Beomaster 2400 & Beogram 4004 Remote Control: A look at the control signals

Before Bang & Olufsen came out with their Datalink system of implementing remote control from a Beomaster to a Beocord and Beogram they implemented a very basic remote control of a Beogram 4004 from a Beomaster 2400.  This was in the late seventies around 1978. The Beomaster 1900 and 2400 were modern looking receivers that were good sellers for Bang & Olufsen.  The two receivers are almost identical except the Beomaster 2400 has remote control functionality to switch music sources, adjust the volume level and turn the Beomaster on/off.  After its release of the Beomaster 2400 the B&O engineers decided to implement and add remote control functionality for a Beogram turntable (the Beogram 4004). They implemented this by using two additional pins in the DIN plug for the Beogram turntable, pins 6 & 7.

The remote control functions for the Beogram are very basic. The Beogram 4004 can be turned on, turned off, cued up and cued down.

B&O released a Beomaster 2400 mod kit for service shops to add the Beogram 4004 remote capability to the early Beomaster 2400 units. The Beogram 4004 PCB8 boards came with that remote control circuit from the factory.

In finishing up my recent Beomaster 2400 restoration project I was tasked with also making sure the remote control functionality worked with the owner's Beogram 4004 turntable I had restored a year ago.

Initially the Beomaster 2400/Beogarm 4004 remote functionality was not completely working. I used another Beogram 4004 to troubleshoot the problem and it worked fine. The problem ended up being in the ground switch of the owner's Beogram 4004 and now everything works as it should.

In troubleshooting the problem I measured and collected the Beomaster 2400/Beogram 4004 remote control signals as measured on the Beogram 4004 PCB8 board.  For anyone else interested in seeing what those signals look like I am presenting them here.

First a quick look at the Beogram 4004 PCB8 board and schematic.

Starting with the Beomaster 2400 standby state and with the Beogram 4004 turned off (and in the parked position), here are two control pins from the BM2400 to the BG4004.  They come into the BG4004 on P9-2 and P9-4.

NOTE: The voltage measurements shown on the oscilloscope vary a bit depending on the vertical scale sensitivity (Volts/Div)  I used for the measurement photo.

In this photo I had the voltage resolution on P9-4 set to 2V/division and the measurement of 13.4V is what is expected.  Later when I use a 5V/division resolution my reference measurement drops a little down to 12.9V.

Here in standby/turntable parked mode P9-4 is around 13V and P9-2 is about 0V.

When "P" is pressed on the Beomaster 2400 remote control that sends a command to the Beogram 4004 (through the Beomaster 2400 receiver) to play (<< On).

Looking at the other relative signals at the same time I get this at PCB8 P10-1 (On Command)

and I get this on the PCB8 P10-3 <<ON signal

These next traces show the Beogram 4004 in the playing (On) state.
This is with the tonearm down.

While the Beogram 4004 is playing (arm down), pressing the "P" button on the remote control will send a "cueing" command that causes the tonearm to cue up.

Here is the cue command at PCB8 P10-9

Pressing "P" on the remote control generates another cue command.  This time the Beogram 4004 tonearm cues down.

and here is the PCB8 P10-9 cueing signal

Pressing "0" on the remote control will cause the Beogram 4004 to stop playing and turn off. At the same time the Beomaster 2400 will go into standby mode.

Note: Pressing "0" on the remote or pressing the off/standby button on the Beomaster 2400 when the Beogram is on but not playing (cued up) will not turn the Beogram off.  The Beogram must be playing a record for the remote control off button or the Beomaster 2400 button to also turn off the Beogram.

and here is the PCB8 P10-4 >>OFF signal

Very basic remote control functionality but it works and is very convenient.
It also saves touching the Beogram 4004 control panel buttons (and causing those wear spots you so often see).