Nintendo Space Fever
- Thread starter Hexen
- Start date
I need some assistance on my Space Fever, I know the CPU board is good as it has been tested in another machine so the issue must lie in the I/O board, I dont get anything on the screen really see pic, this is what comes up once I have the boards attached. Clock signals seem ok getting pulses on the two test points. If i try and play the game nothing so not even playing blind from what I can tell, any ideas on what to test for on the I/O board, will check the LS74 as that has been mentioned.
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Hi, in addition to the two 12V clock signals to the CPU itself there are two TTL level clock signals and the CPU reset signal also originates on the I/O PCB.
The Black and White I/O PCB is basically the same circuit as the colour except for the colour overlay but all of the circuit locations are different.
There are also at least two versions of the B&W I/O, if yours is the 500803 type the pin connections should match the ones I traced out and marked in red here:
http://www.jbretro.com/ninty.htm#090723
Apart from the main clock and reset signals it may be worth checking the outputs of all the 74(LS)161s to make sure they are all counting / dividing as all of the sync signals are derived via these.
Hope that helps, regards John.
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So did a few checks clocks good, reset good, had a look at the LS74 mentioned in this thread and all high. I then noticed something, on the 161 at 4J and in fact the on 3J the IC looks like it’s lifted in the middle almost cracked, hard to describe I took a photo But not that obvious, defo lifted / cracked can feel it when running my fingernail over it, I have seen something similar when I put 240 down a 24 line as an apprentice 😂 and killed a micro controller way back when. Ordered some 161s so let’s see what happens. These feed the 74 I looked at.
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Well I have made some serious progress, I took all four 161’s from 2,3,4,5 J out and all failed in my tester, I have four, which I found after ordering new (typical) and socketed and replaced, fired up and still similar, so checked the LS74 at 4G and only getting pulses on one output. Took out tested and it failed, put in socket and replaced with a tested working one and we have something happening now. Screen has changed with lots of what I would almost say is a scrambled screen like loss of sync. I checked the output of the four 161’s and on 3J I have output 13 &14 just sitting high., double checked swapping around with other 161 no change. So now trying to work out why these are high and should they be, I would assume looking at the schems they would also pulse as 11&12 are. God knows what happened to this board but the 161’s had all lifted in the middle so suspect power issue in the past.
More testing and found another 175 had failed, annoyingly I have tested a few more yet to find anything else and a few pads lifted which required jumper wires 😩, screen as attached pic, sound is erratic making all sorts of strange noises. Still no solid picture on the screen. Maybe get some more time to look tomorrow.
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Hi, there seems to be a horizontal sync issue in that image, the patterns on screen appear too wavy to just be random video. It would probably be a good idea to double check the part of the I/O board which divides the main clock frequency down to arrive at the horizontal frequency (with a logic probe) to see if any of the components in that stage appear to have bad outputs or if the horizontal sync signal is missing.
If the timing signals are incorrect the game will never run correctly so that is usually a good starting point. Hope that helps, regards John.
If the timing signals are incorrect the game will never run correctly so that is usually a good starting point. Hope that helps, regards John.