Correcting the FMV on PSX's
What follows is a description of what is involved in adjusting the optics in your playstation in order to correct any FMV skipping that you may be experiencing. First I am not an expert in cd technology and I am not claiming to be one so treat this information carefully!! Although I have a good idea of what is going on part of what I know is from other sources and the rest is from my own success at fixing this problem. This being the case I'll try to be precise between the facts and any speculation.
To begin you must open your playstation by removing the 5 screws on the bottom. Some points here are that once the screws are off, the top part of the casing comes apart smoothly and on my machine at least there were no seals to break which would show anyone that the thing had ever been opened if some of you are scared of Sony. So if that is what is keeping you from having a look then don't worry.
In the area immediately below and slightly to the left of the lens are two very tiny silver heads and just off to the right of this pair you will find another one sitting by itself. Its the pair you are interested in however. If you look the bottom one is labelled "gain" and the top is labelled "bias" on the circuit board. Their exact function is speculation on my part but I know for a fact that when reading data from the inner tracks the drive must spin faster than when it reads from tracks further out in order to produce a steady data stream. So I think gain is related to drive speed or changing speed. I also know that the scanning beam must be precisely focused on the track both vertically and horizontally and again I'm guessing that this is what the bias adjustment has to do with. By all accounts and my own experience it is this top "bias" head, screw, control or whatever that you need to adjust if you are experiencing FMV skipping. Of particular note here is that I noticed many punters posting about turning their units upside down and sure enough this was the case when I tried it. The FMV would be playing with noticeable skipping and as I turned the unit upside down the FMV would run smooth, then right side up it would skip, upside down smooth again and so on. This seems to work because upside down the lens is closer to the disc, a fact you will notice by gently turning your PSX without a disc. (disconnected of course!) Try seeing if turning your unit upside down while skipping is going on solves the problem. If it does then it is a prime candidate for a bias adjustment.
Now actually turning the thing. First if you want to be absolutely sure of avoiding a complete debacle then why not use the proper tool and that is a micro screwdriver of the star shaped variety which you can get for a few dollars at any hardware store. Because these things are really sensitive. Other posters have warned that turning either head too far will completely disable your unit's ability to even boot a disc. This is because in order to read data off the disc correctly the scanning beam must be focused on the track to within 1/4 of the beam's wavelength. If you will all turn to your owner's manual pg. 18 the beam's wavelength is listed as 780 nano metres to give you an idea of the precision involved. So if your beam is off and causing the FMV disturbance it is likely not off by much. Never turn the head more than 1/8 in either direction at a time. For me I gave it a 1/8 turn to the right and thus far (1 week) everything seems ok. If this doesn't work a 1/8 turn to the left might do the trick. I don't know what the effect of turning the bias 1/4 would have but if the problem was slight to begin with and going this far hasn't corrected it then it probably never will (speculation on my part).
To recap, if you are recently experiencing slight FMV disturbances in things like intros, particularly as your machine has been turned on for awhile, if you notice that other titles play fine, and if you notice the problem going away as you turn your machine upside down, then I think you are a good candidate for giving the bias control a 1/8 turn to the right and seeing what happens. If you are careful and keep track of what you are doing you can try the bias, gain, or both to correct more serious problems, but realistically I don't think you are going to have big FMV problems suddenly as a result of these type of factors.
