Beogram 4004 From Canada: Begin The Listening Tests

This Beogram 4004 turntable is doing what it was built to do...play records beautifully.

I finished record play testing of the Beogram earlier on the workbench.

Satisfied with the performance on the workbench I reinstalled the deck panels.

Installing the deck panels can be quick and easy or it can take a while and require a lot of adjusting.
This Beogram was somewhere in between.  The panels fit onto the frame in a specific way but on each of the three floating suspension leaf springs there is a mounting post for the panel that sits on top.
If the deck panels do not appear to be properly aligned the posts may need to be bent appropriately to align the panels.

Similarly, the screws that the leaf springs fit over and are adjusted with may need to be bent in order to shift the floating suspension so the platter is centered in the hole of the deck panel.
Note: Be careful with bending the posts and screws. Make sure the threads of the screws are not damaged if you have to adjust them. I use rubber sleeves made for my pliers that prevent any metal to metal contact.

Here is a photo of one of the three leaf spring mounts. It shows the deck plate post and the leaf spring adjustment screw.

Always assemble everything without making any adjustments first.  If your Beogram 400x turntable is all original and hasn't been readjusted then everything should fit properly without any adjustments except possibly for tension on the leaf springs to adjust the platter height (relative to the deck).

If things do not fit properly then likely someone in the past tried (unsuccessfully) to make adjustments or someone swapped out the deck panels at some point.

Here is the Beogram 4004 moved to my office where I will be doing some listening tests for the next week or two while I set up and polish the dust cover.

I was in the mood to hear some Fairport Convention.  I recently picked up a 180 gram re-issue of "What We Did On Our Holidays" as well as a 1976 copy of  their 1969 release "Unhalfbricking".
I attached an MMC-20CL cartridge for these listening tests and the Beogram 4004 plays perfectly.

Beogram 4004 From Canada: Speed Indicator Lamps, Circuit Measurements and First Record Play

 This Beogram 4004 is getting closer to completion.  I have reached the point where the Beogram can detect and play a record.

To get to this point I had to finish up one more bit of electrical restoration work. That was the replacement of the incandescent speed indicator lamps with Beolover LED replacement lamp assemblies.
It has been noted before on the Beolover Blog posts but bears mentioning again...the speed indicator lamps are part of the Beogram 4002 platter motor control circuit and cannot just be replaced with an LED and a current limiting resistor.  The Beolover speed indicator lamp assembly uses an LED (more than one actually) but it is also a circuit designed to behave as the incandescent lamp does in the control circuit.
There is an added benefit to upgrading to this Beolover lamp assembly.
Platter speed stability testing on the Beogram 400x has shown that the LED assemblies run cooler and are more stable than the original incandescent lamps. This adds a little more stability to the platter motor speed. That stability improvement goes hand in hand with the upgraded speed selection relay, speed adjustment trimmers and of course the restoration of the platter motor.

Here are photos of the speed indicator lamp replacement.

Before jumping right to playing a record I had to check the arm lowering limit, the parallelism of the tonearm, set the tangential arm tracking sensor, adjust the platter motor speeds and check the important Beogram circuit signals with an oscilloscope.

Here is the arm lowering limit result.

Here is the arm length and parallelism check

The tracking sensor adjustment can take a few iterations of adjusting the sensor diaphragm position and checking the servo motor control circuit tracking sensitivity.
There is a detailed discussion of the procedure here.

My result was this Beogram 4004 being able to detect and play a record.

Very nice...but is the Beogram circuitry performing correctly?

I connected up some wires to look at various signals on an oscilloscope.

Here is what the oscilloscope measures at the 1TR3-Collector when the Beogram fixed arm sensor sees and empty platter.

The record detection circuit signal looks just like it should.

Now here are photos of various Beogram record play functions and what the MR/MB servo motor signals are doing as well as the run-off stop (position sensor) signal and arm lowering solenoid signal.

This first photo shows the solenoid signal when it receives the command to lower the tonearm.
The signal starts off at around 30 VDC to engage the solenoid.
After around 30 milliseconds the solenoid engage signal drops in voltage until about 1.5 VDC which it remains at until the arm is commanded to raise.  The 1.5 VDC is able to hold the solenoid in the arm lowered position while a record is playing.

This photo of the same event is at a longer time scale to show both the solenoid engage event as well as the servo motor accelerating through the lead-in groove.

Notice that the position sensor has a pulse where the 30cm set down bar was detected.
You can also see the Servo Motor MR signal accelerate on the run-in groove after the stylus set down on the record.

I looked at these same signals when the Beogram was playing a record and the Fast Forward ("<<") button was pressed to scan forward.

Prior to the Fast Forward button press the Servo Motor MR signal shows it driving the servo motor to track the record with the stylus navigating the record groove.
When the Fast Forward button is pressed the Servo Motor MR jumps up to its high speed and the voltage on the arm lowering solenoid is released (causing the arm to raise).

The signals are similar when the slow forward scan button is pressed.

The last event I wanted to observe on the oscilloscope was the run-off stop event. That is when the stylus catches the record run-out groove.
The Beogram 4004 run-off stop circuit detects that event and causes the Beogram to raise the tonearm and return to home. This happens before the end stop (ES) switch is reached.  For the case where there is no record on the platter and the Beogram fixed arm sensor is scanning forward to look for a record, the ES switch will catch the end of where a record would be and returns the Beogram to home.

You can see that the Servo Motor MR signal increases speed to keep up with the stylus accelerating with the record run-out groove.  The black markings on the position scale pass through the position sensor and the resulting run-off stop signal causes the circuit to generate a stop/return command.
The Beogram raises the tonearm and the Servo Motor MR signal drives the tonearm assembly home.

Instead of playing a test record for the purpose of making measurements I think it is time to reassemble the Beogram 4004 cabinet and test play some records for a listening test. 

Beogram 4004 From Canada: Restoring the keypad

The keypad on this Beogram 4004 functions without any issues.  It is still a good idea to take a look at the contacts, clean them with Deoxit and a fiber brush. That will ensure that they continue working properly for many more years.

Another decision has to be made regarding the cosmetic restoration of the Beogram.
Most Beogram 4002 and 4004 turntables have some visible wear on the keypad button surfaces. Oil from human fingers wears away the original coating on the metal buttons over time.

This Beogram 4004 shows some of that type of wear.

The area of the panel where the buttons are is a polished steel plate that has been sprayed with a matte finish that gives it a brushed look. The contrast look of the design is a distinctive and classic look that makes the Beogram 4002 and 4004 turntables so great.

The owner of this Beogram wants that look returned as part of this restoration so I will exchange his keypad with one I had professionally recoated prior to lock downs.

I stripped off the remaining, original matte coating on the button plate then masked off everything else on the panel. I sent the keypad to a paint shop that could spray the button plate with an automotive grade, matte clear coat finish. It is a very tough finish that is used on automobiles so I expect it to last for a very long time in this application.

The keypad came back looking beautiful.

The two horizontal gaps between the button panel and the keypad frame was originally painted black. That needed touching up so I used some matte black paint for that.

Now on to the button contacts.

I began with taking off the Start button contacts first. 

After cleaning the two contact pieces with Deoxit and a fiber brush I reinstalled them and continued with the remaining buttons.

Contacts cleaned and treated, the button panel is ready to be reinstalled in the keypad frame.

The keypad is installed back in the Beogram 4004 and works like new.

I will replace the two lamps in the speed indicator displays next.

Beogram 4004 From Canada: Assembly for Initial Testing

This Beogram 4004 has enough components reassembled where I am able to do some electrical testing.
The platter spins and the tangential arm travels.

The path to this point did have a couple of hiccups. I did run into a problem with the arm solenoid not functioning properly with my initial mod intended to prevent magnetic build up on the solenoid plunger. That issue was documented with an update to the previous post. I believe the arm lowering solenoid issue is resolved now. 

Here is the arm lowering solenoid put back together as it should be. The only difference is that I disassembled this solenoid and ran a demagnetizer across the metal plunger and frame.

To get to this point where I could test the tangential arm and platter motor I had to reassemble the Beogram floating chassis components back into the cabinet.  Then I had to install the circuit boards I recapped (PCB 1 and PCB 8). 

First a couple of photos I missed posting regarding some Beogram lubrication points.
The bearing for the tangential arm spindle needs a bit of grease. The service manual calls for the Molykote DX (white) paste here and that is what I used. 

The other lubrication point is the shaft of the inner platter and the platter bearing.
I have one service manual that says to use some of the Esso Nuto H44/H32 oil and another one that says to use M4 oil. You can use a good synthetic oil like Liquid Bearings. I have used that before but I have the Esso Nuto H32/H44 so I will use that here.

Setting the platter in the platter bearing and checking the platter height to the top of the fixed arm is another service manual adjustment I decided to go ahead and check while I had the floating chassis out.
It might be easier to wait so you can use the Beogram servo motor to drive the arm further towards the center for checking.  This adjustment can take numerous iterations to get right. With the chassis still disassembled here I had to manually turn the spindle.

Fortunately the initial adjustments were made without too many retries.
The top of the platter surface should be 23mm from the top of the fixed arm.
The platter bearing is threaded so that distance can be adjusted. A large brass nut locks the position down.

Now for the reassembly of the floating chassis back into the cabinet.
The three floating chassis transport locks must be put back together.  Sometimes these need a lot of cleaning.  This set did not need much.  I cleaned them with some alcohol then applied a little dry lubricant to protect against rust.

There is a specific orientation of the locking screws.
The top and bottom threads are opposite so turning the screw locks or unlocks the threaded clamping plates.  Note that the top of the screw is a little shorter than the bottom.

One of the three screws on this Beogram had a burr in bottom slot. It was probably from an over-torqued screwdriver. These screws do not need to be torqued down.  I know I say that a lot on my posts but it is true. These are not race cars. Please don't over torque the screws.

The burr was catching on the mounting hole for this locking screw.  Using a small file I removed the burr and reassembled the locking screws.

I place the threaded locking clamps (upper and lower) so that they are on the last two threads of the locking screw as shown in the following photo.  That gives a good range of travel for the locking mechanism.  I want as much distance between the upper and lower clamps as I can get for the floating chassis to move when the turntable is in operation (not locked down for travel).

After the locking screw assemblies are in place the leaf springs for the floating chassis can be re-attached.

Here are photos of two of the three leaf springs.

Note that the vertical post and the adjustment screw for the leaf springs can be bent.
Do not be in a hurry to straighten those. It is likely that those are as they were from the factory. 
Those posts can be bent slightly to obtain proper alignment of the Beogram 4004 deck components.
Once I get to the final reassembly of this Beogram I will be able to see if any adjustment to those posts are necessary.

The electrical components can now be installed and connected.
Here is the DC platter motor that Beolover restored for me a while back.

Here is PCB 1, the main circuit board of the Beogram 4004.

With this PCB 1 installation I decided I would change the position of a couple of the capacitors I replaced earlier.  I felt like there would be more room for the floating chassis below 1C22 and 1C23 to move if I placed those capacitors on the trace side of the board.  In that location they will have plenty of clearance from the sub-platter so no worries there.  The original capacitors were tantalum capacitors which are a much smaller physical size.  If you decide to stay with the tantalum capacitors here then you can do that.

Next is the PCB 8, Output Board.  It has the audio muting circuit and the Beogram 4004 remote control circuit (for exclusive use by a Beomaster 2400 receiver).

The control button panel fits on top of the Output Board.

Finally, with the speed indicator panel connected I could plug in the Beogram and try it out.

Note that I have mostly just set components in place to run this test.  I will take some of these components back out for additional restoration tasks but for now I wanted to see where I am at with the restoration.  Especially regarding the state of the PCB restoration work.

With the electrical components all connected I could go ahead and check some voltage levels.
I checked the tangential arm position sensor output with the arm positioned where clear plexiglass (of the position scale) was between the sensor and its light source. Trimmer resistor 1R88 was used to adjust the output of the sensor at that point to 5 VDC.

For the record detection circuit I adjusted the new trimmer resistor I installed (in replacement of the fixed resistor 1R26)  so that 1TR3 measured 4 VDC at its collector when the tonearm was over the platter area.
Note that Beolover has a blog post with a video that describes the record detection circuit in more detail here.

That is great progress on this Beogram 4004 project.
It is nice to be at the point where I can start thinking about some actual record play testing.

There are still a few more restoration tasks though.

Regarding the service manual adjustments I have some checks to make now that the Beogram is put back together in a functional state. 

I will be able to do the record play tracking adjustment now, the tonearm lowering limit and record speed calibration.  I also need to change out the lamps in the speed indicator panel with the Beolover LED replacement assemblies.  In addition...the Beogram's control button panel needs to go through a cleaning of the button contacts.

Cosmetically this Beogram 4004 is in really nice shape. However, its coating on the button panel is showing signs of wear. I will need to find out if the owner wants a recoated (new clearcoat) button panel instead of this worn panel.