[sdiy] warning / nightmarish Farfisa problem

[ASSI]

On Montag, 5. Februar 2007 16:41, Antti Pitkämäki wrote:
> Some time ago, maybe a year or most likely more, I tuned my Farfisa
> Professional combo organ. Then I used this substance meant to lock
> screws for locking the adjustement screws of the tuning coils (I
> didn't know I could have simply used candle wax).

The gluing wax we used for the tuning coils of our FM radios definitely 
wasn't candle wax.  The stuff was softer and got really sticky when 
warmed between the fingers; I think it was bees wax based.  It didn't 
leave any oily traces on the fingers like candle wax is prone to.  The 
stuff you can buy for glueing candles to dinnerware should also work, 
it is just far softer and more sticky.  Perhaps mixing that with bees 
wax gives the right texture, I don't know - I still have some gluing 
wax somewhere...

> I had bought the 
> substance from a car parts shop. I said that I wanted the softest
> locking substance possible. Unfortunately as soft as possible also
> seemed to mean as liquid as possible.

Locking means an entirely different thing to a mechanic than to an 
electronic engineer...  The Loctite stuff is meant to replace lock 
washers and snap rings and some formulations (not the ones you can buy 
in your hardware store) are indeed impossible to unlock unless you 
destroy the screw coupling.

> However, I guess it's worth asking, does anybody know of any
> substance that I could use to "unlock" the adjustement screws of my
> Farfisa Professional?

You can try and drill out the ferrite screws (with very high speed tool 
to avoid turing the ferrite and therby breaking the bobbin), but I 
don't think you should attempt to re-thread the coil bobbin.  Just use 
a smaller ferrite core that snugly fits into the bore and fasten that 
with the proper locking wax (not candle wax).  Tuning will be a bit 
iffy, but nothing a hairdryer and a bit of patience can't fix.

> Red:  Apply heat to remove
> Green:   Apply heat to remove

Loctite 222 withstands continous temperatures up to 150°C, I don't think 
the coil bobbin likes any higher than that.  BTW, straight out of the 
datasheet: "This product is not normally recommended for use on 
plastics (particularly thermoplastic materials where stress cracking of
the plastic could result). Users are recommended to confirm 
compatibility of the product with such substrates."


Achim.
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