Ive worked out what is wrong with that saroo saturn... The person modding it used a va7 board and ive spent probably 2 hours working through schematics and also probing the board with my oscilloscope and I have found what the issue is. So the board worked fine in the saroo case, play games etc but sound is all muffled.. Turns out the cd drive board on the VA7 generates an 8.4672Mhz clock signal that it sends to the saturn to provide a clock signal for sound.
So what I found is this... here is the schematic and if we measure the board without the CD drive we are missing SCSPCLK...
To test I attached up a cd drive but only that clock signal by scoping out a clock on the cn4 connector (all the schematics are for the va13 so its a bit of a minefield)...
This is our clock as measured by my oscilloscope bottom left you can see the clock measured at 8.484mhz...
This clock signal is actually generated from this 33.8688 crystal:
It then goes into this chip which will basically divide that signal with bit counters so it cuts it in half twice:
After that it spits it out back down into the saturn board and provides the sound clock.
This is the mess I made working it out
Instead of messing around trying to make a signal from the parts on the cd drive board I decided to just buy an active oscillator which ill wire up to the saturn board to provide a sound clock. That way you can then run a va7 pal saturn without a cd drive and without any sort of ODE but still have everything work.
There is a reason that all the saroo saturns you see on aliexpress pre made are all JP VA13 boards and that's because the VA13 generates its clock using that same oscillator on its main board and then passes the signal to the CD drive rather than the other way around. It's probably also why the case kits you can buy are provided without instructions and its a case of "off you go - good luck". It's also no surprise that it was sent to me as a half done project missing its cd drive because they could never get it working properly.
This board also had an old school region mod on it so I removed that and have a new pcb coming for a more modern region mod, I also have an oscillator coming to fix the sound issue. I searched high and low on all my donor boards for an oscillator I can make work but had to order one in. If I was a lot better at this than I am I should have been able to create some sort of circuit that could divide the signal down from that current oscillator but thats beyond me right now... I started looking it up and found myself looking at flip flops:
en.wikipedia.org
I'm telling you Flip-Flops are no joke.
- switch port/m92 - if you lucky its just the port.
