BL4s Evolution mirror shutter fault.

tom mcgarrity · May 2

I bought this camera on eBay from a guy in
Melbourne. I’m in Scotland, shipping and import duties were considerable. I had it checked out at Progressive in Glasgow. Although the motor works, the mirror shutter hesitates and doesn’t spin.

Any help would be welcome.

Tom.

Aapo Lettinen · May 2

Sounds like a belt problem. Probably detoriorated old belt gave up. Get it checked in the UK, there is local arri techs who can help and probably straightforward if it is otherwise fine

Giray Izcan · May 2

The shutter belt has to be replaced.. last time I got one from Arri in LA for my 4s, it cost around 900.. sorry I know a rubber ring that's the size of a quarter costing that much sounds insane but yea... good luck.

Edited May 2 by Giray Izcan

Tyler Purcell · May 2

Yea, the ladder belts are kinda shitty, the older ones are made out of a polyurethane style material which the ozone corrodes over time. They fail from simply existing. Usually they last 20 years or so, but most people don't understand and they see the shutter spin, not realizing its not actually spinning properly because the belt has shattered and it's just barely moving along. The BL's are also a nightmare to work on, one of the most tricky cameras because of the way the movement isolation system was developed, so installing them can be very labor intensive. Arri moved away from these belts in the cameras after the BL, which means they are less prone to this issue. So you probably just have a belt failure.

It's part of the reason I always suggest to people; its better in today's world to buy cameras like the Moviecam SL or Compact, because they use very much off the shelf belts which will be available forever and they are made of a rubber compound that doesn't degrade nearly as much. Also, BL's have many other issues, like the paper thin foam gaskets failing on the mags, especially around the mag throat. I've seen major corrosion on the film slides, which hold the film from the supply sprocket to the throat area, which need to be taken apart, re-aligned and put back together again on MOST mags before use. The 535 has a spiral slide, which is easier to work on, but those coaxial design cameras are a nightmare magazine wise. If you aren't a tech, you'll be spending most of your money fixing them rather than using the camera.

Most of the time when I service BL's, they need a lot of parts. We have been making new gaskets/seals using a special 3D printed material which do fill the requirement, but aren't perfect. The aging rubber mounts for the mid plane to the chassis are liable to also be falling apart, which are tricky to get a hold of. As a tech, the screws sometimes get stuck and it's challenging to get the cameras apart sometimes because of corrosion. I'm always replacing screws in cameras that lived in humid climates, they're always a problem.

tom mcgarrity · May 3

Thanks to all, much appreciated.

Steve Switaj · May 3

As Tyler says, there are two Berg-style belts in the BL4 that rot away with age. (There's a third, conventional, timing belt off the motor, but that one ages much better)

The main main belt connects the drive sprocket, mag drive and movement. Once you get the camera apart it's fairly straightforward to replace.

The second, smaller, belt is the issue. It drives the shutter from the movement, and sits under that shutter. Unfortunately, the front face of the camera has to come apart and the shutter has to come off to service this belt. Then it all has to go back together and be retimed and reset for depth.

Richard Bennett has a post on his blog with some pictures

https://cinemagear.com/blog/2024/08/16/arri-bl-4s-finally-on-the-bench/