Beomaster 8000: Inputs Not Working

A Beomaster 8000 that I rebuilt last year arrived a few days ago for trouble shooting. The owner told me that he suddenly lost all the inputs. No matter what input button was pressed nothing was audible, while the display would show the right input etc...This indicated to me that the uProcessor was working properly. So I opened it up with the plan to look into the chain of command between the uProcessor and the input selector chips. Since both channels of any input did not work, I hoped I could rule out a failure of the input selector chips. 

Once I had the unit open, I turned it on. Everything worked. That is of course frustrating if the problem is intermittent. I started methodically wiggling the connections between the uProcessor and the input chips. Nothing came up, everything was stable. 

Upon further reflection (while listening to some nice NPR jazz on the frustratingly working Beomaster) I determined that an interruption of the power supply of the preamp board would have a similar effect. So I checked the connections between the power supply board and the preamp. And indeed, when wiggling P46 that carries the power rails to the preamp board, I was able to get the inputs to turn off occasionally. So there was a bad contact somewhere. Here is a picture of the area:

The colorfully wired vertical plug is the one in question. This area is also prone to cracked traces on the circuit board due to the multitude of connectors that torque the board in that corner. A bit of a design weakness.

I took the board out and inspected for cracks and the like, but was not able to find anything obvious. So I resoldered all the headers and cleaned them and put the board back in hoping that a hairline crack in one of the header pin solder points was the root cause. After reconnecting all plugs, I fired the Beomaster up and wiggled the plugs in that area again, and nothing happened anymore. Seems everything is stable now. So it seems this issue may be fixed...but of course with intermittent stuff, one never really knows until one knows.

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!

Beogram 4000: Polishing the Hood

A last labor-of-beolove tribute to the Beogram 4000 that I restored in recent weeks: Time to polish the hood! It is always quite a workout. It usually takes me several hours in a multi-step process. This Beogram had fairly damaged plexiglass surfaces. Here are a few impressions:

Whenever there are deep scratches that one can feel with a fingernail, then it is time to crank out the 220 grit sand paper. With that the surface needs to be sanded until the deep marks are gone, and only the homogenous scratches from the sandpaper are visible. This hood definitely needed this drastic step. But first the B&O trim needed to be protected. It is very easy to 'delete' the B&O labels in the heat of battle when going at it with the sanding block. I usually use three layers of insulation tape:

After this I gave the 220 grit a go:

Looks almost like wood after this step. Once you have a smoothly sanded surface, it is time to work your way back to shininess. This is done by using about 10 grades of sand paper and micro-mesh policing cloths. This is finished with polishing liquid. It is important to change the sanding/polishing direction between every step. Also avoid rotating motions, it is best to just go in linear strokes. The chance in direction allows to see whether one has polished all the scratches left behind by the previous coarser step behind. Here are a few pictures taken in between the steps (not all are shown, but you get the idea):

After 400 grit:

After 800:

After 1800 Micro-Mesh

After 3200 Micro-Mesh:

After 6000 Micro-Mesh:

After Micro-Gloss polishing liquid:

And that is pretty much as good as this can get...it is virtually impossible to get back to 100% like new. But one can get pretty close. And this pretty much concludes the restoration process of this Beogram 4000!

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!

Beogram 4000: Adjusting the Solenoid and the Switches

Still a few odds and ends to take care of in the Beogram 4000 that I am rebuilding right now. Any complete restoration should include an adjustment of the solenoid and the switches that it controls to specifications. The solenoid not only takes care of the tonearm lifting and lowering, it also actuates three switches that control the audio muting function, the solenoid current (power), and the carriage transport enabling function. The audio muting switches are responsible for grounding the cartridge coils until after the needle has hit the record. The solenoid current limiter is responsible for lowering the current in the solenoid once it is engaged. This prevents the solenoid from overheating while the record is playing and the arm is down for extended periods of time. The carriage transport enable switch enables the servo motor once the arm is down. This prevents accidental carriage motion in case the arm is touched when it is up.

I made a short video that discusses the circuit and shows how to adjust everything to specifications. Enjoy!:

Beomaster 8000: Shipping Damage - Return Trip in a Double Box

Finally, it is time for the return trip for the damaged Beomaster 8000 that did not make it back well to its owner. I made the mistake to trust the original B&O packaging and did not insist on double boxing. This did not go well. Some ruffian must have dropped the package and a cracked uProcessor PCB and erratic performance resulted. Furthermore, and I am not sure if this was related to the shipping accident, my fix of the missing control panel lid spring retaining metal clip turned out to be unstable. The Beomaster sent out a piece of shrapnel and the spring broke out. I fixed this with a 3D printed insert. After fixing all this I put the Beomaster in our living room and embedded it into my Beosystem 8000 to test it for a few days to see if there are any intermittent issues. All this went well, and so I decided to try shipping again.

This time, however, I double boxed it using industrial HD packing foam that I cut to size to create a 2 inch foam cocoon around the original B&O box. The HD foam is perfect for slowing down the deceleration during impacts, while giving solid protection.

The outer shell is a double strength 12x24x36 box that I adapted to be 14 inch high to accommodate the additional foam layer on top. Here are a few pictures. I definitely recommend to make this extra effort whenever shipping one of the heavier B&O units. And this Beomaster 8000 definitely qualifies as heavy! The total package weight is about 70 lbs. Like a nice sack of cement, if you ever carried one up a few floors, you know what I mean...;-). If there is no original box available, a 10x20x30 box and some more HD foam is perfect as inner box.

I usually put some cardboard in between the foam layers to add some resistance to penetration:

Putting the Beomaster in:

I put a sheet of polyurethane foam on top to protect the surfaces a bit better:

This original box had some nice spaces to put the cord:

Here comes the double layer of foam on top

And an additional cardboard shield:

Folding the flaps over:

Due to the open area in the center I added yet another cardboard sheet and then about one roll of tape around everything:

And that's it! Let's try this again. I hope this trip goes better! Fingers crossed! May the FedEx man find some Beolove in his heart this time...;-)!