Technics SLQ33 : infrared sensors won't detect disc presence nor size.

AlexDev

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Hi everybody here.

I would need some help to fix my Technics SL Q33.

Everythings works properly but the Leds circuit for size detection won't.

After some researches and attempts to clean and check every leds inside the mecanism, and under the plater, it seems that the turntable doesn't receive any data from the infrared Leds circuit that is used to check disc présence and sizes.
All auto functions performs well, and start stop will just work as it should. Manual start also rotates the platter as soon as I move the arm.
However, if I place a 7 inches disc on the platter the arm just always set down on the 12 inches edge.

infrared sensors under the arm are 3 Ok (they emit visible red light when I set the turntable on, and the red light stops on the 3 together when I set off)
Nothing visible on the prisms under the platter.
The rubber mat is OEM. ( with the holes)
Everything works very well and auto fonctions are Ok, but size detection isn't.

Please help.
 
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And the Leds that are used for presence and size detection through the prisms on the platter :
 
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Check infrared leds with smart phone camera. Ensure your cam can detect ir by first checking it held against an IR remote control. If that is ok, check the IR receptor post on the deck and it’s wiring. Look for any wires that may have come out from board.
 
Are the LEDs under the platter lighting up, and are they visible through the platter prisms like in this video?
Hi reubensm

Thanks for replying.

No, the leds under the platter will only flash just once ( using the cellphone camera method to see the flash, advised to me by Saket) when I power on/off, but nothing is visible when I hit start or after.
That shows that Leds are functionning, but also that there may be an issue with the pulse generator wich should , to me, make them flash at least once when hitting start to enable detection.

Moreover, I can also make the platter spin just by moving the arm, even if there is no disc.

It's as if the entire infrared loop was shut down at start, and the turntable acts as if there s always a disc on the platter.

As I couldn't find any data about IFR detection in the SLQ33 manual, I also had a look in the SL 1600 mk2 just to have an idea and because IFR detection devices are relatively similar.

There's effectively a page in this one wich explains that the detection can be in some way "shut down" by "manually locking the turntable".

I am still looking for what it means.

Here s that page :

 
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Oh, I get it better : according to this page, platter would need to rotate to enable detection loop and LEDs action ( on the 1600 mk2, Ok...)
That may explain why the LEDs do not flash when I hit start because checking the LEDs firing requires to set the platter off. How could the detection loop perform if there is no platter and by this way no rotation detected?
 
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So,
I finally managed to discover the cause of the issue : just to see, I checked the Led sensor inside the detector post at the left of the arm base : the little translucid sensor itself was taken down into the aluminium section of the post, probably by pulling on the cables underneath the post base.

I just had to unscrew the micro screw that hold the black little cover, then pull the sensor upwards 3 or 4 mm and reassemble everything carefully.


Fixed! The sensor sees the vinyls presence and size again! No IC involved un the issue. I am happy.
 
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