Problem Nintendo Space Fever CL - Help Needed

[KoniTec]

Ok so looks like nothing happens at pin 12 when powering the unit on. Heres a video showing the oscilloscope.

8080 pin 12 - power on

I also checked pin 23 which os for the Ready signal, and it has the same 2.016 MHz clock. See the picture.

As you can see from the previous video all i get is a red screen and a startup tune, but nothing else.

I only have the oscilloscope for today then i have to return it. So any help is appreciated.

Thanks

Chris

 

[Lurch666]

That looks like you are missing reset.
Check the data and address pins of the 8080 and see if you have any activity.
Also double check the voltages to the CPU especially the -5V.

 

[KoniTec]

So i checked all voltages at the 8080. All are ok. I also checked all the D and A pins.

It was easier for me to capture 2 videos of the oscilloscope showing the output of those pins.

This video shows pins 10 - 1, missing out pin 2 which is GND:

8080 - D0, D1, D2, D3, D7, D6, D5, D4, A10 - Or pin order 10, 9, 8, 7, 6, 5, 4, 3, 1

And this videl shows pins 25 - 40 missing out pin 28 which is +12v:

8080 - A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A15, A14, A13, A12, A11 - Or pin order 25, 26, 27, 29, 30, 31, 32, 33, 34, 35 , 36, 37, 38, 39, 40

Also an odd observation, during the process of testing these pins, at some point the screen output changed from solid red colour, to a solid yellowish green colour.

Thanks

Chris

 

[Lurch666]

So it's looking like there is some activity on the CPU.
Try touching +5V breifly to the reset pin of the 8080 to see if that causes anything to happen.

 

[KoniTec]

Ok so did that. The screen seems to switch from fully yellowish green to having blue bars. See picture.

Also the sound output changes each time i tap the reset to the +5v, but it cycles only the same handful of sounds.

Seems to be an explosion sound, a musical track of some kind, what seems to be the alien moving sound, and the startup tune you can hear on the previous video.

Thanks

Chris

 

[Lurch666]

Ignore the sounds.
They are separate and nothing to do with the game working.
It possibly trying to run code but failing. The next thing to do is check the eproms.
What type are they? If they are 2708 there's no easy way for you to check them.

 

[Lurch666]

Ignore me - you already tested the CPU board on another system so apart from the reset I'm going to assume it's working.

Looking at the schematics the I/O board uses 161's to draw the picture so your lines possibly show those are working but maybe you are getting no data from the CPU PCB.
Check the 198 at 1L as well as the 175 at 4E

 

[philmurr]

I thought you'd ruled out the CPU board as it tested ok with @cNp's I/O board?

Another thing that may be an easy fix is to replace the ribbon cables which can cause all kinds of problems

 

[Stickman]

Has anyone ever found schems or a manual for the B/W version, I have searched everywhere without luck. About to embark on my rebuild and only have the colour manual

 

[philmurr]

Has anyone ever found schems or a manual for the B/W version, I have searched everywhere without luck. About to embark on my rebuild and only have the colour manual

I don't believe the B&W schematics exist but there are hardly any differences between B&W and colour boards.

Unless your issue is where the board connects to the monitor (where the B&W circuit is a bit odd) you will be fine with the colour schematics.

 

[Stickman]

perfect thanks, need to racap the monitor, what a simple chassis that seems to be, and once I can check to see if the crt and board are a worker I can then get the 'Ninty Minty' set up