So, today I was able to have a look into the matter. What I found out is the following:
KSS-320b in fact IS compatible to KSS-220a, but one has to exchange all the cables from the KSS-220a to the 320b version. This isn´t an easy thing and can be time consuming. I spend half a day checking the procedure and playing around to get it done, including building it into a drive. I was able to play music from CDRs as well as from original CDs. I did not test it for gameplay, as I was using my CDR-35 as a test base (which isn´t capable of playing games...). But I guess it will load games as well with a little tweaking of the pots.
At least I ended up with a working FrankenLaser
KSS-220a prep:
First you have to unsolder the cable leading to the lens head, which is rather easy. Once you removed the four solder tabs (careful!) you can GENTLY pull it off, as it is only glued to the cable below (which leads inside the head).
Second you need to unsolder the 3 contacts from the laser diode. This is very finicky (at least for me) and needs a very quiet hand. I used a fine braid to remove the excessive (original) solder from the pins. Take you time, as the pins are long and there is no way around desoldering! If you are not careful enough you can easily burn the cable - goodbye new laser! Then unscrew the little board right next to it holding the famous laser pot.
Third you need to remove the whole plate (yes!) holding the efm sensor. The plate is glued to the metal body of the laser unit. You can scrape of the glue with a sharpie and pry it of the body. You will see a little hole and inside you see a tiny tiny tiny sensor. Do not touch the surface, as those sensors will be responsible for the alignment of your laser on track! You better mark the position of the hole on the plate, as you will have to glue it onto the new laser unit! If you don´t align it in the right position you will never be able to re-align your new laser...no games - sorry!
KSS-320b:
Now unsolder the cable leading to laser head like you did on the KSS-220a, gently pry it off afterwards and be very very careful not do damage the leftover cable leading to the inside!
Then clip off the cable from the diode and scrape off the EFM sensor, as you don´t need them anymore - remember you are going to use the cable from the 220a!
Now carefully desolder the cable end from the Diode and clean the contact so that they are as thin as possible - you need to slide the cable end from the 220a onto the 3 contacts without damaging them!
No comes the hard part:
I recommend you start with sliding the cable on the contacts. If this goes wrong you´re f*cked - so it doesnt make sense to begin with the easier stuff first
Carefully solder the contacts, then screw the tiny board with the laser pot on (remember?).
Next you need to glue the EFM board onto the body so that its hole matches the hole on the outside of the new laser unit. Since you´ve marked the hole position on the outside this shouldn´t be an issue. I recommend you use epoxy and apply it where the original glue was sticked to. This will make it easier for you. I also recommend that you start with one side and wait until the epoxy has dried up, and then go for the other side. This will leave you with enough headroom for correct adjustment.
If you finished this part, then its downhill - you just have to solder the remaining cable to the other side on the lens head - and you´re finished
You still will have to build it into a unit again, and then comes the part of readjusting - which will be timeconsuming, because your EFM sensor isn´t factory-aligned. This means you need extensive tweaking of VR103 and VR104 (which are responsible for this). In my case VR101 and VR102 almost didn´t change. So I guess it will be the same for you...
I hope this will be help to some of you. The KSS-320b is a cheap cheap laser and can be head for next to nothing. If you happen to have a dead KSS-220a, and you´re willing to test your skills - then I suggest you give it a try.
EDIT: Can we make this a sticky? I would add a few photos as well. I think it would be a good tutorial for all interested...
