Sunday, 21 July 2013

The Base

Removing the base would probably have been easier on models without sensors, but with a little persuasion, the board eventually came out:

The circuit board consists of two main parts - motor drivers and computer interface circuitry.

Driver board

A quick blast of the air duster removed 30 years of dust from the board...  Must actually remember next time not to do that inside the house !

The large edge connection shown in the picture above is where the hand controller connects.  This is not the same interface where the computer would be connected.

A couple of heat sinks were loose, so I pulled these off, and will remount them later with suitable thermal adhesive.

Interface board

On the surface, nothing really alarming to be seen here...

However, on the reverse side, one of the tracks for the edge connector appears to have been purposely cut!

A good 3 - 4mm of track has been scrapped away which can be clearly seen here:

At this stage, I really don't know which track has been cut!   And can't imagine why!

I know the 10 way interface comprises eight data lines (D1 - D8) and power (+5 volts and ground).  The data lines represent data (4-bits), motor select (3-bits), and finally a sync bit.  The sync bit indicates the direction of data travel, to the motors when low, from the micro switches when high.  The transition of state from high to low causes the step pattern to be latched, and allows for more complex, and parallel operations to be performed.

If this track is power, it's not so critical, but it's still an inconvenience, especially for interfacing to a Raspberry Pi (more on this later).  Of course, if this is one of the data lines, then I'll have no option but to repair or replace the circuit board.

As for the interface connection - this is where my documentation gets a bit sketchy.  It would appear Colne Robotics must have revised their circuit boards design at some point.  The documentation describes this interface as a 10way IDC, and certainly I've seen many examples pictured on the internet, but mine uses an Edge-style connector.  The circuit diagrams also bare no resemblance to reality, so reverse engineering, and some common sense will have to make do.

Final thoughts for the day :  I'm somewhat concerned about this interface board, the hand controller connects directly to the driver board which means none of this circuit board has been tested by myself.  I actually have no idea if the electronics work or not!  I'm going to put the base back together for now, and continue sorting out mechanical problems first.  The track can in theory be repaired, luckily this is 1980's technology after all - not your modern multi-layer boards with microscopic SMD componentry, making servicing virtually impossible!