720fan
Member
720 - atari series 2, +15v on audio and video board..where does this come from?
so, im still stumped on my 720 machine... so far here is what happens when i turn it on.
all lightbulbs light up on coin doors and marquee.
monitor turns on and goes white when i adjust the "screen" control.
there is NO sound at all.
the video board and the cpu board light up red, and when measured i adjust my switching power supply to get to 5-5.1 volts... still nothing.
on the audio board when i switch to and from self test mode, nothing happens.
i measured the voltages (AC) coming off the transformer and they are 12, 12, and 18, so i now know it is not a bad transformer.
the only other power to measure is the +15vdc off PIN 7 of the P13 connector on the video board which goes to the +reg on the audio board - where do i measure this and what am i hoping it is? where does it come from?
and there is also a +15/-15vdc coming to the cpu on the P15 connector that on the other end is coming off the audio boards +reg/-14vdc.
when i measure on the back of the audio board when all is connected this +reg and the ground only show me about 5v...why am i missing the other 10 volts? is the +15 taken from the 18 that comes in and stepped down on the audio board?
this is all i can think my problem is, but any other ideas/suggestions on what to check, where to check are greatly appreciated...
thanks
joe
i have tried this machine with 2 separate boardsets (both believed working) and 2 different audio boards.. and still nothing.
so, im still stumped on my 720 machine... so far here is what happens when i turn it on.
all lightbulbs light up on coin doors and marquee.
monitor turns on and goes white when i adjust the "screen" control.
there is NO sound at all.
the video board and the cpu board light up red, and when measured i adjust my switching power supply to get to 5-5.1 volts... still nothing.
on the audio board when i switch to and from self test mode, nothing happens.
i measured the voltages (AC) coming off the transformer and they are 12, 12, and 18, so i now know it is not a bad transformer.
the only other power to measure is the +15vdc off PIN 7 of the P13 connector on the video board which goes to the +reg on the audio board - where do i measure this and what am i hoping it is? where does it come from?
and there is also a +15/-15vdc coming to the cpu on the P15 connector that on the other end is coming off the audio boards +reg/-14vdc.
when i measure on the back of the audio board when all is connected this +reg and the ground only show me about 5v...why am i missing the other 10 volts? is the +15 taken from the 18 that comes in and stepped down on the audio board?
this is all i can think my problem is, but any other ideas/suggestions on what to check, where to check are greatly appreciated...
thanks
joe
i have tried this machine with 2 separate boardsets (both believed working) and 2 different audio boards.. and still nothing.