sequencer won't work, need some help

[evostars]

I take it you have checked pin 9 of the processor first?

If that looks ok you need to check if there is a short. Suspect would be pin 18 against ground; but check bopth pin 18 and 19 against ground and each other; and also check continuity between the pins and the resonator.

And don't worry too much.

yeah checked pin 9 its 5V, as is pin 40. pin 20 is ground.
I looked at the connections, they all look good. I'll measure again without the cpu in it.

I wonder if there is 5V on pin 40, how much volts should there be on pin 18 and 19?

I've been working days to get this monster running, loads of disappointments. But I wont give up... I'm just a emotional person...

[mmm]

I wonder if there is 5V on pin 40, how much volts should there be on pin 18 and 19?

About 0.6V to 0.8V or so when the CPU is installed and the xoxbox switches on. (without CPU of course there should be nothing)

That's why I suggest measuring those pins against digital ground (pin 20) and against each other. If for example pin 18 is shorted to ground on my test board the voltage on pin 19 will drop to about 0.2V (and pin 18 of course will be 0V then). In my opinion this looks a bit like your scenario.

And yes, I've seeen pretty much this very problem before. One xoxbox with copper bridges from pin 18 (and in this particular case also pin 17) to ground.

[evostars]

I wonder if there is 5V on pin 40, how much volts should there be on pin 18 and 19?

About 0.6V to 0.8V or so when the CPU is installed and the xoxbox switches on. (without CPU of course there should be nothing)

That's why I suggest measuring those pins against digital ground (pin 20) and against each other. If for example pin 18 is shorted to ground on my test board the voltage on pin 19 will drop to about 0.2V (and pin 18 of course will be 0V then). In my opinion this looks a bit like your scenario.

And yes, I've seeen pretty much this very problem before. One xoxbox with copper bridges from pin 18 (and in this particular case also pin 17) to ground.

Indeed, pin 18 is shorted to ground!
Whoohoo another step in the right direction

[evostars]

Strange pin 18 doesn't short to pin17 or 19.
It looks like the new crystal has one pin to ground, but i can't see where.
Better take it out....

[evostars]

Hmm crystal is out, still 18 is grounded.
That means I'll probably have to desolder 40pins ... Oh oh

[evostars]

Hmm crystal is out, still 18 is grounded.
That means I'll probably have to desolder 40pins ... Oh oh

No way,
I'm going to bend pin 18 out of the socket and hard wire it to the crystal. Saves me alot of trouble

[mmm]

You could also try the following:

1. Hold the PCB against a bright lamp and check with a magnifying glass for copper bridges. Perhaps the bridge isn't under the CPU but near the resonator pads?
2. If you want to verify is the bridge is under the CPU (or it's socket) cut the trace between pin 18 and the resonator (cut it directly next to pin 18). If the pin 18 the is still grounded the short is near the CPU; if it isn't the short is near the resonator.

And yes - I had to desolder a CPU socket, too... With the right tools it isn't that bad.

[evostars]

I took out pin18 and cut the trace to the crystal.
Ground is gone from 18. Hooray

I can see the 16 mhz on my (10mhz) scope. Looks good.
Only odd thing:
Pin 18 is 560mV
Pin 19 is 700mV
To ground, dc that is.

I guess thats normal?
The signal also doesnt look like a sinus. But hey, that could be the scope.

Most important. Still no sound and no interface....

Next thing to check is the selector to cpu.

[evostars]

Pin 1 and 5 of the selector switch(sw4) are shorted. That's wrong isnt it?

[evostars]

Hmm its a bit hard to check those connections with the switches in place ....
Going to give it some rest.

Thanks for the help so far!
All ideas are welcome

[mmm]

I can see the 16 mhz on my (10mhz) scope. Looks good.
Only odd thing:
Pin 18 is 560mV
Pin 19 is 700mV
To ground, dc that is.

I guess thats normal?

Perfectly normal.

[evostars]

I can see the 16 mhz on my (10mhz) scope. Looks good.
Only odd thing:
Pin 18 is 560mV
Pin 19 is 700mV
To ground, dc that is.

I guess thats normal?

Perfectly normal.

Cool.
I wonder if there are more pins under the cpu, that are shorted....

[mmm]

Hmm its a bit hard to check those connections with the switches in place ....
Going to give it some rest.

Also keep in mind that the switches can go bad as well. I've even found switches that would short to ground on certain positions.

Apart from that it is not that hard to debug because you can just remove the associated diodes. This will give you an idea where the error is located. In fact if you remove D3 to D6 you should get the "Pattern Play" mode (if I'm not mistaken) unless there is another error.

[evostars]

removing the diodes is a lot easier indeed. Thanks.
I remember seeing a chart with all the selector positions. I'll look that one up.

[aminoacid]

go evo!!!