Beogram 4002 (5513): RPM Stability Test and an Updated Display on the BeoloverRPM Device

I spent some time learning to program the small display that I integrated into my BeoloverRPM device that is useful for precision RPM adjustment as well as long term RPM stability characterization. I added min and max values as well as the total measurement time. Here is an impression of the display:

Quite high res and a nice contrast! However, guys of my age at least will need reading glasses to appreciate the small font...;-). Is life ever perfect??. 

Anyway, I applied this new BeoloverRPM version to the Beogram 4002 that I just got going again and I performed a 12 hour RPM measurement. Here is the resulting graph:

This is a pretty good result about matching the specified 0.05% fluctuation number of the service manual. There are four spikes that exceed this specification (they are about 0.15% deviations). I have now measured a few 4002s with DC motor, and they all seem to have these spikes once in a while if one waits long enough. I think we see here the shortcomings of purely analog feedback systems. While these spikes are clearly measurable, they will be hardly audible. Most people can only detect changes of about 0.3 to 0.7%. So this Beogram should be fine for enjoying music.

Beogram 4002 (5513): Adjustment of Sub-Chassis, Platter Height, Tonearm Lowering Limits and Tracking Weight

With the top aluminum plates now properly seated I was able to do the sub-chassis and platter adjustment, which by itself form the basis for the adjustment of the arm lowering limits and finally of the tracking force. After that this Beogram will be ready for a first test drive. I have blogged about the chassis and platter adjustment process extensively and there are two videos on my YouTube channel that show how to adjust the platter bearing and the subchassis (in a Beogram 4000, but the process is very similar in the 4002). So I am only showing the end result here, a platter that is flush with the surrounding aluminum plates and that is centric to the cutout in the aluminum plate:

After this it was time to adjust the arm lowering limits. This is a very important adjustment since it may save your cartridge some day down the road in the event of a failing light sensor in the sensor arm, which will allow the system to lower the arm even if there is no record present. And of that happens, the needle better not hit the black 'ribs' that are on the platter. For that reason there are the lowered section where the set-down points are, that one can adjust the arm limit to keep the needle above the ribs but well able to descend into a groove on a record. There is another video on my youTube channel that shows how to adjust the lowering limits. 

Here is an impression of the end result. The needle is just a tad above the lower part of the ribs:

Once the limit is established, the arm should be calibrated for proper tracking weight. I do this now at the 1g setting since that is the setting range that is interesting. And of course there is yet another video that shows this process!...;-). This shows the tracking force gauge for a well calibrated arm at 1g:

After all this was done, I connected the Beogram to my Beomaster 6000 4-Channel and listened to my most recent vinyl acquisition, the seminal "In-a-gadda-da-vida" by the Iron Butterfly. I just love the drum part in the middle of this psychedelic delight!...admittedly a somewhat acquired taste, but that is part of the Beolove equation!

Beogram 4002 (5513): Repair of a Missing Leaf Spring on a Plate Lock

When I set out to do the sub-chassis, platter and tone arm lowering adjustments on the Beogram 4002 (5513) that I am currently rebuilding I realized that the larger aluminum plate was not seating properly with the plinth pushed back. If that happens it is impossible to properly adjust the platter to be flush with the plate.

The plate was wiggling up and down in the back left corner where one of the locks that are supposed to pull the plate down onto the frame when the plinth is moved back did not do its job. The locks accomplish the pull-down with a leaf spring that is attached to the bottom of the lock plate. This shows the right-back lock that still has the leaf spring attached.

I thought a bit about how to fix this, and I know that many Beograms either never had the springs or they fell off at some point and were discarded. In these cases often a tech bent the lock plate to act as a makeshift spring itself. Now in this case since the other three lock plates still had their springs attached, I did not want to bend just one of them. Somehow this did not feel Beoloving enough. So I came up with this fix:

A 3D printed wedge that fits to the bottom of the lock plate:

I glued it to the bottom of the plate using double sided tape. I always try to do things in a reversible way in case someone comes up with a better fix in the future and wants to remove my fix. 

When I put the aluminum plate in and pushed the plinth back, this wedge very satisfyingly pulled the plate down to where it should sit. All good now with this plate lock! No detail to small for my attention! This is Beolove! On to the platter and sub-chassis adjustment.

Beogram 4002 (5513): Replacement of the Tracking Sensor Light Bulb with an SMD LED Light Source and Adjustment of the Feedback Sensisitivy

This particular Beogram 4002 had a bent tracking sensor aperture impeding the lateral arm movement. This mechanically prevented any reasonable feedback response from the tracking system disabling the mechanism. This shows the original setup with the incandescent bulb light source:

After taking off the bulb housing I saw that the aperture was bent down, chafing on the optical sensor housing:

I bent the aperture back to a reasonable position and then I replaced the bulb assembly with my most recent design of the SMD LED based light source that integrates a potentiometer allowing the adjustment of the light intensity. A great feature for precise adjustment of the tracking sensor feedback sensitivity. This shows an original bulb assembly and the SMD LED based replacement in comparison:

This assembly is plug and play, i.e. all that is needed is to take the old assembly out and replace it with the same form factor replacement:

After installing it the tracking sensor sensitivity had to be calibrated to specifications. Time for using my least favorite record, a free jazz album by Sam Rivers. It is also a great idea to use a cartridge that is not pristine, since there is a real danger of damaging the tip if the tracking system 'goes wild' during the adjustment process. I have a special dented MMC20EN cartridge that suffered some bad ebay fate for that purpose. This shows when I did the coarse adjustment of the mechanical position of the tracking sensor assembly using the excenter that allows to move it left or right:

If you are interested in doing this yourself, I recently made a video that shows the tracking sensor adjustment procedure in detail (it uses the prototype for the current assembly, but the process is the same):

Beogram 4002 (5513): Restoration of the Arm Lowering Mechanism

I started working on the most recent arrival, a Beogram 4002 (5513). As usual the starting point is the arm lowering mechanism, which showed the usual hardened lubricant issues of sluggish behavior. Here is a picture of the setup:

I took out the linkages and the damper to clean and lubricate them:

This shows the damper taken apart and the linkages:

There is a video that demonstrates this procedure in detail:

After putting the mechanism back together I took care of the damper to arm linkage. The restoration of this function requires the disassembly of the sensor arm mount to get to the pivot point of this linkage (This video shows how to get to the damper to arm linkage and re-lubricate it):

This shows the linkage taken out:

After cleaning and re-lubricating with a dab of silicone grease I put everything back together and aligned the arms to be parallel. Next step: Tracking sensor.

Beogram 4002 (5513): A New Arrival on Beolover's Bench

Over the Holidays another Beogram 4002 (5513) arrived for some TLC. Today I did a first evaluation. The packing job was excellent and featured some new ideas how to safely package a Beogram. Here are some impressions:

The hood was filled with soft foam blocks to hold the sub platter and the RPM panel down:

One of the foam blocks contained the MMC20E cartridge, which traveled well:

Here an impression after taking it out:

I appreciated the precisely cut cardboard that held the sub-platter in place. The arm support also worked very well:

I took the hood off and the back part of the enclosure to give the inside an examination. It all looked original and pretty clean. Then I plugged the unit in and pressed start. The carriage started moving, but at the 30cm set-down point it lowered the arm, but then kept going at a rapid pace. An examination of the tracking system revealed a bent tracking sensor aperture which is stuck in the bulb housing. 

So that definitely needs rebuilding. Also the arm linkages are somewhat hard to move due to the usual hardened lubricants. Nothing that a good cleaning and re-lubricating could not fix.

I also noticed that the motor runs pretty rough, so it also needs to be taken apart and cleaned and it needs to get some fresh lubricant injected into its sleeve bearings.

Other than that, as far as I can tell right now this unit is in pretty good condition mechanically.

Cosmetically, the plinth is in great condition, the aluminum panels could do with a deep clean and the keypad has the usual three-finger usage pattern, but not too bad.

The hood, as usual, could do with some polishing.

All in all no obvious show-stoppers. It seems this unit is a great starting point for a restoration. This Beogram has an excellent potential to be as good as new once I am done with it.