Installing the Board (Type A)

Here you will find some basic instructions for installing the Type A composite video board.
This is how I do it, of course it's not the only way, and all the usual disclaimers apply.

Removing the RF modulator

The first step after removing the motherboard from the computer, and removing any
shielding on the bottom, is to remove the RF modulator box.

You will need a temperature controlled soldering iron for this, as it takes quite a bit of heat.
Somewhere around 350º C is appropriate, otherwise the large ground plane under
the modulator sinks too much heat to get the solder for the box ground connections liquid in a 
timely manner, or heat the signal pins enough to melt the solder at the top of the pin where
they are connected to the modulator pcb.

First the modulator pins carrying the various signals should be removed.  Special care needs
to be taken not to damage the pads these pins are soldered to.  I've found the safest way is
to heat the pin from the motherboard bottom while applying moderate pressure to the end of the pin.

When it gets hot enough, you'll be able to push it up into the modulator box.  At this point there is
enough of the pin protruding on the top side so that it can be grasped with a pair of need-nosed
pliers or the like, and pulled (with moderate force again) while it's heated again from the bottom
until free.  Repeat for the other 7 pins.

Heat the large solder connections where the RF box is connected to the ground plane, using a solder
sucking device of some sort to remove the bulk of the solder.  Use soldering wick to get what that won't
until the sheet metal tabs of the box are free.  A couple of them will need to be straightened to fit
through the slots in the board where they were originally bent to hold them in place prior to soldering.

The modulator should now be easily lifted/gently pried free.  

Whew...  The hard part is done!


Preparing the motherboard for installation

Use solder wick to clean up the pads for the pins, and also the rearmost slot in the ground plane where
the modulator box was soldered.  This is where the ground lug on the new board will attach.
You’ll want to be sure that slot is completely open (free of solder).

Next, insert the board (pins and ground lug), make sure it’s fully seated and level.
Solder one of the pins to hold it in place until you are sure you’ve got it positioned as you want
it (down all the way and parallel to the motherboard).

Solder the rest of the pins, and then the ground lug.  The ground lug is soldered to the board, so you’ll
want to apply enough heat long enough to solder it to the motherboard, but not so long that it melts the
connection on the Composite board; not really an issue as it can’t move around at that point anyway,
just something to be aware of.

All that’s left now is the power leads.  The WHITE wire connected to P2 is the AC power to the board, 
and will be attached to the anode of one of the large power diodes on the motherboard.  
This should be ~ 8.4 VAC,  you can use a voltmeter to verify.  The RED wire connected to P1 supplies
DC voltage to the board, and will be attached to the cathode of one of the large power diodes.  
It should read ~ +9.9 VDC.

Type A Composite Board Installed

Once the power leads are attached, you just need to trim the pins sticking out of the bottom of the 
motherboard (the ground lug is pre-cut and should not need trimming).

I will have already set the potentiometers while connected to a TV and an oscilloscope for testing, 
before sending the board.   They can be adjusted if needed on your particular setup, but try it first.  :)

And that's it!  Put it all back together and enjoy Composite video on your CoCo2.


Notes for the Type B

Installing the Type B composite boards is essentially the same, but watch the power connections
carefully.  The diodes are reversed in their orientation on the motherboard.

Power connections for Type B (American) motherboards

Comments