3/22/2023 0 Comments Zipster coco![]() Next, insert the board (pins and ground lug), make sure it’s fully seated and level. You’ll want to be sure that slot is completely open (free of solder). This is where the ground lug on the new board will attach. 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. Preparing the motherboard for installation The modulator should now be easily lifted/gently pried 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. Use soldering wick to get what that won’t until the sheet metal tabs of the box are free. 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. 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. When it gets hot enough, you’ll be able to push it up into the modulator box. 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. Special care needs to be taken not to damage the pads these pins are soldered to. ![]() 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.įirst the modulator pins carrying the various signals should be removed. You will need a temperature controlled soldering iron for this, as it takes quite a bit of heat. The first step after removing the motherboard from the computer, and removing any shielding on the bottom, is to remove the RF modulator box. This is how I do it, of course it’s not the only way, and all the usual disclaimers apply. Here you will find some basic instructions for installing the Type A composite video board. Type B, American motherboards, ‘vertical’ Here are some pictures taken during development. I would say considerably better than the simple reference circuit in the MC6847 data sheet, which was all I’d been able to find previously.įurther working with this circuit, I decided to develop versions for both major modulator types, the ‘vertical’ modulator found in early American produced CoCo2s, and the ‘flat’ type found in Korean models. The board is a direct replacement for the RF modulator, requires no modifications to the case, and uses the channel switch to select between B&W / COLOR. Here is an early prototype of that effort. I decided to reverse-engineered the circuit and design some modulator replacements of my own based on this design. It’s also interesting to note that this ‘educational’ model uses the T1 variant (XC80652P) of the MC6847 VDG. I was very interested in this as I had just been working on something similar, but this was clearly a different circuit that Tandy used. ![]() Tandy factory original composite/sound boardĪfter a little research, I discovered this was a variant that had been intended for educational sales, where a composite monitor was prefered to TV sets as a display. It had factory composite and sound output in place of the RF modulator! What a surprise! Not long after I did my first CoCo project (a composite A/V board) I happened to buy a CoCo2 that had an interesting difference from the usual models.
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