Broken oscillator?

[mtwallet]

well, I got a problem with my Philicorda GM752
and I'd like to know the SYMPTOMS of a BROKEN OSCILLATOR

I still hear a beep in B when I play the B's (the 4 ones)
but they're all at the same octave, very high
so I wonder if the oscillator is really broken or not

my question is: if an oscillator is broken, do you hear SOMETHING or NOTHING?

[karl]

Hello mtwallet,
If all of the B notes are sounding the same, I suspect you have a problem with the divide down circuit. Electronic organs usually have 12 master oscillators which generates the highest tone or "top octave" of the keyboard. These notes are divided down
to provide each aditional octave of notes. I would look carefully at all wiring inside the unit and look for any loose wires or parts.
A great many problems can be fixed with a soldering iron. Over time vibration can work components loose, causing all sorts of problems. Also look at any electrolytic capacitors ( looks like little
cans) . These guys dry out and fail.

Good Luck, and let me know if I can help further.
Karl

[mtwallet]

thanks for your help, man!
well, yes, I don't think the oscillator is broken because all the B's sound as the highest one (3951hz)
so I think the divider are dead or something
here's the cards
hiddenpage.free.fr/B1.jpg
hiddenpage.free.fr/B2.jpg
do you think the dividers are the little yellow things?
thanks!

[Time Lord]

One thing that you can try. If you can open it up and have it turned on without electrocuting yourself. Just curious, what is your mains voltage in France?

turn it on and turn the volume down. Get a plastic, pointy thing or a pencil and tap the components, poke the board around the B note circuitry. If the other notes start working or if you hear a POP, you have some bad solder connections. You may just need to re-flow the solder around the components.

There could also be a break in one of the traces between components. Very hard to see sometimes, but the poking method usually
will help you find it.
Do you have a schematic drawing to show us? That would be helpful.

[mtwallet]

thanks

the schematics are here
egrefin.free.fr/images/Philicorda/PhilicordaGM751.pdf

actually, the organ is always "on"
and I touched the yellow things, and they do a little beep, just like all the other ones, so I think they work...

I'm trying all the connections with a iron wire but it seems I can't find where the problem is...

I can tune the highest B too (even though the little stuff into the oscillator is going to dust, like a pencil!!!), so the oscillator's not dead

[igor]

Hi mtwallet.
1.The scheme mismatches.
2. If division does not occur, probably, that the chain of dividers has breakage of circuit GND, or circuit VCC.
It is necessary to check up these lines.
Igor.

[karl]

Hello mtwallet,

Okay , The yellow guys are really accurate capacitors used to hold the tuning stable. The coils are the taller guys at the end of the circuit board. These are used to adjust the tuning. The rest of the circuits are the divide downs. A divider usually consists of
two transistors " the little three legged black things" some capacitors. " the little two legged brown guys" and resistors
" the guys with the strips on them" BTW This circuit is called a flip flop. Each one of these guys divide the frequency in half.

I notice on the back side of the circuit board what looks like contamination or something. ( lower edge of board near the yellow wire) Turn the unit off and get some alcohol and an old toothbrush and clean the back side of the circuit board real good. Let it dry and follow Rods' excellent advice. Cleaning the circuit board may reveal a loose component or loose trace. The good news is you can still find most of the parts I see. "Maybe not the coils" . If the divide downs where integrated circuits you would have a hard time finding replacements.

Keep me posted,
Karl

[mtwallet]

thanks to all for your knowledge
I'm gonna buy myself a multimeter within the week
so maybe I know where to locate the problem

I too had a problem with the reverb unit which didn't work
I removed it, then replaced it, and it works : but I don't know why!

so now, the only problem is those d**n B's... argh!

[mtwallet]

here's the information I managed to get today

[karl]

Hi mt,

Good troubleshooting. Before replacing any parts try re flowing the solder around the area you indicate (with power disconnected of course). See if this changes anything.

Karl

[mtwallet]

I finally changed the transistor (the one down with the purple point)
and it works now!
I mean this problem is fixed

the reverb unit is still working from time to time, but that's not my priority

thanks y'all

[mtwallet]

has anybody here already change an oscillator?
on my elka panther, the LA# card don't work
it's been borken under the oscillator
all the components are good except the oscillator ; it don't always work
so I tried remove it but the very small wires got broke

I ordered another LA# oscillator from a Farfisa Compact (I think it's the same frequency), and when I removed it from the card, i broke one those d*mn wire again

are they definitely dead or can I fix them?

here's the pic of the original oscillator (the plastic part got burned)
hiddenpage.free.fr/osc.jpg
there's one more wire connected left, 2 are broken "very short", and another one is long but without the little thing on the right (is it essential or can I link it directly on the card?)

here's the pic of the other one, the one from the farfisa
hiddenpage.free.fr/osc2.jpg
there's 3 wires still connected ; and the 4th one is broken "short"
(the 3rd from the left on the pic)