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Beolover SyncDrive: DC Platter Motor Replacement for Beogram 4002 and 4004 (Type 551x and 552x)

Late Beogram 4002 and the 4004 (Types 551x and 552x), which have DC platter motors instead of the earlier synchronous AC motors usually suff...

Wednesday, February 27, 2019

Beogram 4002: DC Motor Restoration

A Beogram 4002 DC motor recently arrived for restoration from Iowa. This shows the motor as received:
I took it apart to get the bearings out. Most Beogram 4002 and 4004 motors need their Oilite bearings re-infused with oil. Such bearings are made from porous brass, and after operating the motor for some time the oil in the pores is drawn out and the bearings run dry. This causes RPM variations and eventually the motor will seize and stop running. This shows the motor disassembled:
The bearings are the two small donuts on the black pad upfront. I immersed them in motor oil and pulled a vacuum:
Immediately vigorous bubbling started. This indicated that the air in the pores of the bearing material was pulled out by the vacuum. This process creates space for the oil to diffuse into the bearing. After about 24 hrs the bubbling stopped, which indicated that the infusion process had completed. I extracted the bearings
and re-installed them into the motor housing:
I use a specially made 3D printed tool for pressing the tabs of the ring that holds the upper bearing in place back into their original shape.

This shows both bearings back in place:
I put the motor back together and installed it into one of my Beogram 4002s for a 24 hrs RPM stability test with my BeoloverRPM device:
The BeoloverRPM device allows logging the RPM in 10s intervals for extended periods of time, perfect for spotting intermittent RPM issues. This motor passed with flying colors:
This is as good as it gets for the Beogram 4002 DC motor. This motor is back in business! Time to send it back to Iowa!

Monday, February 25, 2019

Beomaster 1900 Type 2904: Cosmetic repair - side trim replacements

Before reassembling this Beomaster 1900 for testing I took a little time to replace the two "wood" side trim pieces. Actually, the trim pieces on these Beomaster 1900 units are a plastic base to which a thin rosewood veneer is applied.

The rosewood veneer on this Beomaster has started to peel and has some unsightly damage. I had originally hoped to save it but there is just too much deterioration of the veneer.

There are areas where the rosewood is missing so just re-glueing what is left wouldn't do much good in my opinion. The plastic base pieces can be saved and reused in the future. It probably wouldn't be too difficult to find, cut and glue new veneer onto the plastic bases...but I'll save that for a future project.

On this project I am taking the two side trim pieces off a parts Beomaster 1900. It works out well for this project because my parts unit is missing its front trim veneer but the side trim pieces are perfectly intact.

Here they are installed on this Beomaster 1900.

Sunday, February 24, 2019

Beomaster 1900 Type 2904: Service manual adjustments and first play

After the indicator lamp replacement I set up the Beomaster 1900 for the no-signal current adjustments of the amplifier.

The adjustment procedure is to measure the voltage across the left and right emitter resistors (R256/R356 respectively) and adjust the left and right trimmers (R249/R349 respectively) so the voltages read 12mVDC.

The emitter resistors are in a bad location to connect up probes from the top of the main board so I connect the measurement probes on the underside (trace side).

There is just enough room to get to the trimmers on the component side for the adjustment.

Here is the left channel

The measurement and adjustment are to be made when the amplifier is cold and first turned on. The volume level should be at its minimum and no speakers should be connected.
Here is the measurement for the left channel emitter resistor

Here is the right channel

Another service manual check and adjustment is for the FM1 tuning voltage.
This test measures across the tuning board 4R1 (4TP1) while setting the Beomaster 1900 to FM1 and the FM1 tuning slider to 88 MHz.  The 4R2 trimmer is adjusted so 4.7 VDC is measured at 4TP1/ground.

The same type of test is performed for FM5. The measurement is again measured across 4TP1 to ground but the FM5 is the selected FM source. The FM5 tuning wheel is turned to 88 MHz then the 4R8 trimmer is adjusted to 4.8 VDC at 4TP1.

Once these adjustments were made I connected up my FM antenna and my workshop Beovox S55 speakers.

This Beomaster 1900 is playing music again and sounding quite nice.

I let the Beomaster play overnight to burn in the new components.  Later today I will start reassembly of the Beomaster then run some performance tests.

Saturday, February 23, 2019

Beomaster 1900 Type 2904: Lighting it up

In the last post of this Beomaster 1900 restoration I was briefly concerned when I powered the Beomaster up and there was no Standby lamp. When I selected one of the sources I could hear the Beomaster power relay engage but most of the lamps were not functioning.

I breathed easier when the power supply tests all checked out and I verified that the lamps all had correct voltages to be illuminated. So it just that the majority of the lamps were shot.

My fix for the lamps is to replace the two volume level indicator lamps, the two FM tuning lamps and the single FM stereo indicator lamp with new incandescent bulbs that I acquired from Martin Olsen of Beoparts. The bass, treble, balance and source selection indicator lamps are all replaced with LED modules that I build (just a 3/4 inch, white, through-hole LED with a 1KΩ series resistor).

I like using LEDs on the bass, treble and balance indicators because the LED lamps run a lot cooler than their incandescent counterparts. That makes it easier on the plastic mask material for those displays. On the source indicators the heat factor is not really an issue but I prefer to use the LED replacements there because they are less delicate and likely to last longer.  All of my LED replacement modules are built to just plug in the board the same as an incandescent bulb with the exception that polarity must be taken into account with the LEDs. Switching back to an incandescent lamp is just a matter of desoldering the LED assembly and soldering an incandescent lamp back in.

Finally there is the Standby lamp which is already a red LED. However the Standby lamp in this Beomaster has failed so it will get a new red LED lamp.

Regarding the five lamps that I am keeping incandescent type bulbs...the reason for that is because those lamps are part of their respective Beomaster circuit function. Changing those to an LED would negatively impact the circuit function.

Here is the indicator board with the most lamps to replace...the FM tuning and source selection indicator board.

Here is the board with new indicator lamps. This picture shows the Beomaster 1900 in Standby mode and the new red indicator LED is working.

I ran through all of the source selection options and all of the new LED indicators work. So do the two new incandescent lamps for the FM tuning.  I didn't check the stereo indicator lamp yet.  I will get to that one when I start bench testing the receiver functions of this Beomaster and an FM antenna is connected.

Here is the bass, treble and balance indicator board as I received it. All three lamps were not working although +15 VDC was measured across them.

Here is the bass, treble and balance indicator board with the LED replacements. I used two LED lamps on each indicator for a better light coverage.

There are two Beomaster 1900 volume level lamps on the volume indicator board. One of the two was burned out.  Here is the board with two new incandescent lamps.

Now the display indicator lamps are all working again. I can move on to adjusting the no-load current setting on the output amplifier stage then see how this receiver sounds playing music.

Friday, February 22, 2019

Beomaster 1900 Type 2904: Initial Power Supply Voltage Checks

This week I checked out the recapped Beomaster 1900 power supply. This is the first time to power the receiver on since the restoration work began.

Plugging the Beomaster 1900 in did not illuminate the LED Standby indicator. That is always a little scary but when I touched one of the program selection touch terminals the Beomaster powered up.

So I do have power. The picture above shows there are problems with the lamps though. The illumination lamps for the bass, treble and balance slider controls are not working. I tried some other source select functions and most of the lamps are out as well.

I needed to actually measure the Beomaster 1900 power supply voltages to verify the problem is with burned out lamps.

Starting with the ±31 VDC rail voltages I checked the two big reservoir capacitors.

Those voltages are present and look healthy.
On to the +15VDC power supply check. It's reservoir capacitor and regulator output look good (measured at TP16).

Another place to check for +15VDC is the TP15 test point.

There is also the -12VDC, TP14 test point.

Finally, a few checks of the indicator lamps that are not illuminating.

The lamps have voltage so they must be burned out.

Today I will replace lamps then revisit the voltages. Once those tests pass I will adjust the output amplifier idle current and start on some functional tests.

Beogram 4004 (5526): Tracking Sensor LED, Non-Working Carriage Switches, Final Adjustments and Test Drive with Eddie Henderson

The restoration of the Beogram 4004 (5526) that is on my bench is coming to an end. This post describes the final tasks of the project. After replacing the sensor arm bulb with an LED, I tested the carriage functionality and it behaved like the end switch and the turn off switch both did not work. It turned out that the wires that connect the switches to the main PCB had broken off from their solder points (white and grey wires):

I reconnected them (the grey wire needed to be extended a bit since it was pretty short after taking some insulation off for re-soldering):

After this repair everything seemed to work in terms of carriage motion.

The owner decided to also let me replace the bulb in the tracking sensor compartment with a LED assembly. I recommended this since this is also an essential light source, whose failure would disable the Beogram.

This shows the original tracking sensor light source in place:
I removed the bulb housing, which reveals the aperture that activates the sensor in the lower half of the assembly:
This shows the original bulb and the LED replacement in comparison:
The LED is in the same location like the filament of the bulb. This shows the LED assembly in place:
The blue trimmer allows fine tuning of the tracking sensor response, which makes it easier to adjust the system to spec. I also replaced the standard often rusty sheet metal screw that secures the aperture assembly in place with a M2 stainless socket head screw and a matching nut. This makes the initial coarse adjustment of the aperture position much easier.

Now it was time to adjust the platter height and the floating chassis horizontality. Then I moved on to the tonearm adjustments. An important item is adjusting the arm lowering limit. It needs to be set in a way that the needle 'misses' the ribs on the platter at the setdown points as an additional safeguard against needle damage should the record detection mechanism ever fail and the arm gets lowered onto the naked platter. This shows the adjustment result:
Then I moved on to the tracking weight. The first step is usually replacing the flimsy retaining clip on the counterweight screw with a M3 nut. This allows tightening the counter weight position down, which preserves the calibration over time and during shipping. This shows the original setup:
And with M3 nut:
Then it was time to calibrate the measured weight with the adjustment scale. I usually do it at 1.2g, since that is the weight at which most B&O cartridges track best. The weight scale on the adjustment wheel is notoriously imprecise, i.e. it is always best to confirm the weight with a digital gauge:
After this I adjusted the tracking feedback:
And then I tried to play a record...and all I got was a very loud hum from the speakers! Unbeolovely, entirely!
Hum usually means a broken connection in the grounding system between amplifier and turntable. It turned out that the shield connection in the DIN plug was disconnected:
Since the original DIN plugs cannot be opened up without destroying them, I needed to install a new plug:
The gold coated pins are a nice improvement in the signal path over the original corroded pins. This quenched the hum and the deck started sounding properly.
So it was time to listen to a nice record and enjoy this lovely 4004! I picked a recent addition to my collection, "Comin' Through" by Eddie Henderson. Of course this vinyl was cleaned with a CleanerVinyl Easy6 before I played it! Henderson recorded this album in 1977, and there are a few great funky tunes on it. My favorite is "Movin' On" on the first side. 
Beolovely! I will play this Beogram 4004 for a few more days and then it will be time for the return trip to its owner!

Thursday, February 21, 2019

Beogram 4004 (5526): Replacement of Sensor Arm Bulb with a LED

After restoring the record detection circuit and the PCBs it was decided that the sensor arm light bulb should also be replaced with a LED to ensure operability of the deck down the road. These old light bulb like to fail, especially during shipping, i.e. it is a good idea to replace the bulbs with LEDs when restoring a Beogram. This shows the original light bulb in the sensor compartment together with the replacement flexPCB-based LED assembly:
I removed the bulb and inserted the LED board, which folds snugly into the compartment:
This shows the LED in action:
The LED is a warm-white type, i.e. there are enough red photons to ensure a properly colored B&O logo.
Whenever the light source in the sensor arm is replaced, the sensor response needs to be checked. The signal strength is highly dependent on the location of the light source in the compartment. The signal at the collector of the signal amplifying transistor TR3 needs to be close to 6V or better. This shows the measurement I made after the installation:
This Beogram record detection circuit is now operating better than spec (7.9V amplitude), i.e. we can confidently press the START button. 

Sunday, February 17, 2019

Beomaster 1900 Type 2904: Capacitor Replacement Part 2 and Slider Control Repair

All of the electrolytic and tantalum capacitor replacement tasks are complete now on this Beomaster 1900 project.

The last board was the tone control and FM tuning board.

There are are only eight capacitors to replace on that board. Here are two before pictures.

...and here are the after pictures. Very straight forward.

The larger task on this board is the repair of the three slider controls (bass, treble and balance).
It is very common for these controls to fail on the Beomaster 1900. The failure is mechanical and involves the plastic slide that holds the left and right channel contacts for the respective control.

A small plastic tab that holds the metal contact in place breaks and the contact becomes free to move around. This results in faulty or no sound in one or both channels.

I noticed at least one loose contact when I did my initial assessment of the Beomaster. To be sure of the condition of all the sliders they must be disassembled and checked.

It is a good idea to label the slide controls as they are removed from the board.

Two small, metal tabs on the end of the control must be bent straight so the metal clamp/holder can release and allow the contact slide mechanism to be removed.

Here are all three sliders disassembled. I found three with broken contact mounting tabs.

The repair for this problem is best made using a repair kit from Martin Olsen. Martin makes a number of  accurate replacement kits for various vintage Bang & Olufsen components that he sells on his Beoparts website.

In this case the kit consists of three replacement (plastic) slider control parts plus some useful instructions.

I cleaned the metal contacts and slider areas with Deoxit (cleaner and fader lube). Then I reassembled the slider controls.

Next up are the lamp replacement tasks.