PAL Frontloader goes from color to black and white

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Claes
Posts: 4
Joined: Sat Aug 23, 2014 1:29 pm

PAL Frontloader goes from color to black and white

Post by Claes »

Hi, I'm new here and sorry for my first post being a question. But I figured this is probably the best place to ask.

I somehow broke my nes while trying out overclocking for the first time. It looked easy, I had done mono mixing earlier and cut the pin to disable region lock.

I listened to advice from people who had overclocked before, checked everything. And honestly I don't know what I did wrong, but it seems I fried the 150k resistor.

When turning on the nes all I had was a gray screen, I removed the overclock mod and wired the orignal clock signal to the cpu since I cut the trace when trying to overclock. Still gray screen. I thought I had fried the entire board, but when I tracked connections I found out the 150k resistor was fried so I replaced it with another one and now I do get picture and sound atleast.

Now I'm left with an odd problem. The game starts out pretty good, then yellow/greenish stuff start to appear, the color goes over to black and white and finally it crash the game.
I'm thinking overheating. But this is not the kind of stuff I usually do. I dragged out an old tv at work just to make it a bit easier testing the nes. I recorded a short video of the problem.
Sorry for the crappy picture(sound does work, I just didnt hook it up).
https://www.youtube.com/watch?v=bIht-hcvhGs

Any help appreciated. I would love to get this working again and a working overclock.

/Claes
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Jeroen
Posts: 1048
Joined: Tue Jul 03, 2007 1:49 pm

Re: PAL Frontloader goes from color to black and white

Post by Jeroen »

B/W suggests the color carrier is acting up. I'm guessing the crystal inside the nes has shifted over time and as it heats up falls out of tolerance. Not sure why its crashing though.

edit: somehow I missed the part about you trying to overclock. You might've actually physically damaged your ppu doing that.
Claes
Posts: 4
Joined: Sat Aug 23, 2014 1:29 pm

Re: PAL Frontloader goes from color to black and white

Post by Claes »

Thanks :)
I left the nes at work so can't do anything with it right now, but I'm going back tomorrow. Would be nice if I could try out some stuff.
Which part holds the crystal?

Edit: I was suspecting something like that. I don't know how, I was more then careful with it. I'll try take some photos of it tomorrow and show how it looks.
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Jeroen
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Joined: Tue Jul 03, 2007 1:49 pm

Re: PAL Frontloader goes from color to black and white

Post by Jeroen »

Well overclocking by its nature is pushing the chip beyond it's intended scope and could already damage it. (although a bit unlikely in this case)

The crystal is a little metal can part with two pins on the board. It looks like this http://www.surplussalespa.com/catalog/i ... 110592.jpg typically.

If you had an oscilloscope you could probably the clock line and see if its off.

edit: the easiest way I can think of testing whether or not the ppu's broken is to actually desolder it and pop it into another (confirmed working) nes.
Claes
Posts: 4
Joined: Sat Aug 23, 2014 1:29 pm

Re: PAL Frontloader goes from color to black and white

Post by Claes »

Unfortunately I don't have an oscilloscope. I wish I did, I remember we used those in school(around 15 years ago). I might need to buy one in the future.

I only overclocked it to 2mhz as far as I know. I used a 32mhz oscillator which I miscalculated. I thought I would get 2.66mhz but the pal nes divides by 16 so I got 2mhz instead which should be extra safe. But I'm mostly trying this because I think its fun. Is there any pin differences on the cpu and ppu from pal to ntsc?

At moment all I got to measure with is a pretty crappy multimeter.

edit: That would be useful. I've seen people socket the ppu, cpu and even ram. and I've been thinking on socketing this, but not sure what sockets to use. do you have a recommendation?
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Jeroen
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Joined: Tue Jul 03, 2007 1:49 pm

Re: PAL Frontloader goes from color to black and white

Post by Jeroen »

Just any generic chip socket with the right amount of pins will do.
Claes
Posts: 4
Joined: Sat Aug 23, 2014 1:29 pm

Re: PAL Frontloader goes from color to black and white

Post by Claes »

Thanks :) I really appreciate the help.
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