Update time
This is gonna be a VERY long one, three days of fiddling and testing and non posting all coming out in one post here
You have been warned.
Again, I seem to have found some interesting patterns which I think are giving some small bit more info on how this works, how it doesn't work, etc. in the case of my GP at least.
Okay, first I want to point out, again, that the first time I did this, I was doing all my testing with Castlevania... but I wasn't actually PLAYING anything, just testing (too excited to settle down and play for more than a few minutes of anything at a time). Only after a few days did I go back to just playing games normally, and that's when I noticed it would lock up on Sonic 2 within minutes. After trying a lot of different combinations of putting different levels of graphite on both resistors and then doing all my testing with Sonic 2... trying to get it to be stable at around 192mhz or above, nothing seemed to work... 10 mins tops before it would lock up. But then, going back to test with Castlevania, I'd still get 30 mins before just shutting it off myself. At the same settings that I was having problems with Sonic 2, Castlevania would never seem to lock up. So discovery #1 for me is, for whatever reason, Castlevania runs more stably with this voltage mod, at least compared to Sonic 2 (and Sonic 3, the other game I tried for testing).
Now... I want to point out that in MY case, I have very clearly discovered EXACTLY how MY GP will indicate to me if I'm giving it too MUCH voltage or too LITTLE voltage. Too little voltage... well we should all know what happens when you try to OC with too little... I find that in DrMD, as I up the clock speed one increment at a time and exit out of the menu, when I hit a speed that's too high for the voltage, it usually just goes black screen when I exit the menu, OR, it will play the game for 2-10 seconds and then freeze. At most I may get a few minutes of playtime (used to always get 15mins at 166mhz of GP Engine before it'd freeze).
Now the symptoms I've found for when I get it running too MUCH voltage, is #1 of course you will be able to clock very high
In my case... if I'm able to stably do more than 188mhz (at some points, I had gotten to where it would run up to 224mhz w/o instantly locking), it is too MUCH voltage for MY GP. This will usually cause the GP to reset after a few minutes of play (which indicates it's only slightly too much) or will cause the game to freeze and the screen to flip out, flickering white bars and crazy stuff that will make you think you just killed your LCD. This is what was happening in Sonic 2 for me.
Thru tweaking and tweaking, and observing these symptoms and taking NOTES this time, being much more methodical than I was the last time (I'm VERY sorry everyone... in my rush and excitement I brought incomplete information to the table to share with you wanting to be helpful... I believe it's not electromigration burning my CPU out slowly, it was me not testing thoroughly enough the first time to see that it was REALLY stable). I found that in my case, my CPU is very sensitive to too much voltage. My target was to be able to sustain 180ish mhz stably... never wanted to go too insane with it. 180mhz has even the roughest games (all but Vectorman) running at 30-40fps in DrMD so no more framerate 'chugging'. So... with that in mind, I tweaked the graphite to get the barest minimum voltage I could get to sustain this speed. The way I have it set now, I can only run up to 184mhz stably... at 188mhz in DrMD, it will usually lock up within a few minutes (freeze, no screen flickering) and at 192mhz, it will freeze instantly when leaving the menu (black screen) or run the game for no more than 10 seconds before freezing. So... not a whole lot of voltage increase over stock *I think* (considering I could do 164mhz stably before and run 166mhz for about 15 mins). Then I loaded up Sonic 2 at 184mhz. This time, it ran well over 45mins with no lockups or resets. But if I up the voltage even a little more, so that I can do 192mhz stably but it locks instantly at 200mhz, and then test Sonic 2 within 10 mins it locks with the flickering screen... too much voltage.
I've said it 10 times already, this mod is VERY sensitive. As others have pointed out, even one stroke of the pencil can make a HUGE difference in what your GP will do. This time around I also followed Jcabrer's tip that he added to his first post well after the thread started, which is, just add tiny amounts to the R52 (one light layer at a time) until it's clocking where you want it to clock, then once your GP shows signs of too much voltage, add even tinier amounts to the R48 (which REDUCES voltage) until it is stable. Trooper seems to be a lucky one that his will take 200mhz apparently indefinately, or you might end up like me, only being able to support a much smaller increase before your CPU cries for mercy. Obviously, Sonic 2 would probably be a great game to test on... at least in my case it is. And I'm betting the symptoms of too much or too little will be the same for everyone or for most of you.
Now... this time I'm bringing much more thorough info to the table, and I hope this helps
I've been doing a lot of testing over the last 3 days (hence why I haven't posted) to make sure that my 'findings' made sense. NOW my GP will run 184mhz all day... well until the batteries run out
my record now was just over an hour on Sonic 2 until my batteries quit and almost had me going thinking it was messing up again!!! Thank god I took Troopers great advice this time... if the TV wont work, be sure it's plugged in before trying to fix it
Put in charged batteries and did another hour of Sonic 2 (to ease my mind) to be sure all was well.
EDIT: thought I should mention, ALL testing has been done using 2300mAh 1.2v NiMh batteries. When I did some testing with 1.5v alkalines, I seemed to get an increase in long term stability, as well as being able to OC higher, w/o changing anything else. Same thing might happen with an AC adapter I bet.... Trooper you cheater!
and Reesy - I don't do this the 'proper way' becuase #1 I don't have a soldering iron anymore so that would increase cost for me right there and #2 ARE YOU KIDDING ME??? The points you have to solder are SOOOOOO small I would not DARE try to do this myself... I've sodered a few things in the past like mod chipping my Dreacmast and PSX and let me tell you those connections were small and a PAIN in the ass to get right w/o the sodder getting onto other contacts... there's no way I would try doing that 'proper' mod on my GP. Anyways, I'm fairly confident that THIS time I got it right.... I have tested it much more thoroughly... and I feel that since the voltage increase is very likely only a small one to only be able to run 184mhz, I am probably perfectly safe, if Trooper's daredevil marathons are any indication. Yeah this method is still a pain in the ass to get it right (though some have gotten lucky and got it on the first try or so instead of spending several hours like me, though now I feel confident I could do it in less than 1-2 hours) but at least it's much easier to UNDO it if I find I messed up.
