View Single Post
Old 15th May 2019, 8:08 pm   #2
af024
Heptode
 
Join Date: Jan 2003
Location: Ashby-de-la-Zouch (it's not by the sea)
Posts: 853
Default Re: Bell and Howell TQII 1652 16mm projector

Anyhow, a day later (I kid you not!), all was ready to accommodate the new worm which actually arrived the very next day (impressive!).

By the way, the old worm just wouldnít let go of the axle. With all grub screws removed, I twisted, shoved, pulled, pushed, squirted WD40, all sorts. It was an absolute pain to get it off and my hands are still aching even now!

So I carefully positioned the new worm, special cam etc and started the careful re-build.
I was doing fantastically well, quite proud of myself actually, but somewhere along the way, when I was trying to free off some seized sound drum clamp arms (which I also noticed at some point), the stupid photocell fell out of the sound assy and must have got wedged under one of the projectorís feet. Needless to say that the black plastic surround got damaged. I ended up drilling two tiny holes through the side of the bit of plastic that broke off and the main body of it in an attempt to stitch it back together with pins and glue. It actually worked ok and probably would have been fine, but Iím a bit fussy, so I went on the hunt for a NOS replacement. To my amazement I actually found one, so that was also placed on order. It too arrived the following day (amazing). The next problem was to try and work out how it was mounted. This wasnít easy as it relies upon being wedged in down the side of the sound drum with a metal wedge and grub screw affair. Whatís worse, you canít actually get to it without removing the optical lens from the sound drum assy (which I must reposition and focus up later).

I suspect that the photocell was already on the move way before I started the job as I seem to remember that the last time I used the projector, the sound seemed rather muffled. So another problem found and fixed (hopefully).

OK, it was all back together and time for a test. First of all, I undertook a manual (laborious) lace-up to see if all the timing looked ok - it was thank goodness. I didnít fancy another strip down or attempt to twist any offending sprocket relative to its gear to correct anything. I guess itís lesson to would be other brave people though Ė always worth a check before it all goes back into the projector!

So time for switch on.

Well we have another problem now. The motor is running like the clappers (technical term). Itís trying to shift film at circa 40-50 fps instead of 24! The 18/24 speed switch does nothing Ė it remains flat out.

Whatís more, the shuttle arms make one heck of a racket. I think thatís a combination of the crazy speed and perhaps some bad adjustment (except Iíve not messed with them Ė they are where they are and everything went back where it should be). The manual isnít very helpful on how I might adjust these arms (special tools etc), but it does say to resist adjusting them to Ďminimise noiseí. Iím hoping that some kind soul on here might be able to give me some tips about this. It looks like 1 x grub screw.

So thatís something to remember to attend to later once the speed issue is resolved.
Well this is a bit of a mystery. Was it a case of excessive speed seeing an already compromised worm gear off, or was it a case of the worm gear failure, followed by mech seizure and excessive motor current being drawn that damaged the speed servo? Not sure.
The servos took a bit of finding actually, itís tucked behind the motor, low down and looks like a small potted box. Itís states EXM030 on it. This doesnít agree with the manual (which states EXC030 or perhaps EXO030?). Mine also has some additional diodes present which are not shown in the manual. Not sure whatís going on there, but it does look like a factory fit.

So Iím guessing at this point that all of my efforts have come to nothing as this part is no doubt unobtainable from anywhere. I canít even open it up to see what might be duff inside. Itís clearly a servo as there is feedback from the motor Ė see the circuit extract. I suppose a substitute (redesign) might be possible, but thatís tough going to obtain a reinstatement of switchable 18/24 fps, especially when I donít know the nature of the feedback etc. Thereís also the racket from the shuttle arms (which actually look like they are about to fall out of the mount, they are that loose!).

So guys, any ideas please?

Iím really disappointed and depressed about this, as this particular projector has some sentimental value attached to it. So near, yet so far. Is this how these servos typically failed back in the day?

Regards,

Andy

Photos

ē P1010427.jpg -wide view of projector insides
ē P1010428.jpg - close-up of cracked worm gear
ē P1010445.jpg - shuttle arms and removed shutter
ē P1010447.jpg - gear meshing
ē P1010451.jpg - seized film/sound drum tensioner arms (and photocell/PCB assy)
ē P1010456.jpg - servo module
ē P1010459.jpg - servo location (plus diodes)
ē P1010460.jpg - grub screw adjuster Ė shuttle arms (shown at the top)
__________________
Now where on earth did I remove that from?
af024 is offline