Featured Post

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...

Sunday, July 31, 2022

Beogram 8000 Type 5613: New Project From Houston

A while back a local, kind of...same state, :-) owner dropped off a nice Beogram 8000 for restoration.

It looks worse than it really is.

Some parts were in a plastic bag.  The metal deck lids were detached.  The keypad keys had fallen out.

Inside, the circuit boards look original and untouched. The keypad frame is missing most of the plastic tabs that hold the keypad PCB to the frame.  I will have to find a replacement frame for that.

Surprisingly, the original tachodisc is in place and is not showing any signs of deterioration.
Usually the plastic tachodisc has a peeling decal.

The main PCB and microcomputer board PCB are early serial number boards.  They look to be in good shape.

Being an early serial number Beogram 8000, it doesn't have the additional "Settling Circuit" board attached to PCB 1 and it doesn't have the HEF4013 flipflop board that B&O added to the Microcomputer PCB.

I will do the initial restoration with this original configuration then see if anything further will be done regarding the later circuit mods that B&O prescribed. 

Sunday, July 24, 2022

Beogram 4000: A First Look at a New Arrival from Berlin

The first project that I am undertaking while in Germany this year is a Beogram 4000. It arrived well packaged from Berlin. I had a first look. Unfortunately, the otherwise nice-condition hood of this unit got cracked on one corner due to poor packaging by the ebay seller when it was shipped initially. Here are a few pictures of the unit. Overall the cosmetic condition is pretty good:

The aluminum surfaces are mostly intact. There is some scratching where the arms assembly touched the small plate during shipping. The seller probably forgot to engage the transport locks.
The plinth is also very good. The right side is pristine
but the left corner came loose. But it should be no problem to glue things back together.
This is the sad and completely unnecessary damage to the hood:
I removed the plates and had a look. The unit seems largely original, and no obvious signs of previous human interaction are noticeable. Of course the carriage pulley came loose since the seller forgot to secure the carriage:
The platter motor looks different from all 4000s I worked on so far. It seems this is an early version, which is supported by the short serial number and the belt guides near the pulley:
I switched the unit to 220V, installed a new aluminum pulley and a new belt and then plugged it in. I pressed ON, and the carriage started sluggishly moving to the LP setdown point, and the solenoid engaged. Also the strobe light came on, which is great!
Despite the poor ebay experience, the red position indicator also survived un-cracked. 

In summary, I think this should be a more or less straight forward restoration. The only unknown is the platter motor. It seems to run nicely, though, i.e. it may be just fine.

Saturday, July 9, 2022

Beogram 4004 Type 5526: Ready for record play

In this post I wrap up the service manual adjustments and reassemble the Beogram 4004 so I can begin playing records.

The first service manual adjustment is to set the platter height so the surface of the platter is 23mm from the top of the fixed arm.

I set my calipers to 23mm then adjusted the platter bearing screw so the platter measured 23mm from the top of the fixed arm.

Next, I adjusted the tonearm lowered position limit so the tip of the stylus is about 1mm from the top of the first platter rib.

Then I checked the stylus tracking path by stretching a string from the center of the platter to the edge of the Beogram cabinet.  As I placed the stylus at various points along the string I checked that the distance of the stylus to the string stayed consistent.

Following that adjustment procedure I checked the tracking sensor sensitivity.

With a test record on the platter, I lowered the Beogram 4004 tonearm onto one of the middle tracks.
The platter was not connected to the motor (the belt was removed) so nothing was moving.  
I manually rotated the platter and observed when the servo begins to move the spindle (to track the record)
The Beogram 4004 servo should start rotating the spindle pulley within one or two platter revolutions after the tonearm sets down.  After that the servo should move the spindle on every revolution.
I set the tracking sensitivity to rotate the spindle after one revolution.

All of the adjustments so far were without the platter belt installed.  Any moving of the platter was done manually.

Now it was time to install the platter belt and begin checking the platter speeds (33.3 and 45 RPM).
For the platter speed adjustment I used the two trimmers that were installed on the reworked PCB 1 board to adjust the 33.3 and 45 RPM turntable speeds. The speed adjustment knobs on the speed indicator panel were set to the 0 position.

I use the Beolover RPM Tool to check the platter speed as I adjust the speed trimmers. The following two pictures show the RPM tool and adjustment.

The last adjustments are to put the Beogram 4004 deck panels back together and check that everything aligns.  

The platter needs to be centered in the deck opening and the top of the platter should be even with the top of the deck plate.

Those adjustments can take quite a while to get correct and you often have to go through several iterations of the adjustments.  That was the case here although it wasn't really to bad.

Here are the pictures of the Beogram after all of the adjustments were complete.

This Beogram 4004 is ready for playing records.
I will test this turntable in a listening room for a few days to make sure everything works properly before returning the Beogram to its owner.

Friday, July 1, 2022

Beogram 4004 Type 5526: Control Signal and Sensor Signal Measurements

In this post I will show some bench measurements of this Beogram 4004.
It has been performing great and it is time to look at what is going on electronically (since I completed all of the electrical work).

I used an oscilloscope to monitor four key control signals.  Then I measured the Run-Off Stop circuit signal from the position sensor.  Last, I measured what the record detection sensor circuit looks like as measured at transistor 1TR3.  

Here is the relative part of the schematic that shows the four control test points I measured.
I wanted to capture those test points for various key Beogram control events (i.e. Start, Stop, Cueing, etc.).

Highlighted on the diagram are four control signal test points (ON, OFF, Cue Down and Cue Up).

Note: B&O changed the wording on the Beogram 4002/4004 control buttons so in some Types there are buttons: ON (<<) and OFF (>>) while on other Types the buttons say START (<<) and STOP (>>).

The diagram also shows 1D41 where I measured the Run-Off Stop signal.

Here are the test point wires connected for making the measurements.  It also shows the test point wires for the Record Detection circuit and the Run-Off Stop.

The following three pictures are oscilloscope screenshots for various Beogram 4004 events.

Viewing Tip: If the enlarged photo is too small to read the printed measurements, right-click the photo and select "Open link in new tab" or "Open link in new window".  The image in a stand-alone tab will allow you to zoom in for more detail.

In the first grouping I have a reference measurement of the four test points when the Beogram is turned off.  Next to it are the signal measurements when the START button is pressed.
Below those two measurements are the signals when the Beogram finds the set down point and lowers to play a record.  Last, are the signals when the arm is lowered and playing a record.

The next grouping continues with another picture of the control signals during record play.
That is followed by a cue up (arm raised), pause event.
The third picture shows the signals when the Beogram is operated in Slow Forward and Slow Reverse.
The final picture shows the signals when the Beogram is just paused over a record.

Note that the Cue Up signal is only active when the Beogram is in play mode and is either paused or scanning slowly (forward or reverse).  The Cue Up signal is off when the Beogram is scanning fast (forward or reverse) or cued down.

The final grouping shows the signals during the event where the Beogram is operated in Fast Forward mode until it reaches the ES (End Stop) switch and reverses to Fast Reverse.
The picture next to that is the event where the Beogram is in Fast Reverse mode and reaches the SO (Shut Off) switch.
The bottom left picture shows the event where the Beogram is cued down (playing a record) and the STOP button is pressed.  
The bottom right picture changes out the ON (<<) TP with the Run-Off Stop TP and shows the Run-Off Stop signal in relation to the OFF (>>) TP.

This photo shows the Beogram 4004 position sensor and scale that generate the Run-Off Stop signal.

This final photo of this post is another oscilloscope screenshot of the Record Detection circuit.
The test point is at the 1TR3 transistor collector and shows the signal generated by the Fixed Arm sensor over an empty platter (after processing through transistor 1TR3).

That is what I want to see.  A very healthy signal showing an empty platter.  The low part of the signal drops all the way down to zero volts and the peak is around six volts.  Very nice. 

This Beogram 4004 is performing great and in the next post I plan to wrap up the service manual adjustments.