xray2
Member
As most of you know, I'm an Atari Vector head but, a buddy asked me to look at his Donkey Kong board (2 board set TKG4-13) which shows no signs of life. I replaced a couple of bad roms on the CPU board, connected up all the voltages and got nothing.
I started probing around with the scope and was getting erratic frequency readings on pin 6 of the z80 cpu and pin 12 of the 8257. The frequency would drift from low KHz all the way up to 25mhz! I started to work my back back through the clock circuit and, let's just say, it is a rather different design that what I am accustomed to dealing with. Simple 2 page schematic I am working from is a little abstract and a huge pita.
Can anyone out there confirm clock frequency measurements at various points on the board or provide pointers on where to go next? I did some extensive searching last night but after looking over 400 threads, found nothing similar.
I started probing around with the scope and was getting erratic frequency readings on pin 6 of the z80 cpu and pin 12 of the 8257. The frequency would drift from low KHz all the way up to 25mhz! I started to work my back back through the clock circuit and, let's just say, it is a rather different design that what I am accustomed to dealing with. Simple 2 page schematic I am working from is a little abstract and a huge pita.
Can anyone out there confirm clock frequency measurements at various points on the board or provide pointers on where to go next? I did some extensive searching last night but after looking over 400 threads, found nothing similar.