Dreamcast overclock switch question.

[Brian 503]

https://s.amsu.ng/P38K8u979zRN

Above is a link to a image of the 10% dreamcast overclock and how to install it. My question is, Is it possible to remove the three existing resistors from the motherboard then duplicate the  3 resistors and add the 2 new resistors (To overclock) to a 0603 breakout board then be able to control all resistors to the motherboard using a switch to run the factory settings to the 3 original resistors and switch then off and the other 2 resistors back on? So basically a switch to make it run stock and the other to overclock.

[RDC]

Yes you can do it that way. Those lines are just control lines for the clock generator that get set Hi or Lo, so extending them will not mess with anything.

You could do that with just a DPDT switch and a couple of 10k Resistors though. I'll make up a diagram a bit later when I have some time, but you can do that however really as there's no actual clock signals or anything on there that would turn to crap extending them.

[Brian 503]

A diagram even crude would help. I'm just wrapping my head to if the resistors have a +- side for proper orientation and what side to run my wires off the resistors to the dpdt switch. Basically all wiring lol. I'm so horrible I haven't done this stuff in ages.

[RDC]

This assumes you have a VA1 version board, since that's what was in the pic in the link.

1 - Remove R346, R348 and R350

2 - Replace R348 and R350 with 10k 0603 Resistors, leave R346 open.

3 - Wire up the back of the DPDT like the diagram. I didn't draw all over the board, just connect the same colored dots with wire.
The X spots get no wire installed. The Orange and Black spots are 3.3v and Ground respectively. You can use the spots marked at C250 or any 3.3v and Ground spots you prefer.



The way this works is with the switch in one position R346, R348 and R350 will all be connected to ground. R348 and R350 will be going to ground thru the 10k, and will be connected together, but it's the same difference as those lines will be pulled Lo and get changed together anyway, so the clock speed will be stock.

Flip the switch and R346 will open (aka removed) and 3.3v will go to the lines for R348 and R350, pulling them Hi since they were replaced with the 10k, same as the 3 Resistors removed and 2 Resistors installed for the overclock.

[Brian 503]

Yep rev 1 board! This is perfect. So the two purple connections both tie into the same spot on the dpdt switch from the motherboard I assume? And the yellow is the gate so to speak, so if the switch is on the yellow side that would be normal clock and if slide the switch to the left to the purple side that would indicate the 10% clock gain? If I wanted to put 2 led indicator using some 0805 leds could I just tie the leds to the yellow and purple connections off the dpdt switch to let me know what circuits I'm running off of? Apologies for all the dumb questions, I just dont want to brick my dreamcast and be 100% sure of operation using leds to let me know what mode is what. I'm the type that will forget what switch does what if not properly labeled or with visual leds for knowing order of operation. Thank you for your time sir RDC. It's always a pleasure speaking to u, thanks!

[RDC]

Well that's what I get for going off someone else's diagram and not checking it over first. They only have 2 Resistors installed for the OC, but according to the DS for that clock generator it will take all 3. I just looked thru the DS for that chip, so not sure how they are getting the 36.7MHz as the way they have done it, and the way I redid it up there, that would still be the 33MHz clock, but have a 1% spread versus the stock 0.5% spread. Maybe the chip has internal PU? No idea, point is forget that last post.


So here we go, ignore the mess above as that will only get you the same 33MHz clock +/- 1% or 32.67MHz to 33.33MHz

Technically there are 3 control lines for the clock generator IC, and each one has a place for 2 Resistors in a divider layout, to either tie the control line Hi or Lo, aka 3.3v or Ground.

Control 1 - R345 (Hi), R346 (Lo)
Control 2 - R347 (Hi), R348 (Lo)
Control 3 - R349 (Hi), R350 (Lo)

The stock speed setting is all 3 control lines tied Lo, so R346, R348 and R350 are all populated with 0 ohm jumpers.

In order to get the 36.7MHz, that has a 2% spread or 35.96MHz to 37.43MHz, all 3 control lines need to be tied Hi. So again, forget the above and go about it this way instead.

1 - Remove R346, R348 and R350.

2 - Install 10k 0603 at R346, R348 and R350. Tolerance value doesn't matter.

3 - Here you can just use a SPST switch now, or half of a DPDT, either one.



The way this works now is all 3 control lines are tied together, the violet spots to the switch. They all get set Hi or Lo anyway for the stock or OC setting, so there's no real point in having them all separate as that would require a 3PDT switch, or a DPDT and SPST or 3 SPST switches if you wanted to be able to go thru every clock setting, but they are all 33MHx +/- some small percent, so basically all of them are 33MHz so no point in going thru all that mess.

The switch has 3.3v in the middle, flipped one way the 3.3v goes to the Red spot of the switch, just to light up the stock speed LED as the 10k you swapped in there will keep all 3 of the control lines pulled Lo for the stock speed setting.

Flipping the switch the other way, the 3.3v goes to the violet spots and pulls all 3 control lines Hi for the OC speed. You can also wire up your OC LED to that side of the switch.

Swapping out the original jumpers in step 2, the R346, R348 and R350 for the 10k keeps the control lines pulled Lo if the switch is removed or goes open for some reason, so the stock speed will be the default if that happens or if anyone just removed it and did nothing to the board.

Side note: It should go without saying to never flip this switch while the DC is on, just to put it out there. Best case the thing will just lock up an need to be power cycled, worst case who knows, but no point in risking it.

[Brian 503]

Man so much win in this, thank u. This is perfect and simpler than before. I just have to wait for the resistors to come in. I have some spst switches laying around so this should work out perfectly. I have a spare dreamcast v1 motherboard that had a old internal vga mod but was disassembled and a via or tp was destroyed, short ver it works in rgb mod so I can test this out before taking it to my main one. Thank u for everything and I'll let u know how it goes!

[RDC]

Welcome.

[citrus3000psi]

The clock gen has internal pull ups.  I think it even states this in the datasheet IIRC.  The mod I wrote up I tested on a physical board with a scope. 

[RDC]

Yeah it's in there, right above the Freq Selection table I was looking at, doh. Control 1 has a PU on it, then Control 2 and 3 have PD on them, and explains why only 2 new Resistors were installed.

[Brian 503]

Thank u for sharing this information. I wanted to be certain their was no hidden things going on which was why I contacted Citrus3000psi. So original schmatics should work with a dpdt switch like originally stated. Thank u RDC as well for awnsering my questions and providing schmatics! I appreciate both of your help today, thank u again.

[Brian 503]

I have a question hopefully someone can answer for me. I'm almost ready to overclock my dreamcast and I'm looking at led replacement for the main controller port. Can I take out the stock 5mm led and bridge those two vias together to delete the led so the power can continue its course through the controller port?

Other question, will a 3v-5v Diffused 2-Pin Led work for my dpdt switch on the overclock. I'm assuming that the two pins are both connected to a power source? Or would I hook it to say C250 with the hot wire to the orange hot lead and the ground wire to the black schmatic on C250? For this led to work does it need a ground or does it run on two power sources  to a switch so when the switch is flipped it flips the other color? Just want to be sure what I'm doing.

[RDC]

The Power LED on the controller port board does not 'pass power' in any way. It has it's own pin that connects to the 3.3v rail of the DC. If you remove it and connect those spots you'll be shorting the 3.3v rail out, aka bad. If you don't want the power LED to work, just remove it and leave the spots open.

A diffused LED just means the covering on it isn't clear, it's frosted in some way, so there's no real direct light from it.

If the LED only has 2 leads, then it's usually a single color LED, or a 'rainbow' type that cycles thru colors on it's own. In either case it's one positive and one ground on a 2 lead LED.
The Bi-Color 2 pin LEDs are wired opposite of each other, so power on one side ground on the other you get the first color, flip the power and ground and you get the other color.

A better Bi-Color LED will have 3 leads and be in a Common Anode - + - or Common Cathode + - + layout. Alternately it could have 4 leads so each LED is independent of the other.

[Brian 503]

Thank u so much. I just googled the crap out of everything as well and figured it out. I'll be removing the led from controller port, leaving holes open. I'll tie my dpdt switch up to the 3 leg bi color led using the layout u have above for overclock schmatics, then use that in place of the controller port led. That way whatever side the switch is on, when dreamcast powers on it will be the color assigned to the switch from the overclock power and grounds.

[Brian 503]

So just installed the overclock switch and everything is working fine. I want to make sure I'm in the right mode. So if the switch is perpendicular under the  yellow side that's overclock correct? So if its switched over on the violet side that would be stock? From testing it seems to run better when its lines up on the yellow terminal opposed flipped over to where the two violet terminals are.

[RDC]

Depends on the type of switch you're using. If it's a Slide switch when it's pushed left the middle and left terminals are connected. A Rocker switch will be backwards though, when it's flipped left the middle and right terminals are connected.

So if you're using a rocker switch, and it's flipped toward the Yellow, then you're really in the OC mode and have the middle Orange connected to the Violet.

[Brian 503]

It's a double throw double Pole switch on on switches two ways. I went off the first diagram  with your dpdt diagram.

[Brian 503]

Here is a pic of how everything is wired up. Based of first post with dpdt switch.

https://s.amsu.ng/1RC81zxFYjHN

The white wire is hot to C250, the black wire is ground off C250, the brown wire is connected to R346 on your yellow diagram. Violet is tied to R348 & R345 then to the lead on the dpdt diagram in your schmatic. Just need to know if flipped over to the violet side if its overclock and if switched to the yellow stock clock speeds. It's a dpdt switch only goes two ways and it's a on/on operation. I already know how to install the OC leds using a 3v 3 pin 5mm bi color led. Wiring that to the switch is a no brainier but my brain has gone into limp mode trying to figure out what switch converts the clock to overclock.

Edit. Wire my switch wrong. I knew the overclock was not aggressive but I figured I'd be able to tell the difference then reviewing my wiring on the switch the violet leads were on the wrong pin. I definitely know what's overclocked and what's not now. Thank u RDC for everything, it truly means a lot to me.

[RDC]

That's a toggle switch, same as a rocker where the position it's set is reversed on the wiring terminals.

Imagine this as looking thru the top of the switch.

Code: [Select]

Switch flipped to the Right, terminals in the Middle and Left are connected.
-------------
| 1 - 2   3 |
|           |
| 4 - 5   6 |
-------------

Switch flipped to the Left, terminals in the Middle and Right are connected.
-------------
| 1   2 - 3 |
|           |
| 4   5 - 6 |
-------------

That doesn't look wired up right on the switch to me. One set of the opposing corner terminals should be wire free.

Code: [Select]

Back of switch, held so it Toggles left/right.
-------------
| 1   2   3 |
|           |
| 4   5   6 |
-------------

1 = No Connection
2 = Ground
3 = R346 bottom side
4 = R349 bottom side and R347 left side
5 = 3.3v
6 = No Connection

Toggle Left = 1 & 2 then 4 & 5 are connected, DC is Overclocked 36.7MHz
Toggle Right = 2 & 3 then 4 & 6 are connected, DC is stock 33MHz


[Brian 503]

Your absolutely correct about everything sir!!!! Thank u

I have a bug of curiosity,  so say I went about on the second method u posted "before knowing about the internal pull ups" on the DC clock. Would adding the other 10k resistor boost the clock speed past the 10% method above? If so do u know what frequency it runs at or will adding it do absolutely nothing.

Sorry for bugging the hell out of u on this. U dont have to wander this, its just a question to me that sparks my curiosity.