Repairing the balance slider

The malfunctioning pot, is the second one from the left on the picture.
Looking trough the openings of the pot I already could see there was something wrong. Only one half of the slider had a moving copper contact. At the other side the copper contact had come loose, and was forced and deformed, pushed to the end of the space in the slider.

The pots are mounted with melted plastic to the board.

With a screwdriver I broke the plastic away so I could take out the pot, and I unsoldered the connections.

The pot is closed with small copper rivets. I decided to drill out these rivets in order to open up the pot.

Opening the pot showed me that the pins on the white plastic slider had broke off. These pins should hold the copper contacts. One of the copper moving contacts was deformed but this could be repaired by use of pliers.

No, this blog is not sponsored by Pattex. This is the glue I used to glue pins into the white plastic slider.

I drilled holes on the spot where the pins used to be. In the holes I could stick new pins and glue them in. For the pins I used two stiff wires. Ordinary wire you use in electronic projects.

The new pins now can hold the copper contacts again.

A view of the opened slider. The inside was sticky, so I cleaned the internals with isopropylalcohol. I only cleaned the upper resistance counterfoil, not the graphite counterfoil below. I did not want to take the risk the graphite would solve into the isopropylalcolhol.

Remounting the slider was not easy, and had to be done very carefull. I closed it up with thin copper wire, just in case I ever have to open it up again.

Then I glued the slider back in with Tec 7.

Now the balance slider is working again perfectly without any crackling.

Defect Balance Slider

The next problem I encountered was a defect balance slider.
The symptoms :

• A lot of crackling while moving the slider
• The lower voicing is not working at all, or working intermittent

The slider is a pot 2x50k of the make 'Preh'.

On the website http://www.eminent310.nl/ I found out this is a common problem. Again I contacted Huib De Bruijn of http://www.esbdebruijn.nl/ to ask if he had this type of pot in stock. No luck there.

So there is only one solution, try and repair the pot.

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.

Repairing a hanging note

After cleaning the contacts of the lower manual, the first real problem becomes clear.

The lower C# (keynr. 9 of the lower manual) of the sustain registration group hangs, and sounds always when the 'lower manual sustains' is switched on.

First I suspected a spring of the key contacts always being closed. That prooved not to be the case.

Studying the schematics pointed me towards the divider print. Measuring with a voltmeter and an oscilloscope I narrowed the problem down to three components, a malfunctioning resistance, transistor or capacitor.

Turned out to be the capacitor shown in the picture, marked with the yellow arrow.

Exchanging the capacitor of 33 µF - 40V solved the problem.

Cleaning lower manual key contacts

The key contacts where in very bad condition.

First I cleaned the springs and bus bars with isopropylalcohol and a wadding rod. The wadding rod turned grey, but that did not seem to do the trick.

The springs are gold coloured, the bus bars where silver coloured. Scratching the bus bar with a screw driver turned the colour into gold. So the busbars where oxidized.

Next I also had to scratch the springs.

Finally lowering the print with the contacts a little bit, in respect to the keys helped also.

Cleaning the keys

The keys where very dirty. I washed them in the sink.

Here is what they looked like afterwards.

Dirty keys

Because the keys where very dirty I decided to remove all keys of the keybed, and clean them.

To remove the keys it is necessary to :

Unhook the springs

Unclamp the key from the key articulation

To unhook the springs you can simply use your two we fingers. Start with the first key from the right or the left where the spring is reacheable.

After you unhooked the spring you have to unclamp the key. There is a trick involved. I used a big flat screwdriver. Place it on the white articulation as in the picture. Hit your screwdriver with the back of your wrist, in the direction of the key. The key will come out of the articulation.

Determining the condition

I read the manual while testing the organ.

A lot of the functions seem not to be working :

• Half of the keys do not sound at all
• The volume pedal does not work, the organ sounds only at the loudest level
• A lot of crackling and bad contacts
• Register groups are not working correctly
  

It isn't even possible to get a clear overview of what is working and what is not.
I decided to take it step by step.
Seems to me it is best to start with cleaning the key contacts. It is not possible to determine the register groups are working when the key contacts are bad.

In the service manual are some instructions on how to open up the organ. They seem not to be complete. There are different versions of the eminent 310. The service manual probably had to be universal. I had to search for the proper order, and the right screws on opening it up. On the photograph you can see the fully opened up position.

Moving in

First problem I encountered was moving the Unique 310 into my appartment.
Since I live on the second floor, and no elevator, it was not easy to move the organ in.

I decided to take the four speakers out since they are responsable for a lot of weight, also I removed the top wood lid. I opened up the back, unsoldered the cables to the speakers, unscrewed them, and took them out.
Still, even then the organ weighs very heavy. Together with my wife I decided to take a shot moving it up the stairs.
It was a hell of a job! I hope it never has to come down again.

The Eminent Unique 310

Jarre's oxygene organ

While I am restoring my Eminent Unique 310, it seemed a good idea to share my experiences.