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.

Michigan Beogram 8002 Restoration: Cabinet Repairs

In the previous post on this Beogram 8002 restoration, the turntable electronics and record playing related functions were tested successfully.

Now it is time to work on the Beogram 8002 cabinet components.  

As with most Beogram 8002 turntables, the original double-sided tape that secured the aluminum platter deck, the metal lid over the tonearm compartment and the tonearm compartment panel had completely deteriorated.  All of those pieces mentioned are typically loose prior to this type of restoration.

The first step is to remove all of the old double-sided tape residue. It's not difficult but it is messy and not my favorite restoration task.

Here are some photos of the afore-mentioned components and the tape residue.

This photo notes (with a red dotted circle) that the metal spring that should be underneath the aluminum deck is missing.  The Beogram 8000 turntable did not have this spring. At least not during most of its production.  I believe the spring was added on the Beogram 8002 to remove any static electricity from the aluminum deck.

I will supply a replacement spring.

I soaked the tape residue in Goo Gone fluid for a couple of hours.

I did that with all of the cabinet components requiring tape residue cleanup.

Here is the hinge plate for the metal lid over the tonearm compartment.

Here are the loose components - aluminum deck panel, tonearm compartment panel and the metal tonearm compartment lid in soak mode.

The cleanup process involved scraping, cleaning up the messy residue goo, applying more Goo Gone and repeating.

After the residue is gone, the cabinet must be thoroughly cleaned to remove all of the residue traces.

Some of the old tape outlines could not be removed from the aluminum deck, even with a razor blade.

To re-attach everything I use VHB double-sided tape. It is more durable and should not deteriorate over time like the original double-sided tape did.  I use the RP32 VHB tape which has a thickness of 0.8 mm.  That is just high enough to connect the aluminum plate to the plastic platter frame. 

Note that I also installed a new spring (circled in red).

As you can see in the next photo, the aluminum panel fits perfectly onto the frame.

While I was working on the platter deck I decided to tackle the small rubber bumpers that are always worn down or missing from the front of the dust cover.  There are supposed to be two rubber bumper pads on the front of the dust cover where the dust cover rests on the aluminum deck.

Fortunately Danish Sound Parts supplies these rubber bumper pads.

I cleaned out the old, deteriorated rubber pad residue and inserted the new pads.

Here are the pads with the dust cover lowered onto the re-attached aluminum deck.

Now for the metal lid over the tonearm compartment.

The lid installation went smoothly but I discovered that the damper mechanism for the metal lid had absolutely no damping grease.  The lid would open and lock in the open position but when it was lowered, it just dropped down with a bang.

To access and apply the damping grease I had to remove the metal deck lid along with the damping lever.

The easiest and safest way I have found to do that is to push the metal hinge bar that holds the dust cover and metal lid to the rear cabinet frame.

I only push it out towards the dust cover side far enough to allow the metal lid to be removed.

I then use a spare hinge rod to insert from the metal deck lid side for re-testing the lid damping.

The rod is inserted for testing and removed to take the lid off for more application of damping grease.

After a few iterations of applying damping grease the lid started lowering at a slower, steady rate.

The cabinet was now ready for me to start re-installing the Beogram 8002 turntable components.

Unfortunately, I discovered the other metal hinge mechanism, the hinge between the cabinet base and top, had a broken piece for one of the hinge sections.

The red outlined area in the photo below show the broken area.

I could probably get the internal components installed with the broken hinge area if I am careful.

When the Beogram 8002 is put back together there is no activity on that hinge.

That wouldn't be very Beolovely.

I will attempt to repair the broken area using some very strong Bondo epoxy.  However, I only anticipate a 50:50 chance that will work.  Pressure from the metal hinge rod will likely be too much for the repair to hold.

Another consideration is to design a 3D printed part that spans past the broken area.  In that case, I would both epoxy the repair piece and drill holes for some screws into the plastic frame.

Of course sourcing another Beogram 8002 cabinet is also an option.