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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, May 3, 2024

Beogram 4002: Restoration of Short Circuited Solenoid Coil and Repair of Main PCB

I recently received the short circuited solenoid coil from a DC motor Beogram 4002 together with the main PCB from a customer in Texas. I asked for sending the PCB along since there is usually a reason when solenoid coils burn out. And in the later DC motor 4002 and 4004s this reason is usually to be found on the main PCB.

This shows the components as received:

First, I measured the coil to confirm my customer's diagnosis:
Indeed, the resistance was much too low at 1.6 Ohm. A good coil usually shows about 9 Ohm.
To my surprise this coil assembly looked a bit different from those I restored so far. The 'normal' coil assembly (left) has a locking washer that holds the tube inside the coil in place:
In contrast, the present assembly (right, already with the plunger removed) seemed to have been assembled using a press fit. This shows the back end of the assemblies (the present one is on the right in this picture). Also a bit different.
Since I was not able to see from the front end how the tube was exactly mounted, I decided to try removing the coil while the assembly was still together. I hoped this would give me some more clarity how to disassemble everything.  Since it is impossible to unwind the coil with the assembly together, I used a Dremel with a cutting wheel to cut into it:
With a bit of 'measured violence' I was able to get most of the coil windings off:
With most of the coil gone I was able to see that it is possible to press the tube out with an arbor press. this shows the liberated parts:
The tube was basically riveted into the orifice in the mounting bracket:
Next time I will probably use a drill to remove the front end of the pressed-in tube before using the arbor press. I installed a new coil made with a 3D printed plastic core:
If you need one, my replacement coils are available via the Beolover Store.
I installed the rebuilt coil assembly into my bench 4002:
I also put in the main PCB that came along with it. Then I plugged my Beogram in, and immediately the coil activated. I quickly unplugged the unit before the coil had a chance to get hot. This behavior suggested a burned through 1IC4, which controls the solenoid current:
I removed the original TIP125 Darlington and replaced it with a stronger TIP107, hoping it will last a bit longer:
This fixed the issue and the Beogram operated normally by lowering the arm at the LP setdown point:

My experience is that most Beogram 4002 and 4004 have issues with their power transistors and I usually replace all of them preventatively when I restore one of these vintage beauties. 
At any rate, this main PCB is again able to control the solenoid! It is time to send everything back to Texas!

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