Beogram 4002 (5513): Another Beogram From Houston - Mechanical Work

The restoration work on this Beogram 4002 (Type 5513) begins with the various mechanical restoration tasks.

Those include cleaning out the debris from the cabinet base and some disassembly of the floating chassis components for cleaning and lubricating.

The arm lowering & raising lever is attached to the fixed arm.  The pivot for that lever can occasionally get gunked up so we typically remove it for a clean and lubrication.

The arm lowering damper is also cleaned.  The rubber washer on the end of the plunger gets replaced with a new washer and the metal part of the plunger is lightly lubricated with a silicone lubricant.

The tangential arm spindle parts are removed for cleaning and lubrication.
I don't immediately re-install the spindle however as I find it easier to make a few Service Manual mechanical adjustments with the tangential arm assembly free to slide back and forth.

Before making any Service Manual mechanical adjustments I like to move the four set screws that sit underneath the two metal rails the tangential arm assembly rides on.

These set screws are for adjusting the height of the rails but the slotted end to make the adjustment with sits underneath the floating chassis.  I remove them and re-insert them from the top.  This allows any change in their height to be made from the top side of the floating chassis without having to remove the floating chassis from the cabinet.

Here is a photo of one of the re-inserted set screws.

That gives a little peace of mind in case some change in the tangential arm assembly height is necessary.  Normally it shouldn't be but the set screws allow about 3 mm of height adjustment.

Next I reassembly the tangential arm assembly and go through the adjustments to make sure the arms are perpendicular to the back rail, parallel to each other and have the proper distance to the platter.

The Service Manual says the distance between the Fixed arm and Tonearm is 7.7 mm.

The top of the Fixed arm to the top of the platter (metal) surface has to be 23 mm.

After that is set the tops of the two arms (Fixed and Tonearm) should be even.  If they are not, the Tonearm height can be adjusted. 

With a phono cartridge mounted I check that the Tonearm and cartridge vertical alignment (azimuth) is good.

I set the Tonearm lowering limit so the stylus of the cartridge is about 0.5 mm above the lower platter rib.

I calibrated the tracking force of the Tonearm/Cartridge so that it measures 1.0 gram with the tracking force knob set at 1 gram. 

After that calibration I set the tracking force knob to 1.2 grams.

Before installing the Beolover Tracking Sensor Lamp component to the Beogram 4002 Tracking Sensor Assembly, I checked and adjusted the metal aperture so it is 1 mm above the Tracking Sensor.

The Beolover Tracking Sensor Lamp was then installed followed by the Tangential Arm Assembly spindle parts.  The plastic pulley on the spindle was replaced with an aluminum pulley.

When the spindle was installed I lubricated it with a mixture of grease and oil.  Not too thick and not too thin.

The floating chassis components can now be re-installed in the Beogram 4002 cabinet base where the suspension will be adjusted so the top of the platter is even with the cabinet aluminum deck.

Along with that, the platter motor and reservoir capacitor assemblies will be installed.

I'm pleased with the mechanical adjustments so far.  The re-installed floating chassis aligns good with the aluminum deck plate so it is on to the rest of the electronic restoration tasks.

Those include the restoration work on the main PCB, the output (audio muting) PCB, the LED lamps for the speed indicators, the arm detector lamp (in the Fixed arm) and the contact cleaning on the Beogram control panel buttons...Plus all of the related adjustments.

Beogram 4002 (5503): Repair of a Dead H-Bridge and Some Other Updates

Sadly, an AC-motor Beogram 4002 (Type 5503), which I had restored in early 2020 needed to return to my bench. The reason for the visit was that the carriage would not drive towards the platter anymore. This is usually an indication of a dead power transistor in the H-bridge that drives the carriage motor.

Since the completion of this restoration project I had come to realize that this is a frequent issue with this circuit, and I now routinely replace the H-bridge transistors when I restore a Beogram. Unfortunately, in 2020 I had not grasped yet that there was a 'pattern'. So this Beogram unfortunately had to make the trip back to me to give me a chance to replace these transistors:

Of course I also updated all the other problem components that I learned about since 2020. It is definitely a good idea to replace the power transistors of the push-pull stage of the AC platter motor drive. This shows the original npn/pnp complementary TIP31/32 pair:

I replaced them with stronger TIP41/42s:

Ditto for the solenoid transistor: I replaced the original TIP41

with a higher voltage TIP41C:

This 4002 still had a light bulb set-up in the carriage position sensor assembly. This shows the original components:

I replaced the light bulb with a white LED:

It is important to place the LED not too close to the sensor and approximately 6-7mm above the PCB. Otherwise the 'run-off-stop' mechanism may not work anymore.

Like many AC-motor Beograms this one also had a 'troubled' fuse F1. It is directly soldered to the PCB. I extracted it:

I measured its resistance, yielding ~13 Ohms. Way too high. So I replaced it with a new one. I had to solder the wires to it:

This shows it implanted:

Another weak point of the AC motor Beograms is the solenoid lever, which came with a riveted plastic extension for activating the solenoid current limiting switch. In all Beograms of this type that I came across so far, the plastic extension developed stress cracks around the rivet:

It is important to fix this since a missing extension will result in an overheated solenoid. I drilled out the rivet, which liberated the extension. This shows the separated parts, as well as my 3D printed replacement ready for bolting on:

This shows the replacement extension in place:

This shows the repaired arm in action. It properly activates the solenoid switch:

Finally, I also replaced the as usual hardened damper gasket with a new one:

This ensures a consistent arm lowering experience. 

This Beogram is now updated to the latest 'Beolover restoration standard'! I will play it for a bit and then it will return to its owner in California.

Beogram 4000: Repair of a Cracked Solenoid Arm, Replacement of the Damper Gasket and Re-Glueing of a Plinth Corner

After replacing the wiring sleeve of the carriage harness and repair of an intermittent solenoid this Beogram 4000 needed tying up a few more lose ends before it could be sent back to its owner.

I had originally restored this Beogram 4000 in 2020, and back then I was not aware of some of the 'standard issues' that these decks can develop. One item that learned about in the meantime is the damper gasket. They seem to harden and as a result arm lowering can become erratic causing the arm lowering speed to vary due to random air leaks around the gasket.

This shows the original gasket:

And the new replacement installed:

This Beogram 4000 also came with a solenoid lever that has a plastic extension for activating the solenoid switch:

As I learned over the years from AC motor 4002s, where this type of lever is standard, these attachments tend to break off at the rivet that attaches them to the metal part. This one also already had a hairline crack:

Since it can lead to a fried solenoid when this plastic extension breaks completely off I replaced it with a 3D printed part that I developed for this occasion:

Here a shot from the side:

This shows the lever after re-installation in rest position

and in extended position:

It properly activated the solenoid switch.

In 2020 I also had not realized yet that the BC142/143 power transistors often go out of spec over time. This resulted in occasional carriage drive H-bridge failures, which caused some unhappy returns to my bench. Hence, I started replacing these transistors preventatively in my Beogram projects as a standard feature. I still needed to catch up this Beogram in the transistor department. This shows the original H-bridge transistors:

And with new compatible replacements:

I also replaced the rest of the power transistors:

Finally, this Beogram had a plinth corner that came unglued:

I removed the plinth and glued it back together:

Beolovely! This Beogram 4000 is performing very nicely again. Let's hope it will stay away from my bench for longer this time!

 

Beogram 4004 (5526): Restoration of the Arm Lowering Mechanism and Exchange of Tracking Sensor Bulb with a LED Assembly

I started working on the Beogram 4004 (5526) that I recently received. As usual, I rebuilt the arm lowering mechanism and installed a LED assembly to replace the original tracking sensor incandescent light source.

This shows the arm lowering mechanism consisting of solenoid (left) and motion damper (right; to gently lower the arm once the solenoid activates):

I disassembled the setup

and cleaned away all the hardened lubricants. Then I re-lubricated everything and re-assembled the mechanism. The next step was to do the same for the linkage that connects the damper to the tonearm. To get to the pivot point of the linkage, the sensor arm assembly has to be taken out. This shows the arms from the back

and after removing the sensor arm:

After removing the retaining washer and the small spring that presses the linkage towards the sensor arm post (do not loose this spring if you try this at home, it has a tendency to vanish in 'small parts nirvana' and is never seen again...;-). This shows the removed linkage:

I cleaned, re-lubricated and reassembled. Then it was time to adjust the arms to be orthogonal to the carriage and parallel to each other:

This can be a bit tricky and listening to calming music is recommended.

After taking care of the arms, I exchanged the tracking sensor light source, which is originally a small bulb that frequently burns out, disabling the Beogram. Installing a LED ensures longterm stability. This shows the original part in place:

I removed the bulb housing revealing the aperture that controls the tracking feedback by varying the amount of light that hits the light sensor in the lower part of the housing:

This shows the original part and the Beolover replacement side-by-side:

The LED sits exactly in the spot where the filament of the original bulb is located. I installed the part and also replaced the sheet metal screw that holds the aperture in place on the lateral tonearm bearing with a stainless M2x16mm screw and a corresponding nut (this makes it much easier to properly lock the aperture position in place once the tracking feedback has been calibrated):

On to restoring the electronics of the deck.