Beogram 8002: Preparing the Restoration

The decision has been made to do the full restoration on this beautiful Beogram 8002. The first step is to open it up for service and prepare the parts for restoration.

These early eighties Bang & Olufsen audio components were designed to open up for servicing similar to an automobile hood. The modular design makes it nice to work on. There are still some tricks to learn in properly opening the units up and some out of the ordinary tools are a big help.

I already removed the dust cover and tonearm compartment lid assembly. I need to check why the alignment is off on that later so by removing it the lids won't accidently flip open and get damaged when the deck is tilted up.

To get the Beogram deck open there are only two screws underneath the left side that have to be removed. However, to open the deck up you must carefully detach the three suspension springs and when the deck lid is tilted up you have to maneuver the platter assembly to the right slightly. The reason for that is there is the deck cannot clear the tonearm assembly unless the platter assembly that holds it is shifted.

Here is the Beogram with the deck lid up (dust cover and tonearm compartment lid assembly already removed).

As noted in the photo, with the Beogram open I discovered another missing trim piece. There should be a black plastic cover for the exposed wiring board on the tangential arm assembly. I will look for a spare or fashion one out of a sheet of Dura-Lar.

Turntable adjustments and tests can be made with the Beogram opened up in this service position. For restoration work though I fully remove the Beogram assemblies so they can be worked on individually or connected together and tested.

This picture show the Beogram 8002 assemblies removed from the case and operating.

When I had first examined this Beogram I noticed the horizontal parallelism of the reference arm and tone arm was off. The tops of the two arms should be the same. In the picture below you can see the tone arm is slightly higher. The service manual has a procedure for adjusting that and it requires taking the tangential arm assembly out to get at the underside. That isn't a big deal as I was going to lift out the arm anyway to check the lubrication of the tangential arm drive.

Besides the service manual mechanical adjustment procedures this restoration will rework the Beogram 8002 main board. The electrolytic capacitors will be replaced and solder joints re-flowed on all of the board connectors. Here is the Beogram 8002 main board opened up.

...and inside the metal box with the microcomputer.

There is also a capacitor Bang & Olufsen engineers mounting in the transformer box. This capacitor is a coupling capacitor for the platter drive motor. It is obviously too big to have fit on the main board or on the platter chassis so it was put in the transformer box.

That is it for preparing everything for this restoration. It is time to start the work.

Beomaster 4400 (2419): Headphones Jack Restoration

I thought I was done with the Beomaster 4400, but I had completely forgotten about the jammed in 3.5 mm headphones adapter:

After removing it it looked like this:

While I was blissfully listening to some nice jazz on the public radio on this lovely Beomaster 4400, it occurred to me that there was something missing. Then it dawned on me that the receiver was lacking its headphones jack bezel. It must have been pushed in when the adapter hit something hard and then went missing after someone opened the Beomaster up to have a look. The headphones jack was also mashed in. Ruffians!:

After taking the jack out it looked like this:

I straightened the jack bracket as good as I could with my vise. In the meantime I obtained a spare bezel. This allowed me to finish up the repair:

With a straightened bracket the jack sits close enough to the bezel to hold it in place from the backside. From the front it looks like this:

Too bad that the banged-in adapter damaged the panel cutout a bit, but I guess for a more than 30 years old unit, this Beomaster is in pretty nice shape nonetheless.

Allright...looks I am finally done! All good in Beomaster land! I really started to like listening to this receiver, but now it is time to ship it back!

Beomaster 4400 (2419): Missing Preset Cover Replacement

It seems the Beomaster 4400 (2419) that I recently restored runs stable. I have it connected to my Beogram 4002 and I also tested it with the Beocord 9000 that I am working on right now, and everything functions very nicely. The final task was to replace the missing preset cover. There must be a big heap of these lost covers somewhere on this planet, but as long as we do not know where this Preset Cover Shangri-La is, getting authentic reproductions (injection moulded as the originals) from 'Dillen' (beoworld.org) is a great option. He recently sent me a few, and I installed one. Fits very well, maybe a bit tough to remove, but that will keep it (hopefully) away from their hiding place...;-). Here is a pretty shot of the cover:

Time to double box this Beomaster 4400 and send it back to its owner. That is the hard part of Beolove! Constant separation trauma...love can be pain...;-)

Beomaster 4400: Full Recap and Output Trimmer Replacement

Today I completed the replacement of all electrolytic capacitors in the Beomaster 4400 (2419) that I am currently restoring. I also replaced the quiescent current trimmers of the output stages. This is probably the most important item to do in these models due to the design of the output stages. If these trimmers go open circuit due to old age, the output transistors immediately die, i.e. whenever one opens up this model, these trimmers should be replaced and the quiet current adjusted properly.

But first I removed the input/output board that is bolted underneath the main PCB. Here you see it still bolted on:

It is easy to remove it. It is only held with the four screws next to the Tape 1 and Phono jacks. Take the screws out and the board can be removed:

It is connected with one wire-to-board connector to the system, so it is easily taken out. I really like the models they designed after they discovered the existence of such connectors. It makes it so much easier to work on them. The 4400 design is somewhere in between..still a lot of directly soldered connections, which can make id difficult to work on certain areas in these units. Anyway. Here it is taken out:

While I had it out, I decided to do the caps first. So I replaced everything with quality Japanese made 105C types for a long lasting restoration:

The next step was to remove the shield of the power switch. It makes it hard to get to a couple capacitors that are located underneath the switch. I did not want to touch the switch, and it seemed that after removing the shield, there would be enough space to get the task done. This shows the switch as I found it:

And here after unsoldering the resistor and taking the shield out:

Then I replaced all the electrolytic caps on the main board and put in new trimmers. Here some impressions of the original condition:

Left channel and a view on the tone control and preamp section:

And the right channel:

A few capacitors had been already replaced by a previous tech, but he used low grade 85C types, so I decided to bring everything up to 105C spec. Here are a couple pics:

This shows the left channel. I replaced the original single-turn 100 Ohm trimmers with 25 turn cermet trimmers. These are encapsulated and allow a precise adjustment of the quiet current that will remain without drifting over time. My experience shows that regular single turn trimmers can drift through repeated temperature changes, while the worm gear mechanism in a multi-turn trimmer will effectively prevent this, since the gear cannot turn as long as the 'worm' is not turning. This is the left channel:

And here is the right:

The next step was to adjust the quiescent current in both outputs. The manual prescribes to adjust it to 10-15mV across both emitter resistors in the output. The way the resistors were soldered in in this unit, it was more convenient to do the measurement just across one of them, and adjust to 50% of the above range. Here is how I did that:

I prefer to adjust to the lower end of the range, since this will make it run much more cooly. I checked with the oscilloscope, and there was no measurable crossover distortion in this unit with this adjustment.

After all this I fired the unit up and I listened a bit to the radio. It sounded very nice, and the heatsinks stayed very cool. When I received the unit it it ran pretty hot, indicative of misadjusted or problematic trimmers. Even after extended periods of low-volume listening the heat sinks should never get warmer than 30-35C. 

After the radio got boring, I decided to hook up the Beogram 4000 that I recently restored to try out the Phono input. And this was disappointing. It worked briefly, and then started cutting out intermittently on both channels. Still some issues I guess...time to explore the circuit diagram...I always enjoy doing that. This is Beolove!

Beomaster 4400: Replacing the Main Reservoir Capacitors

Today was output capacitor day in my Beomaster 4400 restoration process. I always enjoy replacing the 'big cans'. It certainly has something satisfying to it. Also, it turned out that this Beomaster definitely needed new ones. It is a fairly painless operation in these units, since the capacitors are only held in place with one clamp, and the grounding wires are well organized on the center bridge of the capacitor assembly. The clamp is even adjustable, i.e. new smaller diameter capacitors can be fitted without the need for adapters. Here is a picture of the original setup:

Here is a shot of the empty bay after removal of the old caps:

This shows the new ones loosely fitted:

After fixing them in place with the clamp it was time to solder them in. I usually use 'helping hands' to hold the wires in place. It is important to insulate the wires from the alligator clamp with some cardboard to avoid them melting through the insulation while the leads get hot during soldering:

And don't forget to put the cable tie back in!..;-). Done:

As usual I measured the old caps, and this ones, while looking o.k. definitely showed signs of their endgame. Their capacitance was out of spec (should be 10,000uF). The 4400 still worked with them, but would have probably shown signs of distortion if played loudly:

On to replacing the remaining electrolytic capacitors in this vintage beauty!

Beomaster 4400: Recapping the FM Decoder PCB

The Beomaster 4400 that I am currently restoring works seems to be nicely now. I listened to it occasionally the last two days, and nothing else came up. So we decided to go ahead and do a recap. Definitely worth doing for this unit due to its excellent cosmetic condition. I already did the IF stage during the trouble shooting process. Today I followed up with the decoder board, that also can be removed. Here are a few pictures:

This shows the board 'in situ':

Taken out. It can be a bit tricky to get this board out since the plastic clamps can be fairly difficult to push through the holes. I usually put a touch of Ballistol around the routed openings in the PCB to ease the strain on the often brittle material:

And after exchanging all electrolytic caps with quality 105C Japanese models:

After this was done, I cleaned the headers on the main PCB and coated them with DeoxIT D100L for long term stability. Then I plugged the board back in and turned the Beomaster on. All good. The reservoir caps are next!

Beomaster 4400 (2419): Tuner Repaired

The Beomaster 4400 that I am rebuilding right now seems to be running on all cylinders again. But a little more work was needed: 

After restoring the 15V rail the tuner came alive, but with a very weak output, while a standard 1Vpp signal piped into the tape input yielded a normal output response. So the problem was definitely not in the amp section. So I poked around on the IF board (#2). First I suspected a broken filter crystal, but the three turned out to be o.k. But while I was messing around out of a sudden the tuner started blasting full volume, indicating another broken trace/bad contact issue. I cleaned the contacts of the two board-to-board connectors and plugged it back in...no change. So I re-soldered all the contacts of the plugs and I also replaced the two electrolytic capacitor on this board with quality Japanese 105C types while I had it out. I also put in new headers and jacks for the signal meter connectors. They looked strangely corroded with some white coating. Here is a picture of the rebuilt board:

After I plugged everything back together the tuner came to life at full volume, but only on the presets. The main FM dial still did not work. This indicated some more contact issues, since the FM dial is nothing but another tuning voltage delivering trimmer in the context of the circuit diagram. Just looks more important...;-). I finally figured out that the culprit was a crack in the switches PCB (#6):

This was a pretty big one. It separated the 4.7V end of the main dial 100k pot from the voltage source, and so the pot was not able to change the tuning voltage from the 26V on the other end, i.e. the tuner was permanently set to 108 MHz independently of the pot setting.

I installed a jumper (grey) to bridge the crack (the grey/white wire goes to the pot):

This brought the FM dial back to life. Then I epoxied the PCB back together using a couple PCB snippets that I had laying around from designing Beogram 4000 scale illumination LED boards:

Here is a nice shot of the tuning indicators after the repair. Both tuning lights work again, and the stereo indicator is on. Beautiful! Beolove!

One the two capacitors that I replaced on the IF board was completely dead. It showed the characteristic cracks in the can, and measured 25nF instead of 4.7uF. This makes this Beomaster 4400 a definite candidate for a recap:

Beomaster 4400 (2419): 15V Rail Restored

I made some progress with trouble shooting the Beomaster 4400 (2419) that I am currently restoring. When turned on, the ON light did not come on, and also no sound from the tuner, but the Tape input worked...Both phenomena suggested that there is a problem with the 15V rail, since the ON bulb is powered via the 15V supply, while the tuner is the main part of the Beomaster that uses 15V. So I started following the 15V traces and wires. They are red throughout, that makes it a bit easier. I started out at C3 and the 15V were present. This meant the voltage regulator was working. I measured the resistance of the ON bulb (6 Ohm), which indicated the bulb is o.k. I finally found the spot where the 15V went lost: A crack in the main PCB (#5) under the Decoder board (#3) at one of the plastic clamps that hold it in place:

Since it is difficult to get directly to the trace at this location, I bridged directly from the power supply at R8. The red wire goes directly to the location after the crack:

This is where it comes out on the other side. I soldered it directly to the red jumper that goes from the main PCB to the PCB that connects the switches (#6):

This improved things:

Now the ON lamp is on and also one of the tuning light came on. However, there are more issues: The tuner only works with the presets and not with the main dial, and the volume is very low. This indicates that there is some issue on one of the tuner boards. Tomorrow is another day...;-)

Beomaster 4400 (2419): First Contact and a Peek Inside

I recently received a Beomaster 4400 for a checkup and restoration. I took it out of the box and had a first look:

It looks very nice...very little damage to the cabinet and the sliders are fairly pristine. The only thing that was less than beolovely was the headphone adapter jammed through the opening in the front panel doing a bit of minor damage at the opening. And, of course, the presets cover is missing. Luckily, Dillen of Beoworld.org sells authentic replacements, one of which will grace this unit when I am done with it.

The next step was to open it up and have a look before firing it up. I always do this to make sure not to fry the output stages. The 4400 has a similar output topology as the Beomaster 8000 and therefore the quiescent current trimmers are the most crucial parts that need to be checked before turning it on. If they go open contact during transport/due to corrosion, it is the end of the output transistors.

Thankfully the Beomaster 4400 comes with instructions printed on the bottom plate of the enclosure how to open it up:

I removed the bottom plate and then took the cabinet off:

Looks pretty clean. A bit dusty but nothing out of the ordinary. I found a few recently replaced capacitors in the output stages:

Unfortunately, they not only used inferior 85C capacitor types, but more importantly they did not replace the crucial output trimmers (one is visible here right next to the blue cable). Since they are difficult to get at due to a PCB that is mounted below the solder points of the main PCB, I measured the set resistance of the trimmers and then turned them a few times to make sure they would not go open circuit when I turned the Beomaster on the first time. 

After putting them back to the set values (that seemed reasonable based on my experience) I plugged the unit in and turned the radio on. Nothing visible happened. No ON lamp no nothing. Then I plugged in speakers and tried again. There I got a healthy sounding 'bump' when I turned it on again. So something seemed to have powered up. Then I connected my waveform generator to the Tape 1 input, and pumped a 1Vpp/1kHz signal in. And voila, the speakers emitted a pristine signal.

So it appears the tuner has an issue.