ALPS RK 27 motorized reinforcement volume Lite

Dear Friends,
I kindly need a little help: I have Lite G-05 similar to MV02-04-06, and I have to pilot 3 ALPS RK 27 in parallel. I've tried many ways but the circuit board is able to pilot perfectly well only two potmeters at the same time, outputting 4,5 volt approximately as foreseen. If I put a third motor in parallel to the other two, the voltage fall to 800mv approximately. I have tried to wire them in series or putting limiting resistors (10ohm) on each one, but it doesn't help.

The circuit seems simple but it works with two polarities, and also I have no experience with the outputs of a microprocessor... what will you reccomend to modify to increase the piloting strenght?
Thanks a lot! Gianmaria.

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Nifty ckt
Motors must be parallel
How about duplicating the control circuit for the 3rd pot? Maybe try first to double C5,C6 to 22uF
300mA per motor using bc560c? Max Icurrent is what? Try a higher current Darlington mpsa? Or a high current >1A zetex/diodes inc low Vce saturation transistor for the job
 
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Neurochrome.com
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BC550 and BC560 are rated for 100 mA, max. Install BC327 and BC337 instead. They can handle 800 mA. BC327 is the PNP so put those in for the BC560.

You could also build a little circuit board for each of the pots. The board would have the drive circuitry on it and take input from the uC. Then you could use BC550/560 (or BC546/556). BC550/560 are low-noise (for the time) transistors. BC546/556 are the more generic types.

Tom
 
Hi and Thanks to everybody for your prompt advice, I replaced BJT with BC327-40 e 337-40 and it works! The three pots now go together but, unfortunately they do not rotate at the exact same speed and even differently between rotate up and rotate down..
At the end I was looking for a cheap solution of a good 10k log analog potmeter with 10 (ten) ways....