fredag 23 oktober 2009

Opening up

My newly acquired Tubon was in quite good shape, but there were two obvious problems:

1. There was no cable.
2. The keyboard had taken a blow, resulting in a cracked keybed.

Regarding the cable, it will not be a major problem. I have to order the necessary four-pole DIN plug and make myself a new one. Five-pole plugs are easy obtainable anywhere, but four-pole ones aren´t exactly stock at my local radio/tv shop.
Of course, I could replace the four-pin socket, but then it wouldn't be original anymore. Two pins are audio signal output, the other two I believe are shorting to turn the instrument on. Plug in = Tubon on. Plug out = Tubon off.

Anyway, defective or not - it is part of my newly-aquired-gear-ritual to open it up as soon as possible to have a curious peek inside. So here we go...

 Tubon up on the table. Yank the end cap off and remove all fastening screws. The keyboard assembly slide out a bit, but can´t be completley taken out at this stage.

This is because the cables going from the keyboard goes into the head end of the Tubon, and is soldered to a terminal strip in there.

The head end is removed, and the cables to the keyboard are de-soldered. Now both the keyboard and head end can be removed from the tube.

Here we have the main cirquit board with almost all of the electronics. There are a few germanium transistors (2N1302, 2N3703 and BCY31), a few Cs and Rs and a really large coil.

On the keyboard end, we can clearly see the cracked keybed. The rest of the mechanic stuff seem OK. A few bent keyboard contact springs, but most likely these can be straightened out.

This is the back side of the keyboard assembly. We see a bunch of sealed trimmer pots and a somewhat traditional one-buss keyboard of the "J-wire" type.

Here is a close-up of the key contacts. As you may see, a few of the contact pins are bent towards the camera. This will be easy to fix with a gentle hand and a pair of flat-nose pliers.
There is one thing I have never seen before: note the small angled guide-wires that will force the key contacts to move slightly sideways before making contact.

Here are the cables coming from the keyboard assembly. They are routed through the bulkhead, and will terminate in the head end.

More cables below the cirquit board...

Then I removed the fastening screws to the cirquit board, unhooked the contact wires from their actuators, and took the entire cirquit board off.
By now it was late at night and I decided to call it a day, and continue the following evening.
Next, I will remove the keys - I need access to both sides of the keybed to be able to repair the crack, and strengthen the structure.

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