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Beolover SyncDrive: DC Platter Motor Replacement for Beogram 4002 and 4004 (Type 551x and 552x)

Late Beogram 4002 and the 4004 (Types 551x and 552x), which have DC platter motors instead of the earlier synchronous AC motors usually suff...

Friday, November 20, 2015

Beogram 4000: Redesigned Drop-In Tracking Sensor Light Bulb Replacement

It was time to replace the tracking sensor light bulb in the Beogram 4000 that I am restoring right now with the SMD LED based replacement light source that recently I developed. I used this occasion for redesigning the part with the aim to incorporate the intensity adjustment trimmer into the light shield of the source to hold it firmly in place. I did not like that the trimmer was only held in place by the leads in my previous design, which resulted in a slightly wobbly appearance when adjusting it. In other words, this part was not yet fully up to Beolover standards!

So I designed a new circuit board which allows to directly solder the trimmer to it. This, however, required the concurrent redesign of the 3D printed housing part to enable the trimmer to protrude from the PCB. Here are some pictures. This shows the original light source.

This Beogram had the optional 100R trimmer installed that is mentioned in the supplement of the service manual. This allows the adjustment of the intensity of the light bulb which is a great feature that much simplifies the adjustment of the tracking feedback circuit sensitivity. 
This shows my redesigned part from the light source side. The LED is powered by 6V as it would in the Beogram 4000:

This shows the part from the other side prepared for insertion into the tracking sensor

The potentiometer protrudes through a opening in the plastic part and looks now fully integrated. Lovely! The negative lead is curled around one of the bolt holes. This makes the ground contact (the Beogram chassis is tied to the system ground). This setup essentially copies the original setup with the 100R potentiometer. The other lead is bent up to be able to go into the 6V rail solder point on the PCB from below:

After the installation I adjusted the tracking sensitivity to the prescribed 4 rounds of the record before the tracking mechanism kicks in after the needle is put into the groove. A few months ago I made a video about the tracking mechanism and the adjustment process:

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