Beogram Commander Remote Control: Successful Test of New 4002 (550x) AC Motor Version

I received a few inquiries about making the Beolover Commander remote module work with AC motor Beogram 4002s. My recent update of the Commander for Beogram 4002 and 4004 only works in DC motor Beograms since AC motor versions have no keypad plug socket on the main PCB. Their keypads are hard wired to the PCB. So I thought it would be nice to offer an AC version. But this made a redesign of the Commander module necessary.

This shows the redesigned version:

The main difference between DC and the presented AC version is an additional small breakout PCB (the long and narrow item on the picture) that can be soldered to the keypad wire-to-board solder pads. It feeds the keypad signals into a small connector that then connects to a matching connector on the Commander board. That is what the green jumper is for. The final version will come with a custom made jumper that has an appropriate length.

I thought it would be perfect to celebrate the arrival of the AC Motor Commander by implementing it for the first time in a rare early 5501 version (the first 4002 series they ever made after discontinuing the original 4000). This 5501 Beogram recently revisited my work bench from Australia due to the malfunction of the solenoid transistor and a non-working carriage motor. My customer agreed to let me delay return shipment to try out the AC Commander on his precious deck! Thank you very much!

The first step of the installation was to solder the breakout to the keypad PCB. This shows the original PCB after extracting it from the keypad assembly:

The wire harness from the main PCB connects to the pads up front from below. The two resistors on top are 22k pull-ups for the 33 and 45 RPM transistors, which seem to have been added after the fact due to operability issues in this early version. In later AC motor versions the PCB was changed and the resistors are placed on dedicated solder pads on the central part of the PCB. 

Unfortunately, on the 5501 they are a bit in the way of installing the Commander breakout board. When I tried to push them slightly out of the way for removing some of the solder on the pads, one broke apart:

I replaced them both with 20k resistors that I had in my stash. The 10% different value is not important, they only pull up the RPM switch transistors to make their ON/OFF states more reliable.

This shows the two resistors in place. They now allow some room for Commander breakout PCB:

The next step was to solder the breakout across the pads, which was easily done by putting some flux on the pads and then touching their orthogonal contact area with the soldering tip carrying a bunch of solder:

This is how it looks when the PCB is inserted back into the keypad:

The next step was bolting the Commander onto the main PCB and connecting the two connectors with the green jumper:

Then came the moment of truth, when I powered the deck up. And hurray, no magic smoke arose!

So I flashed the chip. The next step was pairing the Apple remote to the Commander board.

On the DC version Commander this involves pressing two buttons for ~6 min until the 33 RPM light comes on and the platter moves very briefly, indicating the completion of the pairing process.

I did the same here: And nothing happened! Panic arose, but pressing the Start button on the remote set the carriage in motion! So it seemed to have paired properly! 

And then it dawned on me: The AC versions does not have the 'record cleaning function', which is activated by pressing the 33 RPM key with the carriage in its home position. On the DC versions, pressing 33 RPM simply sets the platter in motion until the key is let go again. This is very convenient for wiping the platter before playing the record.

B&O probably introduced this function with the DC motor since the DC motor has a much lower torque than the AC motors, causing strong RPM fluctuations during swiping the platter. On AC motor units one can wipe the platter while the music plays, and there is almost no RPM slowdown. But with the DC motor one has to do it before actually pressing START for listening.

Anyway, so far so good! V1.0 seemed to work!

But the above made me think: It would be nice to have a record swipe functionality like on the DC models! And of course the pairing process feedback needed to be changed.

So I changed the code:

• Instead of the 33RPM/platter twitch response to a completed pairing process, now the auto-repeat LED briefly lights up.
• Now one can press the 'select' button on the remote for platter swiping like on a DC Beogram. This was done by replacing the absent swipe circuitry by a combination of activating START and then immediately "<" to stop the motion of the carriage. So it only moves a few mm until the 'shut off (SO)' switch is cleared that the deck can run the motor. Subsequent release of the select button activates the STOP function and the carriage goes back home and the platter motor goes off. What would we do without microcontrollers these days!!...;-)

Beolovely!! I estimate the AC Motor Commander should become available in 2-3 weeks when I will hopefully have received the proper jumpers for connecting keypad breakout and Commander board. Stay tuned!