It is good that I always listen to a restored Beogram for a while before I send it out. Some issues can only be detected after a longer period of use since they are intermittent or subtle. This also applied to the Beogram 8002 (Type 5633) that I recently sold to a customer in the UK. While I played it, I realized that the pickup occasionally skipped on records that I knew were perfectly fine. This only happened on a few sides that I played. But it indicated that something was wrong.
I encountered a similar issue a while back, where I resorted to tweaking the H-bridge gain to give the motor a bit more power. The reason for such behavior is increasing friction in the motor or elsewhere in the carriage mechanism, causing 'sticktion' where the motor does not get enough power to overcome static friction, while the arm moves inward on the record. After a few more turns of the record, the tracking sensor is finally at a point where the voltage at the carriage motor is high enough to overcome the stuck mechanism, and the motor suddenly starts running at a high speed so the carriage can catch up with the arm. This rapid catching-up process can cause sufficient mechanical turbulence that the very light tonearm skips a groove.
In this case, there was yet another indication that the motor had an issue: During runoff, the carriage moved in a few big jerky steps instead of a smooth, quick motion tracking the needle as the runoff groove drags it towards the center of the record until auto-return is triggered.
This time I thought, why not see if one can replace the Beogram 8002/8000 carriage motors with the Beolover Carriage Motor for Beogram 4000, 4002, and 4004. A quick measurement on the motor terminals indicated that the motors in the 8002 run at similar voltages to the motors in the 400x.
This shows the open carriage motor compartment of the 8002:
First, I unsoldered the brown lead and connected my multimeter in current measurement mode between the wire and the motor terminal. Then I operated the turntable to see what the maximum current might be that this motor draws:
As expected, the motor draws the most current (~70 mA) during the carriage return after pressing STOP.
I removed the motor:
This shows the original motor in comparison to the Beolover motor:
The new motor is a bit smaller. Like most new designs, it is more efficient than the original motors due to better magnets and better manufacturing techniques available today.
Due to the size difference, I had to design an adapter to make the new motor fit into the original motor housing. This is what I came up with:
I 3D-printed two plastic clam shells to increase the diameter and length of the motor to match the original form factor. The additional two EPDM rubber rings serve as vibration insulation. They are put on the motor like this:
Then the plastic pieces are fitted around the motor:
The plastic pieces have two protrusions that hold the motor in place and prevent it from sliding inside the housing:
The new motors have a small round mark next to one of the terminals. The brown wire needs to be connected where the mark is, and the blue one goes to the other terminal.
I soldered the blue wire:
Then I did another current measurement between the brown wire end and the unconnected motor terminal:
Like the original motor, this motor drew the largest current during carriage return. At 50 mA, it is about 30% smaller than the value of the original motor. This was to be expected. In the Beogram 400x series of turntables,
I saw a similar power reduction for the same performance. Some things get better as time marches on!...;-). Lower power is always preferable. It reduces the stress on the H-bridge components and also results in a quieter and lower vibration operation. After this test, I connected the brown wire. Since it is shorter, I had to put in a wire bridge to extend it to the motor terminal:
The cover still fits perfectly:
This is how it looks from the front:
After this installation, I listened to a few records with the new motor, and everything worked very nicely. I noticed how much more quietly the motor operated during <</>> and START and STOP operations. Significantly fewer vibrations compared to the original motor! Beolovely!
At that point, I realized that it would be nice to get some oscilloscope shots of the tracking signal on the motor terminals. So I opened the motor housing again and connected my oscilloscope between the motor terminals. This trace gives a nice summary of the motor operation. It essentially captures the voltage fluctuations during the last few turns of the record before the 'run off' groove, then the signal during run off until auto-return is triggered, followed by the actual return:
I wanted to compare this signal with the original motor, and so I installed the original motor for another measurement. This shows the same operational sequence as above:
While the overall pattern looks similar, there are notable differences: The voltage jumps during regular tracking are larger for the original motor. They also have a higher baseline. This indicates that the tracking sensor needs to send more voltage before the motor moves. Secondly, the run-off signal confirms what I observed visually, that the carriage makes bigger jumps. Comparison to the new motor shows that the original motor moves in 3-4 big steps, while the new motor gets a much larger number of voltage pulses, causing it to move the carriage much more smoothly.
In summary, I think the Beolover carriage motor is an excellent substitute for the original motors, which seem to be on the verge to develop age related issues. If you are interested in upgrading your Beogram 8002 or 8000 with a new carriage motor, it is
now available via the Beolover's DKaudiolover store!
