Devised, researched
 and written
  Peter King Smith BSc

                                                         The mid-1960s, German-built multi-track tape recorder with FM/AM/SW radio

Top-4 Faults

The four biggest faults with these music centers were (still are):

    1. Heat-sensitive components.

    2. Low humidity.

    3. Electrostatic problems.

    4. Trouble with relays.


1. Heat-sensitive components

While repairing Schaub-Lorenz Music Centers, Mike frequently found that the original long copper wires (leads) that had been attached to heat-sensitive components (light-dependent resistors), had been trimmed far too short during initial assembly. This created two problems. The very short copper leads conducted excessive heat, during soldering, to the light-dependent resistor, causing its plastic sheath to soften.


In addition, as the copper wires cooled, air tended to get inside the components through a small gap in the sheath, damaging the components. The result: "The components passed all the quality-control tests in the factory, but failed after a while, either at Henson's or in the customer's home".


2. Low humidity

Low humidity was a "problem of the era", Mike says. The music centers bought and used in Germany fell victim to German cultural traditions. The Germans love to "turn their central heating on full blast during the winter". This had disastrous consequences for the Schaub-Lorenz tape units.

Once the air in German homes became too warm and dry, the tape would trap lots of "air bubbles in the tape" (similar to what happens when you wind and unwind Sellotape). The tape would then "bunch up during fast rewind, causing the tape to collide with a bit of circuitry", damaging (i.e. shredding) the tape.


3. Electrostatic problems

As it turned out, the Germans were not the only ones 'abusing' their music centers with heat. One "real catastrophe" occurred when Mike was called out to repair a music center in a large semi-detached house near Heathrow airport.

The machine, which was running in a hot, dry, ground-floor room of the house, was being used to pipe non-stop music to all the rooms in the house. The room was empty except for a central-heating boiler that was radiating large amounts of heat. This caused electrostatic problems, which in turn resulted in expensive damage to the tape unit.


Mike had to remove the original, damaged tape and wind on a new one onto the tape drum. That procedure was not without its dangers. While rewinding the tape, Mike was able to "draw big sparks off the tape in excess of 100,000 volts", which effectively turned the music center into a Van de Graaff generator. "I learned a lot about static electricity from that experience!", Mike wryly remarked.


It was only when he was on his way out of the building that he unexpectedly came across "a number of underdressed young ladies wandering about", that it suddenly dawned on him that the place was being used as a brothel!


Remedy: Although "there was no answer to the humidity problem", Mike does however, offer some advice. The problem of low-humidity can be avoided by ensuring that the music center is stored in a more humid environment. Tip: Hang an inexpensive humidifier on the radiator. This will create a more appropriate climate for the magnetic tape.


4. Trouble with relays 

(a) Mercury relays


The two mercury-based relays were never reliable, and can cause baffling faults.


Remedy: These relays should be checked during a normal maintenance checkup. If necessary, defective relays should be replaced by suitable modern relays. The repairer will need to modify the circuit so that it matches the chosen relay. However, the circuit is tolerant, and so it will probably adapt to any suitable replacement relay.


(b) Under-chassis relays

Characteristic of these music centers, the under-chassis relays are of good quality and reliable.

Remedy: If one of these relays fails, try cleaning the contacts first before trying to find replacements. In the early days of repairing these relays, Mike would "replace (defective) relays, when necessary, with new ones". Later, however, he simply cleaned the relay contacts and then exchanged the cleaned relays in future repairs, "with no ill effects".


Recommended cleaning procedure:
Remove the relay case.

2. Wipe the contacts clean (use a very fine abrasive).
Tip: tear a small strip of photocopy paper (good, cheap abrasive) and slide it between the contacts, which must be held in a 'closed' position.

3. Reassemble.