Beogram 8002 (5633): Full Restoration and Installation of a Beo4 Enabled Commander Remote Control System

This post describes the functional restoration of the Beogram 8002 (Type 5633) that I recently received from a customer in Massachusetts. This unit also received a Beolover Beo4 enabled Commander Remote Control for Beogram 8000 and 8002. A great way to integrate a Beogram 8002 into an existing B&O setup. My initial assessment of this Beogram is posted here. 

Here is an impression of the final result of my efforts:

Let's see what it took to get there:

This shows the Beogram in 'service position', i.e., with all functional parts removed from the enclosure. I usually put everything on my Lazy Susan, which lets me work on it from all sides without having to move the delicate setup:

I started by rebuilding the main PCB. I unplugged it from the wire harnesses:

I removed the microprocessor can and started working on replacing all the electrolytic capacitors.

Here is a detailed shot of the large reservoir capacitors:

The main reservoir capacitor on these boards has a 'historic' 4-pin package, which is no longer manufactured. I replaced it with the Beolover 4-Pin 2200uF Reservoir Capacitor for Beogram 8000 and 8002. This shows it in comparison with the original part:

This shows the rebuilt reservoir capacitor section:

I also resoldered all the board headers. They tend to develop intermittent solder joints due to mechanical and thermal stresses.

There is one important capacitor inside the microcontroller can. It is responsible for decoupling the processor power supply from the motor noise on the power rails. This shows the can with the top lid removed:

Like in maybe a third of all cases, the microcontroller came off together with the lid:

The thermal compound often is strong enough to extract the package from its socket. Usually this is not a problem. Just remove the processor from the lid and stick it back into the socket before replacing the lid. It is actually good if the processor is not in place while working on the setup, so there is less chance that static charges damage the IC.

The capacitor is located under the small piggybacked board. Pulling the board up usually reveals some insulating tape and the capacitor:

Sometimes the insulating tape covers the capacitor, too. In this case it did not.

The interesting aspect of this capacitor is that the negative lead is soldered to the board on both sides, i.e., it acts as a via. In the 1980s, they did not yet have through-plated vias on consumer product-level PCBs, and so they used through-hole component leads as 'convenience vias'. Since one cannot get to the top solder of the negative lead without doing some damage, it is best to unsolder the positive lead first

followed by breaking off the other lead from the capacitor can by rotating it until the wire breaks.

This is how the board looks from the bottom after removing the bottom lid from the can:

It is best to remove the tacked-on shielded wire before removing the capacitor. This shows it after pulling up the insulating tape:

I removed the wire:

After removing the broken-off wire stump, the new capacitor can be soldered in with the negative lead first:

This shows it in place with the processor back in place:

After tacking the wire back on 

and putting the lids back, I installed the assembly on the board:

If you do this at home, make sure that the wire leads of the ribbon cables are properly inserted into the header underneath the board. It is easy to get adjacent wires into the same female header position. If this happens, 'interesting' effects on the turntable operation occur!...;-).

After completing my work on the main PCB, I exchanged the capacitors on the voltage regulator board next to the sub-platter. This shows the original capacitors still in place:

And with the new capacitors in place:

It is a good idea to remove the tacked-on wires before replacing the caps. This prevents potential damage to the wire insulation with the soldering iron.

An important capacitor that usually needs replacement is the phase-shift capacitor in the transformer block. This shows the replacement block that I had in my stash without its lid:

It turned out I had already replaced the original capacitor with the Beolover Motor Capacitor for Beogram 8000 and 8002. The Beolover replacement part uses modern multi-layer ceramic capacitor arrays, which are 'natively' non-polar. A much better solution for use as a phase capacitor! The part fits neatly next to the fuse and contact terminals assembly. The Beolover part can be used for both 50 Hz and 60 Hz versions of the transformer block. Depending on the frequency, the phase capacitor has a different value. Simply solder one of the two wires to the appropriate capacitance terminal and the other to the COM pad. 

Next came the replacement of the output relay. This shows the bottom side of the DIN7 jack output assembly. The relay is concealed by a clamped-on shield:

Pulling off the shield reveals the relay:

I replaced the relay with a new one:

The new one has the same form factor as the original one, so the shield clamps back on without a problem:

As usual, I also installed a (red) switch that allows connecting the signal and system grounds:

Connecting both grounds usually quenches any hum when connecting the Beogram to an amplifier.

The next step was to replace the incandescent light bulb in the <</>> button assembly on the PCB that is clipped to the back of the keypad. This shows the keypad with the PCB still installed:

The light bulb is in the black box mounted to the board. Its replacement requires the removal of the board from the keypad. After lifting up the board with a suitable screwdriver on the right side so

that it can clear the locking plastic feature, it can be slid out to the right.

I usually take this moment as an opportunity to clean

the keys and their recesses in the plastic panel. The keys come off easily after the PCB has been removed:

Make sure the keys are in the right order when reassembling the keypad after cleaning everything.

I usually clean the keys with a moist Mr. Clean eraser pad. Don't use the pad on the LED display cover. It can scratch the plastic! A lens cleaning cloth is perfect for cleaning the LED cover.

The plastic panel is best cleaned with some warm water and dishwashing soap. Never use alcohol on Beogram 8000/8002 components.

After this cleaning excursion, it was time to replace the bulb. This shows the black box with its lid removed:

The bulb is in the center of the assembly. The two whitish components, left and right, are photoresistors. When pressing the << or >> buttons, the amount of light impinging on the resistors changes by means of two apertures that are moved with the buttons. This allows the gradual adjustment of the carriage speed depending on how hard the <</>> buttons are pressed. Nifty!...;-).

This shows the white light 5 mm LED before installation:

The LED needs to be Dremelled a bit to roughen up the surface of its plastic bulb and to reduce its diameter slightly. This ensures the LED fits and that the light is dispersed homogeneously onto the photoresistors. LEDs emit a more directed light pattern compared to incandescent bulbs.

This shows the LED installed:

The light bulb runs on 15 V. Therefore, a suitable current-limiting resistor needs to be connected in series with the LED. I usually solder it on the 15V side: 

If you try this at home, make sure the resistor is approximately in the location shown in the photo above. Otherwise, it is possible that it will interfere with the plastic panel when the board is reinstalled behind the keypad.

My customer wanted a Beolover Commander Remote Control for Beogram 8000 and 8002 installed. Installation requires removal of the angled board header and the grey ribbon cable from the board:

Next, the header and the cable need to be transferred to the Commander PCB:

]

The Commander PCB itself gets soldered to the main PCB:

After replacing the cover of the black box, 

I focused on the carriage assembly. I removed the carriage rods and spindle parts for cleaning. As usual, they were encrusted with old, hardened lubricants:

I put them into my ultrasonic cleaner.

While the cleaning process went on, I replaced the light bulb in the tracking sensor with the Beolover Tracking Sensor LED Light Source for Beogram 8000 and 8002:

The bulb sits in a small compartment under the arms, which is covered with a piece of sheet metal:

The cover can be slid out to the left after it is lifted a bit up with a screwdriver to clear the locking feature:

This reveals the whitish photoresistor on the upper side of the grey tracking aperture and the light bulb below. Both parts are mounted on a small PCB. The exchange of the bulb requires the extraction of the PCB. The PCB is connected to four leads that come in from the bottom of the tracking sensor compartment. This shows the bottom view with the wiring. The wires are held in place with a small rubber ring stuck onto a plastic nipple:

Removal of the rubber ring allows pulling the wires out of their conduit:

This is necessary to give the wiring some slack so that the small PCB can be pulled out a bit to access the solder pads of the bulb.:

This is how the board looks from the component side:

I removed the bulb. This shows it together with the Beolover LED assembly:

This shows the LED assembly soldered to the bulb pads:

The board is in the correct position when the end of its narrow part is flush with the solder side of the PCB. Also, make sure the LED is facing the photoresistor (;-) if you try this at home:

I pushed the board back into place:

Then I stuck the wires back into their conduit and replaced the small rubber ring:

While the carriage is 'up', it is the only moment the vertical arm can be adjusted. The screw can only be accessed when the carriage is liberated from the rods.

But before I could do the adjustment, I had to glue a piece of Kapton sheet to the bottom of the counterweight where the adjustment screw touches:

This prevents the screw from sticking to the counterweight during arm lowering. This can sometimes result in undamped and delayed arm dropping when the screw sticks, while the arm lowering mechanism has already released the arm. After putting the Kapton piece in place, I adjusted the arm vertical parallelism:

Simply turn the screw until the arms are parallel:

In the meantime, the carriage components came back from the ultrasonic cleaner:

I put everything back together. It seems the best way is to first put the longer rod in place together with the plastic 'fork' that connects the white nut on the spindle with the carriage, and then insert the spindle with the nut approximately in the center, as shown here:

Then simply tilt the carriage towards its horizontal position while inserting the other end of the spindle into its ‘bearing’. Once the spindle is in place, the shorter rod can be inserted and locked into its cradles.

At this point, everything was back together, and I adjusted the 'idle voltages' of the <</>> assembly. Both left and right voltages need to be ~620 mV when the buttons are not pressed:

This voltage is adjusted by turning the screws on the black <</>> box on the keypad PCB in or out.

After this adjustment, I set the tracking feedback, and then I used the Beolover Arm Alignment Tool for Beogram 8000 and 8002 to get the arms perfectly perpendicular to the carriage rods:

After this adjustment, I replaced the original carriage motor with a new Carriage Motor for Beogram 8000 and 8002. The Beolover motor runs more quietly with less vibration and also draws less current for the same performance. This shows the original motor together with the Beolover replacement components after opening the clamshell motor enclosure:

Installation is easy: Insert the new motor without the alignment pieces. Then solder the blue wire to the terminal not marked with a dot and the provided piece of blank wire to the one marked with the dot

Then put the alignment pieces into place so the motor is aligned. Then cut the blank wire to an appropriate length and connect it to the brown wire end:

Now the enclosure can be closed again. This shows it from the pulley end with a new carriage belt installed:

Then I adjusted the tracking feedback. This is done by adjusting the aperture position inside the tracking sensor housing. The aperture is moved by a screw on the side of the housing:

The feedback should be adjusted to get about 2-3 platter rotations before the carriage motor starts running after the needle is down.

And finally, it was time to give this functionally restored Beogram 8002 a first spin! I selected a great recent addition to my collection:  'Collaboration', which was released by George Benson and Earl Klugh in 1987. I seem to have the original US release on Warner Bros. Records (925580-1):

The Beogram played perfectly!

I played it in the service position for a couple of weeks until I received a new dust cover fitted with the original black "Beogram 8002" labeled trim. Co-Beolover Beomazed figured out a while ago how to transfer the original labeled hood trim to a new reproduction hood. A much happier solution than using the unlabeled black trims the DKsoundparts store sells. The original labeled trim on a new hood definitely helps give a Beogram that sharp 'like-new' look!...;-). 

After I had received the new hood, I put the Beogram back into its enclosure. When I seated the PCB, I realized where the plastic piece came from that I had found in the box when I received the unit:

It was one of the two 'hooks' that hold the PCB in place on the transformer end. This shows the area where the piece broke off to the right of the rectangular opening:

I decided to try to fix it instead of ignoring it, which might have been possible. But since the transformer end of the board needs to be able to withstand the transformer block being pushed onto the board header, this hook is actually a bit important. I drilled a hole through the broken-off piece

and into the enclosure:

The plan was to use a small 2mm self-tapping screw to reinforce the epoxy glue I would be using:

I added a screw head recess, so I was able to get the screw sufficiently far in to have enough turns into the hole in the enclosure:

This shows the piece back in place with some epoxy added at the fracture:

After the epoxy had hardened, I put the board in:

Like it never happened! Beolovely!

On to another issue: This unit came with one of the leaf spring hooks unhinged due to a missing wire piece. This gave me the idea to design 3D-printed receptacles for the hooks:

It turns out that these are actually a nice improvement over the original setup since they cannot liberate themselves after the wire hook is in place. This makes it much more straightforward to hang the sub-chassis back on the leaf springs.

Now it was time to glue the aluminum plates back into place and install the new hood. First I needed to remove the deteriorated double-sided foam tape they used back then to attach the parts. I usually soak some cut-to-size paper towel strips in isopropyl alcohol and then put them on the tape spots:

The other half of the tape remnants is usually on the aluminum plate, so it is convenient to catch them too by putting the plate in position on top of the paper towel. This also reduces evaporation, so the soak can last a bit longer:

Once the tape remnants were removed, I glued the plate into place with some epoxy. I used carpenter clamps and a mallet to hold things together while the glue hardened:

With the plate back in position, I installed the Beogram back into the enclosure. This unit also had a leaf spring that had been mutilated for whatever reason. Someone felt the need to Dremel the slot for the adjustment screw a bit wider. This shows the damaged piece together with one that I found on ebay:

Then I installed the new hood, and then it was time to attach the aluminum lid back to its hinge. I usually do that with double-sided tape:

The final step was gluing the metal shield back under the small black panel that sits under the arms. I usually also use double sided tape for this task:

This shows the plate reattached:

Then it was time for a test spin of the fully assembled unit:

I selected an old favorite of mine that I had bought in the 1980s: "ein deutsches album" by Peter Gabriel. He released it in 1980 on the Charisma label (6302 035). Here are a couple of impressions of this interesting album playing on the newly restored Beogram:

The Beogram 8002 performed perfectly. So it was time to take a bunch of nice pictures of it in my photo studio to celebrate this successful restoration!

Enjoy:

Beogram 4004 Type 5526 - Restoration Project - SyncDrive and Remote Commander Installation

Continuing on from this project's previous post, I needed to install a Beolover SyncDrive platter motor and a Beo4 Remote Commander.

However, there were still some other follow-up tasks like checking the 21V supply voltage (to make sure it doesn't have any noise), adjusting the TR3 collector voltage with the new R26 trimmer, installing a Beolover platter detector lamp replacement, installing Beolover RPM indicator LEDs and running the platter speed calibration.

Here is the 21V measurement check.  The inset oscilloscope screenshot is zoomed in on the 21 V line so I could check the ripple. The measurement looks very good.

Next, I installed a Beolover platter detector lamp module so I could check (and adjust) the platter detection signal with the 1TR6 trimmer I installed (in an earlier post).
Once the 1TR6 trimmer was properly set, I moved it over to the component side of PCB1.

I changed the speed indicator lamps in the Beogram 4004 RPM indicator panel to Beolover LED modules.

Now I could install the SyncDrive platter motor, run its speed calibration and test the platter detection functionality of this Beogram 4004.

SyncDrive speed calibration...

At this point I was able to calibrate the Beogram 4004 record tracking.

I removed the platter belt for this calibration procedure so I could rotate the platter by hand and check the Beogram 4004 servo motor performance when advancing the tonearm.

While this procedure is usually a repetitive adjustment and measure series of steps, I was pleasantly surprised that I was able to lock in the correct setting only using the coarse screw adjustment shown in the picture above.

Usually I get the setting close using the coarse adjustment, then dial in the final setting with the Beogram 4004 eccentric screw adjustment and/or the Beolover tracking lamp trimmer.

Now for a quick check of the platter detection signal and the position sensor run-out groove detection.

The empty platter detector signal looks good.

Previously I had adjusted the position sensor to output 5V when the clear part of the position scale was in front of the detector.  Note that when the blacked out part of the scale is blocking the sensor, the voltage is around 10 V.  Those can be checked and adjusted (using PCB1 trimmer 1R88) without the platter motor if desired.

The last section of the position scale has a series of narrow black bars.  This is so the position sensor will generate a series of pulses that the detection circuit on PCB1 can interpret as the run-out groove of a record. Each run-out pulse adds to the voltage level that capacitor 1C33 charges up to in the detection circuit until the detection threshold is reached. At that point, the run-out detection circuit initiates a stop and return to end the record play.

This picture shows the position scale bars entering the position sensor area. The inset oscilloscope screenshot shows what the run-out sensor signal looks like when the tonearm is moving through the run-out groove.  In this case the run-out detection circuit triggered on the third pulse.
Note: My measurement point here was at the node for 1D41, 1D42, 1C33 and 1R82 on PCB1.

Last, but not least, was to install the Remote Commander...but first, I still had to clean the old oxidation off the Beogram 4004 control panel button contacts.  I applied some Deoxit fluid on the cleaned contacts.

While checking the button panel I discovered that one of the buttons was badly damaged and would not work.  I replaced the plastic button with a spare.

With the button panel restored and tested, I install the Beolover Remote Commander.
This version of the Remote Commander is designed to operate using a Bang & Olufsen Beo4 remote control.

Also...note that the Remote Commander installation is using the Beogram 4004 options.

Using the Beolover Remote Commander with a Bang & Olufsen Beo4 remote control can be a little bit tricky.  That is because the Beo4 remote control is configurable and may not be ready to work with controlling a Beogram right out of the box.

This was the case I ran into with this Beo4.  It did not have the Phono option in its list of supported components.  Adding that to the Beo4 menu list is not difficult but it wasn't intuitively obvious.
Beolover describes the setup in this video.

This Beo4 had one additional wrinkle however.  It did not have a Phono named function in its memory to add to the list of components.  It did have "N. Radio" which, it turns out, is another function name that works as a phono selection.

My next step will be to reassemble the rest of this Beogram 4004 and do some record play testing.

Beogram 4002: Restoration of DC Platter Motor

I recently received a Beogram 4002 DC platter motor from a customer in France for restoration. His Beogram had the usual randomly occurring RPM variations. Something that will most likely be fixed by re-infusing the dry motor shaft bearings with oil under vacuum. Most of these motors have bearings that lost all of their stored oil, and this causes the shaft friction to increase significantly.

This shows the motor as received:

I disassembled it to extract the shaft bearings:

The bearings are the two small donuts upfront on the black pad. I submerged them in synthetic oil and pulled a vacuum. Immediately, strong bubbling started around the bearings:

The bubbling indicates that air is being drawn from the pores of the Oilite-bearing material. The leaving air is successively supplanted by oil in a diffusion process. The process has completed when the bubbling stops. In this case, this happened after about two days. At that point, I extracted the bearings from the vacuum chamber:

Then I reassembled the motor with a new Beolover DC Platter Motor Pulley for Beogram 4002 and 4004 and installed it in my bench Beogram 4002 for testing with the BeoloverRPM device:

The BeoloverRPM is able to log the RPM in 10s intervals into a serial port of a computer over long periods of time. This allows precise detection of intermittent RPM deviations that otherwise would be difficult to detect. This is the graph I measured after about 24 hrs:

This flat curve is 'as good as it gets' with Beogram DC platter motors! This motor is ready for duty again! It is time to send this motor home to France for another tour of duty in its Beogram 4002!

 

Characterization of a MMC 6000 Cartridge Restored by Tonabnehmerservice.de in Comparison to Two Good Sounding Original Cartridges

I recently sold a fully restored Beogram 4002 (Type 5503 with AC platter motor) to a customer in California. The customer also wanted a newly rebuilt cartridge. He settled on getting a restored MMC 6000 from tonabnehmerservice.de. Franz Josef at tonabnehmerservice has provided a number of cartridges to some of my customers over the years, and they all seem pretty happy with his work. This particular cartridge is one of his top-of-the-line restorations with a beryllium cantilever and a nude Shibata diamond. 

In this case, my customer asked Franz Josef to send me the cartridge directly so I could check it out before sending it along with the restored Beogram. I received the cartridge last week. It arrived in a little box fitted with a proper plexiglass protector:

I carefully extracted it:

Looks very nice! This shows the beauty playing on the restored Beogram:

The test setup for cartridge characterization is simple. All I had to do was plug the Beogram DIN5 output plug into proper adapters to interface it with the BNC inputs of my new QuantAsylum QA403 audio analyzer. All measurements were done at 1.2g tracking weight (calibrated with a digital gauge).

A few years back I wrote a couple blog posts about this type of measurement. This one discusses the frequency response measurement and this one the 'trackability' measurement.

Let's focus on the frequency response first:

There are several ways to do it. In the old days, they used test tracks that actually played a frequency ramp from 20 to 20000 Hz. The cartridge was hooked up to an AC voltmeter, and a voltage vs. time plotter recorded the signal as the test track played. Add a proper scale to the time axis that translates the time it took to play the track into the proper frequency scale, and the frequency response becomes visible. 

These days we can play a noise track and use an audio analyzer to record a Fast Fourier Transform Spectrum (FFT). A FFT spectrum shows the volume of all individual frequency components of the measured audio signal on a frequency axis. A clean 1kHz test tone would, for example, show up as an isolated peak at 1kHz. A noise signal would look more like a line parallel to the frequency axis since noise is a composition of many frequencies.

I used Tracks 2 and 3 on Side 2 of the Analogue Productions "Ultimate Analogue Test LP" as noise tracks and played them directly into the QA403 analyzer. 

Tracks 2 and 3 are "Pink Noise" tracks: Unlike white noise, pink noise distributes its energy equally per octave rather than per individual frequency. Because of this, its Fourier transform (FFT) is not ideally a horizontal line along the frequency axis, but rather a downward-sloping line that drops at exactly -3 dB per octave (which translates to a -10 dB drop per decade). In plain English: pink noise emphasizes the lower frequencies and gradually reduces the volume towards the higher frequencies contained in the noise. White noise features all frequencies at the same level, i.e., would be a parallel line to the frequency axis.

Now let’s go from the theoretical construct of pink noise to its real embodiment on a test record. Records are usually cut with RIAA pre-emphasis, which superimposes an upward tilt of roughly +6 dB per octave (or about +20 dB per decade) to the signal. If you go to the link, you will see that the RIAA curve is not a line, but has some wiggles in it. That is a consequence of the fact that in real life electronic filters are used to produce the pre-emphasis. But for simplicity's sake, let's assume a +20dB/decade line.

Therefore, if a pink noise test track is played back from a record without using RIAA de-emphasis, it has the RIAA pre-emphasis superimposed on the original pink noise signal. In practical terms, this means that the -10 dB drop of the pink noise signal is overcompensated by the ~ +20 dB RIAA signal increase per decade. This results in a measured FFT spectrum that should roughly slope upward at about +10 dB/decade.

At this point we did not consider the influence of the electromechanical characteristics of the cutting and playback processes on the signal. The good news is that in a first-order approximation we do not have to! To understand why, consider the ‘constant velocity characteristic’ of the cutting and reproduction processes by the cutting machine and the cartridge. Both have cantilevers that end in iron pieces inside coils. On the cutting side, signal voltage changes fed into the coils translate into cantilever movements cutting the groove, while the cartridge does the exact opposite: It translates the 'wiggles’ in the groove back into a voltage signal at the coil leads. So in a first-order approximation, we can say that the influences on the signal by the cutting machine and the cartridge basically cancel out! Therefore, for understanding and discussing the measured FFT curves on the test track, we only need to consider the pink noise characteristic and the RIAA pre-emphasis (since we plug the cartridge signal directly into the QA403 without RIAA de-emphasis).

Let's have a look at what I measured:

This graph shows the frequency response of the restored MMC6000 cartridge measured on Track 2 (lateral pink noise):

I tried to 'graphically evaluate' the slope of the spectra and found maybe +9dB between 100 Hz and 10000 Hz, less than the above estimate of +10 dB per decade. This result probably has a bit of an error bar on it due to the superimposed 'RIAA pre-emphasis wiggle'. I think this probably means that the pink noise tracks do not precisely follow the theoretical -10 dB/decade energy distribution across the bandwidth. This is supported by the fact that I see the same slopes for the other cartridges I measured.

Nice is that both channels match very well. The two peaks at the bottom end of the spectrum at 60 Hz and 120 Hz are interference from the power grid. Not surprising considering the very small signals coming from the cartridge. The sharp drop-off after 20,000 Hz is probably caused by the pink noise signal itself. It probably only contains frequencies up to 20,000 Hz. Sadly, there is no detailed information about the Analogue test record available, and my emails have not been answered so far. I guess analog audio is only analog if there is a bit of woodoo in the signal path!...;-)

The next measurement I did with this cartridge was on Track 3 (horizontal pink noise):

This spectrum looks pretty similar, but there is an approximately 5 dB difference between the channels between 15,000 and 20,000 Hz. This difference means that the left channel will reproduce very high frequencies at a slightly lower volume. In the bigger scheme of things, 5 dB is not a very big difference. I certainly did not notice it when I listened to records with this cartridge. 

This is not surprising for several reasons. The most important one is probably that the 62-year-old Beolover likely has a significant roll-off at around 15,000 Hz and does not hear much of the frequencies under consideration here in the first place.

Furthermore, music has only very little information in this frequency range; only the sizzle of cymbals and similar noises are there. We also need to realize that the vertical signal contains the stereo localization (L-R), while the lateral (horizontal) signal contains the mono information (L+R). So a bit of difference in the vertical signal only affects the localization of instruments on the sound stage. Since the human brain does the locating mainly with mid-range frequencies, a small difference at high frequencies is not very significant for this process.

On to the next cartridge: A Beogram 4002 (5523) that I recently restored for a customer in Louisiana came with its original MMC4000 cartridge. I played it a bit with the restored unit, and I thought it still sounded very good. Here is Track 2 played by this cartridge:

and Track 3:

Very similar spectra compared to the MMC 6000. Left and right are in good agreement in both directions.

Next, I measured my favorite MMC20 EN that I use for daily listening in my workshop. These are the measurements:

First Track 2:

and Track 3:

These curves also look very similar to the previous curves, but here both directions have a small difference between the channels. Here, the left channel is a tad stronger than the left in both directions.

In my opinion, this cartridge also sounds very good.

On to the trackability measurements:

I use a Clearaudio "Trackability Test Record". This record has tracks of a 333 Hz test tone at different volumes. They give the 'volume' directly as lateral deflection, i.e. the physical dimension of the 'wiggles' superimposed on the groove. The tracks start at 50 um lateral (i.e. mono) deflection, and then they go to 100 um in 10 um steps. To put this into perspective: Loud dance music tracks have maximum amplitudes around 70 um. So if a cartridge can track 70-80 um without too much distortion, it is pretty good and can play most music ever pressed on vinyl.

So I played all the tracks with each of the three cartridges and noted the total harmonic distortion (THD). THD is essentially the ratio between the fundamental peak and its harmonics. As an example, these L/R spectra were measured on the MMC6000 playing the 50 um track:   

You can see that the THD estimated from the ratio of the second harmonic to the fundamental peak is less than 3%. After measuring six sets of spectra like the above for the three cartridges for each of the test tracks, I ended up with this plot of THD vs. amplitude:

All three cartridges track fairly well up to 70 um. At larger amplitudes, the original cartridges begin to distort fairly strongly. The restored MMC 6000, on the other hand, is considerably better. It has the lowest distortion across the entire range and could even reproduce 100 um signals with tolerable distortion.

So the conclusion of these measurements is maybe that 'good-sounding' original cartridges are still good enough for everyday listening, but that for audiophile listening experiences a restored cartridge should be procured. My money is on tonabnehmer.de. I think Franz Josef does a very solid job, and you can send him your original cartridges for restoration without hesitation!