Beomaster 1900 Type 2904: Cleaning, polishing and reassembly

For about a week since the last post this Beomaster 1900 has been sitting on the workbench playing music for hours on end. No problems surfaced during that time so with the new parts broken in I am ready to reassemble the Beomaster before going into the final stretch of testing.

The trickiest part of the reassembly has to be the touch control panel.
The copper, spring leads for the touch controls must fit onto corresponding posts on the Beomaster 1900 circuit boards. A trick Martin Olsen taught me was to install this panel with the Beomaster 1900 bottom cabinet plate still removed. That way you can inspect each touch control contact from underneath and use some tweezers or probe to maneuver the contacts into place.

I reinstalled the indicator masks for the bass, treble and balance slide controls at this time.
I also used some plastic cleaner and aluminum cleaner on the touch panel as I installed it.

The next piece to install is the other part of the top cover. The grooved section for the heatsinks and the access door hinge had a lot of dirt and grime from wherever this Beomaster was stored.

I cleaned it with mild cleaning solution and a couple of brushes to get into the channels.
The right side hinge of the access door was loose and came off so I reattached it with some epoxy.
Before reinstalling the base of the cabinet I gave the Beomaster a quick test to make sure all of the electrical connections were still good.

Finally I could install the cabinet base. This cabinet was missing all four of its feet so I used the replacement feet I recently got from Martin Olsen.

While the Beomaster 1900 was upside down I noticed that the Phono DIN jack is a 7-pin DIN connector.  There isn't anything wrong with that but the Beomaster 1900 will never utilize the number 6 and 7 pins of that connector. The Beomaster 2400 is the receiver with a remote control and can control Play/Stop functions of a Beogram 4004 via the 7-pin DIN. Except for the remote control the Beomaster 1900 and 2400 share the same circuit board so I guess Bang & Olufsen just started installing the same source connectors on both receiver models.

The Beomaster 1900 is all assembled again so I turned it over and started another play test session.

This week I will connect it up to my audio analyzer and make some measurements. After that I will hook it up to a Beogram and Beocord to round out the functional testing.

Beogram 4004 (5526): A New Arrival From New York State - A First Look

A Beogram 4004 (5526) arrived for restoration from New York State. Shipping went well, and I had a first look:

This spring revealed itself during unpacking:

Looks like one of the two springs that hold up the mounting screws for the hinge in the back. The unit has decent aluminum panels without major damages, the keypad is also in pretty good shape:

So are the plinth corners up front:

Like most 400x we receive, this unit also has a scratched up hood:

Unfortunately, the MMC 4000 cartridge that came with it is missing the tip:

I took a look under the aluminum panels:

As far as I can tell at this point things look pretty original. That is always a good starting point for a restoration. 

I plugged it in, and pressed START. The carriage started moving, but passed by the LP set-down point and went all the way across to the center and then returned. Since the 33-to-45 switchover occurred during this trip, the carriage position sensor seems to work. This suggests that the record detection circuit has an issue. Another obvious issue with this deck is the DC platter motor. It emitted a knocking sound while it was running, a clear indication that the bearings need to be re-infused with oil. This is a common issue with this Beogram vintage. 

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!

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.

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.

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.

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.