Farfisa Mini Compact Version 1

[theseacowexists]

Just picked up a Farfisa Mini Compact version 1 (no bass keys) from a crumbling house out in the sticks. It was dirty and grimy as all heck, but it powers up, all the tabs work (except the strings tab, part of the tab is broken inside), knee lever works, somewhat weak vibrato, and some divider issues on D# F# and G. Ordered new caps for the offending divider circuits and electrolytics for the entire organ, cuz why not? Started with the 500uf cap in the power supply followed by the 1000uf cap on the preamp board, stopped and turned the organ on to check my progress only to be greeted by nothing but a loud hiss. No sound from the keys and no changes when switching tabs. Pilot light still lights, getting 8V at the preamp board. The hiss is affected by the volume control on the power supply chassis, however, it is not affected by the knee lever. When testing for DC voltage, if I put the multimeter probe on the outputs of the generator boards, I get an audio signal from the respective generators. Not a loud one, and it is not affected by any of the tabs or the knee lever.

I'm fairly certain I must have mucked something up on the preamp board. However, I traced all the wires from the pins of the board to their other ends, and there is continuity on each one. Could the bulbs in the knee lever not be getting their 9V anymore? I put back the original caps and all the new symptoms remained the same. Anyone familiar with these symptoms?

The other thing is that the only schematic I can find on the web is for the second version with the bass keys. The preamp board and power supply seem to be a little different on this first version. No swell pedal socket either. Anyone know where to locate the correct schematic?

[Drawbar Dave]

Google combo organ io. I can't paste the link using my iPad. That is the new home of the combo organ yahoo group who are also linked to the combo organ heaven website. They might have what you need in their files section.
Dave

[theseacowexists]

I'm checking in over there. Doesn't appear to be in their files section but I asked anyway. Might pop open the knee lever assembly later today to see if those bulbs are still lighting. Can't think of another place to check anything yet.

[Jaim]

Check the ground between the preamp bd and the PS. If the pilot lights, then the 9vAC should be ok - but check it anyway.

Jim

[Drawbar Dave]

I'm checking in over there. Doesn't appear to be in their files section but I asked anyway. Might pop open the knee lever assembly later today to see if those bulbs are still lighting. Can't think of another place to check anything yet.

I think the swell pedal socket is on the knee lever assembly if I remember correctly. I'm not familiar with the single manual Compacts with built in PSU/amplifier I'm afraid.

[theseacowexists]

The grounds between the PSU and the boards seem to be good. I took out the knee lever assembly and those bulbs are lighting.

[Jyvoipabo]

Good evening,

You will find diagrams of the power supply here.
'FarfisaComboCompactCompleteUserServiceManual.pdf'
Throw it in google and normally it should do.

At the end there are several schematics of Power supply / Preamp / Vibrato and some are folk.
Particularly for voltage values.

I had noted a coupling between the vibrato stage and the Preamp.
I remember that when nothing is plugged in it oscillates.

JP

[theseacowexists]

JP, what do you mean about nothing plugged in?

[theseacowexists]

I think I might have fried the SFT353 transistor when I was replacing the 1000uf cap. I noticed tapping the case is very audible in the signal. Also, it's testing bad. I'll see if I can find one on the 'bay...

[Jyvoipabo]

Hello,

Nothing connected.
This means on the workbench powered by flexible wires.

The SFT 353 is a french Cosem PNP germanium junction transistor intended as AF amplifier.
I believe that the collector is connected to the case.
If it makes noise when you touch it it is normal.
In fact it is only used for the headphone output. You can also remove it.

JP

[theseacowexists]

The other SFT353 tests OK and does not make noise when touched. Anyway, I ordered a pair of them so we'll see what happens. I can trace the signal from the generators to the suspect transistor, the signal stops after that. I don't think this transistor is just for the headphone output - that transistor appears to be mounted to a terminal strip that is located right near the headphone jack. Again, the preamp board in this organ is different than the one in the schematic that seems to be widely available online (the Yahoo forum doesn't seem to have the correct one either).

[theseacowexists]

Replacement SFT353 did the trick, and we are back in business. As far as the vibrato, the other SFT353 on the board had one of it's leads broken. Fixing that brought back the vibrato. Tuned all the generators and got it back in the case and it sounds fantastic! So glad I finally got one of these guys. Thanks for all your advice!

[Drawbar Dave]

Well done!