I recently got my first PU-7 machine and wanted to write down my experiences with it. The AAM drive in this console was toast, unsurprisingly, could never get past the boot screen even on pristine games. I swapped in an original ACM from another console and still had issues, then I tried running it without the lid, pressing down the door button manually and it worked consistently, so I believe there is some bizarre issue with the plastic piece that is holding down the door button... I've had a few rubber rings for PC fan mounting around, they fit perfectly and seem to help it run more consistently when placed there. Trying a lightly scratched copy of Tekken 3 I was getting lots of stutter with the audio tracks, so next thing I swapped in a clone ACM drive and discovered that the 1000's actually have different plastics compared to the 1002's, and these clone drives aren't tall enough, so the CD would always grind on the plastic. I tried raising the drive with one of these rubber rings on each of the 3 stands, but it would still scratch, so I think several of these things would be needed to raise it enough. I went back to the original ACM and tried to calibrate it. Now unfortunately I forgot to write down the initial values but for me this guide didn't work at all, with the 11mV it lists there the drive wouldn't even start spinning. I played around with the pots until I arrived at 24mV on the drive, 1.48V bias and 1.8V gain. With these values it would play a few rounds of Tekken 3 arcade mode without any hitches at all, so all seemed good, but trying a pristine copy of King's Field it just skips the intro sequence every time and also freezes a lot when changing floors... that game for some reason I've always found to be a challenge for these bad old drives, so perhaps redbook audio and certain game data can place different requirements on optimal drive calibration? Either way in the long run I'll probably just find a way to make a clone ACM work on this thing. Edit: with 1.41V bias KF1 would work fine, but Tekken 3 would have skipping music; with 1.44V Tekken 3 wouldn't load at all, and with 1.339V both games work without issues now. KF1 would also boot with a garbled title screen/load screens with other values I've tested, definitely the pickiest game I've seen on these old drives. And I do know the proper way for this is to use a scope, but I don't have one at hand and clearly this sort of manual calibration can work very well for individual games. I tested a few "universal" values from the net as well and these two games would not even boot with them.
I can help you put one variable out of the picture: The gain setting is useless for the type of problem you have. It can be set to 10 o clock and then left alone. Your problem is that medium to heavy worn drives do not work in this machine. They cannot correct the problems with the motors and the misaligned read head. You need to take your best working drive and thorougly clean it, then put on new (white lithium) grease *only* on the guide rails. Ideally you should replace the 2 motors as well, or try cleaning them out with lots of WD40 and compressed air to get the rust out. When you've put it back together, you adjust the laser power pot carefully down (to the left) until the disk doesn't start spinning anymore. That's your lower point. Now you slowly increase power, so the disk spins again, and keep increasing until you either hit a decent amount on the pot (use good judgement) OR you hear an unhealthy sounding whine. If you get the whine, back off immediately, as you just went into overdrive. This is your maximum setting. Now adjust to the middle of your 2 points. Note: If you think the laser power pot hasn't been messed with before, just keep it as it is.
Well, you probably haven't tried this King's Field yet it suddenly stopped working again despite me not having changed any settings. Trying various bias levels from 1.4 to 1.7V didn't help, but fiddling with the gain caused it to boot again. I can calibrate the drive fairly easily for the couple other Japanese games I have but this one is the real benchmark, letting the intro roll through might work 4 times, then on the 5th the music starts garbling up... there's definitely something about this game, maybe a weird data layout from the early days; can't imagine it's just my disc as it's original and in basically pristine condition, also hasn't been resurfaced from what I can tell. I do know about the BAMs working in this, but I don't have any PSones and still think the clones are the easiest way to get a decent drive without much hassle into these old Playstations, also don't have to take a drive from another working system. I'd never use one of these things as my regular console, but there's something about playing on a launch system that I like I do wonder if the differences in drive chipset make this one even more temperamental than the PU-8 machines...
Regarding PU-8 vs PU-7 capability, I don't know. Usually there's a trend to improve the electronics in each iteration, while they try to decrease cost. But as far as I know, the first real improvement was the higher integrated PU-18. Your King's Field is a normal game disk like any other. It probably has a unique set of defects though that has to be corrected by a higher gain. The gain setting is typically not critical, as long as within the working range, which is quite big. I suspect your disk is warped and doesn't spin evenly. In any case, don't run your console with the gain turned past 12 o clock / center position of the pot. If you listen to the laser coils, you can tell that it's not healthy
Do you have info on actual voltage levels for the gain? Pots seem to differ between console revisions - here the position marker seems to be the different looking side on the right, so I'd interpret those as being at 2 o'clock, for example. On my PU-7 system the marker seems to be a little arrow indentation between the screwdriver slots, while the metal piece itself is symmetric. Going by this, the gain pot on mine is exactly at 12 o'clock now, which equals to about 1.82V, but when I turn it any more to the right it drops all the way to 1.4V, causing the drive not to run (it just clicks intermittently). About the sound: not sure how I'd pinpoint the sound of the laser coils, but the pickup movement does seem fairly loud right now. I'll look into adjusting the gain downwards a bit to get a better feeling for this.
Both pots are at 11 o clock in that pic! Incidently, that's also a pretty good default position. Maybe I shouldn't be using a clock as metapher, what with all the differences in reading worldwide + different pot constructions. I don't have any voltages because they're very bad indicators. Going by voltages, all you can say is "this is way too high" or "this is way too low". But if you tune gain to the position in that picture and then start the console, you should be able to hear the coils working pretty hard already. You need to get your ear close to the spinning disk. If you increase gain a little more now, past the middle position I warned you about, you will hear what I mean
Ah, I guess you were using the solder joints of that pot as 12 o'clock instead of the top of the board itself - got it
