April 22, 2015

Opening up Bescor MP-101 Head

MP-101 Pan/Tilt Head patent makes for an interesting read.  Schematics in the patent depicts two H-bridges built from bipolar transistors.  And RF500T motors!  Are these Mabuchi RF-500TB?  Looks about right.  I now seriously think about opening the head and see whether I can discard all the electronics except the motors and have them wired to an existing DIN7 connector.  So that I could drive them both using a single TB6612FNG driver controlled by Arduino.  Hope to get more predictable results - love simplicity.

So, here is a perfectly working MP-101 head which I am about to disembowel...

After removing 6 screws you gain access to the electronics compartment.


The very first thing I noticed are those two ICs which look like LB1930 motor drivers.  This is fantastic because I now know which wires lead to the motors. It appears that yellow/orange wires lead to tilt motor and green/blue to pan motor.  Should I power the head up and see what voltage is used?  Never bothered to do that!

Here is a closer view with motor wires already unsoldered.


Few more screws and the PCB is released. I can see ST LM317T voltage regulator.

And the rest is just discreet elements.  Now, should I do something about those 45°, 90° and 340° end-switches?  Well, I tried.  But failed.

First note that there are no wires leading to +60 and +30 contacts.  Here are my notes on endswitch wire colors (note that in the photo colors are shifted because of the blue microscope light):
+60 - n/a
+90 - bluish-white
+30 - n/a
+0  - yellow
-0  - orange
-30 - green
-60 - brown ?
-90 - red

All these are neatly routed through a white tube:



Not only the +60 and +30 wires are missing, but I failed to discover how endswitches work.  It does look like my Bescor head was tampered - note other contacts missing - there are soldered points with no wires coming.  Despite being frustrated with time lost I do not mind it too much - I have now dirrect access to pan/tilt motors.  And after selling the remote with cable for $20 my cost is just $50 - I do not think I could remotely approach it with a DIY solution.

So my plan of action is to expose motors contacts via an RJ45 jack and to use regular CAT3 cable to connect the head to the controller!  Piece of cake!







2 comments: