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).

Beomaster 2400: Replacing the audio input panel

The last post on this Beomaster 2400 showed that it had a broken mount for the audio input source panel.

I was able to find a good replacement panel from another Beomaster 2400 I had purchased for my own use. It also has the 7-Pin DIN jack for the Phono input I need because this Beomaster 2400 will be connected to a Beogram 4004 and we want the remote control functionality between the two.

No worries on the Beomaster I am stealing this part from. I will actually just trade connector panels and figure out a repair solution with pieces from Beolover's DIN panel repair kit for the Beomaster 8000.

Here is the diagram of the Beomaster 2400 DIN source panel from the B&O upgrade kit to add Phono DIN connector pins 6 and 7 for remote control capability of the Beogram 4004.

Here are front and rear photos of the new input source panel. Its mounting tabs are intact and I have added text to the photos to show the pin numbers and function to match the B&O diagram.

Now to begin soldering the Tape and Phono wires to the new DIN jacks.

I removed all of the Beomaster 2400 control panels yet again to work on this audio source DIN connector panel. Here are the wires connected to the new DIN panel.

...back in business again...

Beomaster 2400: Dealing with a broken audio connector

While connecting up audio sources to test this newly restored Beomaster 2400 I discovered the audio source connection panel is broken. I didn't notice it earlier so it must have been barely hanging on. When I started to use it the weak plastic tab holding it in place finally gave way on one side.

As you can see in the photo the loose connector panel can pull away. It still works but no longer stays in place.

Here is more detail on what the broken DIN connector mounting assembly looks like.

The DIN Phono connector on the Beomaster 8000 can fail in a similar fashion.  Beolover makes a 3D printed repair kit for it but this one is a dual DIN panel.  I might be able to still use part of the kit but I think it will be better in this case to just replace the dual DIN jack panel with another one that is still intact. In the next post I will change this connector panel out and then I can get on with the Beomaster 2400 testing.

Beomaster 2400: Reassembly and First Play

The Beomaster 2400 lamps all function. The power supplies are good and the no-load current adjustment is complete.

Note that the phono jack on this Beomaster 2400 is the 7-pin DIN type plug. It supports the Beogram 4004 remote control connections.

This Beomaster 2400 had a couple of shoddy left and right cabinet trim pieces. I found a couple of good ones, did some light sanding and applied some boiled linseed oil.

Before I attach the tone controls and FM tuning panel and before I attach the bottom plate there are a couple of service manual adjustments I need to complete. There is an FM1 tuning voltage adjustment and an FM5 tuning voltage adjustment. In both procedures a trimmer is adjusted while monitoring the DC voltage at 4TP1. The measured voltage level in both adjustments should be 4.7VDC with the tuner at the 88MHz stop.

When I attached the Beomaster 2400 bottom plate I also had to replace the four plastic feet. All of the Beomaster 1900 and 2400 units I have encountered so far all have deteriorated (or missing) cabinet feet. Fortunately Martin Olsen can source these.

Now for a quick play test. I connected an iPod Nano to the Tape 1 DIN input and my FM antenna cable to the Beomaster 2400 antenna jack. I am currently out of functioning Beogram 4004 turntables so I will have to wait to test that.

As you can see from the photos I also checked out the Beomaster 2400 remote control. The receiver works and sounds great.

I will let it run for a while to burn it in before I hook up my dummy load resistors to run some performance checks.

This is the fun part.

Beomaster 2400: Power Supply Checks and No-Load Current Adjustment

The lamps are now all replaced and tested.  I am ready to move on to the power supply checks.

First however, I installed the Beomaster 2400 control panel and rechecked the operation of the touch buttons and lamps. This panel is sometimes tricky to install as there is a spring contact for each of the touch control buttons.  Those must all align properly to their metal posts.

Here are photos of those checks. Note that the color of the indicator lamps isn't accurate to how they actually appear in person. It is always difficult to capture lighting pictures and still have enough light to see the audio component in the photo.

...and finally...Standby

Now for the voltage checks.

First is the +15VDC power.  Here is the +15V supply reservoir capacitor. 22V at the reservoir capacitor is a good value. Next is to adjust the output of the +15VDC regulator.

The service manual says to use the 2R151 trimmer to set the +15VDC supply to +15.0V making the measurement at 2TP15.

No problems adjusting that. Now to measure the Beomaster 2400 ±31VDC supplies. I measured those voltages at the two large 5000uF reservoir capacitors (0C7 and 0C8).

I have a couple of wires connected to the test points for the Beomaster 2400 no-load current adjustments.  The space is too cramped to easily attach measurement probes across the emitter resistors (2R256 and 2R356) for this adjustment so I like to temporarily solder some test wires for the no-load adjustment. Both channels easily dialed in to the service manual stated 12mA with the multi-turn trimmers I installed earlier.

Everything tested good so I can finish up the re-assembly of this Beomaster 2400 unit.