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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...

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!