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PostPosted: Fri Aug 04, 2017 7:06 pm 
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I'm a fool. A moron. I failed to heed the warnings that the PPU had some solder points that needed tons of heat to work, and rather than be more careful, I got in a hurry. I tore up traces, and broke pins off of my PPU.

I have since gone through as carefully as I could and jumped all of the damaged traces I could find, and installed the dip socket that came with my NESRGB board - but I must admit that I am in over my head. I get a black screen when powering up - but if I use my multimeter to check the composite video signal, I get what amounts to 1Vpp, which if I understand it correctly, is a proper voltage for a composite video signal. I get black screen from composite video, svideo, and RGB.

I have installed the PPU into a second socket that it will permanently live in, dremeled part of the package itself away and soldered wires to the exposed copper to repair the chip as best as I could. I get 5v at the NESRGB board.

Here's a bunch of pictures of the disaster I have created. I am acting out of paranoia at this point checking continuity all over the place, using this pin map:

Image

Right away I'm concerned, because I don't have continuity from pin 3/D1 on the PPU to pin 10/D0 on U1 (sram) - but I have bridged continuity D1 to D2 on SRAM, and D2 on the PPU has continuity to those two points - however no continuity D1 to D2 on the PPU itself. Very odd. :\

Anyway - here's the pictures of where I am with this:

http://imgur.com/a/8EgIZ

Halp. I can't tell if I have killed the PPU or not. I don't currently own an o-scope or logical analyzer, and from what I can tell a replacement PPU will run me $60. At that point I could almost afford to just buy a new one and start over. :|

What can I do here? Right now I'm just matching up pin names and testing continuity out. Finding things that leave me confused, like the PPU diagram I have shows pins 14, 15, 16, and 17 as R, G, B and I assume sync (it's black). Yet from my pictures, it looks as though 14 and 15 were bridged, and 15 and 16 were bridged, and all 4 have continuity to ground, so that's what I reproduced as best I could.

As you can see, I'm floundering here. :(


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PostPosted: Fri Aug 04, 2017 7:48 pm 
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numbski wrote:
Finding things that leave me confused, like the PPU diagram I have shows pins 14, 15, 16, and 17 as R, G, B and I assume sync (it's black). Yet from my pictures, it looks as though 14 and 15 were bridged, and 15 and 16 were bridged, and all 4 have continuity to ground, so that's what I reproduced as best I could.
2C03 wasn't used in the NES or most Famicoms, but rather only in the Vs. System, Playchoice 10, and Famicom Titler.

In the 2C02, those four pins are instead a digital input/output bus that's used by the NESRGB to get the pixel values from the PPU.

Remember that you can use your computer's soundcard as a cheap oscilloscope. It's not great bandwidth (you'll probably only be able to sample at 48, 96, or 192kHz, and there's a strong lowpass filter at 10kHz) but it'll be enough to actually see if signals are high, low, or changing at slow-ish rates. (Just remember to add current limiting on the input).

numbski wrote:
Right away I'm concerned, because I don't have continuity from pin 3/D1 on the PPU to pin 10/D0 on U1 (sram) - but I have bridged continuity D1 to D2 on SRAM, and D2 on the PPU has continuity to those two points - however no continuity D1 to D2 on the PPU itself. Very odd. :\
D0 should be connected to D0, and D1 to D1, and D2 to D2 ... why are you looking for connectivity otherwise?

Have you found both the original famicom schematics (http://nesdev.com/Ntd_8bit.jpg ) and the reverse-engineered NES schematics (https://console5.com/wiki/Nintendo_NES-001#Schematics ) already?

The NES is basically "W"RAM <-> CPU <-> PPU <-> "V"RAM. When you're testing continuity, are you testing the correct side of the PPU for the RAM you're testing against?


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PostPosted: Sat Aug 05, 2017 4:31 am 
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Joined: Sun Jun 12, 2011 12:06 pm
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Location: Poland
There's an easy way to check if the bond wire was not broken and there is connection between pin and internal chip core - set your multimeter to diode test, touch + of your probe to GND and - to the pin you're testing. If multimeter shows some value (other than infinity), then it wil probably be the forward voltage of internal clamp diode and it means there is connection to the pin.

I tested in on UA6538 and all pins could be tested that way.
Image

Of course there might be other damage to internal structure due to heat.


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PostPosted: Sat Aug 05, 2017 8:29 am 
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lidnariq wrote:
numbski wrote:
Finding things that leave me confused, like the PPU diagram I have shows pins 14, 15, 16, and 17 as R, G, B and I assume sync (it's black). Yet from my pictures, it looks as though 14 and 15 were bridged, and 15 and 16 were bridged, and all 4 have continuity to ground, so that's what I reproduced as best I could.
2C03 wasn't used in the NES or most Famicoms, but rather only in the Vs. System, Playchoice 10, and Famicom Titler.

In the 2C02, those four pins are instead a digital input/output bus that's used by the NESRGB to get the pixel values from the PPU.

Remember that you can use your computer's soundcard as a cheap oscilloscope. It's not great bandwidth (you'll probably only be able to sample at 48, 96, or 192kHz, and there's a strong lowpass filter at 10kHz) but it'll be enough to actually see if signals are high, low, or changing at slow-ish rates. (Just remember to add current limiting on the input).

numbski wrote:
Right away I'm concerned, because I don't have continuity from pin 3/D1 on the PPU to pin 10/D0 on U1 (sram) - but I have bridged continuity D1 to D2 on SRAM, and D2 on the PPU has continuity to those two points - however no continuity D1 to D2 on the PPU itself. Very odd. :\
D0 should be connected to D0, and D1 to D1, and D2 to D2 ... why are you looking for connectivity otherwise?

Have you found both the original famicom schematics (http://nesdev.com/Ntd_8bit.jpg ) and the reverse-engineered NES schematics (https://console5.com/wiki/Nintendo_NES-001#Schematics ) already?

The NES is basically "W"RAM <-> CPU <-> PPU <-> "V"RAM. When you're testing continuity, are you testing the correct side of the PPU for the RAM you're testing against?



I was testing D1 to D1, and my probe slipped on U1 making contact with the next pin. I didn't do it on purpose, but after I saw I had continuity that didn't seem like it should be there, I got curious.

Thank you both for the tips. I will try to follow up this afternoon!


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PostPosted: Sat Aug 05, 2017 8:51 am 
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re: using my sound input as an oscilloscope, everything I am finding is for windows. I'm a Linux and Mac user - so I either need to get that software running under wine, or I will have to play some games to get it going under a VM. That's still more than I was aware of before, so I super appreciate that!

Now I just need a logical analyzer. :)

EDIT - never mind, I have a bus pirate from an old project that apparently can be used as a logic analyzer! :D


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PostPosted: Sat Aug 05, 2017 11:59 am 
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Location: Seattle
Linux: Xoscope.

Might need some help, I was playing with it last night and the current Debian packaging didn't enable sound card input (oops) ... and the current build only allows sample rate of 44.1kHz and lower right now (double-oops)


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PostPosted: Sun Aug 06, 2017 2:57 pm 
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krzysiobal wrote:
There's an easy way to check if the bond wire was not broken and there is connection between pin and internal chip core - set your multimeter to diode test, touch + of your probe to GND and - to the pin you're testing. If multimeter shows some value (other than infinity), then it wil probably be the forward voltage of internal clamp diode and it means there is connection to the pin.

Interesting...
I've tried this on a MMC3 clone named 9112 that seems dead, and have found many pins to have infinite resistence and a short circuit in the M2 and GND.

Seems that it's death is finally confirmed. :cry:
I just would like to know why.
Have I messed very badly with the IC and end killing it?
I could not read anything other than FFs from this game ROMs too, so, maybe it was already dead when I got it.
But again, what can cause this kind of failure on a cartridge? Static eletricity? A ray storm?
Sorry to go off-topic... :mrgreen:


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PostPosted: Sun Aug 06, 2017 3:16 pm 
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Location: Seattle
Not resistance ... I mean, it could be, but that depends on the specific multimeter. You want the diode testing function instead.


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PostPosted: Mon Aug 07, 2017 5:36 am 
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I used the diode/continuity test.
The multimeter usually gives a very high number.
In some pins it gave no number.
On M2 it beeped.

Now I'll try to find a substitute for this clone.
Seems difficult, since it uses a very different pinout than the AX5252.
Any cheap preprogrammed MMC3 clone around that can ship to Brazil?


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