Electronic Hints and Tips for Topsy-3 Organ

by Mr Rose Bunce

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Electronic Hints and Tips for Topsy-3 Organ
1) On the "Full Topsy Register" circuit, there is a wiring fault with IC5a. Pins 1 and 2 on the tremulant circuit are shown connected. If built as shown, the circuit will not work. Pins 1 and 2 should not be connected for correct operation.
John is aware of the error but his updated circuit still has the fault, so anybody with any problems with a non-working tremulant, check this area. Also, check John's web site, some faults, printing errors are listed.

2) On the booster board, you will find a PNP / NPN Darlington pair. Built as shown the circuit could exhibit hand capacity effects.  This is because the base of the PNP is floating above ground. Although unlikley to cause the solenoids to operate, there is the possiblity that the NPN transistor could come on partly and this will cause it to get warm, (or other wierd goings on!!!).
To help the circuit work correctly just add a 10K (10 Kilo-ohm) "pull up" resistor from the base of the PNP transistor (T1) and the +12 volt line. This holds the PNP OFF, till the decoder board pulls the Base low, switching on the PNP transistor, which then switches on the NPN.
The 10K resistor just helps the circuit work correctly. Higher values could be used but as differing combinations of transistors could be used, just stick to 10K and avoid problems.

3) For those not fully conversant with electronics, building the circuits, let alone buying the correct components, could find it all rather daunting. If you are unsure how to proceed and need help, then help is only a short distance away.  Most towns and cities have Ham radio clubs. If you find out where your nearest one is and pay them a visit, or phone the secretary of the club, you are sure to find some-one willing to help.  Failing that, approach a local ham radio operator. If like me they are a full license holder, then they will be qualified to give you a hand with the electronics. All you need to do is ask. If they cannot help, they should be able to direct you to some-one who can.

4) And if that fails, then ask other organ builders!  But if you decide to do it yourself then take time to build in stages.  Use sockets for the CMOS chips. Use vero board for the constuction, and remember to double check before cutting a track or fitting a component.

Best order is this:-

A- Draw it out with pencil and paper on lined paper. (this bit is very important)

B- Fit sockets.

C- Cut tracks. (with sockets in place, and a drawing, you can see where to cut).

D- Fit wire links.

E- Fit resistors, capacitors, diodes and transistors. (Check to make sure they ARE correctly fitted before soldering).

F- Check very carefully and fit ICs, taking care to fit the right way round!  (The black boxes with multiple legs).

G- Now double check and test. If something is not working, switch off and look for faults. Blobs of solder shorting the tracks are most likely.

As someone who did Electronics as part of my work, and my hobbies, this is how I learnt to build these sort of circuits. It is also how I used to design and build prototype circuits professionally. If at all unsure, then either seek help or stick with the Relay circuit. Although very simple, it will work as well as the more complicated electronics.

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