EEVblog Electronics Community Forum

Electronics => Projects, Designs, and Technical Stuff => Topic started by: ChristofferB on January 05, 2021, 10:47:43 pm

Title: Troubleshooting an optical chopper - and a bizzare motor
Post by: ChristofferB on January 05, 2021, 10:47:43 pm

Hi all!
I just received a brookdeal 479 optical chopper (=ortec 9479) and it's not in the best shape electrically.

The motor is full on all the time, even though the frequency should be adjustable via a potentiometer.

Here's my main issues: the motor has 4 leads. 2 in the central smaller cylinder, see the pic below.

Has anyone seen this before?

How would the speed be regulated? Is it using its freq. Output as regulator, or is it just a pwm thing?

Thanks, I'm at a bit of a loss after checking all the usual suspects!

Title: Re: Troubleshooting an optical chopper - and a bizzare motor
Post by: doktor pyta on January 05, 2021, 10:55:20 pm

This could be brushed DC motor with tacho generator for precise feedback.
My guess would be that smaller cylinder is a tacho.

Title: Re: Troubleshooting an optical chopper - and a bizzare motor
Post by: langwadt on January 05, 2021, 10:56:40 pm

probably a DC tacho, so just a DC voltage proportional to speed

Title: Re: Troubleshooting an optical chopper - and a bizzare motor
Post by: ChristofferB on January 05, 2021, 11:26:59 pm

That was quick! Didn't know that existed but it makes perfect sense. There is a single op amp nearby, it's likely feedback for that, then!