Hi,

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?

Kind Regards

Steve

wrote in message
oups.com...
Hi,

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?

Kind Regards

Steve


Probably the pickup itself, but you just have to replace it to find out for
sure.

Welcome to the exciting world of electronic repair.


Mark Z.

Hello,

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.

Regards,
Tim Schwartz
Bristol Electronics


wrote:

Hi,

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?

Kind Regards

Steve

"Tim Schwartz" wrote in message
...
Hello,

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.

Regards,
Tim Schwartz
Bristol Electronics


wrote:

Hi,

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?

Kind Regards

Steve

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.

Mark Z.

Hello all,

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.

Regards,
Tim Schwartz
Bristol Electronics


wrote:

Hi,

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?

Kind Regards

Steve

Tim Schwartz wrote:
Hello all,

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.

Regards,
Tim Schwartz
Bristol Electronics


wrote:

Hi,

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?

Kind Regards

Steve

I`d scope the supply lines looking for ripple from a dodgy cap in the psu.

Ron(UK)

--
Lune Valley Audio
Public address system
Hire, Sales, Repairs
www.lunevalleyaudio.com

wrote:
Hi,

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?

Kind Regards

Steve

Hi all,

Many thanks for the replys, very interesting.

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)

Cheers

Steve

Hi all,

Many thanks for the replys, very interesting.

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)

Cheers

Steve