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Beolover SyncDrive: DC Platter Motor Replacement for Beogram 4002 and 4004 (Type 551x and 552x)

Late Beogram 4002 and the 4004 (Types 551x and 552x), which have DC platter motors instead of the earlier synchronous AC motors usually suff...

Saturday, February 29, 2020

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).

Beogram 4002 Type 5513: Initial Assessment

A local Beogram 4002 owner dropped off a turntable for assessment of restoring it.
This is a long time owner of this turntable and I can tell before opening it up that it has been well taken care of.

There is the typical wear on the control panel buttons that comes from a well used Beogram 4002.
The dust cover has minor marks but overall is shiny and can be cleaned up with a light polish.

There is some issue with the tonearm. It functions but is out of adjustment.
You can see that the tonearm is hanging a little low when the Beogram is parked.

Opening the Beogram up I can see that it is very clean inside. Signs that this turntable always enjoyed a very comfortable environment.

Surprisingly the original washers for the floating suspension lock down are intact. The are looking a little dry but haven't cracked and crumbled like most. I can apply some plastic restoration cream on them and they should be okay.

Looking at the tonearm issue a little closer I can see that everything is intact. It may just need the service manual adjustments.

I plugged the Beogram in and ran a few operational tests.
The buttons all work and the turntable appears to function.
With the tonearm needing adjustment I won't attempt to play a record.
The Beogram runs very smoothly although I spotted the LED light source for the carriage position sensor is out.  The tangential tracking lamp does function and so does the record sensor in the fixed arm.

I will check out all of the sensor signals in more detail later.

Here are more photos of the inside of this Beogram 4002 Type 5513.

Very clean and in excellent shape.
The tangential drive screw pulley is in really great shape. Those usually have a small crack somewhere in the plastic where it attaches to the shaft. I will look at that closer with a magnifier later but it operates very smooth.
The platter motor works nice but we know from all of our other Beogram 4002/4004 restorations that at forty plus years old the two bearings in the DC motor have to be low on oil.
I will pull this platter motor and send it to Beolover for a rework. After that the motor will be good for another forty to fifty years.

So from this initial assessment I see that the platter motor should be restored by Beolover.
The Beogram mechanical service manual checks need to be performed.
The voltages on all of the sensors needs to be checked and the Beogram needs a new carriage position sensor LED.
We typically recommend recapping the electrolytic capacitors and replacing the trimmers for the platter speed.
Changing the two speed indication lamps on the display panel is also recommended for maximum stability of the platter motor (those lamps are actually part of the analog control circuit).
Cosmetically the dust cover could use polishing and the control panel could use restoring.

There could still be some hidden problems I don't know about but from what I see this Beogram 4002 is in as good a condition anyone would want to begin a restoration.

This Beogram is also a good example of why a forty year old turntable should be given a thorough check and adjustment. It is in beautiful condition and for the most part functions nicely. But with a proper servicing this turntable can be functioning perfectly and at its full capability again.

Thursday, February 13, 2020

Beogram 8000: Strange Behavior Caused by an Intermittent 5V Supply

**********************This post is a sequel to this restoration.***************************

I declared 'mission accomplished' after restoring a Beogram 8000 recently, and I sent it back. After about 2 weeks I received an email describing some strange behavior, where it would shut down during play, but sometimes only very briefly and then start up again etc...
The Beogram was sent back to me and I had a look. First I was not able to reproduce the issue, and after playing more than 20 albums, desperation set in. So I gave it a bit of impatient rapid play and stop and other buttons, hoping to provoke a reaction. And after a while, indeed, it gave me a signal. The display showed this after it returned home after pressing STOP:
The dot on the right should not be on! This encouraged me to continue pressing buttons and I got this:
and this:
After each of these display readings I was only able to go back to normal after pulling the power plug and reconnecting. I continued working it for a while, and finally I got it to loose power briefly, and then it came back on. So I started thinking there must be a problem with the 5V supply. The 800x often has power issues, but mostly due to bad capacitors or bad solder joints on the headers that connect to the transformer block. Of course I already had re-soldered these headers and installed new capacitors, i.e. these standard root causes could be ruled out.

Since the issue seemed to be based on very brief outages or brown-outs that confused the processor, I needed to find a way to monitor circuit nodes for brief voltage dips while playing with the buttons. I decided to use the external interrupt pins (2 and 3) of an Arduino nano board, which I outfitted with a npn transistor and a 20k resistor on one pin to be able to sense higher than 5V signals, so I could also go between the transformer and the 5V regulator. After the 5V regulator the voltage is stabilized, i.e. Arduino pins can directly be connected. LEDs were used to signal power drops on each pins. This shows the board:
First, I connected the two pins to the green marked nodes in the circuit diagram to test if the 5V chain was interrupted between regulator and the plug that connects to the micro controller can:

After I was able to produce another failure the Arduino told me that on both green points the voltage briefly dropped to zero. This verified my power outage hypothesis, but did not show me where it occurred. Suspecting a bad regulator, I connected the transistor-buffered lead to the red marked spot right at the transformer-facing side of the fuse holder.
I played the buttons again, and again, and after a long time, I was still not able to reproduce the problem anymore, while before it took me always less than 5 min! This indicated to me that I might have had accidentally fixed the issue when soldering the test lead to the solder spot on the board:
It turned out that this solder spot serves to connect a black jumper wire between the fuse holder and the 5V rectifier:
So I suspected that the wire had a bad connection, and re-soldering the solder point while tacking on the measurement jumper accidentally fixed the problem. I replaced the back jumper with a new one, and had a closer look at the connector:
Indeed, the wire had pulled out a bit from the solder terminal, but was now soldered to the terminal. I suspect that some of the solder I put on the point during attaching my Arduino jumper managed to go inside the terminal, which fixed the intermittent contact.
Therefore, in conclusion, I think that the wire was loose, but still stuck inside the solder terminal, and the intermittence of the 5V supply was caused by vibrations when I pressed the buttons in quick succession etc...I will play it for some longer, but I am pretty confident that this problem may have been fixed with the new wire.

Wednesday, February 5, 2020

Beogram 4002 (5503): A First Look

I started working on an AC-motor Beogram 4002 (5503), which was procured from ebay a while ago.  I had provided the seller with a Beolover double boxed shipping container and detailed instructions. Luckily the seller heeded my advice and did a decent job, which ensured that the unit arrived in good condition. Here are a few first impressions:

The aluminum surfaces are dirty but in pretty good condition. Especially the platter has very few blemishes, which is pretty rare.
The keypad has the usual finger smudges on the most used keys:
One of the plinth corners is pretty nice:
The other has some veneer damage on the corner:
I found a paper clip taped to the tonearm, which indicates there may be some issues with the tracking weight adjustment:
I removed the aluminum panels and found a largely original setup:
There are the usual transport lock fragments, indicating crumbled lock bushings:
I plugged the unit in, and was able to start the carriage and the motor. But the STOP key does not work, and I had to drive the carriage all the way to the end to trigger the automatic arm return mechanism. Maybe just a broken cable or bad contact. We will see. 
The hood is in pretty good condition, but has the usual scratches and marks from storing the unit in an unkind environment. It probably can be restored.
In summary, a pretty good starting point for a restoration.