B&O Beogram 4002 & 4004 Motor Substitution

[BinaryMike]

Replacement turntable drive motors for these models have become nearly impossible to procure, so I decided to attempt replacement with a motor from the Beogram 2400 series. This item carries part number MHN-3P2RDS. Physical fitment isn't a problem, but hookup and tacho (FG) output frequency differ markedly from the original MHN-5P2RDS. I solved the hookup difference with a simple adapter so as to avoid burning any bridges:





I wasn't able to reverse-engineer the servo control circuit to my satisfaction due to the lack of a datasheet for the IC, but a comparison of the 2400 and 4004 schematics allowed me to deduce that one or two capacitor value changes might be sufficient to accommodate the FG frequency difference. After a bit of calculating and experimentation, I ended up replacing 1C3 with 39nF (was 220nF) and 1C7 with 1.0nF (was 47nF). I'm not sure what 1C7 is doing in this circuit. I used the value found in the 2400 schematic and didn't alter it after determining a new value for 1C3. Both platter speed settings are now well within range of the on-board trimmers. There's no perceptible speed drift with a polyester cap at 1C3, and speed settles with authority after perturbation. I'm too lazy to hunt down my W&F test record, but piano recordings sound good.

 

[petehall347]

nice job . do you have a pic of original motor so i can check my box of nos motors . they are mainly Panasonic so might be a wild goose chase anyway . i would like to find homes for the motors i have as seems a waste them sitting there .

 

[BinaryMike]

The original motor looks almost identical to the photo above, except for a white plastic pulley and three-wire hookup with colors same as my adapter. Part number markings are as given in my first paragraph.

 

[petehall347]

will check for 3 wire motors .. what voltage ?

 

[BinaryMike]

They're both 3V DC motors.

 

[petehall347]

written myself a note .. 3v bit doesn't sound promising but there are lots of them .

 

[monkeyboy222]

Hi,
I'm following in your footsteps, replacing my Beogram 4004 motor with a 2400 series, with the same model number, as it's impossible to find a replacement 4004 motor.

Just sanity checking really;
The capacitor replacements you mention - 1C3 and 1C7, these are C3 and C7, next to each other on the 1 board, yes?
I'm replacing with 39nF Wurth Polypropylene and 1nF Wima Ceramic respectively, and wiring the motor as you have shown.
Do you see any problem with this?

Thanks for your time,
Glen

 

[AndyB]

Let me check. Think I have a 4002 motor.