[Coco] 26-3022 Disk Controller Question

[Barry Nelson]

> Garrett Reynolds
> Sat Sep 2 23:26:00 EDT 2017
> 
> I picked up a Drive 0 1st generation (grey) single floppy drive and controller.  The original label is missing but I assume this is the 26-3022 as it is equipped with the WE FD1793B-02.  I understand this controller is not very popular or reliable.  I've read that it will not work on the CoCo2/3 (I have a CoCO3).  I believe this is because it needs 12VDC to function which is not present on the later computers or needed by the newer controllers (that's weird to say, "newer controllers").
> 
> Anyway, I've read that if you replace this DIP CHIP with a Fujitsu MB8877A that it will then work with the CoCo2/3.  I found several of these chipsets on ebay for around $10.  Does anyone have experience with this controller, the modification that I speak of and any recommendations as to making this controller work with my CoCo3?
> 
> I did open the controller, seat the components, and cleaned up the pins and confirmed that controller boots to DECB.  I did not attempt to plug in the drive or access it pending answers to these questions.
> 
> I also read that if you have a multi-pak that this controller will work without modification, but I do not have one.
> 
> Your ideas/suggestions are graciously invited.
> 
> Garrett
Don’t assume, the 26-3029 also can use the WD1793B-02, but doesn’t have all the adjustment pots. If you don’t have another disk controller, and you don’t mind soldering, you can probably get this controller working. I don’t know about replacing the chip with a MB8877A in a 26-3022. The MB8877A says it is a direct replacement for a WD1793B-02 and it does not require 12V however when I looked up the schematic for a 26-3022, the schematic showed a potentiometer connected to the 12V line. The 26-3029 is another story and does not have this connection. The controller won’t care HOW it gets 12V though, so if nothing else, if you hook up an external 12V supply to the correct pin and connect the ground side of the supply to ground, it should work. You could even get the 12V from the floppy drive, as it also requires 12V to run, so the floppy drive power supply will have a 12V supply line. According to the schematics I looked up the missing 12V power should be supplied on pin 2 on the cartridge connector.