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Beogram 4002: Restoration of DC Motor Video Published - Check It Out!

By popular request (really, I got quite a few emails about this!...;-), I finally completed my Beogram DC motor restoration video! It demon...

Sunday, July 15, 2018

Beomaster 4400 (2419): PC5 Recap

Today I tackled the large PC5 board. The service manual titles it the AF Amplifier, Power Supply, Muting and Silent Tuning board. I'll often refer to it as the PC5 board, main board or output amplifier board.

The PC5 board has the most electrolytic capacitors to replace and it has six trimmer resistors.

Here is a picture of the board before recapping.

Beomaster top opened up

Boards and reservoir capacitors removed

Since this board is the largest and kind of difficult to remove for recapping I will take the opportunity to measure the output transistors (the ones mounted to the heatsink). I will also check and reflow solder joints on the board to board wires and the output amplifier transistors.

The transistors measured good but there were a couple of bad solder joints where the transistors attach to the PC5 board.

The recapping of this board takes a while as it has quite a few capacitors. There are a lot of 1uF, 2.2uF and 4.7uF capacitors. I think this particular Beomaster may have set a new personal record for the number of out of tolerance capacitors found. I found 1uF capacitors measuring as high as 4uF.

Here is the recapped PC5 board.

Tomorrow I will install the new reservoir capacitors and this Beomaster will be about ready to try out.

Saturday, July 14, 2018

Beomaster 4400 (2419): Recap Review Leads to Preamp Rework

A nice side benefit of documenting these Bang & Olufsen restorations is that it forces me to review and double-check my work. Several times I have thought a task was complete only to look at the photos of the work and spot a problem.

In the case of this Beomaster 4400 I started thinking about the next few steps of the restoration and when looking at the preamplifier (PC4) board I realized that I had made the source input level adjustments more difficult in the way I installed the trimmers.

The original trimmers are designed for top and bottom adjustment. That is nice but I wanted to replace those single turn, open type trimmers with some Bourns multi-turn, sealed trimmers. The new trimmers only adjust from the top.

Here is a photo of the Beomaster 4400 preamplifier as I received it.

Most of the time these Beomaster receivers still have the seals over the input level trimmers as people leave them per the factory settings. If they need adjustment the paper seal can be broken and the trimmer adjusted from underneath the Beomaster.

In my initial PC4 - preamplifier board recap I oriented the multi-turn trimmers as you normally would on the component side of a board.

Unfortunately that would mean making the adjustments before fully installing the Beomaster 4400 preamplifier board.

Like we do on the Beogram 400x RPM trimmers, I flipped the input level, 50KΩ trimmer resistors over so they adjust from the trace side of the PC4 board.

That is much more practical. The owner can then tweak the input levels without opening up the receiver.

Thursday, July 12, 2018

Beomaster 4400 (2419): Into the Recap

These seventies era Beomaster receivers have a low profile and are quite a challenge to open up into a service position. I like the way the eighties era Beomaster units were designed with some consideration for the service technicians. Oh well, it is what it is. The Beomaster 4400 is an improvement over the Beomaster 4000. There are some board connectors.

Here is the Beomaster opened up and ready for recapping.

The PC5 board has the most recapping work and does not unplug completely for removal. I disconnected enough wires to it so I can get to where I need to with regards to replacing capacitors but I will tackle the PC5 board after I recap the smaller boards.

I started with the PC3 - Stereo Decoder and Indicator Circuit board. It is a good one to warm up on.

Here is the recapped board. For now I am leaving the trimmer resistors as they are on the FM boards. I will replace them as necessary during the Beomaster performance testing. 

Next are the PC1 and PC2 FM boards. There are just three capacitors to replace between them.

...and here are those boards after the recap.

Now for the PC4 - Preamplifier board.

On this board I also changed out the six 50KΩ trimmer resistors as I recapped the board.

Tomorrow I will tackle the large, PC5 board and the two reservoir capacitors.

Friday, July 6, 2018

Beomaster 4400 (2419): New Beomaster Project From Canada

With the Beogram 4002 (5513) project moving into its listening test phase I can put a new project on the workbench. I have been looking forward to this next one as it is a very nice late 70's era Beomaster 4400. This unit comes from a friend up in Canada so it has travelled quite a ways to get here.

When it first arrived I had to see how it looked in a recent Bang & Olufsen MC40 cabinet I acquired.

Looks like a great fit :-)

Now on to the workbench...

Very nice. This Beomaster has been well taken care of.

The task on this receiver will be to replace the old electrolytic capacitors and some of the trimmer resisters. Then I will see what the state of it is.

Thursday, July 5, 2018

Beogram 4002 (5513): First Record Play Testing

Finally....time to see how this restored Beogram 4002 (5513) turntable does playing a record for listening pleasure.

First though, a couple of pictures showing some tidying up of some loose ends. In the last post I neglected to post the pictures of installing new cabinet guides and the rework of the phono cable.
So before showing the first record play photos here are a couple of pictures showing the Beolover Beogram 4002 3D cabinet guide parts.

There are five total cabinet guides. The last photo shows the lone black one that is used for the front center of the cabinet so it isn't noticeable. Note that these are not washers. The cabinet guides hold the plinth in place but allow it to slide forward and backwards for opening up the Beogram cabinet. The early Beogram 400x turntable guides were made out of a brittle plastic that almost always broke. In the later model Beogram 400x turntables B&O switched to a metal guide to fix the problem. The Type 5513 Beogram 4002 was before the metal guide came out. Even though they are just a small part they make a big difference. A lot of people will just substitute flat washers but they don't provide the function needed.

Now the phono cable. The original DIN plug cable had already been replaced and while the replacement was a nice cable I didn't like the way the wires terminated in the P9 plug to the Beogram phono output board.

I removed each P9 pin and reworked the wire connections. The wires connected to pins 2 and 4 are not used so I removed them.

Here is the reworked cable plugged into the Beogram phono output board. I reused the blue wire and its P9 connector for the left and right channel shield wires. The small switch we install allows the option to short the shield wires to the chassis ground wire or leave it open.

That is a lot cleaner looking. I can live with that.

Time for some lively Jazz from Buddy Rich.

I have used those for Beogram play tests before and keep using them for some reason :-).

Next the Beogram will go through a day of testing like this while I make sure the set down positions are good, the phono muting delay is satisfactory and there are no tracking problems. Once those things are satisfied I will install the remaining cabinet pieces and go through a week of listening tests before this Beogram's owner picks it up.

Thanks to Beolover by the way for another excellent job on parts and the platter motor restoration.

Wednesday, July 4, 2018

Beogram 4002 (5513): Service Manual Adjustments & Preparing for Use

I left off in the last post with the keypad cleaning, deoxidizing and the RPM panel. The keypad response is immediate but the cueing up and down button is too sensitive now. I will have to revisit that switch. There was a delay in the RPM panel re-installation because the molded, acrylic mounting fixtures were cracked. That is very common with these Beogram 4002 turntables. Often they are completely broken. Luckily the mounting fixtures on this Beogram just had one crack in each one and were still intact. I pressed the mount fixture together as I applied acrylic repair fluid in the crack. It dries very quick. That repair by itself is not strong enough if the RPM panel is removed and reinstalled very many times. To supplement the acrylic glue I cut two strips of Dura-Lar and put one strip on either side of the mounting block. I use Araldite AB rapid epoxy. It is clear.

The patched mounting blocks attach to the aluminum frame by set screws underneath.

One thing to note is the mounting screw for the keypad and RPM indicator panel is right underneath the RPM panel so whenever there is a need to get to the keypad buttons or the phono output board, the RPM panel has to be removed. That is why reinforcing the mounting blocks is important.

Here is the panel back in place.

Next I want to make sure the voltages and signals of the Beogram detectors are good.
First up is the 4D1 LED and its 4IC1 optical sensor that detect where the tangential arm is. Markings in the acrylic slide alter the LED light to the 4IC1 sensor and Beogram circuitry reacts to those changes in the signal.

The service manual check for this sensor is to measure the collector of the 4IC1 sensor when a transparent section of the slide is between the LED and the sensor. The voltage level at the 4IC1 collector should be around 5V.  If it is not, the 1R88 trimmer (on the main board) is adjusted to set the voltage needed.

These pictures show the adjustment.

This is an important adjustment because the run-out groove detection at the end of playing a record is dependent on this voltage level being set correctly.

Next though is the fixed arm sensor that detects if a record is present (and if it is okay to lower the tonearm). The fixed arm has a light source that shines down on the platter. The reflected light is read by an optical sensor. If there is a record on the platter the reflected light will be at a low level and won't vary. That steady, weak signal is interpreted by the Beogram arm lowering logic as okay to set down the stylus. If there is no record the black ribs on the platter will affect the reflected light so that it returns as pulses to the sensor. The pulses cause the arm lowering logic to not allow the stylus to be lowered.

Obviously it is important for this signal to be working and is at a proper level.

This sensor is providing pulses that are above the required 6 volt level. No danger of accidently lowering on an empty platter.

I need to check the end groove, run-out stop circuit but first I will perform some more mechanical checks and adjustments to get the Beogram ready for record play.

I caught a break on the platter to tonearm height adjustment. The distance was already at the required 23mm.

The arm lowering limit needs to be set so the tip of the stylus is about 1mm from the top of the first platter rib. This is a safety feature that prevents the cartridge from damage should the record detection circuit fail.

Another remaining mechanical adjustment is to check the tonearm for length and parallelism.
I run a string tangential to the Beogram arm assembly then check that the stylus travel path follows the string.

The check that the tonearm is 7.7mm distance from the fixed arm and that they are parallel were checks I made earlier in the restoration when I took apart the tonearm assembly (for the oil cleanup).

We are getting close to record play now. At this point the tracking sensor sensitivity needs to be fine tuned, the run-off stop needs checking and the platter speeds need to be dialed in.

The tracking sensor adjustment went fairly smooth. It still took quite a few iterations to get the sensitivity set where the tangential arm motor moves after each revolution (2±1 revolutions initially, 1 revolution after that).

The run-off stop check measured good on the oscilloscope.

I was able to easily adjust 1R14 and 1R15 trimmers (on the main board) to set the 33⅓ RPM and 45 RPM speeds using the Beolover RPM tool.

Whew! A lot of adjustments and checks on these Beograms. I still love them though. What a great turntable design.

Now for a break for some food and fireworks (not with the Beogram :-).  Then I will do a quick adjustment on the keypad cueing button. After that I should be lying down and listening to some records.

Thursday, June 28, 2018

Beogram 4002 (5513): Keypad and RPM Panel

I noticed that some of the Beogram's control panel buttons were slow to respond when pressing them. That usually means oxidation on the keypad contacts so I opened up the keypad assembly.
Sure enough, you can see the dull key contacts.

I unsoldered the contact pads and removed them for inspection. They didn't look too bad but the leaf contacts that the actuators press down on are all oxidized.

I used a fiberglass brush and some Deoxit to protect from future oxidation. The contacts all look nice and shiny again.

The last part of the electrical work is to change out the lamps for the RPM indicators. We recommend this because during the platter motor stability testing the LED replacement modules resulted in further stability of the motor speed. The RPM indicator lamps are part of the circuit that controls the platter motor. Each speed indicator has a knob to adjust the pitch (speed).

Here is the RPM indicator module with the original incandescent lamps.

Here is the RPM indicator with the Beolover lamp replacement modules.

The Beolover lamp replacement module is designed to work with the pitch control circuit and the SMD LED components used have been adjusted to mix light colors to match the original incandescent lamps.

Here are the 33 and 45 RPM speeds with the new light modules. The control panel buttons operate immediately as they are pressed now.

All of the Beogram functions are operating now. The next step is to check and adjust the Beogram per the service manual. Once those adjustments are made and all the checks pass it will be time to play vinyl again.