I have found those 4D1 LEDs are often burned out. Here is how I have replaced mine...here and here.

-sonavor

Thanks you for the very comprehensive links. I tried 5mm IR LED Infrared 940nm Light Emitting Diode Lamp Water Clear  and SFH 300 -3/4 Osram Opto 50° IR + Visible Light Phototransistor 5mm. I may have caused more problems and damaged the circuit as when I turned it on the tonearm dropped each time I press the home/ stop button and now with no automatic drop at start 33 position. Occasionally the 45 clicks too when start is pressed.

perhaps the photo sensor inside the tonearm may have become damaged too? 

Otherwise would the arm not drop even if the IR sensor was not functioning properly or is it because it is a looped circuit and they are both dependent on the other?

(Any idea of a modern replacement of sensor if ti is damaged?)

I was also curious that a visible LED (amber) is used, a type 5513. Should types 5524 and 5514 only use IR LED or can it be replaced by either IR or visible LED?

C

The important thing is to measure the signal that the sensor produces when the light source hits it to make sure it matches what is prescribed in the service manual.

There are a number of links on the Beolover Blog for the various types of Beogram 4002 and 4004 turntables with regard to these funtions.
Beolover does make a replacement lamp module for the fixed arm. I have used that part myself a few times. On other restorations I used an incandescent bulb like the original that I source from Martin Olsen of Beoparts (or optionally Dillen through the Beoworld forum). 

In all of the light sensor devices the position of the lamp is critical. Again, that is why measuring the expected signal that is produced is important...to know that the lamp and sensor are correct.

-sonavor

FYI...I just finished going through a Type 5513 adjustment (pretty much the same as your 5514)

Sounds to me there are a number of issues going on here......may be a good idea to sort one at a time, the 45rpm clicking in on start up is familiar, I had this issue myself....I have also replaced the detector lamp and photo sensor, its tricky but can be done, cant find my thread but here's another... 

https://archivedforum2.beoworld.org/forums/p/1632/13942.aspx#13942

Hi both, thanks for the advice. Really appreciated. Thanks for the links too

Just to recap I had a fully working 5514 and wanted to use the main board to get the damaged 5524

Working agin,  while I fix/ replace the original main board. When adding a new IR LED to the arm position and arm position IR photo-resister, It caused some unknown problems. 

When adding a visible LED to the it illuminates and now luckily When I press the start on either the turntable with a strong light overhead and turn it off the arm drops. If I shine an LED torch or phone torch near the sensor it drops and likewise if I shine at the end groove of a 33 it will lift and return to the home position. Less light is needed on the 45 for it to lift and return to the home position with light shone near the sensor. 

*The sensor at the base of the tonearm doesn’t seem to work on the 5524 as the motor doesn’t move as it should when a record is played.  

So with this is mind, does it appear that I am using the wrong LEDs to activate the photo sensor or maybe there’s there a damaged transistor or resister not allowing enough power to get the  arm position sensor. I don’t have a stroboscope and have basic ability with the voltmeter. 

Does anyone have a link or a known supply

A. for replacement sensor at base of the tracking arm?

B. Suitable replacement arm position sensor? 

Thanks again

Hi both, thanks for the advice. Really appreciated. Thanks for the links too

Just to recap I had a fully working 5514 and wanted to use the main board to get the damaged 5524

Working agin,  while I fix/ replace the original main board. When adding a new IR LED to the arm position and arm position IR photo-resister, It caused some unknown problems. 

When adding a visible LED to the it illuminates and now luckily When I press the start on either the turntable with a strong light overhead and turn it off the arm drops. If I shine an LED torch or phone torch near the sensor it drops and likewise if I shine at the end groove of a 33 it will lift and return to the home position. Less light is needed on the 45 for it to lift and return to the home position with light shone near the sensor. 

*The sensor at the base of the tonearm doesn’t seem to work on the 5524 as the motor doesn’t move as it should when a record is played.  

So with this is mind, does it appear that I am using the wrong LEDs to activate the photo sensor or maybe there’s there a damaged transistor or resister not allowing enough power to get the  arm position sensor. I don’t have a stroboscope and have basic ability with the voltmeter. 

Does anyone have a link or a known supply

A. for replacement sensor at base of the tracking arm?

B. Suitable replacement arm position sensor? 

Thanks again

Did you measure the voltage of the 4D1 collector?  You only need to use a multi-meter to measure the DC voltage. When the arm is advanced where a clear portion of the marker lens is in front of the the sensor (4IC1) you should have 5 VDC on the collector of 4IC1. If you don't then you use the trimmer on the main board (1R88) to increase the 4IC1 collector voltage to 5 VDC.

-sonavor

Thanks for your reply. Very useful.

*Update. I have now fixed the record tracking by tightening the aperture adjust eccentric screw re. Beolover blog.