nesdev.org

Hi
Recently I have tried to install NESRGB mod on NES-001 NTSC (front loader) console. After all, I tried to check console, but I got red flashing light on front panel. So, I decided to desolder all thing and solder again, probably I did damage PPU, and the problem actually was in bad cartridge connection

Right now I have crappy screen when NES turned on I think PPU is damaged. All traces on the motherboard are OK.

Also, I have original famicom console 1983 NTSC. As I know, this one has RP2C02E PPU, and NES has RP2C02G. Maybe anyone knows, are those PPU's both compatible? Can I safely swap Famicom PPU with NES PPU and check if problem in PPU or somewhere else?

Thanks

Your famicom and NES PPU are interchangable (if not identical).

I would very carefully desolder the famicom PPU and reinstall it with a 40 pin DIP socket to make sure it still works properly. Then I would try swapping it with the NES PPU as you already suggested, being very careful not to damage anything. If both PPUs work in the famicom, you know the fault lies somewhere else.

I've done this mod a few times myself and I've found that sometimes the PPU pin connections can be very sensitive when desoldered and put into a socket. Doing the NESRGB mod can be a real pain if you ask me, atleast if you don't have one of those fancy Hakko desoldering guns.

Getting properly formed numbers tells you a lot of about the status of the PPU.

In order to get a properly formed number, the data bus must be connected correctly. Any improperly connected bit will show up as a vertical line on the screen.
It also tells you that the low 3 bits of the address bus are fine, as it was able to properly select the graphics for each scanline.

The tile selections and attributes look like random garbage. It might be a problem with the PPU's connection to its RAM.

Which game is that?

I can see that the PPU is generating a picture okay, it's just not connected properly. Could be bad pins, bad traces, etc.

Thanks for the response

I have 2 cartridges: Tetris and SMB/Duck Hunt. Picture was taken on SMB/Duck Hunt, but on Tetris it is similar.

I also discovered strange behavior.
I'm testing on a disassembled console, without case. So, for make console read a cartridge, I have to add a little force on it.
Depending on it, I can get a static image as above. Sometimes I can get even a kind of animation on the load screen of SMB/Duck Hunt, of course with corrupted sprites.

I cleaned all contacts on cartridge pins and motherboard, nothing changed.

SMB/Duck Hunt cart, resets: sometimes different result
Also attached animation load screen @pwnskar
thanks, I guess that is what I will do if investigation will not bring any success. Good to know that PPUs are compatable, probably I will order S-993A Vacuum Pump as more affordable solution, I heard some good responses about it

Maybe try using a voltmeter or oscilloscope to see if the pins have the correct signal levels.

Around 11:55 in this video, https://www.youtube.com/watch?v=N8YVX75Qr-0 (Apple IIc Repair), he uses an oscilloscope to diagnose the address and data lines. At about 14:22, there's a bad data connection seen on the scope.

alextoad wrote: ↑Thu Jan 23, 2020 3:37 pm Thanks for the response

I have 2 cartridges: Tetris and SMB/Duck Hunt. Picture was taken on SMB/Duck Hunt, but on Tetris it is similar.

I also discovered strange behavior.
I'm testing on a disassembled console, without case. So, for make console read a cartridge, I have to add a little force on it.
Depending on it, I can get a static image as above. Sometimes I can get even a kind of animation on the load screen of SMB/Duck Hunt, of course with corrupted sprites.

I cleaned all contacts on cartridge pins and motherboard, nothing changed.

SMB/Duck Hunt cart, resets: sometimes different result

Screenshot_9.png
Screenshot_10.png

Also attached animation load screen demo.mp4

@pwnskar
thanks, I guess that is what I will do if investigation will not bring any success. Good to know that PPUs are compatable, probably I will order S-993A Vacuum Pump as more affordable solution, I heard some good responses about it

I would try checking the connection points on everything you did with a multimeter. When I first installed my NESRGB and turned it on, the image was correct, but all of the sudden it went away and got a black screen. I then realized that the NESRGB module was not properly inserted into the motherboard.

Also, for desoldering the PPU I had pretty good results with the Hakko 20g desoldering pump which costs just about 19 Euros. It took me around 20 minutes to desolder the PPU on my NES with this pump and a 40 watt soldering iron.

thanks to everyone for responses

I have something for update investigation results

First, I noticed that the palette selection was not bridged on a NESrgb board. I had soldered output #3 and GND (as natural palette). I still don't know is it was necessary, but OK. I had checked console again.

Now I can see some recongnizable images on the screen. For example, Duck Hunt title is readable. Also, I can start Duck Hunt game, but SMB is not working.
I swaped cartridge to Tetris and title screen was even more readable. Except something strange, like "PUSH STEVT" and some broken sprites as well. Picture on ther screen also seems like two colored grayscaled and pink. Also, gamepad inputs are working
After, I checked voltage on PPU pins on Duck Hunt title screen. Here is results

D0-D7 0.7-0.8V
RS2 2.3
RS1 1.9
RS0 1.9
R/W 3.5

AD0-AD7 1.5 in average
DA8 1.8
DA9 2.7
DA10 0.6
DA11 1
DA12 1.25
DA13 1.7

VD OUT 1.5
VCC 5.0V

I have no oscilloscope to test, but I can easily order in 3-4 days, if it can help

Did you short jumpers j5 and j3?

j5 shorted, j3 used when nes is no fitted with external regulator (according by manual)
I can remove external regulator and short j3 just for a test. Also I've to say I have no any audio from AV / or RGBnes 3.5 jack

Is the exact text "PUST STEVT"? Improperly connected address lines cause the wrong tile to be fetched. I don't know any combination of address line failures that would produce that exact message.

alextoad wrote: ↑Sat Jan 25, 2020 11:02 am j5 shorted, j3 used when nes is no fitted with external regulator (according by manual)
I can remove external regulator and short j3 just for a test. Also I've to say I have no any audio from AV / or RGBnes 3.5 jack

Yeah you are right, I thought it was the other way around. Looking at pictures I took from when I installed my NESRGB, I did not short J3. Yo only need to short J5 for NTSC. Why is the image coming up without any colors? what is your output setup?

Is the exact text "PUST STEVT"?

exact text is "PUSH STEVT"

Why is the image coming up without any colors? what is your output setup?

I'm testing on NES board, installed NESrgb, connected to CRT tv via default composite video output. As I know, it has to work. I didn't try to use component nesrgb output yet, because of those problems. I don't have a clue why colors broken. When I tested SMB/DuckHunt cart, it randomly has colors, cometimes not.

On Tetris - one time I got a colored picture. Can a problem be in the cartridge slot? When I put cart in different ways and power on/off console, one time I got colorful image (but with broken title, btw) make 72 short wires and connect directly to cartridge, for example

I would try to connect it to your tv through component or rgb and see how the image comes up. To avoid any problems derived from a poor cartridge connection, I would use a different type of connector. Maybe a blinking light win or just build a custom connector using a 72 pin edge card connector, or a connector from an old game genie.

alfredocalza wrote: ↑Sun Jan 26, 2020 6:38 am I would try to connect it to your tv through component or rgb and see how the image comes up. To avoid any problems derived from a poor cartridge connection, I would use a different type of connector. Maybe a blinking light win or just build a custom connector using a 72 pin edge card connector, or a connector from an old game genie.

I removed external voltage regulator, audio output from nesrgb, solder J3 and added component YPbPr output. Turned on console - capture card displays no signal YPbPr. Connect composite - same broken signal on CRT as before. After that, I checked YPbPr outputs.
Y - 1V
PB - 1.5V
GND - 0V
RP - 0V

I would try checking continuity on all traces from the PPU and into the sockets on the main board. Maybe something is not properly soldered or connected?