Would like some input on this one but for the moment I think I've got the end result covered. For those who don't know, when you overclock your Dreamcast you can't use stock VMUs. The clock used in the VMU is normally 6mhz to the Dreamcast's 200mhz and in this case it is safe to assume (to some extent) that the two are tied together somehow. I'm not well versed on Dreamcast hardware to know why but for this purpose it is mostly irrelevant. If you take a look here: http://fileforums.com/showthread.php?t=77928 --=FamilyGuy=-- found out that if you swap the xtal of the VMU for an clocked xtal (using a ratio derived from the crystal being used to overclock your Dreamcast) you can use the VMU again. I was attempting to do this one myself but hit a snag. Pulled out my iron, grabbed my desoldering braid and removed the solder from both sides of the existing xtal then tried to gently prod it off. After about half an hour of gentle poking I took another look at the images --=FamilyGuy=-- had posted. What you can't see too clearly is this: Circled is the xtal in a "smoke" VMU someone sent me to overclock along with some extensive Dreamcast modifications. Easy enough to remove right? Wrong. When you look at --=FamilyGuy=--'s picture of the VMU with the replacement xtal you can clearly see that the solder pads run right under the xtal and if you're like me you have 0 experience removing something like that and only the faintest of idea's how to (I'm guessing a hot air station would be a good start but not part of the budget for this project). The two black arrows added lovingly with MS Paint point to the two vias that connect to the xtal with the middle line solder pad to be nothing more than helping to hold the xtal to the PCB. For purposes of compatibility and usability the individual who commishioned me to perform these mods wanted to be able to switch it between stock 6mhz and 7.2mhz (IIRC) so that he could continue to use the VMU no matter what state the Dreamcast was booted into. No problem, two replacement xtals will fit just fine with tons of room to spare with a foot or three of wire and a small switch in the lanyard area. Since I can't remove the original xtal I'm planning on cutting one trace to the existing xtal, piggybacking the 7.2mhz xtal on top of the existing xtal and running wires to them both and the now severed via to a switch. I don't have much experience working with xtals in such close contact to each other so I'm praying this won't cause some sort of interference. Hopefully this info helps someone else looking to overclock their DC. I'll update it later once I perform the surgery. If anyone has any insight into proper removal of the existing xtal by all means lay it on me. I'm self-taught on a budget of a broke ass college student. :thumbsup:
Dude needs to get a hot air station... or learn how to cover each side in solder to remove parts like that.
My DC is overclocked to 240MHz and I really have not had problems with VMUs in their stock speed, I do have my main use VMU overclocked to 7.2MHz just in case.
I do. :crying: Though I could use the appropriate tools to be able to melt the solder on both sides of the component at once. Hopefully I can get one for a lot cheaper than a hot air station within the next day or so.
The ChipQuick method is what I ment - but you can do it with normal leaded solder. All you need to do is put solder all across 1 side of that part, then put the soldering iron in the middle. All the solder will melt and all the pads will be free at once. then lift with tweezers or something. Failing that, you can buy SMD tweezers for next to nothing which you can melt both sides at once.
Not so sure that would work in this case. I think I found my ChipQuick that I ordered some time ago, at least I don't have any solder on hand with such resistance to being bent normally. About the same length as the ChipQuick I bought... Not sure myself that I could heat up all three pads at once without destroying something. At the very least I'm not willing to chance a procedure I've not done myself on a VMU. I will try testing a VMU unoverclocked for kicks to confirm what TmEE said. Also of note, some Dreamcast games don't like being overclocked. Big shocker I know, whoda guessed? I had Jet Grind Radio get to the first loading screen. The music was playing, the graphics were pretty and then everything video related froze with the music continuing to play in the background. Never did get any further than that. Flipped the switch, booted it back up and it played without a hitch.
Those 3 pads run all the way under the part. So all you would need to do is flood 1 side with solder. then putting your iron anywhere that side would melt everything in 1 go - and just lift the part off. This picture gives an idea of what im talking about oh and if replacing a resonator with a crystal, there should be 2 caps added.
1) Apply chipquick to all three pads 2) Hold iron across all three pads 3) Remove resonator Is what I'm getting? I've read repeatedly that using capacitors is a good idea, though my knowledge of electrical engineering stops short of knowing why or how to derive appropriate values. Time to crack open the textbook I just got and hit up Google, unless anyone can offer any suggestions. :thumbsup:
