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 Post subject: Snes Mini CPUN pin 155 mod
PostPosted: Wed Sep 06, 2017 8:51 am 


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Joined: 09 Aug 2017
Posts: 1458
Location: Australia
Just did a quick 3 wire RGB mod without 1.2k resistors, lifted pin 155 of the cpun and put a 20ohm resistor inline, power regulator upgrade to a L78S05 2A and a cap on the regulator.

The regulator killed the vertical white bar on comp on my LCD tv but there was still a dark bar where it was. The cap did nothing but it's a 220uf not 470uf so I'll need to test that.

Doing the pin 155 thing was not fun but I figured out an easy way.
I bent a thin spring straight and slid it behind the pins on the cpun till it was behind pin 155. I put some tension on the spring, got my soldering iron hot and dry and applied it to the pin. Ting! Came straight off the pad. Then I straightened the pin by placing a blade across the top of all the pins on that side to support it and stop it from bending at the chip.
That's the easy part.
Soldering a resistor to that pad is not. It's a weak trace.
I lifted It, soldered it to 154 then 156, finally got it free and decided to glue the resistor to the cpun and bend the legs to have 0 tension against the pin or trace then soldered in place. It's strong and got the job done.
I wired up RGB from the internal amp with 75 ohm resistors in series and skipped the 1.2k terminations.

Fired up the mini and was instantly impressed by nice bright writing with no ghosting.

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 Post subject: Re: Snes Mini CPUN pin 155 mod
PostPosted: Wed Sep 06, 2017 4:58 pm 



Joined: 12 Jun 2017
Posts: 229
You don't need to connect the resistor to the same pad, there's a much easier +5v via near the top-right corner of the CPUN.


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 Post subject: Re: Snes Mini CPUN pin 155 mod
PostPosted: Wed Sep 06, 2017 7:35 pm 


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Location: Australia
Ryoandr wrote:
You don't need to connect the resistor to the same pad, there's a much easier +5v via near the top-right corner of the CPUN.


I wasn't sure if it was 5v or variable. Should of probably used the meter to check.
Thank you Ryoandr for pointing it out. I'll take a look.


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 Post subject: Re: Snes Mini CPUN pin 155 mod
PostPosted: Wed Sep 06, 2017 9:54 pm 


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Joined: 09 Aug 2017
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Location: Australia
I think you were refering to an SNES1 1chip.
Image

The mini has the pads in opposite corners, yet to test which is 5v.
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 Post subject: Re: Snes Mini CPUN pin 155 mod
PostPosted: Wed Sep 06, 2017 10:05 pm 


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Joined: 09 Aug 2017
Posts: 1458
Location: Australia
Ok did a quick continuity test around the CPUN on the mini, it seems these are viable places for 5v.

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 Post subject: Re: Snes Mini CPUN pin 155 mod
PostPosted: Wed Sep 06, 2017 10:09 pm 


You were just a few seconds quicker than I was. I wanted to suggest you the 5V plane one left hand side of the S-CPUN (your marking next to the "U1" label)


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 Post subject: Re: Snes Mini CPUN pin 155 mod
PostPosted: Wed Sep 06, 2017 10:56 pm 


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Joined: 09 Aug 2017
Posts: 1458
Location: Australia
I ended up choosing the via @ pin 121. Its only present on the mini board I think.
Tested and working, much neater and stronger. Thanks guys.

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 Post subject: Re: Snes Mini CPUN pin 155 mod
PostPosted: Thu Nov 19, 2020 12:48 am 



Joined: 13 Oct 2015
Posts: 55
Would resistor value on an phat snes 1chip still be 20ohms? Thinking it should be less sense for pulldown brightness mod phats use 750ohm and jr uses 1.2kohms.

Have a phat 1 chip with 20ohm on pin 155 and no pulldowns and 75ohm coming out of THS7316 rgb bypass amp. Brightness is too low or black levels rather. Crt test suite pluge screen can hardly see any of the bars.

Edit: Something is wrong with my amp chip I guess. Took it out and restored original amp feed and pluge looks much better now. Also put a 100 ohm pot in the s-cpun 155 pin and about 20 ohms is still good for phat snes.


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 Post subject: Re: Snes Mini CPUN pin 155 mod
PostPosted: Thu Nov 19, 2020 12:07 pm 


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Location: Australia
This is a depreciated mod.

You get a better result changing the input capacitor.


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 Post subject: Re: Snes Mini CPUN pin 155 mod
PostPosted: Thu Nov 19, 2020 4:34 pm 



Joined: 13 Oct 2015
Posts: 55
Is that the cap replacement fix that causes some Capcom games to have missing lines at the top?


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 Post subject: Re: Snes Mini CPUN pin 155 mod
PostPosted: Thu Nov 19, 2020 5:18 pm 


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Location: Australia
Yeah, C11 I think.
Causes black bars on some games instead of a fade in/out.
There are patched versions of some of those games available.


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 Post subject: Re: Snes Mini CPUN pin 155 mod
PostPosted: Thu Nov 19, 2020 6:17 pm 



Joined: 13 Oct 2015
Posts: 55
I've briefly read over the thread of fbx's c11 cap fix. Is there a reason that method is better besides the difficulty compared to pin 155 mod?


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 Post subject: Re: Snes Mini CPUN pin 155 mod
PostPosted: Thu Nov 19, 2020 10:56 pm 


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darknezz19 wrote:
I've briefly read over the thread of fbx's c11 cap fix. Is there a reason that method is better besides the difficulty compared to pin 155 mod?

the cap fix is simply more effective, the relative difficulty is immaterial


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 Post subject: Re: Snes Mini CPUN pin 155 mod
PostPosted: Fri Nov 20, 2020 12:18 am 



Joined: 13 Oct 2015
Posts: 55
Like what? Does it take away ghosting while not affecting brightness? Glitches seem like a drawback.


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