Nintendo Helifire PCB Issue #1

CamaroMurph

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Picture says it all. Game plays fine. Hardware generated background (Blue/Red background, stars) are good but as you can see I have some lines.

Any help would be greatly appreciated.

Murph
 

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Morning Bump.

I know this is a problem on the I/O board. Having trouble isolating it. What type of chip might be problematic here? It looks like a vertical problem correct?

Murph
 
Time for another bump.

Anybody tell me the theory of what is happening? I have the schematics. The tools I have are my DMM and a logic probe.
 
Time for another bump.

Anybody tell me the theory of what is happening? I have the schematics. The tools I have are my DMM and a logic probe.

That kind of problem is usually a ram or connection problem. If you have a spare ram chip just piggy back a new one on each until you find the bad guy. It may be a connection to the ram chips also so check them traces. It can be a supporting chip to the ram also but that is where to look after you verify power supply voltages.

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Have you reseated the chips and verified the +5 and checked/cleaned all connections
 
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Get you some electronic cooler spay it onto the ram chips and see if the image clears.
 
I have verified voltage. 4.98 at all chips. I have a number of baord sets for this game and I have isolated this issue to the I/O board. I have replaced the ribbon cables to also rule out those. All chips on the I/O board are soldered in. No socketed chips. What chip numbers would I be looking for to find RAM on this board. (I ask because I don't think the board has any RAM chips on it) This board has the clock circuit on it and what looks like all the horizontal and vertical blanking chips. I have also given all the chips the finger test and have not found any hot chips so I have not taken out the freeze spray yet.

Murph
 
Can you post a picture of the PCBs? Or a link to pictures?

Are the schematics available online? Link?

Need to see what chips and functions are on the I/O board.
 

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Wow. I usually look for regular patterns in these types of video problems in order to narrow down the problem ICs. But I am not familiar with this game and it is not drawing a lot of variety on the screen.

It looks like there is a problem every 8th vertical line (so the fourth bit, or 4V in some schematics).

Does this game have a test mode? Maybe some pictures of static screens vs some more in game screens would help.

Do you have a logic probe? How about a logic pulser?
 
Wow. I usually look for regular patterns in these types of video problems in order to narrow down the problem ICs. But I am not familiar with this game and it is not drawing a lot of variety on the screen.

It looks like there is a problem every 8th vertical line (so the fourth bit, or 4V in some schematics).

YEah so do I. In fact I usually fill the video memory with a constant value (0x00 or 0xFF) and then trace the output through the sprite ROMs. Or find a NULL character in the character ROM and have the mem point to that. Then trace the output of the sprite ROM through the palette logic to figure out what line is pulled high/low.

Every 8th would mean 8V I think?
MSB to LSB is:
...... 8V, 4V, 2V, 1V

1V toggles every line, 2V every other, 4V every 4 and 8V every 8.
 
I have a DMM and logic probe along with the schematics. You guys need to be patient with me. I can swap different I/O boards onto this stack and I get a good picture.

I will try to upload a picture of the screen when I coin the game up. This stabilize's most of the screen changes. The only thing at this point that is moving are the stars up top and the waves in the middle which are hardware generated. (Just as a pre-look without the picture, it will look the same minus the heli's and sub plus some words)

The I/O board has H0-H4 and V0-V7 outputs. If your looking, it's right in the middle of the I/O schematic page (P10 connector). These outputs are fed by 74LS86 chips.
 
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Here's a picture with the game coined up. Picture with game in game mode is the same as the picture in original post. There really isn't much else to this game.

Murph
 

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YEah so do I. In fact I usually fill the video memory with a constant value (0x00 or 0xFF) and then trace the output through the sprite ROMs. Or find a NULL character in the character ROM and have the mem point to that. Then trace the output of the sprite ROM through the palette logic to figure out what line is pulled high/low.

Interesting. Do you set the values by programming the ROMs? How do you "point the mem"?

Every 8th would mean 8V I think?
MSB to LSB is:
...... 8V, 4V, 2V, 1V

1V toggles every line, 2V every other, 4V every 4 and 8V every 8.

It apperently depends on the game! Q*Bert schematics use H0-7 and V0-7. Galaga uses the binary counting method.
 
The HO-H4, V0-V7 outputs are driven by 74LS86 chips. I have checked these with my logic probe and I think they are all working properly. The LS86's are driven off the outputs of 4 74LS161 chips. I am have trouble understanding what the output's should be from these. The logic probe is pulsing at different frequency's on some but not on others. Or the difference in frequency on some is so small I can't tell the difference. The fequency difference's are highest and easily notable on the V4-V7 outputs.

Any help on how I can use the logic proble and/or DMM to troubleshoot the 161's would be great.

Murph
 
Interesting. Do you set the values by programming the ROMs? How do you "point the mem"?



It apperently depends on the game! Q*Bert schematics use H0-7 and V0-7. Galaga uses the binary counting method.

I use my fluke. I just write a little script that writes the same data to every address in a block of memory.
 
The HO-H4, V0-V7 outputs are driven by 74LS86 chips. I have checked these with my logic probe and I think they are all working properly. The LS86's are driven off the outputs of 4 74LS161 chips. I am have trouble understanding what the output's should be from these. The logic probe is pulsing at different frequency's on some but not on others. Or the difference in frequency on some is so small I can't tell the difference. The fequency difference's are highest and easily notable on the V4-V7 outputs.

Any help on how I can use the logic proble and/or DMM to troubleshoot the 161's would be great.

Murph

You'll never be able to verify the 161 100% with a logic probe because if the probes sample rate. You could sample a 4Mhz clock for example and compare it with an 8Mhz clock. The blink rate would most likely be the same. The led doesn't match the transition times exactly for fast enough signals otherwise it would look like it was high all the time.
 
OK. Sounds like my tools are limiting me here. Based on the schematics, what do you think are the high likelihood areas? I could go shotgun and change a couple of chips. Likely candidates of the H0-H4 and V0-V7 chips to start with?

What would be a good tool to invest in for the future to help with situations like this?

Mike
 
OK. Sounds like my tools are limiting me here. Based on the schematics, what do you think are the high likelihood areas? I could go shotgun and change a couple of chips. Likely candidates of the H0-H4 and V0-V7 chips to start with?

What would be a good tool to invest in for the future to help with situations like this?

Mike

Wow this is a weird game. I've never seen a PCB set with 2 videos outputs even though it only has a single monitor. I see video outs on the I.O board and the ESS board. Anywho...

What about checking the address bits on the palette ram? There's a 2114 on the ESS board (IC 14?) although the schematics only give a chip identification.. not a location. Lame! :)
 
Can do. The video output for this game is the one on the ESS board. Which pins on the 2114 should I check? I know that chip. It's east to find.
 
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