8mm Forum: Elmo-St-800 Potentiometers

This is topic Elmo-St-800 Potentiometers in forum 8mm Forum at 8mm Forum.

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Posted by William Olson (Member # 2083) on December 23, 2015, 03:34 PM:

OK So my wonderful Elmo ST-800 has just been damaged by me. I was adjusting the 2 potentiometers in the circuit board to adjust speed and they broke. Anyone know the specifics of these potentiometers and where I could get them? This pic is not mine. I got it from the internet.

Posted by Steve Klare (Member # 12) on December 23, 2015, 03:40 PM:

Tell you what...

I can either measure mine or try to read a value off of them.

(Coupla' days...It's Christmas!)

I actually wouldn't replace them with the same parts. These aren't even a full turn from one end to the other. This makes the adjustments very twitchy. You give it a little twist and you go from too slow to too fast. You turn it back and now it's too slow again.

I can find you a more modern 20 or 25 turn pot: much more precise and less frustrating too. (Save your patience for something else!)

Ho! Hooooo!!!!

Posted by William Olson (Member # 2083) on December 23, 2015, 05:03 PM:

Thanks. I appreciate it. I know what you mean about them being twitchy.

Posted by Andrew Woodcock (Member # 3260) on December 23, 2015, 05:22 PM:

Steve really is a true ambassador of our great hobby.
He and Janice always go to great lengths to help anyone out here.

I think a special mark of recognition ought to be given here, for all their totally unselfish acts given out 365 "for the love of the game" so to speak, of our truly fabulous hobby!

Well done you guys!! [Smile]

Posted by William Olson (Member # 2083) on December 23, 2015, 07:18 PM:

I second that emotion!

Posted by Martin Jones (Member # 1163) on December 24, 2015, 01:49 AM:

Best wishes for Christmas and the New Year to all Members and Friends.
Martin

Posted by Steve Klare (Member # 12) on January 03, 2016, 10:05 PM:

Coupla' Days turned into a week!

OK, the two pots are two different parts, different values.

The one to the left is 40K. I found a 50K 20 turn pot which will do the job:

50K Pot

In order to hook it up properly, the center terminal would need to be connected to the leftmost one.

the other one is a 1K:

1K Pot

It's a direct hookup: right, center, left.

Both of these have the terminal on the top. I think the best thing would be to lay them on their sides and tack them down to the board with something like RTV. That way the adjustment screws will be pointing outwards towards you.

The best means to do the adjustment is some kind of plastic driver like this:

Bournes H90 Adjustment Tool

They stay on the adjustment screws better and you aren't fishing around live circuitry with a metallic tool!

Posted by William Olson (Member # 2083) on January 04, 2016, 10:35 AM:

Thank you Steve. As usual, you've gone above and beyond. No need to apologize for any delay. Happy New Year!

Posted by Steve Klare (Member # 12) on January 04, 2016, 10:46 AM:

It's sad: I actually had the week off from work!

-my greatest achievement may have been the morning I slept until 10:00. (I haven't done this since college!)

I did assemble the new snow blower...what fun!(?)

-my old one jammed if I hit the newspaper (...and I did!)...this one may blow shreds across the yard!

My advice is before you go to adjust (-even before installing them...) turn the adjustment screw to a limit ("click,click,click...")and then turn it opposite about 10 turns to get right in the middle of the range.

This way you won't start up the machine at some whacky frame rate, but at least in the neighborhood.

Posted by William Olson (Member # 2083) on January 04, 2016, 12:59 PM:

Thanks for the advice.

Posted by Steve Klare (Member # 12) on January 04, 2016, 01:05 PM:

If you really want to go for it:

Remove the old ones from the board first and measure the values. I had to measure them in-circuit and that introduces the shadow of a doubt.

Posted by William Olson (Member # 2083) on January 05, 2016, 10:20 AM:

OK Thanks.

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