16 July 2008

Formant (Part 3)

After the first initial study of the Elektor Formant setup I bought. I decided to completely rewire it. In the picture on the left you see the backside of the Formant completely stripped now. The main reason for doing this is that I didn't like the kind of wire that was used in some places (flat cable) and inconsistent use of colors of the wires. I hate that. Especially because two power buses run through each other One being +15 and -15 Volts and the other being +5 Volts. You don't want to mix them up by accident. For the audio signals coax cable was used. I think that was a wise choice, but I will renew that as well because I want to change the functionality of the modular. Make it less prepatched. I looked more like a semi-modular now.

In the picture on the right you see what came out. It is not even that much wiring, but it did take me about an hour to neatly remove it without doing damage to the card edge connectors on the back of the modules. The coming week I'll pick up some roles of new wire in different colors. I will need that anyway for my ASM-2 and Yusynth projects. I want to use the same colors there so I won't make mistakes easily. Better safe than sorry I guess. I'll also have to pick up some mini jack chassis parts to add some extra patch points on the front panels.

The next thing I did is take the power supply out for closer inspection. I noticed immediately that one of the fuses was blown and after measuring the other two I found that both the +15 and -15 Volt fuses were broken. They are the 2 Amp slow type. I didn't have them in stock so I'll have to pick them up as well and see what happens when I put in new ones. I'll get some extra ones because I don't know what made them break. Could be a short circuit in the wiring, or a broken module or the power supply itself. This is another reason why I wanted to take out the wiring. I will use the short circuit protected lab power supply I bought recently to test the modules one by one.

I also had a look at the bottom of the power supply PCB. Not the best soldering I have ever seen but it looked quite OK for such an old project. I did resolder some joints that looked a bit weird. I also removed the wires that were still attached to it. I was amazed that multiple power take off points are available on the PCB that were not used at all. I think it is better to bring the power to the seperate places from a star topology than to make one long bus that the original builder of this project did.

The Power components I found on the heat sink that was loose in the cabinet belong to the power supply. That is the three 2N3055's power transistors that are on there. There is also one 2N5558 on there. I have no idea yet what that one is for. On the PCB there are clear points were to hook up the 2N3055 neatly marked with E, B, C for Emitter, Base and Collector. The power transistors seem to be in order at first sight, but I did measure them yet.

On the bottom of the heat sink the Emitter and Base are also neatly marked with a pencil. And the base is unmarked but there are extra nuts attached to the neatly insulated housing so I know where they should go. I also took the transformer out of the Formant case. I can rebuild the power circuit now and test it separately. Always an exciting job because you never know if something is going to blow in a power supply with 2 broken fuses. Well I'll update you on that soon.


Bruce said...

That looks very much like the formant I obtained recently. I also rewired the harness, and had a few repairs to make - but it's been a fun and very worthwhile project.
Here are some pics and descriptions of mine...
It's a neat synth - good luck on the restoration

Synth.nl said...

Cool :) Thanks for the link.