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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...

Saturday, November 25, 2017

Beogram 4000: Restoration of the Arm Lowering and Tracking Systems

I started working on the Beogram 4000 that joined me recently from Germany. As usual, I first rebuilt the tracking and arm lowering mechanisms. This shows the solenoid and damper arrangement that controls the arm lowering:
This shows the area after extracting the components that need cleaning and relubricating:
And these are the parts spread out:
After cleaning and lubricating I put everything back together, and then it was time to take care of the stuck damper-to-arm linkage. This part can only be accessed after removal of the sensor arm. This shows the arms from the back:
The sensor arm can be removed after taking out the two screws that hold it at the bottom:
This shows the arm with the linkage already removed. After lubricating the pivot point I replaced the arm and adjusted both arms to be parallel and orthogonal to the carriage rods:
This Beogram came with loose carriage rod bearings:
The white part on the rod belongs press fit into the bottom of the carriage plate. The second bearing was also loose already, and so I removed it too. Then I put a bit of epoxy on the parts and pressed them back into the carriage base:
After that the carriage was held in place again and I moved on to replacing the light bulb in the tracking sensor with a LED based assembly. This shows the original setup. The back square is the bulb housing:
After removing it the sensor aperture was revealed:
I installed the LED based assembly and also replaced the rusty sheet metal screw that fixed the aperture to the tone arm base with a stainless M2 screw and a nut. This holds the aperture in place much more solidly than the original screw, which often comes loose due to vibrations during transport etc...:
The next step was to replace the cracking prone carriage pulley with a precision machined aluminum pulley provided by Nick (let me know if you wanted one, too, and I will get you in touch!).
This shows the original pulley:
and the replacement:
I just love how they look like! Beolovely!
While I was 'in the area' I also checked on the the carriage position switches. To get to the switch terminals the carriage motor leads need to be unsoldered and two screws removed, and then the board can be lifted up:
I cleaned the contact areas with 2000 grit sand paper and then coated them with a bit of DeoxIT D100 to slow down re-oxidation. On to rebuilding the keypad cluster.

Beomaster 1900 (Type 2903): Testing The New Bass, Treble and Balance Indicator Masks

The original display indicator masks for the bass, treble and balance settings on this Beomaster 1900 have deteriorated from long term exposure to the incandescent lamps. I measured up to 118°F on the tone control lamp lenses.

Since the bass, treble and balance lamps display their settings mechanically, by sliding the indicator mask across a fixed lamp source, these are a good case for switching from the hot, incandescent lamps to cooler operating LEDs.

Here is picture of the original incandescent lamps in their bare, illuminated state.

A design goal for a replacement lamp is to produce a reversible substitute part. The LED version of the lamp should just solder on to the same two board pads that the original lamps use. No modifications to the board should be necessary.
Each of the original lamps has a 68Ω current limiting resistor in series with it. For my replacement I decided to go with two LED devices and a load resistor to limit the current further and to control the illumination of the LEDs.

On my test circuit I used a 68Ω resistor (for the existing resistor in the Beomaster), two white LEDs and a 5KΩ trimmer resistor to come up with a good load resistor value. I ended up with a 1KΩ load resistor a and the results are a nice substitute for the original bulb. The illumination of the red indicator lens is nice and uniform.

My final replacement version of the LED assembly looks like this. I put clear heat shrink over the load resistor and color coded heat shrink to mark polarity of the LED (red for positive, black for negative).

Now for a quick test.

The test passes and showed me that I needed to bend the LED leads a little different in order to fit the lens cover assembly for the lamps.  Here is the board with all three replacement lamps in place.

The lens cover assembly fits back on and the new bass, treble and balance indicators are restored.
Before showing the new LED replacement lamps in action here is what the new indicator masks look like.

Here are the new bass, treble and balance indicators with the Beomaster 1900 turned on and playing.

The light source on the bass, treble and balance indicator masks is much cooler now. These newly printed masks should last a long time.

Of course I will have to pull those three slider potentiometers again once Martin's new contact housings arrive. In the meantime I will put this Beomaster through a burn-in test. I will let the local classical radio station play for a few hours.

Sunday, November 19, 2017

Beogram 4004 (5526): Final Adjustments and Test Drive with Freddie Hubbard's High Energy!

After restoring the work keypad of the Beogram 4004 (5526) that I am restoring right now, it was time to do the final adjustments and then give it a spin. As usual I started out by adjusting the subclasses and the platter to be accurately positioned vertically and horizontally within the enclosure The platter needs to be flush with the surrounding aluminum panels, the arms horizontal in the right distance from the platter, while the sub-chassis needs to be centered between the transport lock brackets. Not an easy feat considering the many variables that go into solving this 'equation'. After that was done, it was time to adjust the tracking sensor:
The picture shows the adjustment of the light intensity of the Beolover tracking sensor light source that I implemented earlier. A convenient 'upgrade' that makes it much easier to adjust the tracking feedback precisely. After establishing proper tracking, I went on and adjusted the arm lowering limit:
When the arm is lowered without a record present, the needle should miss the lower parts of the black ribs on the platter by about a mm. This is a safety feature to protect the needle in case the record detection mechanism is malfunctioning.
After that was done, I did the final adjustment, which is the tracking weight. The first step is to upgrade the standard B&O design, which uses a locking washer to hold the arm counter weight in place:
This design may be sufficient if the deck is adjusted after setting it up in your living room, but any weight calibration done with it will not survive the rigors of shipping. Therefore, I usually replace the washer with a M3 nut and a standard washer:
This allows to secure the counterweight in place once everything has been calibrated.
The final step was to adjust the tracking weight with a digital scale:
And then it was finally time to give this lovely Beogram 4004 a spin. I selected a recent acquisition to my rapidly expanding vinyl collection, Freddie Hubbard's High Energy. I bought it via Discogs in near mint condition. After ultrasonically cleaning it with my CleanerVinyl Pro, it sounded like new. This album is usually underrated by the jazz reviewer set, who think that smooth sounding jazz is something that is inferior. All I know is that after I bought it it became rapidly one of my favorite Freddie Hubbard albums...I guess music critics are a bit like oneologists: It is helpful for their resumees if they have strong public opinions...;-). I generally follow my own advice when it comes to music and so here we go:
What a lovely sight and sound! Beolovely!

Saturday, November 18, 2017

Beogram 4004 (5526): Restoration of the Keypad

The Beogram 4004 (5526) that I am restoring ring now had the usual wear pattern of the keypad. The coating gets worn down over time and one starts to see which keys were used most (you guessed it: START is among them...;-). This shows the keypad as I received it:
After recoating it looked like this:
Beolovely! On to final adjustments and then some testing!

Thursday, November 16, 2017

Beomaster 1900 (Type 2903): Replacing The Bass, Treble and Balance Slider Potentiometers

Now that the Beomaster can power back up I performed the 15 volt supply check and adjusted the No-Signal Current setting for the left and right channels.

Since the left and right channel No-Load Current adjustment went smoothly I expected the Beomaster to be able to finally play music again. I used an ipod Nano as the source to the Beomaster Tape input and a pair of Beovox S55 speakers for the outputs. To my surprise I had no sound in the left channel. After some quick debugging I found that the Nano source signals were present in the Beomaster up to the balance slider. It is common for the bass, treble and balance slider potentiometers to develop problems in these receivers.

Checking the balance slider I found that it was the culprit.

Note: The tabs shown by the red arrows below have to be bent straight in order to disassembly the potentiometer.

I thought about doing a creative repair with some glue but figured there must be a better solution.
As it turns out, Martin at Beoworld makes a replacement part for the black slider housing that moves to change the output. That black slider housing is the piece with the broken tabs the potentiometer contacts are secured with. I ordered a set of three replacement parts as all three slider potentiometers (bass, treble and balance) have a broken contact mounting tab.

Since it will take at least a week for the parts to come from Denmark I wanted to keep going with the Beomaster restoration. I pulled the bass, treble and balance slider potentiometers from a Beomaster 2400. The Beomaster 2400 turned out to have nice, intact slider contact assemblies so they will do nicely and I have new assemblies on order. In the exchange of parts I will only take the contact assembly as the Beomaster 2400 Bass slider potentiometer is 20KΩ and the Beomaster 1900 Bass slider potentiometer is 50KΩ.

I cleaned the potentiometer contact strips and contacts with a fiberglass brush and some Deoxit Fader Lube.

With the Beomaster 1900 slider pots cleaned and rebuilt it was time to test the Beomaster 1900 for sound again.

Sly's voice came out beautifully on both Beovox S55 speakers. All of the slider potentiometers really needed that restoration.

After playing a few songs I checked the Beomaster output transitor temperatures. The TIP 141 and 146 transistors measured around 110°F to 119°F.  The heatsink cooling fins measured up to 149°F though.

It appears the heatsink is doing its job. Now I can start reassembling the Beomaster case.