Bell and Howell TQII 1652 16mm projector
 

Bell and Howell TQII 1652 16mm ‘Filmosound’ Projector woes

Well I suppose it was bound to happen at some point. I recently acquired some more 16mm films and thought I’d dig out the projector, which had been resting, probably for 3-4 years in the back of a cupboard.

I didn’t give it a thought and just applied mains, switched on, pressed the auto feed level and offered up a nicely trimmed film with its leader in great anticipation. Well it only ran the film in probably half way, went very noisy then suddenly stopped (seized) with the motor thrashing away on a stalled belt. Well you can all probably guess what the cause was, yes a split worm gear.

I knew what I was in for – not only in tracking down a suitable new replacement but also in stripping the machine down to fit it.

I luckily came across a fantastic solid white nylon new high spec replacement, complete with an unusually nice larger diameter collar into which two grub-type screws are used to clamp it to the axle. Far better than anything else I’ve seen and exactly the correct dimensions/pitch etc. I promptly ordered one, and whilst I was waiting for it to arrive, I started the strip down.

It was far worse than a video on You Tube suggested. The TQII 1652 seemed to have much more to have to remove e.g:-

• Lens
• All lamps
• Transformer
• Motor
• Sound drum flywheel
• Sound head assy
• Numerous gears
• Top internal bracket
• Shutter bracket
• Shuttle arms
• In-out bracket
• Shutter assy
• Belt
• Pulley
• Worm gear axle bearings
• A cam on the worm gear axle

Of course it’s also really important to mark-up how the sprockets are synched with the shuttle/claw and how the gears mesh with the worm (assuming that they still retain the correct timing following the seizure of course.

For good measure, I even measured up exactly where things were, horizontally on the axle, I’d also put a line around the sound head assy prior to its removal (since that’s mounted through slots and its position need to be reinstated later).

/cont

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 wouldn’t 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 projector’s 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 I’m 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 wasn’t easy as it relies upon being wedged in down the side of the sound drum with a metal wedge and grub screw affair. What’s worse, you can’t 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 didn’t fancy another strip down or attempt to twist any offending sprocket relative to its gear to correct anything. I guess it’s lesson to would be other brave people though – 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). It’s trying to shift film at circa 40-50 fps instead of 24! The 18/24 speed switch does nothing – it remains flat out.

What’s more, the shuttle arms make one heck of a racket. I think that’s a combination of the crazy speed and perhaps some bad adjustment (except I’ve not messed with them – they are where they are and everything went back where it should be). The manual isn’t very helpful on how I might adjust these arms (special tools etc), but it does say to resist adjusting them to ‘minimise noise’. I’m 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 that’s 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, it’s tucked behind the motor, low down and looks like a small potted box. It’s states EXM030 on it. This doesn’t 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 what’s going on there, but it does look like a factory fit.

So I’m guessing at this point that all of my efforts have come to nothing as this part is no doubt unobtainable from anywhere. I can’t even open it up to see what might be duff inside. It’s clearly a servo as there is feedback from the motor – see the circuit extract. I suppose a substitute (redesign) might be possible, but that’s tough going to obtain a reinstatement of switchable 18/24 fps, especially when I don’t know the nature of the feedback etc. There’s 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?

I’m 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

• P1010427.jpg -wide view of projector insides
• P1010428.jpg - close-up of cracked worm gear
• P1010445.jpg - shuttle arms and removed shutter
• P1010447.jpg - gear meshing
• P1010451.jpg - seized film/sound drum tensioner arms (and photocell/PCB assy)
• P1010456.jpg - servo module
• P1010459.jpg - servo location (plus diodes)
• P1010460.jpg - grub screw adjuster – shuttle arms (shown at the top)

Re: Bell and Howell TQII 1652 16mm projector
 

Photos (batch 1 of 2)

Re: Bell and Howell TQII 1652 16mm projector
 

Photos (batch 2 of 2)

Re: Bell and Howell TQII 1652 16mm projector
 

I forgot to show the servo circuit. The dc supply comes in on the left hand side - pins 1 and 4.

Re: Bell and Howell TQII 1652 16mm projector
 

Hi!

Try not to laugh too much, but have you tried boiling the servo module in fast–boiling water for about 20 minutes in a pan of water?

Quite a number of epoxy fillings have a "Glass Transition Temperature" of about 70–80°C, so if you boil the module for about 20 min, that will be above the G.T.T., after which you might find the filling material has softened somewhat, enabling you to try digging it out with a screwdriver, etc., if you're careful – it's worth a try, but I'd make sure you can source a spare unit just in case!

Chris Williams

Re: Bell and Howell TQII 1652 16mm projector
 

Hello Chris,

No I didn't laugh, really, I didn't, but I have to say that I hadn't thought about boiling it . Thank you for the tip. I may well have a go at that, assuming that I can satisfy myself that it is indeed the servo that's packed in and not the loss of feedback pulses (or volts), or whatever it gets from the motor.

As for tracking a spare down .. well so far, that's proving to be very tough indeed.

Regards,

Andy

Re: Bell and Howell TQII 1652 16mm projector
 

Normally these things use the freqeuency of the signal from the motor's tachogenerator as feedback. It's a more reliable indication of the speed than the voltage from said generator.

Looking at the circuit, the tachogenerator seems to be the 2 yellow wires from the motor. With the unit off and at least one of those wires disconnected, you should get some DC resistance between them due to the tachogenerator windings. Not shorted, but not open either.

With the motor running, a 'scope should show an AC voltage (sinusoidal-ish?) between those 2 wires.

Alas the B&H projector I have is an older one with an AC induction motor so I can't be more help.

Re: Bell and Howell TQII 1652 16mm projector
 

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.

Regards,

Andy
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?

Re: Bell and Howell TQII 1652 16mm projector
 

Try Kevin Browne aka KB Cine Repairs in Nottingham, who might be able to source you a module or suggest an alternative.

Failing finding an original, there are generic frequency-to-voltage converters that can be adjusted to suit a range of magnetic tonewheel tachos, to provide feedback to a standard DC motor driver module. This is expensive but just shown as an example:
https://uk.rs-online.com/web/p/emi-f...ories/0440509/
There are doubtless direct-from-China equivalents cheap enough to take the fun out of building your own.
See also these people, IIRC we've had some controllers from them and they seem quite flexible and open-sourcey:
https://www.4qd.co.uk/product-category/controllers/

The induction-motor projectors use stepped pulleys on the motor and main shafts, with a striker operated by a lever above the film track. Hence the warning printed there only to change speed with the projector running. The earlier machines with universal motors switched electrically between two centrifugal governors.

Coincidentally, I also had problems with a projector speed control yesterday - a Lenze inverter that drives the 3-phase motor in a Philips DP75. Proj kept on running but lots of smoke came out. Rifa suppression caps, naturally. Grr.

Re: Bell and Howell TQII 1652 16mm projector
 

Can't help with the speed control beyond what the others have said.

I changed the worm on my 8D644 probably 20 years ago. Massive job not to be undertaken lightly, I suspect no-one at B&H ever thought it would need changing. I didn't want to repeat the experience so directed a friend to have his identical machine done by a repairer (not the one listed above). When the machine came back I wondered how they'd dealt with a particularly hard to access bolt I'd struggled with. The answer was simple - they hadn't refitted it!

My machine has the AC motor and ran fine for many years, but has lately started to suffer from wow and my attempts to trace this have failed so far.

Re: Bell and Howell TQII 1652 16mm projector
 

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.

Re: Bell and Howell TQII 1652 16mm projector
 

You may find suitable spares from these people. (They also make the worm gear!)

http://www.classichomecinema.co.uk/

Look under their section for film equipment.
I have no connection with the company, but a friend I know who used to change the worm gears suggested trying them when I was chatting with him on the phone today and I mentioned your Bell and Howell.

John

Re: Bell and Howell TQII 1652 16mm projector
 

Thank you for all of your great comments, links and suggestions. I am encouraged.

Just now I've managed to grab a few moments to drag the 'scope and a multimeter out to see what's what.

Here are the results:-

Motor supply blue/red = 5 ohm
Tacho grey/grey (shown drawing as yellow/yellow on circuit rather strangely) = 408 ohm
Motor supply volts = 38.4 Vd.c.

Scope trace settings (sorry about the bad photo):-
5V/div, 0 Vd.c. on centreline, 0.2ms/div
So I make that circa 29V pk-pk off the tacho, and 1351 Hz (motor running flat out off the 38.4 Vd.c. supply)
The above measurement were taken with the tacho not connected to servo and the motor supply taken from the faulty servo output (38.4 Vd.c.)

There is no difference when the servo tacho circuit is disconnected.

The two diodes that I mentioned seem ok, although I only tested them as standard diodes, not zeners.

I also came across this interesting service bulletin (about the servo and diodes). I'm guessing that they were expecting trouble way back then for some reason!

Regards,

Andy

Re: Bell and Howell TQII 1652 16mm projector
 

It looks like the tach pick-up is OK. As the motor gets faster, not only does the frequency increase, but the peak-peak voltage will rise proportionately.

With a DC motor, it's probably a transistor circuit in the box, and a common failure mode of power transistors is short-circuit, leaving your motor at full speed ahead.

Whatever is in the little box can be replicated once its nature is found out. It could be working on either the frequency or the amplitude of the tach signal, though the amplitude version would be concidered rather crude... but stranger things are found.

David

Re: Bell and Howell TQII 1652 16mm projector
 

Did you check the rest of the speed control circuit? There are two pots that set the speeds and a switch possibly for play and wind/rewind?

Re: Bell and Howell TQII 1652 16mm projector
 

Thank you for you further comments.

I suspect that you are correct David - a shorted transistor. It's an amazingly small module. Goodness knows what's in it.

As for the reference circuit, well I think it's ok. At least I'm getting a change on voltage at pin 5 when I switch from 18 fps to 24 fps - not much though - only 0.4 Vd.c. This might be ok?

For completeness:-

U1/EXC-030/XU1 d.c. voltages (projector running, everything connected as it should be):-

Pin Volts
1 39.2
2 15.3
3 0.7
4 0
5 10.8 at 18 fps, 10.4 at 24 fps
6 9
7 9

Regards,

Andy

Re: Bell and Howell TQII 1652 16mm projector
 

I've just messaged someone who is currently selling a TQII for spares. I thought it would be my chance to obtain a replacement servo, but alas, when I asked if he might be able to check if the speed switch actually changed the speed of the motor, the answer that came back was, 'No it doesn't, it's just stuck on one speed and runs fast'.

So it seems that this isn't an isolated incident.

I tried contacting classic home cinema and regrettably they don't stock much B&H stuff, so that fast became a dead end.

I bet there are more failures out there ...

Re: Bell and Howell TQII 1652 16mm projector
 

It sounds like you don't so much need a replacement servo module as an improved servo module, designed to not blow up.

Anything driving a DC motor will see an inductive load and nasty transients from brush-commutator interruptions and sparking. Without good protection, this will degrade semiconductors leading to eventual failure.

Projector motors take a fair bit of power, and that module looks small. So either it uses the metal it's mounted to as a heatsink, or else the output stage is switch-mode.

The first thing is you need an AC tachogenerator to voltage converter. Have a look at LM2907/LM2917. They're as old as the hills (I used a pair for electronic rev counter and speedo when I rebuilt my old Cooper S in 1979!)

There's an opamp in the chip which will make your loop amplifier... all you need then is a good beefy power stage - well larded with transient protection!

David

Re: Bell and Howell TQII 1652 16mm projector
 

I have spoken again to the person I know who used to change B&H worm gears.
Apparently the model you have is not regarded as a good one. He says that the servo units did not normally give trouble but the motors are suspect in that model.
He is contacting someone else who may have spares, I will post if he has any luck.

John

Re: Bell and Howell TQII 1652 16mm projector
 

Hello David, John,

Thank you for your thoughts.

Yes the module is very small - remarkably so. I suspect that it does use the metal as a heatsink as there is heat conductive compound between it and the metal base of the projector.

It would be great to create a modern substitute, but I suspect I'd be out of my depth here. I did look at some ICs and what they might offer, but then I got stuck on whether or not I needed to convert frequency to volts or just use volts direct as the feedback.

I also didn't know whether to go down a pulse with modulation output or not etc.

I wonder what goes wrong with the motors? Mine appears to be ok, at least for the moment, but it's an interesting observation all the same.

Thank you for asking about possible spares.

Regards,

Andy

Re: Bell and Howell TQII 1652 16mm projector
 

Taking a look at various LM2901 and LM2917 datasheets, I came across this circuit. Perhaps this would form a suitable building block? Of course there are still some challenges as the project supplies an unregulated nominal 40Vd.c. and this IC is limited to 28Vd.c. I think.

I'm not sure what current the motor will pull on full load.

I don't know whether I need a PWM solution to keep the torque up.

My aim would be to try and create something that would just drop in as a substitute, so I have 7 pins (and existing signals, presets etc) to deal with.

Not sure what to do for R1, C1 and C2.

Re: Bell and Howell TQII 1652 16mm projector
 

Hi!

The 28V max needed for an LM2917–8 can be provided by an LM317T adjustable regulator or a 7824 with a 3.9V zener in parallel with a 10u 25V electrolytic in its middle ("GND") lead, or, if you can find space in your Projector, a small "LM317 Adjustable PSU Module", which you can buy cheaply online from Chinese supply sources, either ready–built or as a kit of parts with a bare pcb!

A darlington transistor such as the TIP147 or BDX53 should do for the LM2917–8 circuit example suggested in the previous post!

I wouldn't be at all surprised to find B & H have buried a '2917 in that module to begin with – it is, after all a similar speed control arrangement with simple switched potential dividers adjusted for each film speed!

Chris Williams

Re: Bell and Howell TQII 1652 16mm projector
 

Hello Chris,

I wondered about using a zener or LM317, but also wondered what would happen to the drive in doing so. Perhaps it would still be ok?

After reading the datasheet of the LM2917-8 more closely, I did wonder if it would be ok to run it simply with increased resistance at pin 6 and pin 5? Not sure whether any transient suppression is needed.

The attached (somewhat ragged) sketch is what I was thinking about. I've put the Bell and Howell original module pin numbers in circles.

Of course I have no idea whether the original Bell and Howell present arrangement will work ok and I still don't have much of a clue about R1, C1 and C2.

Re: Bell and Howell TQII 1652 16mm projector
 

Ah, just noticed that the TIP147 is pnp, perhaps the TIP142?

Re: Bell and Howell TQII 1652 16mm projector
 

Actually, perhaps that's not a good idea on my part (increasing the connected resistances at pins 5 and 6). I'm also not sure about the max rating of the LM317T. I mean there's circa 42Vd.c. supply to deal with. I don't know what the IC will pull in terms of current, but how if I used a series 68 ohm resistor off the 42Vd.c. supply and take that to a 1.3W 24V zener diode with, say 470uF strapped across it and use that as the IC supply (then take the other resistor values back to where they were)?

I'm still at a loss when it comes to selecting suitable values for R1, C1 and C2 (even though I've read the datasheet several times). Pages 4 and 8 seem relevant.

Re: Bell and Howell TQII 1652 16mm projector
 

Not sure if something like this might help?

https://tinyurl.com/y3pyvqxj

and presumably, you could replace the pot with the tacho circuit?..but I may be talking nonsense?

Re: Bell and Howell TQII 1652 16mm projector
 

Hello,

I did wonder about those, but they don't use feedback from the tacho. Of course they may still work ok without said feedback, but I'm not sure how stable the speed would be as a consequence.

Thank you for your thoughts though .. keep them coming.

Re: Bell and Howell TQII 1652 16mm projector
 

Speed stability is important for sound projection and I very much doubt that adequate results could be obtained without tacho feedback. Connecting this motor to a constant effective voltage (whether adjusted by PWM or otherwise) would probably result in audiible pitch variation through the length of the film due to change in friction and takeup load, wow at takeup and supply reel rotation rates and sprocket rotation rate, and odd jumps at splices etc.

The only way to obtain a passbly stable drive from a PM motor without tacho feedback, is to size it generously (to minimise the effect of load regulation) and improve the remaining load regulation with I*R compensation - effectively adding a negative dynamic resistance in series equal to the motor's apparent armature resistance, one of the major factors in PM speed regulation. This was used in certain portable devices that did not have centrifugal governors. However, the motor in this projector has to work hard and is subject to sudden load changes at splices etc, so I think this method would be barely adequate. It also requires a regulated supply to achieve correct speed at low load. Since a tacho is available, I would definitely use it.

A commercial PWM motor driver with e.g. a 0-10V input can be driven by a low-power analogue servo block reading the tacho and speed switch setting, and applying PID control to produce the output value.

FWIW, when 35mm sound projectors were first introduced in cinemas in the early 1930s, DC motor drive was often used with magnetic tonewheel speed feedback via valve servo-amplifiers. The cost and (then) complexity of such a scheme are indicative of the importance accorded to speed stability.

Re: Bell and Howell TQII 1652 16mm projector
 

Have you tried to de-pot the old module? At this point I guess you don't care about damaging the components in it, you just what to extract the innards physically intact so you can see what is in there and hopefully reverse-engineer the circuit diagram.

I'd try heating it (at least to boiling water temperature) and if that doesn't work try a hold soldering iron on the compound and then common solvents. If all else fails, a burr in a Dremel tool can get into such things.

Re: Bell and Howell TQII 1652 16mm projector
 

Thank you for your further comments guys. Was that was some kind of (sine wave?) audible tone recorded into a metal disc off the motor shaft? Wow, I didn't know that. I must confess to being rather sensitive to any kind of variation in pitch. I even graters on me when a record isn't pressed concentrically around its hole! So somehow it seems like I need to press on with a tacho feedback-type solution.

By the way, I was also worried about the 30V peak to peak coming from the tacho, that's why I proposed a potential diver before submitting it to the chip.

I haven't tried to de-pot the original module as yet. I'm quite uneasy about doing so as there's still a niggling doubt (ok, hope) that it might be ok. I guess wouldn't think twice if I had a workable spare. That way we'd all know what was inside the little beggar. I guess I'm going to have to work up to it if I can't with your help, come up with a suitable modern substitute.

Thank you again.

Regards,

Andy

Re: Bell and Howell TQII 1652 16mm projector
 

I realise it is human nature to always suspect that the part you can't get is the faulty one. But in this case, I assume you've checked the few components around the module, and we know the tachogenerator is producing a signal. So it pretty much has to be that module.

In which case, I don't think you have anything to lose by trying to get into it.

Re: Bell and Howell TQII 1652 16mm projector
 

With the module disconnected, check between the DC input and motor output terminals for evidence that the power transistor is shorted, which would be a common failure mode and the likely reason for the retrofit zeners. If it is indeed shorted, the unit must be U/S but also can possibly be repaired by replacing the transistor, external to the module if more convenient.

Like Tony, I would try to unpot it. If the potting material is hard and cannot be prised out, I would put in in the milling machine and remove the case leaving only what's apparently attached to the transistor. Then it would be easier to chip away around the transistor leads and attach flyleads to a temporary external device, leaving much of the module potted and therefore mechanically intact. Of course, whatever drives the pass transistor may be damaged too, but unlike a full bridge, failure of one transistor does not automatically jeopardise everything around it.

Re: Bell and Howell TQII 1652 16mm projector
 

The motor pass transistor is on the negative rail (pin 3). Externally the voltages look OK to me so getting to the internals would be the next step!

Pin 1 (39.2/?) = +Power, +Motor
Pin 2 (15.3/15) = +Vcontrol
Pin 3 (0.7/0.3) = -Motor
Pin 4 (0/0) = -Power
Pin 5 (10.8,10.4/10.5) = Control
Pin 6 (9/9) = -Vcontrol
Pin 7 (9/9) = Tacho

Re: Bell and Howell TQII 1652 16mm projector
 

Ah, I had forgotten those readings, and agree it looks more like a transistor driven on rather than one with no junctions left. Pity, it might have been the easiest fix.

Re: Bell and Howell TQII 1652 16mm projector
 

I thought I'd got one the same as yours up in the loft. I went up there a couple of hours ago and fetched it down, but it seems to be the earlier model with a mechanical speed change that moves a belt from one pulley size to another. I powered it up and the amplifier, motor and lamp all worked, but there was a distinct lack of anything else going on. I took the cover off and found that the movable belt was slipping due to the worm drive being cracked and solid, so that's the end of that one!

Re: Bell and Howell TQII 1652 16mm projector
 

That's repairable. Parts are easy to get but it's a dirty job with all that old grease around.
Pity to scrap a repairable vintage item.

Re: Bell and Howell TQII 1652 16mm projector
 

Thank you for your further comments. Yes the worm gear is available (well the standard non-stop motion type seems to be), but boy you need patience to fit one and ensure that everything is properly synchronised up again.

Between pins 3 and 4 of the module (everything disconnected from it), using a standard analogue multimeter, I'm 'seeing' circa 650 ohm (one direction).

I also observe (when everything is connected) 0.7 Vd.c. at pin 3 relative to pin 4 when the motor is running and 0.2 Vd.c. when the motor switch is turned to off. This doesn't agree with the voltages marked on the circuit as it states 14Vd.c. 'at projection'.

Re: Bell and Howell TQII 1652 16mm projector
 

Af024
I am curious to know the shutter's relationship with the take-up spool.
Is it linked mechanically to the one motor? thus although your shutter mech is free running at the moment the take-up spool has also increased speed so it can cope with the faster running film.
Or has the take-up another circuit/motor which say supplies more oomph with a full spool and less with an empty one?

Re: Bell and Howell TQII 1652 16mm projector
 

That's good as far as the output transistor is concerned. There is some drop across it, as though it is being driven on hard, rather than completely shorted. With the motor off there's no collector supply. The 14V is probably an average as measured with an analogue meter, when the output is actively controlling the motor voltage. If the supply is 40V and 14V appears across the output transistor, this suggests a typical 26V required at normal speed and torque.

Yes. Most 16mm projectors use a single motor, with a slipping clutch or other slippable coupling for the takeup (and supply, when reverse projection is available) that tries to drive it faster than the smallest spool centre requires. A standard mechanism on B&H projectors is a weight-controlled slipping belt. The takeup spindle drive pulley 'hangs' in a fabric belt, so that the increasing film load increases the friction on the pulley and hence the torque. Even some full size cinema projectors up to 70mm use a slipping clutch for the takeup, while others use a separate torque-motor with variable torque.

Re: Bell and Howell TQII 1652 16mm projector
 

Yes everything is coupled to the one motor. Obviously sprocket 'pips' need to be in the right place in relation to the claw and shutter mech, else if not, it would either not auto-thread properly or you'd end up with too big (or too small) a loop (or loops) and possible film damage. Obviously the sound drum/mech also has to be in the correct place too. All good fun. Yes mine has the slipping fabric belt idea to couple up the take-up.

Hopefully the output transistor is ok, as mentioned above (thank you for those comments). So perhaps there's something gone wrong with the internal conversion of frequency to volts (or current) in the module? Maybe, when I get a chance, I should de-couple the tacho and substitute it for a signal generator and do a frequency sweep to see if anything happens to the motor speed? It may still kick in but at a much higher (or lower?) frequency than it should.

Re: Bell and Howell TQII 1652 16mm projector
 

As a final test you could run it up on a resistive load (4K7) between pin 1 and 3. You would have to disconnect the Zener from pin 3 and connect it to pin 4 to get the motor running.

You seem to have a large tacho signal so it is difficult to believe this could be a problem although you do say the scope image is when the tacho is disconnected so it would be good to see it when it is connected.

Re: Bell and Howell TQII 1652 16mm projector
 

Ah thank you both..seems a simple (but ingenious) and safe way..a separately driven take up would probably cause havoc if it went wrong?

There are potting softeners around ..but don't think you need 5 litres here LOL

https://tinyurl.com/y6nwbkmn

Re: Bell and Howell TQII 1652 16mm projector
 

I wonder whether there is a difference in the formulation of the potting compound and any resins that might be used in the construction of individual components. It would be a pity if it successfully removed the compound but also attacked the component encapsulation, or even erased any markings.

Havoc is when an unsupervised tower stops taking up at the beginning of a feature, without tripping any guard switches. The show proceeds as normal but the projector dumps the whole movie, up to two miles of film, in a heap on the box floor.

Re: Bell and Howell TQII 1652 16mm projector
 

Yes, I agree that it is a pity to scrap it, but that is actually what I was considering, as it's a heavy old lump and really shouldn't go back in the loft now it's been brought down. As I was up there clambering about ducking under rafters with it, I was thinking to myself whether I would still be able to be doing this when I'm in my 80s and heaving it down the ladder. Heavy items like this I do place where there's a supporting wall below so as not to cause bowing and cracking of ceilings in rooms below. A few years ago when a former work colleague died suddenly, his wife got three large skips and several helpers in to clear all the old TVs etc., that he had accumulated in the loft of his house. I got to hear about it too late, but I was told by someone that had been there, that some of the doors upstairs in the house couldn't be closed due to the weight of stuff in the loft deforming the tops of the frames - ruin your house with your collection!

Replacing the worm on one of these projectors does look like a mucky job, but probably not as mucky as replacing gramophone springs. I already have another 16mm Bell & Howell projector which I've had for decades and is much older and has manual lacing and dating from the early 40s, which works and doesn't have this type of worm drive to go wrong. As regards to the later projector, although I used to operate this same type in the mid 70s as an evening job showing films to various organisations, I've never actually used the one that I've got, as I never did like the look of that worm drive, and just like the 'vintageness' of the big old black square one that I've got. There's some useful components in this more recent one that I've got that's similar, but older to the one under discussion in this thread, such as valves, output transformer, internal speaker etc. so I probably wouldn't sell it, but I would consider swapping it for some more old films to play on the other projector - any offers? The reality is that I shall chew it over as regards to the future of this projector, then after I've fallen over it several times it'll either get broken up and scrapped for its useful parts or it'll end up back in the loft for another time, another day - probably the latter if I'm totally honest. It's in fairly nice condition and has its original padded protective slip on cover, plus there's the large matching extension speaker that goes with it still buried somewhere in the loft. The mains lead with the special plug socket is rather perished and needs dissecting at the projector end and re-wiring with a new cable and insulating for safety, but I see that new ones of these are available on-line for a reasonable price.

Getting back to the OPs projector under discussion in this thread, I've spotted a new replacement part that is possibly a substitute for that speed control module. It says in the advert that it replaces the aluminium block that is now obsolete. I've posted below a picture of the control taken from the on-line advert, also for interest a snap of the innards of my projector for comparison. The last picture is the perished mains connector just to shock everyone (no, not really, I'm sure we've all seen worse in regular use over the years). Yes, I did power it up with it like that, I had to get it in just the right position as all three conductors were bare and I found that the 13 amp fuse in the plug top was already blown, so I replaced it with a 10 amp fuse for possible damage limitation as a temporary measure!

I'll also post a link to the advert for the replacement speed control module. if it turns out to be not applicable to this projector, then perhaps the moderators could eventually remove it....
https://www.ebay.co.uk/itm/New-Speed...4AAMXQQQZR4Yq6

Re: Bell and Howell TQII 1652 16mm projector
 

I need to see if I can understand post #42. Perhaps I could just ditch the connector to save fiddling with difficult soldering around the zener(s) and just use some temporary wiring with thick bear tinned copper wire poked into the socket. I'll see. I still need to try the signal generator idea too.

I think the tacho signal was circa 29V peak to peak regardless of whether it was connected to the module or not, but I will check.

Yes that's what I'm worried about - stripping off component identities or even melting them! I my yet pluck up some courage though.

Losing an entire tower's worth of film horrifies me!

Techman, wow, that's a great find. How interesting! Sorry, in my excitement, I forgot to say something about your lump. Yes they are very heavy and may well (if you have enough of them) damage ceilings etc. Your example doesn't look too horrendous to me (as regards a worm gear transplant that is), just keep everything meshed as is (assuming that nothing has slipped), mark everything up and off you go. No sure if you'll need some Bristol Tools however (they looks a bit like Torx, but they aren't - typical eh!).

Thank you again.

Andy

Re: Bell and Howell TQII 1652 16mm projector
 

Is that a 2SD970 and a 741 I see on that PCB?

Re: Bell and Howell TQII 1652 16mm projector
 

I guess, if it's a 2SD970 in my module, the resistance readings I got between module pins 3 and 4 (out of circuit) make sense as that would be the diode.

Re: Bell and Howell TQII 1652 16mm projector
 

I think I have a pair of late (grey, 1980s) TQ III's with that PCB in, rather than the potted module which was used in earlier examples of the same models. Unfortunately I am not near them to check. That and the fact that the terminal layout is identical, support the suggestion that it is a drop in replacement for the module, subject to mounting bracket.

Re: Bell and Howell TQII 1652 16mm projector
 

I once rescued for somebody an old AEI (GEC etc) 16mm projector. To transport it I removed (what I thought) were the rather delicate glass fibre casings.
Now projectors were probably just a passing party trick for AEI which I believe were mainly into industrial electrical solutions, so with casings off, I could not help but admire the engineering and the main motor (perhaps the only one?) which AEI probably used in a lift or something LOL.