Beogram 4000: Carriage Returns Home Immediately After Setting Down on the Record

Oh well, the Beogram 4000 that I restored in January 2025 came back to my bench exhibiting an issue I had not experienced before:

After pressing ON the carriage went and found the LP setdown point and put the arm down. Immediately after hitting the run in groove, the carriage returned home with the arm down. It did that at a fairly high speed. Once home the unit shut off and the arm lifted.

Since the << and >> buttons worked fine with the arm up, a problem with the H-bridge was unlikely. This meant there must be an issue with the tracking sensor.

The Beogram 4000 features two photoresistors FC1 and FC2 that control the reverse and forward directions of the carriage motor (later 4002/4 models are differently set up, with only one photoresistor for the forward direction). This means the dual photoresistor tracking sensor can control the carriage in both directions, forward and reverse. The carriage is at rest when the forward and backward currents through the H-bridge (i.e. the motor) just cancel out. This condition is reached when the aperture in the tracking sensor illuminates both photoresistors with the same intensity, i.e. when it is positioned just between the photoresistors. If everything is properly adjusted, this condition coincides with the tonearm being parallel to the sensor arm. As the arm gets pulled towards the record center during play the arm gets deflected laterally, which causes the forward current to become larger than the reverse current, and the carriage starts moving forward, following the motion of the arm.

A consequence of this setup is that if one photoresistor circuit is not working properly, the carriage motor will already see a significant current even with the tonearm in parallel alignment, and the carriage will start moving. If the failed photoresistor circuit is the one that controls the forward motion, the carriage will always go reverse, independent of the lateral deflection of the tonearm.

With this in mind, I started examining the forward direction circuit. A good rule of thumb with the Beogram 4000 is that 90% of its issues are typically caused by bad contact terminals in the many switches, or by a wiring problem. The Beogram 4000 is an early 1970s design, when wire-to-board connections were still hardwired (instead of using modern wire-to-board headers and plugs, which are mechanically much more resilient). These soldered wires have a tendency to break off at the solder terminals when the Beogram is handled or transported.

This personal 'statistic' was confirmed in this unit: When I had a closer look at the wiring I immediately found the problem. The wire connecting the forward photoresistor FC2 to the H-bridge was broken off at its terminal on the main PCB (yellow marking in the photo):

I cleaned wire end up and soldered it back to the terminal. And the deck was operating normally again! I will play this Beogram a bit and then it should be time for sending it back to its owner in Australia!

Beogram 4002 (5503): Installation of a New Hood, Restored Keypad, New Carriage Motor and the Commander Remote Control System

This post describes the additional installation of upgrades and the performance of cosmetic restorations on the Beogram 4002 (Type 5503) that I functionally restored in August.

Like many Beograms at this point in time this unit had a fairly badly scratched hood. This shows the original hood

and some of its scratches:

My customer elected having a new reproduction hood from DKsoundparts installed instead of getting the original hood polished. I like these hoods a lot. They are crystal clear and a perfect copy of the original ones. They even improved the design of the bolt holes for the attachment to the hinge, which should make cracking much less likely. Therefore, replacement is a much better option than polishing.

The installation requires removal of the original hood from the metal hinge part. The screws responsible for the attachment can be fund under the vertical parts of the aluminum trim that is glued to the back end of the hoods. The original trim can in most cases be removed by pushing a razor blade in-between the trim and the plexiglass:

After removal of the two screws on either side the hinge part is liberated. This shows the hinge together with the new hood and a new aluminum trip strip (the original trim usually gets damaged/wiggly when trying to remove it from the original hood):

Before the hood can be bolted to the hinge it is a good idea figuring out the alignment of the trim. It needs to be installed exactly centered that the two parts that get bent down at the sides are exactly of same length. For doing this I use 3D printed alignment pieces that can be attached to both sides of the hood. Their 'wings' make it easy placing the strip exactly centered:

I use a strip of blue tape attached to the hood and a pencil to make a mark once the centered positon has been determined:

This mark is used to place the strip after the hinge has been bolted in. Bolting it in is easily done with a suitable Philips screwdriver:

This shows the hood after putting the new strip on it:

This hood is ready for installation!

The next step was the implementation of the Beolover Commander Remote Control for Beogram 4002 (Type 550x with AC Platter Motor). The Commander uses an Apple Remote for controlling all functions of a Beogram. The Commander even ads autorepeat functionality similar to what B&O implemented in the later Beogram 8000/8002 models. A special function of the AC version of the Commander is that it ads a record swiping function like in the later DC motor Beogram models. Simply press the center button on the Apple Remote while the deck is off, and the platter motor will come alive as long as the button is pressed.

Unlike the plug-and-play version for DC motor Beograms, the installation of the AC Commander requires a small amount of soldering due to the hardwired nature of the board to board connections in the 550x Beogram Types.

The first step is the removal of the keypad from the keypad PCB:

Note that the shown keypad is not the original one that came with this Beogram, but a temporary replacement from my stash that allowed me working on the unit, while I waited for the refurbished keypad to arrive. Keypad restorations are available via the Beolover's DKaudiolover.com store.

This picture shows the area of the keypad PCB where the wire harness is attached to the board:

The installation of the Commander hardware requires soldering a wiring adapter onto the PCB that allows the Commander to communicate with the Beogram control circuitry. For this purpose an area of the solder pads needs to be cleared from solder in order to generate a 'landing zone' for the adapter board. This shows the zone cleared after using my Hakko de-solder pump on it:

Once the zone has been cleared, the adapter can be soldered to the board:

It is important to put the adapter in that the white jack is flush with the board edge. Otherwise, there will be an interference between the adapter and the keypad assembly in some Beogram versions when the board is pushed back into the keypad after installation. This shows the Commander board bolted piggyback ontop of the main board and the white wiring harness already plugged into the adapter jack:

The next step was pushing the keypad PCB back into the new refurbished keypad:

This shows the smudgy condition of the original keypad for comparison:

Original keypads often show such patterns. They represent damage to the clear coat that gives the pads their unique sheen. Over time the coating material deteriorates due to the contact with the oils and acids in the skin and mechanical abrasion. Our restoration process is discussed here.

The next step was bolting the auto-repeat indicator of the Commander onto the keypad assembly under the standard mounting screw:

Then it was time for plugging the white wiring harness into the corresponding jack on the Commander board:

This concluded the installation of the Commander module.

My customer also wanted the original carriage motor upgraded with the new Beolover Carriage Motor for Beogram 4000, 4002, and 4004. While there was nothing wrong with the original motor, the Beolover replacement offers lower noise, fewer vibrations and lower current draw when the motor runs. Therefore, it is an interesting improvement for those who want the best possible performance of their Beogram. This shows the original motor still installed:

Four screws and two solder points later the motor assembly was extracted:

I removed the top, which revealed the motor:

I exchanged it with the new Beolover motor:

It is a good idea feeding the leads through the small window in the bottom part of the housing.

Then I bolted the assembly back in and soldered the leads to the carriage board:

This concluded my upgrade and cosmetic work on this Beogram and it was time for another test run. The Commander remote control worked flawlessly and the new carriage motor yielded a noticeably quieter carriage motion during start!

This shows the completed Beogram playing one of my recently acquired Blue Note re-issues, Donald Byrd's album "Stepping into Tomorrow" which he released in 1975:

What a lovely contemporary combination!

Here a detail shot of the pristine new keypad!

This Beogram is now in a near-new condition with improved functionality and performance! Very beolovely! I will play it a bit more and then it will be time to send it back to its owner in Ontario!

Beomaster 4400 Type 2417 - Australia Project - Electronic Restoration Progress Update

After doing the initial assessment of the Beomaster 4400 Type 2417 I started in on recapping the main PCB (PCB 5).

Here is PCB 5 before recapping.

Here is PCB 5 after recapping.

I removed the two 10,000 uF reservoir capacitors for the +-35 VDC rails of the output amplifier.

While I was working with the power supply components I removed and replaced the three bridge rectifiers in the Beomaster 4400.

I replaced the large bridge rectifier attached to the side of the transformer first.

Next, I replaced the two bridge rectifiers at the other end of the Beomaster 4400 PCB 5 board.
I also replaced the 15 V Regulator that mounts to the side of the chassis.

Here are the new +-35 rail reservoir capacitors.

So far I have removed and replaced 39 electrolytic capacitors in this Beomaster 4400.

For next time I will recap the Beomaster 4400 audio input board and the two FM boards to complete the last bit of recapping tasks.
I will also replace the thermal conductor insulators on the output amplifier transistors that mount to the Beomaster 4400 heat sinks. 

Beomaster 4400 Type 2417 - Australia Project - Initial Checks

Here is a really nice example of a Beomaster 4400 Type 2417 receiver.

This one has been sitting patiently in my backlog of Bang & Olufsen restoration projects for a while.

It is the first Type 2417 unit I have seen.  All of my other Beomaster 4400 restorations have been Type 2419 units.

The Beomaster 4400 Type 2419 receivers have a transformer for the US market.  Their transformer is for 117 V, 60 Hz and has two switched AC outlets in the back for connecting other audio components.  I never liked having those switched AC outlets as it means more current through the Beomaster 4400 receiver's power switch when it is turned on.

The Beomaster 4400 Type 2417 does not have any additional AC outlets and it has a voltage selector switch so the transformer can be configured for markets that have AC voltages of 110 V to 240 V. 
Much nicer.

Like so many of the Beomaster 4400 receiver cabinets, the four rubber feet are worn down and there is corrosion around where they mount to the bottom, metal plate.  I will have to replace those and clean off the rust.

The procedure to open the top of the Beomaster 4400 cabinet for access to the internal components is pretty easy.
Two screws need to be loosened in order to move two cabinet latches out of the way.
Four screws have to be removed to allow the wooden cabinet to slide back and up for removal.
A couple of those screws are partially hidden by Beomaster 4400 heat sinks.

With the cabinet opened up I am pleased to see that the internal components look like they are the original factory components.

This photo shows the space between the Beomaster 4400 voltage selection and the transformer.
In the Type 2419 units, this space is crammed with the wiring for the two switched AC outlets.

Normally I jump straight to cleaning and replacing the electrolytic capacitors.

This time I decide to try some basic testing on the Beomaster 4400.

The first thing I did was to check the no-load bias current per the service manual.
Both channels (Left & Right) were low so I adjusted them to about 10mVrms across their respective emitter resistors.

Next, I set up my audio tester.
As in other Beolover Blog posts where I test my restored Beomaster amplifiers, I am using my two 8.1 ohms dummy loads for the speakers.

These dummy loads are made up of a 4 ohms resistor + a 0.08 ohms sensing resistor + a 2 ohms resistor + a second 2 ohms resistor.  In series these measure 8.1 ohms.

The different resistor segments allow me choices of where to place my differential measurement probes to measure the power/frequency/distortion of the output amplifier.  My QuantAsylum QA401 Audio Analyzer can only handle a maximum of 26 dBV (50 W across an 8 ohms load) so the resistor segments let me choose a measurement point that is friendlier to the analyzer. 

In the case where I was going to measure 50 Watts out of the amplifier across my 8.1 ohms dummy load, I would place my differential probes across the 2 ohms sensing resistor of my dummy load.
The maximum dBV across the 2 ohms resistor for the 50 Watts output would be around 14 dBV.

On this pre-testing of the Beomaster 4400 Type 2417 output amplifier, I don't expect to get to a very high output.

The output of the Audio Analyzer uses two single-ended signals for the Left channel and the Right channel.  I typically connect them to the Tape 1 or Tape 2 source input.  The most common test signal I use is a 1kHz sine wave of 0.316 Vrms.

This photo shows the test connections underneath the Beomaster 4400 cabinet.

For my initial testing of the Beomaster 4400 Type 2417 I started with the volume at zero and observed the distortion measurement as I increased the output across the dummy load resistors to 1 W.

The THD measurement was surprisingly good at 1 Watt output from the amplifier.

Things went bad for the Right channel when the output amplifier went just past 7 Watts.

Here is what the workbench looks like during the audio analyzer testing.

So a bit of pre-restoration testing just to have as a reference when the restoration is complete.

My next task is to begin moving/removing some of the Beomaster 4400 internal components to make way for the electrolytic capacitor replacement.  I will also change the trimmer resistors in the amplifier section and rework the thermal insulation of the transistors on the Beomaster 4400 heat sinks.

There are also some transistors on the main PCB of the Beomaster 4400 that get really hot.  I will look at attaching some thermal protection to them as well.

As I do on all of the Beomaster 4400 restorations I work on, I will install an arc suppression device for the power switch.  

Michigan Beogram 8002 Restoration: Final Reassembly

I left off in the previous post of this project with a broken Beogram 8002 cabinet hinge guide...for the service position hinge.

That type of break on these cabinets is difficult to repair with any reliability.

I have tried unsuccessfully to repair these before and it was the same section of the cabinet hinge that is broken on this Beogram 8002.

Without a good spare Beogram 8002 cabinet to replace this with, I had to attempt a hinge guide repair again.

This broken hinge guide presented a new challenge because it also had a crack in it.

So I had two repair steps.

One was to reinforce the broken piece that I needed to glue back onto the cabinet frame.

The second then, was to glue the reinforced piece onto the cabinet so it is strong enough to support any pressure from the metal hinge rod.

I used two glue types for this repair - Bondo Steel Reinforced epoxy and JB Weld reinforced epoxy.  The latter was used in the last fill of the broken section.

The repair effort turned out successful but the various glue steps and time waiting for epoxy to cure took a total of three days.

Here is a look at the repair scar after I was done.

It still isn't pretty but the scar is smooth and is not visible unless the Beogram is upside down.

The important thing is that exercising the cabinet open to the service position and back closed does not cause the repair to break again.

Since the service position is not something a Beogram 8002 owner will typically use, I am satisfied with the repair.

It means the internal Beogram 8002 components can be reinstalled.

Another quick cabinet problem I decided to address was the metal lid hinge damping.
The Nyogel 767A damping grease I used in the previous post did not result in a slow enough closing of the lid.  I could hear the lid when it reached the closed position.  With proper damping the lid should be silent.

I pulled the metal hinge bar out again from the section holding the metal lid to the cabinet so I could remove the lid for re-greasing.

The area highlighted in yellow is where I re-applied damping grease.

This time I used Nye Lubricants PG-44A Grease.  It is much thicker than the Nyogel 767A damping grease and the result was just what I was looking for.

Next was the re-installation of the internal Beogram 8002 components.

That meant removing my test point leads from PCB 1 and attaching the metal lid to the microcomputer assembly (PCB 2).

I put some thermal conductive tape on the uC IC.

Applied some thermal grease.

Attached the metal lid and checked that the heatsink on the lid was pressed onto the thermal grease.

Next up should be some photos of the reinstalling of the floating chassis assembly, PCB 1 and 2, the transformer assembly and the Control Panel assembly.

However, I was so concerned with the service position hinge repair that I spent all of my effort carefully installing the components and did not take any photos :-(

So instead, the next photos are after the internal components were installed.

Here is a sequence of photos I took as the metal deck lid was closing.  It shows the slow lowering of the lid that now touches down onto the cabinet silently.

I did a little polishing of the dust cover and I will now move on to some record listening to wrap this project up.

The only issues with this Beogram 8002 are a couple of cosmetic problems.
The left side front of the cabinet has some small pieces of rosewood veneer missing and the Beogram platter is not pretty. 

Again, the Beogram 8002 platter should never be cleaned with anything other than some very mild soap (if even that) and distilled water.  A pristine Beogram 8002 platter should only be dusted with a dry cloth.  Platters like the one in this project were exposed to some sort of cleaning fluid at some point and the top coating from the B&O factory has been damaged.

That doesn't affect playing records great which is what these turntables do.