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36.7 Mhz point

MastaG

Rising Member


Hi,

I'm trying to overclock my VA1 dreamcast without luck.
My Dreamcast is equipped with a DCHDMI though.
I pretty much followed this guide: <a class="externalLink" href="http://www.racketboy.com/retro/overclock-your-dreamcast" rel="nofollow" target="_blank">http://www.racketboy.com/retro/overclock-your-dreamcast</a>
So I lifted the 33.3 MHz pin and soldered a wire which goes to the left side of the switch.
Then I soldered a wire from the 33.3MHz pad to the center pin of the switch.

I'm using this clock generator: <a class="externalLink" href="https://uk.farnell.com/ael-crystals/o40m000000l126/crystal-oscillator-40mhz/dp/9510168" rel="nofollow" target="_blank">https://uk.farnell.com/ael-crystals/o40m000000l126/crystal-oscillator-40mhz/dp/9510168</a>
Datasheet: <a class="externalLink" href="http://www.farnell.com/datasheets/1806758.pdf" rel="nofollow" target="_blank">http://www.farnell.com/datasheets/1806758.pdf</a>

So it's basically a square thing with 4 pins.
Pin 4 is connected to a solid ground point.
Pin 8 is connected to the 5v rail.
Pin 5 is connected to the right side of the switch.

So when I put the switch to the left side, which basically connects reconnects the 33.3MHz pin back to the mainboard, it will boot just fine, no problems.

However when I put the switch to the right side, it should get the 40MHz signal from the crystal but it fails to boot.

So there could be 3 causes:
1. The 40MHz signal from the chip is not compatible? it's frequency stability is 100ppm, perhaps too much?
2. My Dreamcast cannot be overclocked?
3. DCHDMI is not compatible with a overclocked Dreamcast? according to chriz2600 it should work: <a class="externalLink" href="https://www.reddit.com/r/dreamcast/comments/aak9ml/can_the_dchdmi_be_installed_in_an_overclocked/ectm35a/" rel="nofollow" target="_blank">https://www.reddit.com/r/dreamcast/...chdmi_be_installed_in_an_overclocked/ectm35a/

Now I read about this page: <a class="externalLink" href="http://dansprojects.com/dc_overclock.html" rel="nofollow" target="_blank">http://dansprojects.com/dc_overclock.html</a>

It basically tells me to remove three jumper wires and put 2 10k resistors in the blue spots.
But since I already have the pin lifted and the switch glued to the mainboard, I'd like to know which point supplies the 36MHz signal so I can reroute the wire from the crystal to that specific point <img alt=":)" class="mceSmilieSprite mceSmilie1" src="styles/default/xenforo/clear.png" title="Smile :)"/>
 

MastaG

Rising Member


Nevermind.. overclocking works fine here.
However DreamShell does not show a picture on the VMU when running in 240MHz.
So I thought it didn't boot, but actually it did.

Also saving onto the VMU seems to crash.. so the VMU definitely requires to be overclocked as well.
Is anyone willing to sell a couple of pre-overclocked VMU's for a nice price?
 

Teddy Rogers

Spirited Member

<div class="bbCodeBlock bbCodeQuote" data-author="MastaG">

<div class="attribution type">MastaG said:

<a class="AttributionLink" href="goto/post?id=989664#post-989664">↑
</div>
<blockquote class="quoteContainer"><div class="quote">Is anyone willing to sell a couple of pre-overclocked VMU's for a nice price?[/quote]

</div> Maybe easier to replace the crystal in one of your own VMU's?

Ted.
 

Gizmo613

Active Member


Do a search on the Dreamcast section and there will be a post that I have listed a crystal that works.
 

fafadou

Gutsy Member


I've heard the problem may come from the lenght of 40MHz wire if it's too long compare to the"bandwich" at 40MHz it doesn't work.
 

MastaG

Rising Member


I used thicker single core kynar wire and a bigger switch for the clock signals.
Like I said.. 240MHz seems to work great.. I've been playing Sonic Adventure International for quite some time.
Only the stock VMU doesn't seem to like it.. it sometimes crashes when trying to write data (e.g. save my progress).

Other than that it seems to work great.. 240MHz + Dreamshell + CF card = really fast loading times.
I only need to carve out a slot for my CF reader right above the modem.. which is going to take a while..
 
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