Problems with the colors (especially blue) on the NES

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Liengamer
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Problems with the colors (especially blue) on the NES

Post by Liengamer »

A while back I've got myself another NES for only 3.99€ in a yard sale. At first glance it looks alright and appears to be perfectly fine. Then I've noticed that the colors especially the color blue and everything containing it looks absolutely terrible.
I've looked at the output directly after the PPU which is weak (as expected) but otherwise completely fine. Even the colors are good.
Unfortunately I cant really fine any Information about the many trimmers on the PCB and in the RF-Modulator which might have to do something with it.
I've looked up the schematics and the only real problem could be the 2SA937 or anything in the RF-Modulator in my opinion. Would it make sense to swap out the transistor (since I've already got one of them)?
Attachments
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lidnariq
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Re: Problems with the colors (especially blue) on the NES

Post by lidnariq »

Just making sure, since it wasn't explicitly stated - this NES appears to be outwardly identical to another one you have, but blues don't work well on this one?

If so, go ahead and swap out the transistor - it's certainly easy and cheap enough to be worth trying.
NewRisingSun
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Re: Problems with the colors (especially blue) on the NES

Post by NewRisingSun »

All I see is that the video levels are wrong, causing all $3x colors to clip to white. It's not specific to blues, as the $1x and $2x blue is still blue.
Liengamer
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Location: Germany

Re: Problems with the colors (especially blue) on the NES

Post by Liengamer »

lidnariq wrote: Sun Dec 12, 2021 10:30 am Just making sure, since it wasn't explicitly stated - this NES appears to be outwardly identical to another one you have, but blues don't work well on this one?

If so, go ahead and swap out the transistor - it's certainly easy and cheap enough to be worth trying.
Yeah that's exactly the case. The other one is the one which had the broken RF-Box. For now I'm going to swap out the transistor and recap the RF-Box and PCB.
Liengamer
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Re: Problems with the colors (especially blue) on the NES

Post by Liengamer »

NewRisingSun wrote: Sun Dec 12, 2021 10:40 am All I see is that the video levels are wrong, causing all $3x colors to clip to white. It's not specific to blues, as the $1x and $2x blue is still blue.
Well does this mean that the PPU is probably bad?
NewRisingSun
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Re: Problems with the colors (especially blue) on the NES

Post by NewRisingSun »

No, I think that at some point in the video path from the PPU, the amplification of the video signal is incorrect. You mentioned the RF modulator -- does that mean that the signal is good when coming from the baseband composite AV socket?
Liengamer
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Location: Germany

Re: Problems with the colors (especially blue) on the NES

Post by Liengamer »

Unfortunately replacing the transistor and recapping the Board didn't fix the problem...
Liengamer
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Re: Problems with the colors (especially blue) on the NES

Post by Liengamer »

I've tapped into the signals directly at pin 21 on the PPU and right before it goes into the RF Modulator at the output side of FC2... Really looks like its something inside the RF-Modulator
The first picture is at the output of FC2 and the second directly at pin 21 on the PPU
Attachments
at output of FC2.jpg
directly at pin 21 of the PPU.jpg
lidnariq
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Re: Problems with the colors (especially blue) on the NES

Post by lidnariq »

The baseband portion of the RF modulator is pretty simple - it's something like a PNP-based emitter follower.

For example, look at my trace of an NTSC modulator:
viewtopic.php?p=131845#p131845

Or Electronix Corp's reverse-engineered one:
https://console5.com/wiki/File:NES-001- ... Switch.png

So you should be able to make similar guesses about rebuilding the baseband video path in yours
Pokun
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Re: Problems with the colors (especially blue) on the NES

Post by Pokun »

It's a NES right? It should have composite output as well.
Liengamer
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Re: Problems with the colors (especially blue) on the NES

Post by Liengamer »

lidnariq wrote: Sun Dec 12, 2021 3:05 pm The baseband portion of the RF modulator is pretty simple - it's something like a PNP-based emitter follower.

For example, look at my trace of an NTSC modulator:
viewtopic.php?p=131845#p131845

Or Electronix Corp's reverse-engineered one:
https://console5.com/wiki/File:NES-001- ... Switch.png

So you should be able to make similar guesses about rebuilding the baseband video path in yours
Are the values the same on a PAL-system?
lidnariq
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Re: Problems with the colors (especially blue) on the NES

Post by lidnariq »

Uh ... maybe? Possible.
Liengamer
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Location: Germany

Re: Problems with the colors (especially blue) on the NES

Post by Liengamer »

Unfortunately not... the PCB looks completely different. I'll probably end up having to re-engineer the PAL-PCB because I cant seem to find a schematic for the PAL ones at all.
Liengamer
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Location: Germany

Re: Problems with the colors (especially blue) on the NES

Post by Liengamer »

Just take a look at how complicated/different the PAL version is in comparison to the NTSC version...
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lidnariq
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Re: Problems with the colors (especially blue) on the NES

Post by lidnariq »

The RF portion is much more of a mess than the baseband is.

I have no idea what the 6-pin SOT23 is, however, and no obvious guess.
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