13-05-2020, 09:14 PM
Hi Ian,
Personally I would go for it, however there are a few more factors you need to consider.
1) You will need to cut tracks and alter the output pick off from the Oscillator divider, otherwise you will end up with the processor running too slow. Currently its using a divide by six to go from 12Mhz to 2Mhz when you fit the 13.5Mhz crystal you need to only divide by four to get your 3.375Mhz.
2) Your original Character PROM will likely be a 2516 and if you are producing a new character EPROM yourself it will likely be a 2732, only the later boards had the jumpers available to change between the two so once again some track cutting and changing of signals to drive the new character EPROM.
3) The originals had Z80's and PIO's that were capable of 2Mhz and may not run at 3.375Mhz reliably, if they have an "A" suffix then they will be rated at 4Mhz so will be good.
Your contact problem on the RH side of the Coreboard may be the 25 pin X4 pins or socket these were notorious on the older boards.
If you are going to do any work on the Microbee I would look at changing both the plug and socket of both the X4 and X1 connectors.
Ernest
Personally I would go for it, however there are a few more factors you need to consider.
1) You will need to cut tracks and alter the output pick off from the Oscillator divider, otherwise you will end up with the processor running too slow. Currently its using a divide by six to go from 12Mhz to 2Mhz when you fit the 13.5Mhz crystal you need to only divide by four to get your 3.375Mhz.
2) Your original Character PROM will likely be a 2516 and if you are producing a new character EPROM yourself it will likely be a 2732, only the later boards had the jumpers available to change between the two so once again some track cutting and changing of signals to drive the new character EPROM.
3) The originals had Z80's and PIO's that were capable of 2Mhz and may not run at 3.375Mhz reliably, if they have an "A" suffix then they will be rated at 4Mhz so will be good.
Your contact problem on the RH side of the Coreboard may be the 25 pin X4 pins or socket these were notorious on the older boards.
If you are going to do any work on the Microbee I would look at changing both the plug and socket of both the X4 and X1 connectors.
Ernest