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PostPosted: Wed Nov 06, 2019 4:58 am 
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Hey nesdevvers,

I have worked on at least 100 NES consoles, many of them NESRGB installs or other misc repairs like faulty chip replacements, so I have spent a fair bit of time under the hood of NES consoles.
Since I had a bunch of PAL NES consoles (living in Australia) I decided to try and convert some consoles to NTSC (Pal is pretty bad anyway IMHO).
So, swapped out the CPU/PPU and crystal oscillator from either a NTSC NES or JAP Famicom and the system seemed to work fine after some short periods of testing (usually let Zelda1 intro loop a few times). Once I install a NESRGB and perform testing all sorts of wierd stuff happens (after some time of Z1 intro looping, eg 20mins of it working perfectly, then it started exhibiting wierd behaviour).

-graphics glitches / sometimes colours completely inverting or changing
-the whole console crashes
-sometimes when it turns on I get pink screen
-horizontal interference
-audio goes haywire

I asked Tim (Worthington) for some advice on the subject and he suggested I look at the capacitors on the same circuit as the XTAL oscillator.


Has anyone performed this changeover (PAL to NTSC, then installed NESRGB board) with success ?


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PostPosted: Wed Nov 06, 2019 7:35 am 
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The system hanging up or the audio reading wring suggests it's not just a compatibility problem between the PPU and the mod. It sounds like you're having electrical problems on the buses. A custom peripheral i made had similar problems on simultaneous startup with the base unit - perhaps too much current draw when everything started simultaneously. In your case, maybe the added current draw is a continous hazard to stability. I wouldn't really know what's the problem here, though.

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PostPosted: Wed Nov 06, 2019 12:15 pm 
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Did you install the NESRGB like you would in a NTSC console? E.g. correct jumper bridges? If those are still on PAL settings then there's your problem.

I converted many Famicom to PAL or some NES to NTSC as well as Dendy Clone CPU/PPU and everything was working well. With and without NESRGB installed.


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PostPosted: Thu Nov 07, 2019 5:38 am 
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Thanks for the responses - yes the NTSC pad (JP5) is closed, not the PAL ones. I have read of other people having many troubles with clone PPU/CPU and NESRGB installs - so suprised you are saying you have it working well, glad you have done this tbh. Have you left these units powered on for some-time and they are stable ?

Current draw ? I guess I could try with a second 7805, like the nes front loader, but I dont think the power is the issue. The NESRGB in a regular top loader NES2 (which this is) does not need the second regulator as the heatsink is sufficient. Tim told me in the past the only reason he supplies the front loader kits with its own 7805 is that he left one of his very early NESRGB installs running overnight and in the morning the NES smelt like burning hehe.


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PostPosted: Thu Nov 07, 2019 6:31 am 
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it's not the temperature buildup i'm worried about - Just drawing a parallel to when the differing draws of my custom peripheral could throw the reads and writes of data out of whack, leading to everything from small glitches to complete program freeze. It's not the same device, and i'm just a hobbyist without the proper EE skills, so it could really be anything from my point of view. It just sounded familar to me!

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PostPosted: Fri Nov 08, 2019 12:27 am 
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If I had to guess, I'd say maybe the crystal has failed, maybe from too much heat during the transplant. I don't think that's usually a problem, but I've seen it at least once and the effects were pretty weird and unpredictable. In that case it was on a pinball machine sound board, with a YM2151. It would run fine for 5-10 minutes at a time, then it would sometimes completely go nuts for a few seconds at a time, or start playing normal but have occasional notes in the music be the wrong frequency. Problem completely went away when I swapped out the crystal.

Doesn't really explain why it works without the NESRGB mod though, unless we're to say it was just a coincidence.


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