Nemesis GX400

[Funhouse71]

Funnily enough that same 18A LS245 was responsible for multiple ram failures on Dan's Nemesis board I fixed

 

[Lurch666]

So I've now replaced all the LS245s at 8K,10K,18A and 18C as they were all bad.
Also replaced a couple of bad rams at 2H and 6G.

Before I got a blank screen then the test screen that I posed above.

Now I get a screen of garbage which is normal on boot:

Then this screen which I think is the test screen test but now it's black on black:

Which after a few seconds goes like this:

Really need to get the text to appear so I can see if the customs are all good.

 

[Lurch666]

So close.
Pressing down on the 5292 custom made the text appear. I had checked all the outputs of this but never checked the connectivity.
Fortunately I have some spare sockets of the correct pitch so will replace that and start fixing the character ram.

 

[Lurch666]

Well that was a waste of time.
64 damn pins on that sockets and it's not the issue.
Pressing on the sockets still makes the text appear but pressing near the socket on the PCB has the same effect. I think there's a crack or break somewhere that's touching when pressure is applied. Finding that is going to be fun.

 

[Georgian2]

Well that was a waste of time.
64 damn pins on that sockets and it's not the issue.
Pressing on the sockets still makes the text appear but pressing near the socket on the PCB has the same effect. I think there's a crack or break somewhere that's touching when pressure is applied. Finding that is going to be fun.

It helps bending the PCB from the bottom too. Such things are hard to find. Great progress so far.

 

[Funhouse71]

First try pushing around on the board ribbon cables these also have a tendency to go faulty on these boards

 

[Lurch666]

I have achieved Nemesis!
The text issue hasn't gone away but after checking with my microscope even after failing to find the issue it seems to have changed to where bending the board make the text disappear.
So I decided to see if I could fix the bad character ram issue and piggybacking one ram got the game to boot.
It has an issue with sprite doubling and some controls don't work but I knew that because some chips on the input lines are damaged.
Just glad to finally see this running.

 

[Funhouse71]

Control issues are likely due to faulty optocouplers NEC PS2401 near edge connector

 

[Lurch666]

Thanks for that. Nice to know they are a standard part and easy to obtain. Was worried it might be another hard to find part.

 

[ExZX]

Amazing work. Back from the dead. Very nicely done

 

[r-type]

Well done mate.

 

[Lurch666]

Thanks for that. Nice to know they are a standard part and easy to obtain. Was worried it might be another hard to find part.

Spoke too soon.
After another look the (relatively) cheap ones are from China and it's around £15 to buy one from this country.
Anyone know if I can use a 2501 optocoupler instead?

 

[Lurch666]

Sorted the control issues now. Noticed that the PS2401 at 2J had an unused optocoupler so I've run a bypass to that one and I have left working now. Turned out it also had a bad diode on it's input so maybe this board was plugged in wrong at some point.

Fire also wasn't working but that was down to the fact I hadn't wired up button three on my konami adapter😊.

Just the sprite issue to track down now.

 

[Lurch666]

Final bad ram found at G6. All sprites good now. I think this board is finally done.
Two bad rams are piggybacked at the moment so need to replace them and clean up the bypass for the left direction opto and this board is all good.
Looking forward to playing this and see how bad I am at it now.