UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Gemini 80-Bus System

john_newcombe · 8th Jul 2019, 3:59 pm

I checked the Mux ICs (10, 11, 12, 15, 16, 17) and I can see the negative going pulses on pin 1 in each case.

Turning my attention to the clock, I re-inserted the original ROM and checked pin 6 of IC 3. The clock frequency was 9.38 Mhz and is clearly coming from the VCO as I could adjust the frequency with RV1. Pin 11 of IC 7 was High (6 Low) and as expected given pin 11, no output on pin 10. Just for fun I adjusted the VCO to 16Mhz however, no change.

I will quickly check with the second IVC ROM before coding up a ROM as was suggested by Neal, e.g.

Code:

        ld hl, 0xc000           ; status write 
        ld a, 0x02              ; crystal dot clock
        ld (hl), a              ; write
loop:   jr loop

This should give me something concrete to work with.

8th Jul 2019, 3:59 pm	#141
john_newcombe Hexode Join Date: Apr 2019 Location: Skipton, North Yorkshire, UK. Posts: 252	Re: Gemini 80-Bus System I checked the Mux ICs (10, 11, 12, 15, 16, 17) and I can see the negative going pulses on pin 1 in each case. Turning my attention to the clock, I re-inserted the original ROM and checked pin 6 of IC 3. The clock frequency was 9.38 Mhz and is clearly coming from the VCO as I could adjust the frequency with RV1. Pin 11 of IC 7 was High (6 Low) and as expected given pin 11, no output on pin 10. Just for fun I adjusted the VCO to 16Mhz however, no change. I will quickly check with the second IVC ROM before coding up a ROM as was suggested by Neal, e.g. Code: ld hl, 0xc000 ; status write ld a, 0x02 ; crystal dot clock ld (hl), a ; write loop: jr loop This should give me something concrete to work with.