[Coco] Tandy MPI 25-3024 and CoCo 1 26-3004a

[Bruce W. Calkins]

1) That depends on the mainboard version.  See Allen Huffman's "CoCo 
Chronicles" book for details.  The various details should be on-line 
somewhere too. Given that it is labeled 64k I would supect an E or "F" 
variant board.  the E board required some added wiring, the "F" board 
had third jumper.

T) The old style MPI was really that easy.  The second version needed a 
logic chip wired in with a trace cut.

Bruce W.

On 4/22/20 10:42 PM, Michael Miller wrote:
> So, I recently (well - over a month ago) got a Tandy MPI and a CoCo 1 
> off of EBay and I finally got a good look at them. Both units are 
> filthy, and both had never been opened. Naturally, I opened them up.
>
> The insides actually looked pretty good - nothing obviously wrong with 
> either unit (no burnt traces, no swollen capacitors, no leaky 
> components). The CoCo 1 is missing the ECB ROM and seems to be a 16K 
> unit with 2 jumpers for 64K. I am definitely going to hook these up to 
> Ye Olde CRT TB and see if they still function, and if so, I am 
> peobably going to retrobrite the MPI. The CoCo1 case will just need to 
> be repainted - the gray paint is worn clean off at the base of the 
> keyboard. It looks like the ECB ROM is still available from Ed's store.
>
> My questions are these:
>
> 1) On the 26-3004a mainboard, all I have to do is swap out the RAM 
> chips and change the 2 jumpers for the full 64K?
>
> And
>
> T) Theoretically all that has to be done to upgrade th MPI to CoCo3 
> compatability (because I eventually want one) is to replace the PAL 
> chip in it. Where does one acquire the updated PAL chip nowadays?
>
> Thanks,
> Michael V. Miller
>