Beogram 8000 Type 5613: Reassembly and Search for a New Dust Cover

The last post left off with the cabinet being prepared for repair and the Beogram 8000 floating chassis components only needing a few remaining service manual checks.

The service manual checks I ran were for the fixed arm height to the turntable platter surface, the tracking force calibration and the tangential tracking sensor sensitivity adjustment.

On these checks I want to use the platter while making measurements but I don't want the platter to rotate.
In order to disable the platter drive but still allow the Beogram 8000 to operate you disconnect the P4 connector from the main board.

For the arm height to the platter surface adjustment the procedure is to adjust the fixed arm so that it measures 23 mm from the top of the arm to the platter surface.

After that is set the tonearm is adjusted so that the top of the tonearm is even with the top of the fixed arm.

An inconvenience of this procedure is that the fixed arm is adjusted first and has its adjustment screw in an easily accessible place on top of the arm assembly.
On the flip side (literally), the tonearm height is adjusted second and has its adjustment screw underneath the tangential arm assembly.  That requires pulling off the tangential arm assembly to make the adjustment.

A better execution of this adjustment would have been earlier, when cleaning and lubricating the tangential arm assembly components.  While the spindle is detached the tangential arm assembly can be easily slid over the platter for checking and adjusting the arm to platter height. It is much easier at that point to access the arm assembly underside to adjust the tonearm height.

Once the arm height is set I calibrated the tracking force.
The counterweight for the tonearm is at the back of the tonearm assembly.
There is a small screw on the top of the counterweight for adjusting the position (forward or backward) of the weight.

I like to set the tracking force adjustment knob (along the side of the tonearm) to 1 gram, then move the counterweight as needed to get a 1 gram reading on the tracking force gauge.
The most common setting for an MMC cartridge on the Beogram 8000 will be between 1 and 1.3 grams.

The last adjustment I had to make was for the Beogram 8000 tangential tracking sensitivity.
The tangential arm assembly is moved forward during record play by detecting when the record groove is taking the stylus inward towards the center of the record.

The Beogram 4000, 4002, 4004, 6000, 6002, 8000 and 8002 use a light driven sensor to detect movement of the stylus tracking a record groove to advance the arm assembly.

A metal diaphram bracket attaches to the tonearm pivoting base. As record play causes the tonearm to pivot, the diaphram moves and allows more light to enter the sensor.  The Beogram tracking circuit instructs the servo motor to advance the tonearm when some voltage threshold (from the sensor) is exceeded.  When the arm pivots back to its perfect tangential position, the circuit stops the servo motor again.

That is a simplistic description of how the tangential tracking works of course but important to note that the sensitivity of the circuit that detects and controls the servo motor is adjusted per the service manual.

The adjustment procedure is to place a record on the platter with the platter drive disabled (by disconnecting connector P4 as shown earlier).
Ideally one would have the B&O Test Record 3621001 and use Track #5.
I have never found that test record so I use two or three different test records to make my adjustments with.
The Beogram 8000 record play is started and the tonearm moved to one of the middle tracks where I lower the arm.
The servo motor should be still after setting down on a track since the platter is not moving.

Next, manually rotate the platter and observe when the servo motor first advances the tangential arm assembly.  It should occur between 1 and 3 revolutions of the record.  I like to set the sensitivity where it advances at 1 revolution.

After the first revolution the servo motor should continue to advance the arm assembly every revolution.

If the Beogram 8000 servo motor is not advancing within those limits the sensitivity of the tracking is adjusted using the adjustment screw on the side of the tracking sensor housing.

After this adjustment was successful I unplugged the Beogram 8000 and reconnected the platter drive connector (P4).

Then I plugged the Beogram 8000 back in.  If I have left the tonearm over the track I was using to test with, the Beogram should detect that it has just been turned on and is not at the "home" position.  The Beogram uC should instruct the servo motor to return the tangential arm assembly to the parked position and the Beogram 8000 switches to Standby mode.

Now I can test the Beogram 8000 playing a record.  This will show me if the set down position needs any adjustment and if the tracking sensitivity is satisfactory.

Here is the adjustment point for the tonearm set down position should it require adjusting.

The record set down for a 12" (30 cm) and 7" (17 cm) record was good and the servo motor advanced through the lead-in grooves properly.

Next I checked the Beogram's handling of the run-out groove to make sure it detected the end of the record properly and returned to the parked (Standby) position.

As expected, that was handled successfully by the Beogram 8000 uC.

A final functional test was to check how the Beogram 8000 handled a Pause in record play.
The Pause function invokes automatically if Pause is pressed during record play and the arm left hovering over the spot that was paused.  After a few seconds the Beogram will return the arm to the parked position but without the Standby "dot" displayed.  Instead, it displays a speed integer that the Beogram was at when Pause was pressed.

To continue from a paused record play event the Play button is pressed and the Beogram 8000 should return to the point in the record where Pause was engaged and begin record play there.

This photo shows the Beogram 8000 paused for a 7" (45 RPM) record and a 12" (33.33 RPM) record.

As I was performing the various Beogram 8000 service manual checks I continued with the cabinet reassembly.

This photo show the Beogram 8000 deck fitted with 3M VHB double-sided tape to re-attach the deck panel.

Here is the deck panel back in place.  Note that this serial number Beogram 8000 does not have the metal spring for removing static electricity from the deck panel like later Beogram 800x turntables do.

The next few steps were installing the floating chassis, circuit boards, transformer and control panel.

I closed the Beogram cabinet from its service position and engaged the three floating suspension spring clips.

At this point I would usually already have the dust cover and tonearm compartment lid attached or would be doing that task here.

However, I ran into a problem with the dust cover assembly on this Beogram 8000.

In my earlier assessment I had seen that the dust cover was not assembled correctly but I thought the damage was minimal and would be easily fixed.

That turned out to be incorrect.

The Beogram 8000 turntable's dust cover and tonearm compartment have plastic loops on their hinge frames that mate with plastic loops on the Beogram 8000 rear cabinet bracket like a piano hinge.
A single, metal rod slides through the plastic loops to connect everything and act as the pivot point for the dust cover and metal door.

As this photo shows, the section of the dust cover where the dust cover damping hinge connects has a broken loop.  So does the loop on the rear cabinet bracket.

The hinge rod has to fit through the plastic loops and the two metal holes in the damping mechanism's metal bracket.

With the plastic loops broken (as seen in the photo) the dust cover function will not be reliable.
I attempted to epoxy the broken, plastic loops but even after 36 hours of curing, the epoxied joints did not hold up.

It is unfortunate as well that two key pieces are broken.
The dust cover assembly has a broken loop and so does the back plate of the cabinet.

My repair for this case is to replace the original dust cover and cabinet back plate with a couple of spares.  Luckily I have a set but have to glue the metal damping hinge for that dust cover back on.
The replacement dust cover also needs some polishing to try and remove some of the light dust cover scratches.

Meanwhile I can continue on with record play testing of this Beogram 8000 unit while I work on the new dust cover.

Beomaster 2400 Type 2902 - Canada Project Tying Up Some Loose Ends and Completing the Reassembly

The Beomaster 2400 has been playing music without a hitch since I started the listening/play tests. 

Now it is time to tie up any loose ends and complete the reassembly of the Beomaster in its cabinet.

There is one more service manual check I needed to make.  That is the audio output level setting the service manual recommends for the volume control.  The procedure uses the Tape audio source input as the reference for setting this volume level. 
The adjustment procedure calls for inputting a 200mV, 1KHz sine wave signal to the Tape source going into the Beomaster.
The volume out measurement is made with a DMM connected to the speaker outputs.
The Beomaster 2400 volume preset level set to the Medium position.
The DMM should read 100mV across either of the channel speaker outputs.  Trimmer 2R136 is used to make that adjustment. What the 2R136 trimmer is doing is adjusting the intensity of the lamp inside the Beomaster 2400 volume control module which directly controls the volume level. 

Now to finish the reassembly of this Beomaster 2400...
Here are the Bass, Treble and Balance indicator masks connected back up to the slider controls.

I also installed new plastic feet that I get from Martin Olsen at Beoparts.

This Beomaster receiver arrived with a missing Speaker 2 selection switch lever.  Luckily I had a spare and I got it installed to the bottom plate of the cabinet.

Finally all of the pieces fit back together.

Beomaster 2400 Type 2902 - Canada Project Assembly and Last Adjustments for the First Play Event

The no-load (idle current) adjustments and the power supply adjustments were made earlier.  The lamps were replaced and I performed a little test measuring the source switching volume mute circuit. Now it is time to finish up a couple of adjustments for the FM tuner, partially reassemble the Beomaster 2400 and see how it sounds.

The service manual has a couple of easy FM tuner adjustments that can be made.
One is for the FM tuning voltage on the FM tuner potentiometers. 
FM1 preset is turned to the dial stop for 88MHz and a test point (4TP1) is measured across resistor 4R1. The voltage should be set to 4.7 volts using trimmer 4R2.
The same measurement point is used again to measure FM5's potentiometer set to 88MHz. On this adjustment, trimmer 4R8 is adjusted to get 4.8 volts (across 4R1).

Another quick FM tuner adjustment is for the tuning indicator lamps. Test point 2TP3 is shorted to ground and the Beomaster 2400 is turned on by selecting an FM source.  Trimmer 2R31 is adjusted so the brightness level of the two tuning indicator lamps are equal brightness.

Finally it is time to hear what this Beomaster sounds like after all of the restoration work.
I connected up an iPod Nano to the Beomaster 2400 Tape source input, my FM antenna to the PAL FM plug and the Speaker 1 outputs to the Beovox S-55's that I keep next to the test workbench.

Standby lamp on...

Tape source on

FM1 on

The Beomaster 2400 sounds good.  The control sliders for Bass, Treble and Balance all work nice and cleanly. A nice milestone in a project to hear music coming from the restored components.

I will do more reassembly of the Beomaster 2400 cabinet and continue testing. I will test out the remote control functionality next. That includes testing out a nice Beogram 4004 as the Phono source. In case you didn't know, the Beogram 4004 can be remotely controlled from a Beomaster 2400. 

Beomaster 2400 Type 2902 - Canada Project Indicator Lamps Replaced

 The indicator lamps are now all replaced on this Beomaster 2400.  The old lamps (except for one) were still working but the age of the lamps is unknown so with this restoration it will be documented when they were changed.

The only lamps I converted to LEDs are the three lamps for the Bass, Treble and Balance position indicators.  Those lamps have no function in the circuit except to illuminate the slider positions when the Beomaster is on.  From past Beomaster 1900/2400 projects I like using two LED devices per lamp position here to give the light coverage on the indicator masks.  The reason to change these three incandescent lamps is because the give off the most heat which I have seen cause damage to the indicator masks. You can also see in the photos that the center of the red indicators lenses on these three lamps is faded white due to the heat. The replacement LEDs will run much, much cooler.

The rest of the Beomaster 2400 (and 1900) lamps do directly affect the circuits they are indicators for.
So I will replace those using replacement lamps the Beomaster owner sourced from Martin Olsen.

Here are the Volume Control and Source Select lamp boards with their new lamps.

Now with the lamps all replaced I rechecked the volume muting circuit when a source is selected.

The resulting voltage levels and volume muting duration are pretty much the same as with the old lamps. This is something I can note and use when comparing the next Beomaster 2400 (or 1900) receiver.

I am now ready to recheck the service manual adjustments again before playing some music through this receiver.

Beomaster 2400 Type 2902 - Canada Project Volume Muting Circuit When Source Selection Is Made

Every now and then there are some discussions on Beoworld regarding the Beomaster 1900 and 2400 receivers' volume muting during selection of a music source. It is something that I never have really paid much attention to so the discussion caught my interest and I decided to measure the volume muting activity to see it in action.

Here is the Beomaster 1900 and 2400 source selection muting circuit.
One thing to note...I have a few service manuals for both the BM1900 and 2400 but neither show this circuitry for later model PCB3 Volume Control boards. The circuit didn't change but other things on the Volume Control board did. As a result, the later model boards have different reference designators and the location of the components changed some. I found that the new reference designator for the old 3TR6 transistor to be 3TR29. Since the documentation didn't change I will continue referring to the transistor as 3TR6 though.

Here is the trace side of the newer BM1900/2400 Volume Control Board (PCB3).  I have attached three wires (black, yellow and blue) for my oscilloscope probes to connect to.

Here is the source switching volume muting description from the Bang & Olufsen BM1900 service manual.

Now for a look at the signals on the oscilloscope.  For these measurements I am still using the Beomaster 2400 with its original lamps.

The first photo is of the signals being monitored (3TR6-collector, 3TR6-base, 3TR6-emitter and 5R3)...when one source has been selected (Beomaster 2400 "On").

The voltage measurements are pretty much like the service manual states...except the value of 5R3 was expected to be higher than the voltage at 3TR6-base. I will measure these again when I replace the lamps in the PCB 5 lamp board.

Here are the same signals when a source switching event occurs.

As the service manual described, the 3TR6 collector goes to about -12 VDC. That should mute the Beomaster 2400 volume. The duration of the volume muting event I measured is 324msec. The service manual says it should last about 500msec. So I will check the duration after I replace the lamps.

I performed another series of tests using a different PCB 5 lamp board. This board I replaced the source indicator lamps with LEDs and 1KΩ load resistors (to limit the current through the LED to its rated value).  I have used this type of lamp replacement before and it didn't cause any problem with source selection and the display of the selected source. However, I suspect that it does affect the short, ~500msec volume muting circuit.

Sure enough, the LED lamps negate the volume mute circuit during source switching.  The LED assemblies don't use much current compared to the incandescent lamps and the act of switching the selected source doesn't excite the base of 3TR6 to engage the volume muting.

I could experiment with changing the 5R3 resistor and adding some bypass resistors across the LED assemblies to come up with a combination that excites the muting circuit. I would have to be careful because too much current could result in the volume muting always being on.

For now I believe I will stick with incandescent lamps for these source indicator lamps. That way the volume muting during source switching will be functional. This time I will spend a little more time seeing if I can actually hear a difference during the Beomaster 2400 source switching events.

Beomaster 2400 Type 2902 - Canada Project Power Supply & No-Load Current Adjustment

 The hard parts of the Beomaster 2400 are completed. It is time to put the receiver back together so I can do some basic voltage checks.  

First though I need to re-attach the four output amplifier transistors that mount to the Beomaster 2400 heat sinks. I like using the Sil-Pad thermal interface product rather than the white thermal paste in these low profile receivers. The Sil-Pads do a good job and don't have the mess that paste does.

At this point I decided I wanted to check the Beomaster 2400 restoration I had done so far by powering up the Beomaster and performing some basic service manual tests.  In order to do that I re-attached the Filter & Tone Control board along with the Beomaster 2400 lamp boards.

If you think your eyes are playing tricks on you in the above two photos they are not. I didn't really like the new replacement 2C92 2200uF, 25V capacitor for +15VDC in the Beomaster.  The markings on that capacitor were kind of strange. It wasn't as clear as it should be about which end of the axial capacitor was positive and negative. Normally the (-) marking is a distinct arrow pointing at the negative end. This capacitor looks like it points in both directors and the data sheet on it wasn't any help...so I switched it out with a Vishay 2200uF, 25V, axial capacitor that has clear polarity markings.

Plugging in the Beomaster 2400 and turning the master power switch on resulted in the red Standby LED illuminating.

The first test I performed was for the +15VDC supply. I adjusted it to the required +15V per the service manual.

Next were the left and right channel no-load current adjustments.
The space for attaching measurement wires and adjusting the trimmers is very cramped in the Beomaster 2400. My method of performing the adjustment is to mount the measurement wires across the emitter resistors from the bottom of the Beomaster 2400 main board.

That provides the leads I need to attach my DMM for the no-load current measurements.
I adjusted the left channel for the target 12mV across the emitter resistor test points.

Then I adjusted the right channel.

So far everything looks good.

I want to measure the Beomaster 2400 muting circuit while I have the cover off and the original lamps still attached. That is the volume muting that occurs when the music source is switched.  Pressing one of the Beomaster music source switches should send a volume mute signal to the volume control until the source switching is completed.

I soldered on some test wires so I can watch the muting circuit in action with an oscilloscope.

Tomorrow I will measure what goes on with the volume muting circuit.