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Old 26th October 2010, 11:22 PM   #1
skeksi is offline skeksi  Ireland
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Default Faulty electric organ/synth

HI
I am new to the forum and more or less new to audio electronics bar circuit
bending a couple of things.
Yesterday a i bought a old Logan electric organ/synth
It turns out it is not fully working and they guy who sold it to me aint answering the phone so i'm gonna try fix it.Certain keys don't work with some sounds
the arp doesn't work or the chord section,there is a serious hum from the speakers.Volume pedal is dusty and fuzzy ah there is a couple of other things wrong too. anyway...

I opened it up and it is solid state a row of 12 boards marked for each note in the scale and one marked preamp.
there is alot of other stuff but it is hard to get in at.
I know nothing here so any suggestions would be great.
all i have is a soldering iron. gonna buy a multi meter later.

thanx
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Old 27th October 2010, 02:12 AM   #2
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Default logan organ

I checked organforum.com, there are several types of logan organs mentioned but they have various model numbers. T-249 Pro, Weekend 400, Caravelle. Do try to find a sticker or something on it that describes what it is.
If some keys are working and others not, and the same note names are involved up and down the keyboard,(different octaves of the same note name) maybe the contacts to the note generator board of that name note are bad. Buy a can of contact cleaner, and a fan. Contact cleaners since the ozone scare are basically gasoline in a spray can, so use only in a well ventilated area, no electric switches on or off while you are using it, no smoking or gas burners or water heaters or furnace pilots nearby. With the power off, remove any PCB's gently, spray off the contacts, and reinsert gently.
If random keys are not working, either the key harness plug is dirty (if there is one) or the key contacts themselves are dirty. In that case you would have to find some way to access the key contacts, either by removing the keys with a screw or some other method, to spray them off. Playing dirty keys can also cause the contacts to clean off some just from motion and rubbing.
Best of luck. More help may be available if you know what model it is.
Volume pedal could be dirt again. These are often controlled with a photocell and lightbulb or source, so spiderwebs dust etc. can affect volume. Remove cardboard cover and spray off, or wipe out.
Hum could be overage electrolytic capacitors, depending on the age of the organ. Quality electrolytic capacitors start to dry out and go low capacitance in 20 years. Cheap electrolytic capacitors are bad weeks after the factory ships them. All depends on what quality the vendor installed. More on this subject when you get the notes working. Don't touch anything metal after the power has been on without reading the electrical safety thread for new repair persons at the top of the tube forum. (Tubes are more dangerous than lower voltage transistor circuits, but the principles also apply to transistor circuits which can cause bad burns if they don't quite stop your heart like a tube circuit can. Anything over 24 VDC can be dangerous). Reading with a meter to make sure any metal you touch is below 24 VDC is part of the safety drill, so buy your meter. Also some aligator clip leads to clip the negative to ground or minus. R**** S**** still sold clip leads the last time I was in there, but I don't like their meter accuracy program. If you update your profile to show your country and possibly state, district, or county, someone living there can help you find useful vendors in your area.
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Last edited by indianajo; 27th October 2010 at 02:26 AM.
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Old 27th October 2010, 08:43 AM   #3
skeksi is offline skeksi  Ireland
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Location: Dublin , Ireland
indianajo
Thanx so much for that info.It is perfect to get started with.
It is a Caravelle by the way.I will try get these keys going and post more.
Thanx again :]
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