Repairing a non-sounding note

Again a problem with the 'lower manual sustains'. This time it is not a hanging note, but a non-sounding note. Keynr. 37 of the lower manual, an 'F' does not sound when the 'lower manual sustains' are on.

When the string ensemble is switched on, the F works fine.

Measuring with a voltmeter I discovered a diode was not working. You can recognise the diode on the picture by it's transparant body, and the green and yellow striped colour code.

Searching the internet I found out it is a 1N54 germanium diode.

Normally a diode is made out of silicon. A silicon diode has a foward voltage drop of 0,7 V. A germanium diode however has a voltage drop of about 0,3 V.

I contacted Huib de Bruijn in the Netherlands http://www.esbdebruijn.nl/ to ask if he still had them in stock. Huib informed me that germanium diodes are antique and hard to come by. He advised me to use the PN-junction of a germanium transistor. Still I decided to first search for a germanium diode.

On the internet I found the specifications of the 1N54 :

Peak reverse voltage : 35 V
Mean forward current : 40 mA

On ebay I found a very similar germanium diode, the OA90 :

Peak reverse voltage : 30 V
Mean forward current : 30 mA

Because I measured the diode only conducts a current of 0,04 mA, the OA90 should be an alternative.

Replacing the defect 1N54 with an OA90 turned out fine. The F is working again.

Because a germanium diode is very sensitive to heat, it can be damaged when you solder it to a print. I used crocodile clamps on both sides of the diode as heat sinks while soldering.

Just in case you are wondering. A friend of me also with an eminent unique 310, replaced a defect germanium diode with a silicon diode. The result was that the corresponding note was sounding less loud, due to the higher voltage drop.