8mm Forum: speed adjusting on Sankyo 502

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Posted by Ugo Bo (Member # 1505) on March 14, 2009, 03:30 PM:

Hello to everybody. I'm new on this forum, though I've been looking here for quite a long time and I found some for very useful tips.

Now It's the first time I write and I'm already here to ask for a suggestion about an easy way to adjust speed on my "new" Sankyo Sound 502.

As many of you know this machine is capable of being speed adjusted by means of the two small pots placed on the electronic board.

Unfortunately these pots are very difficult to access: or you remove the whole transformer, or you must use a very long screwdriver, but still there's a very difficult access, and you must work with the screwdriver blade at an angle with the pot, so it is not so handy to do, especially while the machine is running.

I would like to have the capability of easily adjusting the speed while the machine is running by mean of an external pot, but I don't dare to touch anything on the electronic board, so I wonder if it would work just by putting a variable resistor on one of the two wires that run from the electronic board to the motor...

Any suggestion?
Thanks, Ugo

Posted by Martin Jones (Member # 1163) on March 14, 2009, 03:50 PM:

Welcome Ugo,
Do you have a manual for the machine? If so, has it got a schematic (circuit) diagram in it?
If there is, please scan it and send it to me by Email; then I can advise.
martin.

Posted by Ugo Bo (Member # 1505) on March 15, 2009, 04:08 AM:

Thanks Martin. Unfortunately I've got no manual. There's the manual of the Sankyo Sound 800 in the "manuals section" in this forum. Similar machine, but not the same. And no electrical diagram in there...
I think the motor is DC. You can find some pictures of it in this french site: http://pacavideo.fr/sankyo502/index.html (sorry is only in french).
There are only two wires connected to the motor, and seems there are none coming from anything placed on the shutter shaft, so I'm guessing that this machine has got nothing like a tacheometer for speed feedback, but it's simply controlled by the current through the motor...

Posted by Martin Jones (Member # 1163) on March 15, 2009, 09:41 AM:

It sounds as if the motor speed is simply controlled by motor current, but I would not like to say that this is the case.
The main reason for controlling motor current electronically is that the contolling element is a semiconductor which can stand high power dissipations, instead of a large wirewound rheostat, which is bulky.
I can't offer you more than those comments without reference to a circuit diagram. Sorry,

Martin

Posted by Ugo Bo (Member # 1505) on March 16, 2009, 12:15 PM:

Thanks anyway, Martin.
I wonder if I'll make some harm to the circuitry or to the motor if I try with the variable resistor...

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