The four biggest faults with these music centers were (still
1. Heat-sensitive components.
2. Low humidity.
3. Electrostatic problems.
4. Trouble with relays.
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
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".
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
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
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
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
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.
Trouble with relays
(a) Mercury relays
The two mercury-based relays
were never reliable, and can cause baffling faults.
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.
Characteristic of these music centers, the under-chassis relays are of good quality and
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".
1. 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.