Beogram 4000: Complete Functional Restoration

This post describes the work done on the Beogram 4000 from Massachusetts that I recently put on my bench. Please, see this post for the initial assessment of the unit. 

This shows the unit in original condition with the panels removed:

As usual, I started out by restoring the carriage. I focused first on the mechanical aspects. This unit had a lot of grease applied to the carriage sliding mechanism, while the arm lowering assembly showed sign of the usual hardened lubricants:

So I disassembled everything

and cleaned the parts ultrasonically. 

While the carriage is 'up',

it is the perfect moment for extracting the oxidized terminals from the solenoid actuated switches. This is done best by removing the small boards from the main PCB next to the solenoid so the terminals can be accessed with the soldering iron. This task is always a bit challenging since one needs to heat up the solder while pushing the terminals through their mounting slots in which they tend to get stuck. But with a bit of patience this can be done successfully:

The removed carriage also makes it easy to work on the board that carries the carriage position switches:

I lifted it up, and these terminals looked pretty good in comparison to the solenoid switch terminals:

But after removing them it became obvious that the actual contact areas were also oxidized. I also removed the solenoid current limiting resistor since it tends to go open circuit spontaneously, and this disables the solenoid. So it is best to replace it along with restoring the terminals:

With the carriage position board removed it is easier to get to the solenoid transistor next to the board. I replaced it with a new TIP41C, a higher voltage version of the original 41A. Hopefully this will make it last longer while dealing with the solenoid EMF:

After this I de-oxidized the terminals. Then I electroplated them with a layer of Ni, followed by a layer of a gold/cobalt alloy (this is harder than pure gold, while being equally inert against oxidation):

Beogolden! I always enjoy seeing these newly pristine terminals! The next step is to re-implant them. This shows the carriage position board with the refreshed terminals and the new 2W solenoid resistor:

This shows the ultrasonically cleaned switch actuators on the top of the carriage PCB:

Then I re-assembled the solenoid actuated switches:

This shows their small boards re-installed next to the solenoid:

With the carriage loose, it is also convenient to update the MMC cartridge adapter tab at the end of the tonearm. As usual it had issues. In this case the plastic tab was not broken off yet, but the flexible circuit board with the cartridge contacts had come loose:

Since the plastic tab is brittle, it does not really make sense to just reattach the flex board. Instead the entire cartridge mount needs to be replaced. This shows the arm removed from the arm base. This Beogram 4000 already had the newer setup where the mount is connected with soldered wires:

To get the mount out the arm needs to be cooked for a while:

Usually about 30min do the trick, and then the mount assembly can be pushed out with a suitable rod that fits into the aluminum arm tube (and has a blunt end to not damage the wires). This shows the assembly pushed out from the arm:

Then it was time to install the Beolover MMC mount replacement. It is printed from a nylon based material, i.e. is slightly flexible and very resilient. This shows the part with the wiring soldered to the contact traces:

When installing it, it is important to make sure that cartridges can fit flush with the arm tube:

This shows the renewed mount:

After re-installing the arm, I focused on replacing the tracking sensor light bulb:

It is easiest to extract with the carriage up since in this early Beogram design the solder tabs of the bulb plug into the PCB from below, and they do that with a hooking mechanism, which can make it difficult to remove the bulb assembly without access from below. After removing the bulb housing I installed the Beolover LED replacement assembly: 

The blue box replaces the side-mounted bulb intensity adjustment trimmer of the original setup. 

After putting the carriage mechanism back together with the cleaner parts I replaced the original plastic pulley with an aluminum reproduction pulley:

Beo-tiful! This shows the entire assembly back together:

Wait! A couple more things that need to be restored on the carriage. One is the linkage between damper and arm, which can be seen from the back of the arms assembly:

and the usually loose copper-pad that facilitates the lateral movement of the arm while it is up. Here we see it a bit dislocated to the right:

To get to the linkage, the sensor arm assembly needs to be removed. This shows it with the linkage removed:

After putting the linkage back on a cleaned and re-greased pivot point, I removed the degraded double sided tape from the copper pad to prepare it for being epoxied back into the proper position:

This shows the assembly back in place:

On to rebuilding the electronics! This shows the keypad cluster in 'service position':

A slight tug on the strobe mirror revealed the as-usual decayed glue not able to hold it in place reliably anymore:

A closer look at the very oxidized switch terminals. They did look fairly black!:

I removed them for plating:

This shows them after the nickel/gold treatment:

And after reinstalling everything:

I also replaced the light bulbs of scale and RPM trimmer backlighting with LED assemblies. This shows them in action:

Before re-installing the keypad I epoxied the mirror back into its place:

Then I focused on the AC platter motor and the big reservoir and motor capacitors. This shows the original set-up:

I extracted everything:

This shows the motor disassembled:

I put the motor housing in motor oil and pulled a vacuum to re-infuse the bearings with oil:

The restoration of the capacitor set-up should also include the installation of a new 24V Zener diode. The original one is only a 1W type and gets pretty hot causing voltage drift. I usually replace it with a 3W type, which keeps the voltage solidly at 24V:

This shows the entire section restored with re-assembled motor and new capacitors (held in place by a 3D printed fixture):

Next were the main circuit boards. This shows the main PCB in original condition after flipping it up:

While the board is up it is the perfect moment for replacing the two push-pull transistors for the AC platter motor with new TIP41/42C units:

This shows the main PCB after replacing all electrolytic capacitors, power transistors (especially the H-bridge transistors should be replaced since they have a tendency to fail at this point in time), RPM trimmers and relay, and the record detection sensor transistor and bias resistor:

After this I also replaced the two electrolytic capacitors on the power supply PCB and the 6V rail regulating transistor.

Then I replaced the original light bulb in the sensor arm with a Beolover LED assembly. This shows the original bulb and the replacement components:

This shows the LED board installed:

And lit up:

Now it was time to adjust the sensor transistor bias and then measure the sensor response

:

A perfect result with a strong signal. Each dip represents the passing of one of the black platter ribs under the sensor. This is how the deck determines whether there is a record or not.

Now it was time to focus on the signal path. This shows the terminal where the colorful wiring from the tonearm meets the black/grey wiring from the DIN5 output cable:

This is a convenient location for the installation of a switch that allows connecting signal and system grounds if needed in case of humming:

This deck already had its original DIN5 plug replaced. Unfortunately the the implementation was not up to Beolover standard:

It is always a bit tricky to get these filigrane DIN plugs wired up properly. This shows my attempt:

And with metal shroud installed: 

Like most Beogram 4000 this one also had cracked plinth guidance washers:

I replaced them with my 3D printed nylon replacements:

After this is was time to do all the mayor adjustment of the floating chassis/arm parallelism/arm level and platter height. Once these adjustments are in place one can focus on the adjustments of the arm lowering limit and the tracking weight. But before I do this I usually lock the counterweight in place with a nut. This keeps the adjustment solid, even if the deck is bounced around during shipping:

Then I adjusted the arm lowering limit. This is crucial in case the deck should decide to lower the arm on the platter without a record present due to a circuit malfunction:

Now it was time to calibrate the tracking weight adjustment mechanism. I usually calibrate it to be accurate in the 1-1.2g range since this is the range most or all B &O cartridges require:

Then I adjusted the motor voltage. This shows the perfect sinusoidals measured for 33 

and 45 RPM:

Then it was time to calibrate the platter RPM with the BeoloverRPM device. First for 33 RPM

and then for 45:

The BeoloverRPM also allows the logging of the RPM for long periods of time to detect random RPM variations. This is the curve I measured for this Beogram after about 24 hrs:

As usual, the RPM was very stable. One of the advantages of the AC motor synchronous motor designs is that, as long as the Wien oscillator works properly, the motor has basically no way to alter its RPM as long as it can handle its load properly.

And then it was finally time to give this deck a first spin! I selected one of my favorite Miles Davis albums, "Star People" from 1983 (Columbia FC 38657). Of course this album had been cleaned ultrasonically before play on a CleanerVinyl ProXL set-up in combination with a UC-3360 multi-frequency cleaner. This restored it to a like-new condition with very low surface noise and almost no clicks and pops. Beolovely!:

I will now play this deck for a couple of weeks to see if there are any intermittent issues. And then it will be time for its return trip to Massachusetts (with one of these awesome newly available reproduction hoods!..;-).