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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...

Thursday, February 15, 2024

Beogram 4000: Full Functional Restoration and a Test Spin with the Bill Evans Trio

This post describes the restoration work done on a Beogram 4000 that I recently received from a customer in Massachusetts. The initial assessment of this unit is posted here.

This shows the unit with the aluminum panels and platter removed:

As usual, I started my process with rebuilding the systems on the carriage. This shows the arm lowering mechanism and the solenoid-activated switches:
I removed the rods on which the carriage travels, the spindle and the linkages of the arm lowering mechanism, as well as the damper. These parts often have hardened lubricants, which need to be removed and replaced with modern synthetic lubricants:
This shows the removed parts ready for the ultrasonic cleaner:
A special feature of the setup in the Beogram 4000 are the solenoid activated switches. Their contact terminals are usually oxidized and this can create operational issues. This shows the original state of the switches indicating previous issues that someone tried to correct by bending the terminal tabs:
The removal of the contact terminals requires extraction of the small vertical boards from the base PCBs. This shows the carriage upside down, which reveals the solder points of the vertical boards:
Here in magnification:
Sadly, the board that holds the switch that limits the solenoid current after the arm is down was cracked:
This shows the vertical boards after removal, as well as the cracked piece:
With the carriage up, it is the perfect moment for also extracting the terminals of the carriage position switches. This shows the carriage position PCB still in place:
Removal of its two screws and disconnecting the carriage motor leads allows a peek at the switch terminals:
I removed all the terminals of the solenoid and carriage switches to get them ready for nickel/gold plating:
I also removed the plastic actuators of the carriage switches for cleaning:
They are usually full of old lubricants since many owners think the actuators are the issue when operational issues develop, and their easy accessibility encourages the application of generous amounts of lubrication. Luckily, there are ultrasonic cleaners!...;-). It is also a great idea to replace the solenoid current limiting resistor that also resides on this board. It is usually semi-fried due to the fact that it is a bit under-dimensioned for the application:
After a thorough cleaning I coated the contact terminals first with nickel to ensure good adhesion, followed by a layer of gold-cobalt alloy (which is the industry standard for contact plating). The cobalt alloy is much harder than pure gold, while still having an excellent corrosion resistance. This shows the freshly plated terminals:
Beogolden! I re-installed the terminals in their respective boards:
and also put in a new 3W solenoid resistor:
With the carriage board removed it is usually the perfect moment to replace the solenoid transistor, which is originally a TIP41 power transistor. In this Beogram 4000 I found that it was already replaced with a modern BD809, which is an excellent replacement choice. Higher power and higher voltage capability. I left it in place:
Before I put the solenoid switches back together I glued the current limiter base PCB back together with a generous application of epoxy:
This shows the switches back in their place:
With the carriage up it is also a great moment to replace the cracking-prone MMC cartridge mount. For this the tonearm needs to be removed and the MMC mount assembly extracted. This is done best by 'simmering' the arm in hot water for 30-60 min. Then the assembly can usually be pushed out with a suitable rod that fits into the aluminum tube:
This shows the Beolover MMC mount replacement soldered to the original wiring:
The Beolover MMC mount is a 3D printed nylon part laminated with a flex-PCB that has gold plated traces that match the cartridge terminals. I installed the part making sure that cartridges will snugly fit without a significant gap to the aluminum tube. This was achieved by using a special tool that I developed for holding everything in the proper place while the glue hardened:
After this process it was time to re-install the arm. This was a later model 4000, so the MMC mount connected via soldered wires. It is a good idea to fixate the arm for the soldering work:
After the arm was back in place it was time to install the cleaned mechanical parts:
As usual, I replaced the damper gasket:
The original gaskets are often hardened and that causes issues with the arm lowering speed. Sudden drops or not lowering arms can be the result of retaining the original gasket. A new gasket ensures a consistent arm lowering speed.
This late model Beogram 4000 was already outfitted with a solenoid arm with a plastic end piece. Unfortunately, these tend to crack around the rivet that holds them to the main metal part: 
I removed the cracked part and installed a Beolover solenoid arm extension:
This shows everything put back together:
The final linkage that needed re-lubrication is the one that connects the damper to the actual arm assembly. You can see it stick out in the V-groove in the lateral arm in this picture:
To get to the pivot point of this linkage, the sensor arm assembly needs to be removed. This shows the linkage already removed from the assembly (make sure you do not loose the little spring that is under the retaining washer on the pivot point if you try to do this at home):
As usual, the small copper plate that aids the lateral arm movement in up position came loose after a light tug with my tweezers:
I glued it back in place with epoxy and re-installed the sensor arm with the re-lubricated linkage.
The next step of the carriage restoration was the installation of a LED based tracking sensor light source. This shows the original setup with the black bulb housing in place:
I removed the bulb housing, which revealed the aperture that governs the tracking feedback process:
Then I installed a Beolover tracking sensor LED assembly for the Beogram 4000. It is a drop in ready part that directly replaces the original bulb housing:
The final step was the replacement of the cracked carriage pulley. They always crack at the square nut that counters the set screw:
I replaced it with a precision machined aluminum pulley:
This concluded my work on the carriage and I began working on restoring the electronic circuitry and the platter motor. This shows the original main and motor capacitors, as well as the AC platter motor:
I removed everything:
This shows the original motor and reservoir capacitors
and the extracted motor:
Since oil infusion of the bearings can take up to three days, I disassembled the motor first:
I immersed the motor enclosure halves in motor oil to re-infuse the integrated bearings with motor oil. After I pulled a vacuum strong bubbling occurred indicative of the oil infusion process:
While this process was under way, I focused on the remaining restoration tasks. This shows the main PCB in original condition:
I replaced all electrolytic capacitors, power transistors, the RPM relay and the RPM trimmers with modern parts. I also replaced the record sensor transistor and its biasing resistor. This is a frequent trouble point since the original transistors often loose part of their gain, which can disable the record detection circuit. This shows the rebuilt board together with the extracted original parts:
I moved on to the power supply PCB next to the transformer. As found in many Beogram 4000 the 6V supply fuse had disintegrated.
I installed new fuses on the PCB
and also in the main fuse cabinet, where the fuses had the same issue 

Then I replaced the two 1uF electrolytic capacitors and the BC142 power transistor on the PCB:
In the meantime the oil infusion process had completed and it was time to put the main capacitor array and the platter motor back together. But first I installed a new 3W 24V Zener diode:
The original Zeners are under-dimensioned at 1W and tend to get pretty hot, which drives their voltage out of spec causing the 24V rail to actually have 25-27V. Not great. The installation of a stronger Zener solves this issue and the voltage is reliably set to 24V.
This shows the new capacitors and the re-assembled motor installed:
While the main PCB is up, it is a good moment to replace the power transistors of the push-pull stage of the AC motor driver. These transistors are usually TIP31/32 pairs. They are bolted to the enclosure for enhanced cooling:
I replaced them with stronger TIP41/42s:
Before I completed my work on the main PCB, I adjusted the sensor transistor bias with the newly installed 5MOhm 25 turn trimmer to the specified 1.8V DC at the collector:
Then I moved the adjusted trimmer to the component side:
After completing the main PCB I moved on to the keypad cluster. I removed it and put it into service position:
This revealed the four incandescent bulbs that back-illuminate the user-accessible RPM trimmers as well as the carriage position scale
and the switch terminals that are controlled via the keypad:
I removed all of the terminals for nickel/gold plating. This shows them in their original oxidized condition:
And after the plating process:
I re-assembled the switches:
Beogolden!...;-). Then I installed BeoloverLED boards to replace the carriage position back-lighting bulbs and regular 5mm LEDs with suitable resistors to replace the bulbs of the trimmers. You can see the 33 RPM LED lit up in this picture:
The final incandescent bulb that needed replacement was the one in the sensor arm. This shows the small sensor compartment pulled out from the end of the sensor arm together with the LED board and positioning aid:
I removed the original bulb and placed the LED assembly:
This restoration was coming to a close and so it was time to focus on the signal path. First I installed a switch that allows connecting signal and system grounds:
Connecting system and signal grounds is usually a good way to quench any hum issues that may arise, especially when connecting a Beogram to a RCA input amplifier. 
The next step was replacing the original as usual corroded DIN5 plug:
I installed a nice all-metal modern plug with gold plated terminals:
Before I started on the adjustments, I replaced the cracked plinth guidance washers. This shows one of the cracked original ones:
I replaced all five with Beolover nylon guide washers:
Then it was time to do the adjustments of the floating chassis, platter to arm distance, arm parallelism and platter height. This process can be a bit iterative until the sweet spot has been found. Don't give up if you try this at home. Beopatience!...;-)
Then I installed a nut on the counterweight adjustment screw. In its original setup it is just held in place with a retaining washer that sometimes is glued in place:
I removed the washer and put in a square M3 nut which allows tightening the adjustment screw in place. This ensures that my weight calibration survives the rigors of transport:
Next I adjusted the arm lowering limit to stop the needle from going beyond about 1 mm above the lower parts of the platter ribs:
This important adjustment ensures survival of the tip should the arm ever get lowered on an empty rotating platter in case of a record detection circuit malfunction.
After this I calibrated the tracking weight with a digital scale to yield 1.2g at the 1.2g scale setting:
The weight adjustment dials in Beogram 400x are notoriously inaccurate over their entire scale. Therefore, it is best to calibrate them to be accurate around the 1.2g setting, which is the tracking weight of most B&O cartridges.
Now it was time to adjust the tracking feedback to ensure a proper arm alignment during play:
Before playing a first record I measured the RPM stability of the platter drive with the newly re-designed BeoloverRPM device:
It allows a precise adjustment of the RPM as well as logging the RPM in 10s intervals. Perfect for detecting intermittent RPM inconstancies.

The serial port connection simultaneously transmits all data points to the connected PC, which allows  detailed monitoring of the RPM over extended periods of time.
This graph shows a 24 hrs measurement:

This is pretty much as good as it gets. The slow drift of the RPM is a result of the profound temperature change in my work shop between winter days and nights in Albuquerque, NM.

I also measured the motor voltage with the oscilloscope. A nice sine curve together with high motor torque indicated that the motor department was working well:
The final measurement was the record detection sensor response. In the 4000 the amplitude should exceed ~2.2V, which was easily achieved:
And now it was finally time to enjoy this fully restored Beogram 4000 by playing a nice record. My customer sent me a present along with this deck, an audiophile pressing of the seminal Bill Evans Trio recording "Waltz for Debbie", which was recorded live on June 25, 1961 at the Village Vanguard. What a perfect combination with this great looking deck! Like all newly pressed records I cleaned this vinyl ultrasonically to remove any release agent residues before I played it. This was done on a CleanerVinyl ProXL setup combined with a UC-8360 high frequency 132 kHz ultrasonic.
My favorite track on this album is Milestones, a famous Miles Davis composition.
While I was enjoying this restored deck, I worked on replacing the original scratched up hood with a new one from the beoparts-store in Denmark.
But first I needed to fix the hood hinge that had started to corrode:
I sanded the corroded areas and then spray-painted them with satin black. The next step was to align the new aluminum trim with the hood to be centered. I usually place a strip of blue tape and then align the strip with two 3D printed alignment tools before I mark the position with pencil:
Then it was time to bolt in the re-painted hinge part:
This shows the new hood after glueing the aluminum trim into place:
I will now play this Beogram 4000 for bit longer to make sure there are no intermittent issues, and then it will be time to send it back to its owner!

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