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Beogram 4002: Restoration of DC Motor Video Published - Check It Out!

By popular request (really, I got quite a few emails about this!...;-), I finally completed my Beogram DC motor restoration video! It demon...

Monday, April 19, 2021

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.

Wednesday, April 14, 2021

Beogram 4002: DC Motor Restoration

I recently received a Beogram 4002 DC motor for restoration from Missouri. This shows the motor as received:

I disassembled the motor to get the bearings out for oil infusion:
The bearings are the two small donuts on the black pad up front.
I immersed them in motor oil and pulled a vacuum. Immediately bubbling started:
This indicated that the vacuum drew the air from the porous bearing material, which makes room for the inter diffusion of oil. After about 48 hours the bubbling stopped and I extracted the bearings:
Then I re-assembled the motor and installed it in one of my Beograms for a RPM stability measurement with the BeoloverRPM device, which allows logging the RPM for extended periods of time:
This shows the result of a ~24 hrs run:
This is pretty much as good as it gets for Beogram DC motors. This motor is ready for duty again.

Friday, April 9, 2021

Beogram 8002: Arm Moves a Few mm and Then Stops - Replacement of Photo Resistors and Bulb in the Keypad

I guess I celebrated the Beogram 8002 that I recently restored a bit too early. After playing a few albums it gave me the 'after pressing start the arm only moves a few mm and then stops without dropping' phenomenon. This is usually an indication that one of the photo resistors in the keypad is on the frizz. A while ago I made a comprehensive post about this phenomenon and how the << >> scan system works.

So I opened the Beogram up again and extracted the keypad:

Then I removed the circuit board (it slides out to the right after removing the small screw that locks it in place):
I should have done this right away after adjusting the scan voltages, since the two screws that control the base line light intensity on the photo resistors were at fairly different levels, indicative that there is a difference between the resistors: 
Anyway, I opened the assembly up, which revealed the photo resistors, the apertures that are moved by the << and >> buttons, as well as the light bulb at the center of the assembly:
I exchanged the photo resistors with GL5549 types (widely available on ebay), and I also replaced the light bulb with a white LED (Newark 14N9428) and a 1k resistor in series:
Then I installed the keypad again in the Beogram and adjusted the scan voltages. After the adjustment both of the screws were about at the same position as it should be!
After this it played again perfectly. I hope this is the last time I have to open it up again!

Tuesday, April 6, 2021

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.