Beogram 4004 (5526): Tracking Sensor LED, Non-Working Carriage Switches, Final Adjustments and Test Drive with Eddie Henderson

The restoration of the Beogram 4004 (5526) that is on my bench is coming to an end. This post describes the final tasks of the project. After replacing the sensor arm bulb with an LED, I tested the carriage functionality and it behaved like the end switch and the turn off switch both did not work. It turned out that the wires that connect the switches to the main PCB had broken off from their solder points (white and grey wires):

I reconnected them (the grey wire needed to be extended a bit since it was pretty short after taking some insulation off for re-soldering):

After this repair everything seemed to work in terms of carriage motion.

The owner decided to also let me replace the bulb in the tracking sensor compartment with a LED assembly. I recommended this since this is also an essential light source, whose failure would disable the Beogram.

This shows the original tracking sensor light source in place:

I removed the bulb housing, which reveals the aperture that activates the sensor in the lower half of the assembly:

This shows the original bulb and the LED replacement in comparison:

The LED is in the same location like the filament of the bulb. This shows the LED assembly in place:

The blue trimmer allows fine tuning of the tracking sensor response, which makes it easier to adjust the system to spec. I also replaced the standard often rusty sheet metal screw that secures the aperture assembly in place with a M2 stainless socket head screw and a matching nut. This makes the initial coarse adjustment of the aperture position much easier.

Now it was time to adjust the platter height and the floating chassis horizontality. Then I moved on to the tonearm adjustments. An important item is adjusting the arm lowering limit. It needs to be set in a way that the needle 'misses' the ribs on the platter at the setdown points as an additional safeguard against needle damage should the record detection mechanism ever fail and the arm gets lowered onto the naked platter. This shows the adjustment result:

Then I moved on to the tracking weight. The first step is usually replacing the flimsy retaining clip on the counterweight screw with a M3 nut. This allows tightening the counter weight position down, which preserves the calibration over time and during shipping. This shows the original setup:

And with M3 nut:

Then it was time to calibrate the measured weight with the adjustment scale. I usually do it at 1.2g, since that is the weight at which most B&O cartridges track best. The weight scale on the adjustment wheel is notoriously imprecise, i.e. it is always best to confirm the weight with a digital gauge:

After this I adjusted the tracking feedback:

And then I tried to play a record...and all I got was a very loud hum from the speakers! Unbeolovely, entirely!

Hum usually means a broken connection in the grounding system between amplifier and turntable. It turned out that the shield connection in the DIN plug was disconnected:

Since the original DIN plugs cannot be opened up without destroying them, I needed to install a new plug:

The gold coated pins are a nice improvement in the signal path over the original corroded pins. This quenched the hum and the deck started sounding properly.

So it was time to listen to a nice record and enjoy this lovely 4004! I picked a recent addition to my collection, "Comin' Through" by Eddie Henderson. Of course this vinyl was cleaned with a CleanerVinyl Easy6 before I played it! Henderson recorded this album in 1977, and there are a few great funky tunes on it. My favorite is "Movin' On" on the first side. 

Beolovely! I will play this Beogram 4004 for a few more days and then it will be time for the return trip to its owner!