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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...

Saturday, November 9, 2019

BeoGram CD X: Restoring to working order

Here is a BeoGram CD X that was recently dropped off to see if I could get it working again.

This is a really nice design by Bang & Olufsen from the mid-eighties, 1986 to be precise.
Interestingly this CD player was marketed for users who did not necessarily own a B&O system. The CD X only has RCA output plugs instead of the usual five or seven pin DIN plug. It also has no remote control capability.

However, when all other CD players were the typical rectangular box shape, B&O went for a nice, sleek, top loading CD player.


























Quite a lovely design that I have always liked.

A problem and usually "the problem" with these CD players is that they stop functioning due to problems with vias that connect circuitry to the ground plane of their circuit boards.
That being the case my first task will be to rework all of the board vias and see if that doesn't get this CD X unit working again.

The CD X is not too difficult to figure out how to open up. The service manual has instructional diagrams. The bottom cover is removed first.  Then the top can be removed (along with disconnecting a few connections).

Here is the CD X with the bottom cover removed.























Here is the CD X with the top cover removed.





























As with most CD X units that have been sitting unused for a while there is quite a bit of dust inside.






























I will clean out all of the dust as I work on the two main circuit boards.

I started with the Decoder circuit board (PCB 05) on the underside of the unit. It is probably the key board to repair the vias on.

























I actually removed this board to do the vias repair.
My repair method is to de-solder the vias, remove the wire/pin and run a piece of stranded wire into the hole. On the ground plane side of the board I fan out the wire strands and solder them to the board.
After that I cut off the new wire on the underside and solder it to the pad on the board.






























I apologize for not having photos of the other side of the board and for not taking photos of the other circuit board I reworked the vias on (Servo board - PCB 04).  I will make sure to do those for the next CD X unit I work on :-).

After reassembling the CD X I inserted a CD and it played like it should.  This CD X unit is working again!
























Next was some actual listening testing.  I connect the CD X to TP1 of my workshop Beomaster 8000 receiver.  The CD X played great.





























Being manufactured in 1986 it will likely require some recapping of the electrolytic capacitors at some point. I will also want to replace the belt on the motor that opens and closes the CD X lid. Those tasks will be done in the future.

For now I will move this CD player to a listening room for some more testing before I return it to its owner.

Wednesday, November 6, 2019

Beogram 4002 DC Motor Restoration

A Beogram 4002 DC platter motor in need of restoration arrived recently from Australia. This shows the motor as I received it:
I took it apart to get the bearings out for oil infusion:
The bearings are the two small donuts on the black pad. I immersed them in motor oil and pulled a vacuum. Immediately strong bubbling started:
The bubbling indicates that air is being drawn from the pores of the Oilite bearing material to make room for diffusing oil. After about 72 hours the bubbling stopped and I extracted the bearings from the oil:
Then it was time to reassemble the motor for a RPM stability test in one of my Beogram 4002s:
I ran a ~24 hrs measurement with my BeoloverRPM device. This is the curve that I measured:
This is pretty much as good as it gets with the DC motor of a Beogram 4002. This motor is ready for duty again!






Tuesday, October 8, 2019

Beomaster 2400: Packing up the Beomaster for shipment

The Beomaster 2400 played continuously for about forty-eight hours without any problem. I exercised all of the source inputs and even made a test recording from a Beogram 8002 to a Beocord 9000.

Now it is time to properly pack the unit up and ship it home.

The following pictures show how to pack the Beomaster 2400 for safe shipping.




















It is a good idea to use a plastic bag to protect from any packing material scratching of the audio component and to act as a moisture barrier.



















I like to use 1 1/2 inch eggcrate foam for protecting the Beomaster and secure it with non-adhesive packing wrap).



















For the shipping box I glue the bottom flaps together with wood glue then glue polyethylene padding to the floor and walls of the box.






















I place the wrapped Beomaster into the padded shipping box and use more eggcrate foam for the ends and the middle of the Beomaster .












































Now I can place the polyethylene lid over the packed Beomaster and seal up the box.
























This Beomaster 2400 is ready to go.

Saturday, October 5, 2019

Beomaster 2400: Finishing up with the listening tests

Time to wrap up this Beomaster 2400 restoration project. It is reassembled and all of the testing is done. I have had this receiver in one of my listening test rooms for a while. It has performed great connected up to a Beocord 9000, Beogram 8002 and a pair of Beovox M100.2.  Those speakers are rather large for this slim, little receiver but in a ten foot by eleven foot room it works out fine.

This Beomaster is ready for another forty years of music enjoyment.












A few more hours of listening and I will pack it up and ship it home.

Thursday, October 3, 2019

Beogram 4004: DC Motor Bearings Oil Infusion and Spark Snubber Replacement

A Beogram 4004 DC Motor arrived from Oregon for restoration. A brief bench test revealed the usual shrieking noise coming from dry bearings. This shows the motor as received:
I took the motor apart to remove the bearings:
The bearings are the two small donuts on the black pad. I immersed them in motor oil and pulled a vacuum. Immediately vigorous bubbling started:
This indicated that the air was drawn from the pores of the Oilite bearing material to make room for oil diffusion. After about 3 days the bubbling stopped and the bearings were ready for reinstallation. I put the motor back together and installed it in one of my Beogram 4002s for a RPM stability test with my BeoloverRPM device:
The BeoloverRPM allows logging of the RPM for extended periods of time. The red curve in the graph below shows the curve that I measured:

Far from perfect! The sudden RPM drops indicated that a spark snubber was occasionally shorting out one of the rotor coils. They usually start going bad in this intermittent way. I took the motor apart again to extract the rotor for spark snubber replacement. This shows the rotor with the snubbers up (on the black pad you can see the replacement TVS devices that I had prepared for soldering onto the rotor):

I unsoldered the original snubbers ('ring' on the black pad)
and then installed the TVS units:
I put the motor back together for another RPM test. This second measurement is shown in blue in the above graph. The negative spikes are gone, i.e. this motor is ready for duty again!







Thursday, September 19, 2019

Beogram 4002: DC Platter Motor Restoration

A Beogram 4002 DC platter motor arrived from New York for some TLC. This shows the motor:
I took it apart to get to the bearings for oil infusion:
The bearings are the two small donuts on the black pad. I immersed them in motor oil and pulled a vacuum:
Immediately, the usual bubbling started indicating that air was drawn from the pores of the oil depleted bearing material. As the air is drawn out, oil can diffuse in replenishing the bearing material for another tour of duty.
After about 48 hours the bubbling stopped and I extracted the bearings for reinstallation:
I put the motor back together and installed it in one of my Beogram 4002s for the RPM stability test with my BeoloverRPM device:
The BeoloverRPM can log the RPM in 10s intervals for extended periods of time. This allows pinpointing intermittent RPM issues. This is the curve I measured after 24 hrs:

This result is as good as it gets! This motor is ready for duty again!





Monday, September 16, 2019

Beogram 4002 DC Motor Restoration

A Beogram 4002 DC platter motor recently arrived from Florida for restoration. It emitted the usual shrieking noises when I ran it from my bench supply. A clear indication that the bearings were dry. This shows the motor as received:
I took the motor apart to extract the bearings (on the black pad):
Then it was time to immerse them in motor oil and pull a vacuum:
Immediately, vigorous bubbling started indicative of air being drawn from the pores of the Oilite bearing material to make room for oil. After about 2 days the bubbling stopped after the oil was replenished in the bearing. I extracted the bearings:
And then it was time to reassemble the motor. I installed it in one of my Beogram 4002s and ran a 24 hrs stability test with my BeoloverRPM device:
The BeoloverRPM can log the RPM over extended periods of time. This is the RPM curve I measured for this motor:
This is as good as it gets for 4002 DC platter motors, i.e. this motor is ready for duty again.