I recently acquired a faulty model 2 PAL saturn off ebay with a no disc read issue. Upon booting I found the weirdest problem, it boots but really REALLY slowly. Like taking about 30 or 40 seconds to play the boot animation and get through all the audio, which is really slow and distorted like it's playing at about 1/10 the correct speed. All the audio is like this in the menu too, it's incredibly creepy sounding, I kinda like it to be honest, but it does come with the added annoyance of not reading discs. The disc drive tries to do a spin for a fraction of a second on power up and the laser is moving back and fourth and up and down seeking the disc, but it never spins up at all. I put 3v across the spindle motor and it spins fine so I don't think that is the issue. I also swapped the CD assembly from my working model 2 and the unit works absolutely fine, everything normal speed and all games read fine. The CD assembly that is faulty is a JVC EXL-P608 and the working one I swapped in is a JVC-P605. The only difference I can see between them is the working one has the crystal on it, but the faulty one doesn't, so I assume it is getting a clock signal from the motherboard (pin 1 on the ribbon I am guessing from a quick check). I was thinking of doing a recap but I just wanted to check if anyone else had seen this problem before and if it was a chip on the CD assembly rather than anything easily fixed.
Judging by your description, I am guessing that both of your Saturns use VA9 or VA7 PAL motherboards, for which the EXL-P605 is the correct drive. Someone must have put the EXL-P608 in there by mistake, perhaps trying to replace a broken drive but not knowing that there are 4 different drive configurations.
The difference between the two drives is that the EXL-P604 creates its own clock from the onboard crystal and sends it to the Saturn, the Saturn uses it to create the sound chip clocks. With the VA10+ boards it's the other way around: the Saturn generates both the sound clock and the CD drive clock and sends it to the drive (hence why the drive has no oscillator). As a consequence the two drives are not interchangeable.
So with the wrong drive in, the Saturn gets no sound clock input, and the sound chip starts doing weird things like making the sound all ghastly and slowed down. Same thing as if you started up the machine with no CD drive. Which I did before, so I recognized your description. But the P604 working in your console already made it clear that the wrong drive was in it.
Ahh OK, that makes sense and is really helpful to know. Thank you very much for the information!
I may look into the differences between the two boards and see if there is a way to add in the clock signal if that is the only major difference, feel like that might be a fun challenge. Especially since the drives seem to be pretty hard to come by.