often in arcade games the Clear pins on flip flop latch IC chips and the Counter chips Clock Enable pins are tied HIGH together using a pull up resistor. I'm not sure why the counter chips clock enable pin would ever be pulsed low or pulled low because that would mean that the counter would never be counter during clock cycles. The MPU will clear the latch IC chips and pull low the counter chips, but when?
Garbage screen with no CPU is normal. Most arcade machines have a video circuitry that's independant of the CPU and they just draw what they find in memory and since RAM (especially SRAM) defaults to the universe's background noise, you end up with what you saw. DRAM can retain its information for up to a few seconds after power down, but on power up they default to whatever they like. Mostly random, but some have a strong bias towards 1 or 0. Glitching a crystal by scoping it is relatively normal. Try the 10x setting on the scope probe.
so how many volts do you need to do this on a bench to allow the game to work? my millipede has 5 volts, 28 and lots more, looks like the centipede does too, do you need all of these others voltages to run the game for bench testing? or is the 5 volts good enough?
I would have to look to be certain but +5 volts is all you need to boot these boards. The 28volts is for the EAROM score save Typically, the only time you need voltage besides +5v is when the ram being used is trivoltage (-5v, +12v +5v). +12v is usually only needed for sound circuits.
@@jacklick i learn something new everyday doing this, this is neat to know, ill have to do more looking up on this to learn more about what voltages are for on these pcb boards. very cool! thanks for the reply!
If you look in the service manual on some arcade games it will call logic gates as "intercept gates" which I'm not sure what that means when a logic gate is considered an Intercept gate. Do you know what an intercept gate means?
@@jacklick check it out its in the service manuals for arcade games its called Intercept gates but its normal logic gates its just how they are using the logic gates as intercept gates
@@jacklick 1980 Berzerk, the self test 6th LED test says that 12A and 12B are considered Intercept gates which are logic gates but its how they are using them as intercept gates
often in arcade games the Clear pins on flip flop latch IC chips and the Counter chips Clock Enable pins are tied HIGH together using a pull up resistor. I'm not sure why the counter chips clock enable pin would ever be pulsed low or pulled low because that would mean that the counter would never be counter during clock cycles. The MPU will clear the latch IC chips and pull low the counter chips, but when?
I use one of those crystal testing kits on ebay. They seem to work well.
I will need to check one of those out.
Garbage screen with no CPU is normal. Most arcade machines have a video circuitry that's independant of the CPU and they just draw what they find in memory and since RAM (especially SRAM) defaults to the universe's background noise, you end up with what you saw. DRAM can retain its information for up to a few seconds after power down, but on power up they default to whatever they like. Mostly random, but some have a strong bias towards 1 or 0.
Glitching a crystal by scoping it is relatively normal. Try the 10x setting on the scope probe.
Yea, should have known this when I made the video but figured it out later. Still have to occasionally remind myself.
so how many volts do you need to do this on a bench to allow the game to work? my millipede has 5 volts, 28 and lots more, looks like the centipede does too, do you need all of these others voltages to run the game for bench testing? or is the 5 volts good enough?
I would have to look to be certain but +5 volts is all you need to boot these boards. The 28volts is for the EAROM score save Typically, the only time you need voltage besides +5v is when the ram being used is trivoltage (-5v, +12v +5v). +12v is usually only needed for sound circuits.
@@jacklick i learn something new everyday doing this, this is neat to know, ill have to do more looking up on this to learn more about what voltages are for on these pcb boards. very cool! thanks for the reply!
If you look in the service manual on some arcade games it will call logic gates as "intercept gates" which I'm not sure what that means when a logic gate is considered an Intercept gate. Do you know what an intercept gate means?
I haven't heard that term used.
@@jacklick check it out its in the service manuals for arcade games its called Intercept gates but its normal logic gates its just how they are using the logic gates as intercept gates
@@waynegram8907 give me an example
@@jacklick 1980 Berzerk, the self test 6th LED test says that 12A and 12B are considered Intercept gates which are logic gates but its how they are using them as intercept gates