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NES Front Loader nesrgb modded

Posted: Fri Jun 21, 2019 7:45 pm
by conellog
Hi, anyone knows what would be this failing: I modded this board 1 year and some months ago, everything was running fine. Yesterday I was playing when suddenly display turns uneven, sprites became destroyed and lost form, but music was still playing in background however I was able to continuing playing. Each time when I insert a cartridge, every game shows destroyed sprites but with music as it were normal, some games don't start and others get frozen.

I checked cables and retrieve the nesrgb board out in order to check connections, i take my tester and everytring seems to be fine with connections (only continuity between cables and joints), I wired again the switch to turn off the rgb board to testing with composite signal, yet still failing.
I wonder If I replace caps this problem could be fixed or it would be something else, something worst like a main component?

This is megaman 2, it is running but its background looks horrible damage.

EDITED
Dibujo.JPG
Please anyone can give some hint about a solution, best regard.

Re: NES Front Loader nesrgb modded

Posted: Sat Jun 22, 2019 7:09 am
by tepples
First, I would recommend against using the ImageBam service going forward. When I clicked your image, it showed an interstitial page full of advertisements instead of your image.
ImageBam_interstitial.png
Instead, you can upload images to the forum as attachments, like this:
nesdev_t19018.jpg
Second, the PPU appears to be seeing open bus, at least for CHR ROM. I first suspect an enable line (probably PA13, /PA13, PPU /RD) has become unsoldered, either between the PPU and the interposer, between the interposer and the motherboard, or between the motherboard and the cartridge. Others might be able to troubleshoot further.

Re: NES Front Loader nesrgb modded

Posted: Sat Jun 22, 2019 11:20 am
by lidnariq
tepples wrote:Second, the PPU appears to be seeing open bus, at least for CHR ROM.
For everything, in fact. That's the "PPU and nametable fully open bus" picture, with a couple open-bus sprites in a few places.

Re: NES Front Loader nesrgb modded

Posted: Sat Jun 22, 2019 4:11 pm
by conellog
Yes, those are open, I barely remember when I was testing and installing the rgb board one year ago.
I give up, anyone knows what repairing service is good in USA? I don't know any, please. This year I have the chance to send stuff from my country to my address in miami.

I want to still playing nes games w/ rgb signal. However, I start thinking that these kinds of modifications are not reliable at the end all devices fail if oneself do the mod even if I learned how to soldering well.
Regards.

Re: NES Front Loader nesrgb modded

Posted: Tue Jun 25, 2019 7:32 pm
by conellog
I change some capacitors and nothing it shows me the same problem.
I suspect that I burnt something inside the ppu a year ago when I retrieved it but It was working without problems like a miracle. I inspected the solder joints and cables so it seems to be fine.

What if I buy another nes and install whatever ppu from any nes console, would it work? Any ppu could be compatible with whatever nes console?

Re: NES Front Loader nesrgb modded

Posted: Tue Jun 25, 2019 8:41 pm
by koitsu
conellog wrote:What if I buy another nes and install whatever ppu from any nes console, would it work? Any ppu could be compatible with whatever nes console?
When you say "whatever PPU" that's vague. When you say "any NES console", that's also vague. Same with "any PPU" and "whatever NES console". If I answer the question based on those criteria, the answer is a huge big fat strong NO. If you be more precise with what types of NES console you're trying to work on (i.e. exclusively NTSC, PAL, etc.) then the answer becomes "probably". Details:

* https://wiki.nesdev.com/w/index.php/Use ... _revisions
* https://wiki.nesdev.com/w/index.php/Cyc ... ence_chart

Re: NES Front Loader nesrgb modded

Posted: Thu Jun 27, 2019 2:53 pm
by conellog
I'm thinkg of remplacing my PPU. There is a guy who is selling a UA6528 and he told me that PPU works perfectly. In the wiki said "UA6528 UMC-made clone of 2C02G" but what's the difference, just a clone? what about the quality, is there significant differences?

Re: NES Front Loader nesrgb modded

Posted: Fri Jul 12, 2019 9:58 am
by conellog
Hello, Ok I got what it was happening, the Vram is wasted. So before buying anything, Could you please tell me the difference between the wider and the narrowed dip component MB8416A 24 pins, there are two types of fujitsu rams that might be fit in my nes-cpu-10 (this is my old mb8416a-15-sk) but Idk what would happen if I mount the wider one. I know that there are additional holes to mount the wider but what is the difference if it would be better or itd be some incompatibly or else. Regards.

https://www.ebay.com/sch/i.html?_from=R ... A&_sacat=0

Re: NES Front Loader nesrgb modded

Posted: Fri Jul 12, 2019 10:09 am
by Ben Boldt
It's just a packaging thing, you can use the wide or the skinny, no difference based on the width itself. What is most important, check the pinout is correct and the access time is similar.

Re: NES Front Loader nesrgb modded

Posted: Fri Jul 12, 2019 10:38 am
by lidnariq
If you have footprints for both, both should work. 24-pin SRAMs only have one pinout.

Re: NES Front Loader nesrgb modded

Posted: Fri Jul 12, 2019 10:58 am
by conellog
thanks for the reply.
Finally, last question please. I have an additional nes board which I could take out the memory packs at this moment and save some money now, Idk why there are lots of different packs maybe they all work. In this additional nes mainboard, there are these packages: on the WRAM place a BR6116-100, and on the VRAM place the sony CXK5816SPS-15L: Could these IC's work too?

Out there are lots of differents parts from different manufactors, a paradise of parts that i can spare we are lucky.

Re: NES Front Loader nesrgb modded

Posted: Fri Jul 12, 2019 11:21 am
by lidnariq
2K SRAMs were commodity parts during the NES's manufacture life. There were many manufacturers, and as long as any given SRAM is fast enough (<290ns?) but not too fast (>30ns), they should all work.