never come across this so thought i'd post and see what people think.
I just got hold of a Sony MHC1600 cd/radio unit. When in cd mode there is a noise coming from within the unit. I took then unit apart and the noise is the cd lens assembly vibrating. If you put your finger on the lens and press (this has probably knackered it anyway) then you can stop the vibration and noise.
Is the optical assembly the culprit or could it be something else . I can get hold of another optical assembly easily enough which i'll do anyway but anyone seen this before?
Sony had a problem with the KSS-240A optical pick ups having an oscillation problem, usually 800 Hz, and it can be so loud that it causes the unit to start skipping. Sony had a cure of adding a brass weight to the optical pick up, and a felt washer to the clamper. I'm not sure it this applies to all application of the KSS-240A or not.
From a Sony Technical News bulletin that I've got a faxed copy of, the weight is part number 4-962-979-01, and the screw to attach it is
7-685-134-19. The screw replaces the one holding the PC board with the pots to the laser. The felt washer is 4-986-769-01, and goes on the surface of the clamper that touches the disc.
The machines that show this do not do it on all discs, and it seems to be the worse 5-12 minutes into the disc. Please be aware that original Sony KSS-240A lasers have 3 pots on the PC board, a cable connector with a clamp, and that the chip on the bottom is 14 (or is it 16) pins. There are many 'after market' lasers sold as KSS-240A that have a single pot, no clamp on the cable connector and an 8 pin chip.
I forgot about that one! The vibration from the spindle motor sets up a resonance in the pickup. You can see it in the focus error and tracking error waveforms. Lowering the tracking or focus gain a bit can help also, and adding some silicon sealer or RTV where the spindle motor contacts the BD board.
I got a reply from the original poster that this conditions happens when CD is selected on the unit, even with NO DISC in the player, so it is certainly NOT the vibration I was thinking of, and the weights will not cure it.
If the lens is going onto oscillations with no disc, I'm inclined to believe there is more likely to be a problem in the control circuit than with the optical block itself. I'd look for power supply problems too.
I've done a bit more investigation now I have the schematics. I can't see anything obvious like blown caps or anything. However the chip the circuit uses for driving the sled motor, drive spindle and (importantly) the focus/tracking coils (which I think is causing the oscillation) is an LA6525 surface mount IC. When the power is applied and the optical head vibrates, this IC gets very hot, very quickly. According to the datasheet for this iC it does have thermal protection. Anyway if I disconnect the optical assembly ribbon cable, the chip does not get hot.
I have ordered a KSS-240A so I can try it when it arrives. Does anyone think it's worth getting hold of the chip as well (assuming I can)
I've done a bit more investigation now I have the schematics. I can't see anything obvious like blown caps or anything. However the chip the circuit uses for driving the sled motor, drive spindle and (importantly) the focus/tracking coils (which I think is causing the oscillation) is an LA6525 surface mount IC. When the power is applied and the optical head vibrates, this IC gets very hot, very quickly. According to the datasheet for this iC it does have thermal protection. Anyway if I disconnect the optical assembly ribbon cable, the chip does not get hot.
I have ordered a KSS-240A so I can try it when it arrives. Does anyone think it's worth getting hold of the chip as well (assuming I can)
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.