected three stuck pins for P8 (connector to motor row/column
matrix). Tried to dispense from motor not connected to "stuck" circuits
but no response. This could be just the high-side motor driver
(UCN5890A) being dead and the low side driver is actually ok.

4. Connected a motor directly to 24V and it operated ok.

TODO:

A. Check motor matrix with meter to confirm all diodes in matrix are ok.

B. Observe serial clocking and data signals on both drivers are bring
driven ok by MCU

C. Check if low-side driver outputs are driving low so driver is ok.

D. Find high-side (and possibly low-side) drivers and replace. Spares of
these would be handy because they look hard to find.

E. Clean goop from melted redskins from rack that may be stalling motors

F. See if the bernard code needs any more stall amd overcurrent sensing
to disable motors if overloaded and report faults.

msh and zarquin searched the net for the parts and the UCN5890A is
discontinued and looks hard to find :-( Need to check if Mike Langan at
Worldwide has some squirrelled away somewhere.

All for now
Harry