This started in this thread posted by ITRUK.
Namco version of Dig Dug PCB with no sound effects.
There seems to be no online version of the schematic for this, I had to hard trace the board but its SP-202 we figured out in a tech thread.
I offered to verify if it was the board or the AR2 etc while Mark came to pick up a game he'd bought from the USA.
On the bench on a known good JAMMA adapter and game boots perfectly but no sounds.
Mark decided to leave the board with me then for further investigation.
Entered test mode just in case there was an error I hand't seen but same thing - can select sounds but they don't play. Ramping up both the amp and my speakers just produces some mild background noise but not even the sound of the game trying to break through it.
So the deduction is that the fault is past the point that the board's self tests can access.
Best approach here i've found is to start at the very end of the circuit and work your way back into the board.
The board has an MB3730 amp - pin 1 is the input and pin 5 and 6 are the outputs.
As I can hear background noise, i'm convinced the output is fine so lets feed it an input.
I don't have a signal generator in the true sense but my oscilloscope can generate a square wave for calibration at a decent interval as can my logic probe.
WARNING - Be very careful what you do here, make sure you only touch pins that are supposed to be at lower voltages - if you put your scopes calibration point onto a high voltage source (like say a 12v or 24v) there is potential of damaging your scope - TTL voltages should be fine so long as they're brief and I use a resistor in series to ensure no direct shorts - this may not be the best way to do this but done carefully can produce good results.
Right, health and safety lecture over with lets fix this s**t!
Touching pin 1 on the MB3730 gets us a tone out of the speakers - amp chip is fine.
There are only a couple of passive components in this circuit so I worked back manually across them applying the signal and getting a tone - we're good to the perimeter of the amp area.
Need to find the source - some careful manual tracing of the board gets us to a 4066 chip at 8N - looked up the datasheet, gave signal to the outputs first to ensure it's not a bad trace - yep got sound, apply to the inputs, yep got sound - the control pins are all static so the signal just passes through.
Traced back to a LS273 @ 6N - all the outputs are static HI - ok so that's why there's no sound, the inputs are changing, check pin 11 for the clock signal - stuck - right, the 273 is probably fine in that case.
The 273's CLK signal is fed by the 82S129 PROM @ 5N - it's labelled DD1-1 - all the inputs are good, but nothing going on at the output.
I have a spare Namco Dig Dug PCB so I subbed in the DD1-1 and booted up and I could hear a quick pop just before the attract mode starts which hadn't been present before so i was certain we'd cracked it.
Coin up - ta-da, we have sound.
Played a few games - all good, left to soak test for a couple of hours, no problems.
Job done.
Took a few hours tracing the board mainly but the problem was quite simple instead of just a fuse - its just a PROM
Namco version of Dig Dug PCB with no sound effects.
There seems to be no online version of the schematic for this, I had to hard trace the board but its SP-202 we figured out in a tech thread.
I offered to verify if it was the board or the AR2 etc while Mark came to pick up a game he'd bought from the USA.
On the bench on a known good JAMMA adapter and game boots perfectly but no sounds.
Mark decided to leave the board with me then for further investigation.
Entered test mode just in case there was an error I hand't seen but same thing - can select sounds but they don't play. Ramping up both the amp and my speakers just produces some mild background noise but not even the sound of the game trying to break through it.
So the deduction is that the fault is past the point that the board's self tests can access.
Best approach here i've found is to start at the very end of the circuit and work your way back into the board.
The board has an MB3730 amp - pin 1 is the input and pin 5 and 6 are the outputs.
As I can hear background noise, i'm convinced the output is fine so lets feed it an input.
I don't have a signal generator in the true sense but my oscilloscope can generate a square wave for calibration at a decent interval as can my logic probe.
WARNING - Be very careful what you do here, make sure you only touch pins that are supposed to be at lower voltages - if you put your scopes calibration point onto a high voltage source (like say a 12v or 24v) there is potential of damaging your scope - TTL voltages should be fine so long as they're brief and I use a resistor in series to ensure no direct shorts - this may not be the best way to do this but done carefully can produce good results.
Right, health and safety lecture over with lets fix this s**t!
Touching pin 1 on the MB3730 gets us a tone out of the speakers - amp chip is fine.
There are only a couple of passive components in this circuit so I worked back manually across them applying the signal and getting a tone - we're good to the perimeter of the amp area.
Need to find the source - some careful manual tracing of the board gets us to a 4066 chip at 8N - looked up the datasheet, gave signal to the outputs first to ensure it's not a bad trace - yep got sound, apply to the inputs, yep got sound - the control pins are all static so the signal just passes through.
Traced back to a LS273 @ 6N - all the outputs are static HI - ok so that's why there's no sound, the inputs are changing, check pin 11 for the clock signal - stuck - right, the 273 is probably fine in that case.
The 273's CLK signal is fed by the 82S129 PROM @ 5N - it's labelled DD1-1 - all the inputs are good, but nothing going on at the output.
I have a spare Namco Dig Dug PCB so I subbed in the DD1-1 and booted up and I could hear a quick pop just before the attract mode starts which hadn't been present before so i was certain we'd cracked it.
Coin up - ta-da, we have sound.
Played a few games - all good, left to soak test for a couple of hours, no problems.
Job done.
Took a few hours tracing the board mainly but the problem was quite simple instead of just a fuse - its just a PROM
Really looking forward to fitting it and finally getting a good few games on it.