Beogram 4002 (5523): Repair of an Intermittent Sensor Arm Light Source

Recently a Beogram 4002 (5523) returned to my bench, about 14 months after I restored it in May 2022. The reason was a 'not working sensor arm LED'. This made me concerned since this deck was the first to receive my redesigned sensor arm LED assembly.

Luckily, when I set the deck up on my bench and plugged it in the LED was working normally! This indicated some kind of intermittent issue that somehow 'fixed itself' during shipping. 

I wiggled the plugs and cables a bit but to no effect. The LED stayed on! Only when I started to flex the main PCB a bit around P4 where the components of the sensor arm light power supply are grouped nearby, I was able to get the LED to turn off sporadically. 

A closer inspection of the solder points relevant to the sensor arm circuitry revealed a bad solder point on the collector of the transistor that powers the light, TR5:

The collector of TR5 is connected to the 24V power rail via 1R36, which powers the LED.

I re-soldered the point, and that solved the problem. 

This Beogram restoration was done before I realized that the H-bridge power transistors of the carriage drive also need to be replaced preventatively. They seem to frequently go bad after using the decks again for a while, so I decided to add their replacement to the Beolover '400x restoration canon'. Therefore, I used this occasion to update the main PCB in this respect. This shows the original BC144/143 cans in place:

I replaced them with more modern 2N3019 and 2N4033 components. They have the same package, i.e. drop right in:

I will play this deck a bit before it goes back to my customer in Colorado to make sure that there are no other issues.