View Single Post
Old 18th May 2019, 12:21 pm   #12
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 4,020
Default Re: Bell and Howell TQII 1652 16mm projector

Originally Posted by af024 View Post
Thank you Tony,

I'll have a prod around and report back.

The servo package is really small - I'm quite amazed by that given the size of the motor.

I'll have to do some jumpering about with some croc leads or something, but I'll do that and report back. I'm not sure whether the tacho will need some exciting from the servo module however. I'll see what happens with it disconnected.


PS Funny how it looks like the older machines will live longer eh! Well done you for having the AC type. Does that use gears for the two speeds then Tony?
Normally the tachogenerator is a spinning magnet and a wound stator (often a single flat coil with pole pieces that appear as 'teeth' round the hole in the middle). They will thus give an output without any excitation from the control module. In fact spinning the motor fairly fast by hand should give some signal on a 'scope.

It's been some time since I've had the covers off my projector (Filosound 655Q) but the service manual indicates that the speed change is a belt that's mechanically shifted between 2 pulleys on the motor shaft.

As for your last comment, I often find the older something is, the easier it is to repair and thus the longer I can keep it going. It's a lot easier to find spares for a 1970's PDP11 than for a 5 year old PC in my experience.
TonyDuell is offline