Repairing an early Arriflex 16SR (french motor)

[Vincent Wolfram]

I recently came across this 16SR on a local classified website. Owner stated it was stored for 20+ years, unknown history. Since the Price was right i bought it.

This is how it arrived:

 

Initial observations:
PL Mount for both S16 and N16 (seems to have been converted by P+S Technik)
Viewfinder realigned for S16
Swedish radio engraving on the Mag

Upon connecting it to 12v the camera would audibly hum and vibrate, the motor didnt start turning smoothly, and when it did it drew quite a lot of amps, around four to five.
I immedeatly suspected a commutation error, meaning that the electronically controlled motor didnt get the right power signals to start turning smoothly.

I've never worked on a SR before so i carefully started taking parts off to discover how to take it apart.

my steps: (i will eventually take good pictures -  i'm in the middle of moving)
Take off cover plate around the inching knob and the light meter.
unscrew 4 bolts holding on the handle.
unscrew 6 bolts holding the entire front casting in place .
unscrew the 4 special nuts holding the motor with its rubber isolators.
unplug 2 connectors between the motor wiring loom and the rear camera case casting (they are directional, cant be put back the wrong way later)
unscrew 6 bolts on the underside, closest to the front.
remove transmission belt.
carefully lift up the rear camera case casting.
unscrew 6 bolts on the top of the electronics compartment
unscrew 2 bolts on either left and right side of the electronics compartment
unscrew 4 bolts on the underside holding a heatsink for the power transistors
pull out the PCB
unbolt the double layered connector for the motor wiring loom

The camera is now taken apart as far as i needed to diagnose/fix this issue
notice: we havent taken anything apart that critically needs to stay in its factory calibration!
generally Arri used green laquer on screw and bolts that you really shouldnt take out without having access to factory service tools!

Everything taken apart:

the infamous french motor. Ive seen it described online as being a 3 phase brushless motor. Its in fact a 2 phase motor, as can be checked by measuring the resistance between the windings.
Note all the optical triggers on the back, theres 7 total. My first suspicion lay in those, but they turned out to be fine.

The PCB taken out and folded apart. Notice 4 transistor pairs, they are doing the switching of the motor current. under close inspection i could see that most of the transistor legs had cracked solder connections. Resoldering those fixed the issue.



when putting it all back together its important to time the motor to the film movement, else the mirror will stop in the wrong position, its easy enough to do it by trial and error. If the belt seems cracked or is already broken the right replacement is "T2.5. 160 x 4mm", just put this into google and find a professional supplier in your location where you can order one.


here's the camera running after fixing it

if you have any questions about this project be sure to write them here, i am not professionally certified by Arri or working for any other service company, just someone who as a deep technical interest in motion picture cameras.
 

Edited March 22 by Vincent Wolfram
accidently sent too early

[Dom Jaeger]

Well done, you approached it carefully and systematically, and repaired the fault. Dry joints can be a common issue in older electronics.

One thing I would mention is that when you replace the front, it can sometimes happen that the flange depth is altered a bit. A tiny bit of debris or a hair in the join or even different tightness of the screws can actually shift the flange depth by a few hundredths of a mm. So a technician would always double check the flange depth after front removal. But this requires a depth gauge, accurate 52.00mm blank and a gate block. Chances are, it’s probably good, but you could ask a rental house that has film gear to check it. 

The other setting that is good to check is the ground glass depth, as reflected off the mirror, which should match the flange depth. But again you need special tools - in this case a collimator and an accurate test lens. If you didn’t remove the mirror, or the ground glass holding assembly, or the gate, it’s probably still at the correct depth, but it’s such a crucial setting that it’s worth checking. Again a rental house might be able to help you.
 

 

[Vincent Wolfram]

Thanks Dom,
I'm worried about flange depth as well. Currently i sadly don't know of any rental place with its own Workshop in my city. Sending it out to a professional Service is currently not within my budget constraints, as much as i'd like to do that.

I still wonder about the P+S Technik conversion on this Camera, the PL mount was set to S16 when i got it, but the gate is N16. The mirror shutter wheel doesnt seem to be modified to 172° which would be needed for the SR1 shutter to cover S16. 

P+S also upgraded SRI and SRII cameras to SR3 movements which are timed slightly different and as such can keep the 180° shutter. I'll send P+S an email and enquire about any documentation that might still exist for this serial number

[Dom Jaeger]

Curious that the gate is N16. Some conversions had a removeable piece that could block the S16 gate aperture back to N16. P&S Technik did indeed do movement conversions rather than mirror replacement, you can check if the timing is ok by marking some film with a sharpie and inching it through while looking through from the lens port. The film will move just before the mirror fully covers or uncovers the gate if the timing is off (so mark the film with squiggles that go to the edges).

A small flange depth error only matters with primes if you want to rely on the distance marks, but with a zoom the focus will drift as you zoom out. This is assuming that the lenses are accurately collimated of course, and the drift may be so small as to be unnoticed except perhaps at maximum aperture. So I wouldn’t worry too much if you can’t check it, shoot a test and see how it goes. 

[Maxim Lequeux]

9 hours ago, Vincent Wolfram said:

Currently i sadly don't know of any rental place with its own Workshop in my city.

If you are in Hamburg Cine-Mobil has a camera tech who can service Arriflexes and the like

[Vincent Wolfram]

21 hours ago, Dom Jaeger said:

Curious that the gate is N16. Some conversions had a removeable piece that could block the S16 gate aperture back to N16. P&S Technik did indeed do movement conversions rather than mirror replacement, you can check if the timing is ok by marking some film with a sharpie and inching it through while looking through from the lens port. The film will move just before the mirror fully covers or uncovers the gate if the timing is off (so mark the film with squiggles that go to the edges).

Gate and fiber screen are definitively N16. Weird setup.

I'll test it with some film soon, right now i'm waiting for an Arri B to PL adapter as i dont have any PL lenses

 

 

[Vincent Wolfram]

P+S got back to me, apparently it was modified by them in 2004. No records on what exactly was done survive sadly.

 

 

[Robin Phillips]

8 hours ago, Vincent Wolfram said:

Gate and fiber screen are definitively N16. Weird setup.

I'll test it with some film soon, right now i'm waiting for an Arri B to PL adapter as i dont have any PL lenses

 

 

lightbeam has a super 16 SR gate assembly for sale in their spare parts site if you need it. I have no affiliation with them, I just check their parts site every now and then and saw it. heres the link https://lightbeamequip.com/shop/arriflex-sr-super-16-gate/ 

[Vincent Wolfram]

3 hours ago, Robin Phillips said:

lightbeam has a super 16 SR gate assembly for sale in their spare parts site if you need it. I have no affiliation with them, I just check their parts site every now and then and saw it. heres the link https://lightbeamequip.com/shop/arriflex-sr-super-16-gate/ 

Thank you, looks like its just a machine N16 gate? i'd presume the sliding surface would be narrowed on an original Arri gate.

 

A prototyping machine shop i worked with has wire edm capabilitys. might be worth discussing with them -  also a good oportunity to get funky with gauge blocks, parallels and an indicator to measure flange depth.