xodaraP
Legendary
Hi all,
I have come across an issue on a CPS2 A board (confirmed B board works fine on another A) where the sound/music runs a lot faster than it should be. I have so far replaced the Z80 and tested with no change, and the LS245 in the sound section (the only TI branded chip in the area) with no change
Given this is a speed issue, I am thinking it may be related to the clock circuit on either the Q Sound CPU or the Z80. More likely the Z80 as the Q Sound has 60Mhz coming in, and outputs 60Mhz to the DAC.
The Z80 has an 8Mhz. clock and the bus and /WAIT signal run with this unchanged. The interrupt line for the Z80 is derived from several 74LS390 ICs (11L, 9L) into a 74LS161 (8L) which divides the 8MHz. clock down to 250Hz into a 74LS74 (11M) which outputs the Interrupt signal if requested by the OR gate 74LS32 (9M)
Has anyone run into a similar issue in the past and can confirm if I am on the right track or if there is somewhere else I should be looking?
I am thinking of replacing the entire clock division circuit starting with the LS161 as it is the final link in the division, continuing onto the LS74, LS32 and then the 390s if none of these correct the issue
I have come across an issue on a CPS2 A board (confirmed B board works fine on another A) where the sound/music runs a lot faster than it should be. I have so far replaced the Z80 and tested with no change, and the LS245 in the sound section (the only TI branded chip in the area) with no change
Given this is a speed issue, I am thinking it may be related to the clock circuit on either the Q Sound CPU or the Z80. More likely the Z80 as the Q Sound has 60Mhz coming in, and outputs 60Mhz to the DAC.
The Z80 has an 8Mhz. clock and the bus and /WAIT signal run with this unchanged. The interrupt line for the Z80 is derived from several 74LS390 ICs (11L, 9L) into a 74LS161 (8L) which divides the 8MHz. clock down to 250Hz into a 74LS74 (11M) which outputs the Interrupt signal if requested by the OR gate 74LS32 (9M)
Has anyone run into a similar issue in the past and can confirm if I am on the right track or if there is somewhere else I should be looking?
I am thinking of replacing the entire clock division circuit starting with the LS161 as it is the final link in the division, continuing onto the LS74, LS32 and then the 390s if none of these correct the issue
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