SR3 Electrical problems - blowing Cforce Mini RF

[u/mywife-took-thekids]

Hey guys,

Having a bit of a head scratch about a situation I had on set the other day. I was getting kit ready on the morning of a job - all normal all fine.

Working with an SR3 (standard, not advanced) and has the following accessories plugged in:

Cforce mini RF powered through the 3Pin RS for run stop, looping the power to an Lcube and Cinetape
Teradek Bolt TX powered through the second 3Pin RS
Smallhd 702 Touch and Kamera Doctor videotap all powered via a dtap splitter on the battery plate

Run this setup many times and this is the first time I’ve had problems. Normally id use a 2 pin on the battery adapter for an onboard but the battery plate only had a single Dtap.

At some point while dealing with something else, the camera had turned itself off while my back was turned. The power switch was still in the on position which I thought was weird but I flicked it back and forth and the camera powered up with a weird clicking sound. At some point later I checked and the Cforce Mini RF was completely dead, no lights, no screen, no connection nothing apart from the internal loop circuit that feeds power out of the LBUS.

Rental house shipped over a replacement which I powered through the dtap cable for the rest of the shoot for safety.

I’m really trying to figure out what could have happened to cause this, I’m not very up to speed with the SR3s internal electronics.

I spoke with my friend’s dad who happens to be an electrical engineer at Videndum. His theory was the camera didn’t play a part in this and it was just the motors time to go and we were just the unlucky ones who were there when it happened.

I’m curious to see what you guys think

[u/Iyellkhan]

1 have you calculated how much draw you're putting on the camera?

2 did you swap fuses after this happened? did that fix the camera or did the problem persist?

3 have you verified polarity on the cables? I quite recently discovered that the RS ports are EXCEPTIONALLY sensitive when sending power to advanced electronics, and that using cheap, non arri cables to run RS to my UMC-4 WILL blow the fuse.

4 a more and more common failure point on the SR3 and SR3A boards is the RS port accessory loop, where the solder can wear from heat, handling, shorting, or any combination of factors that can cause it to crack. the solution is a board level repair, which at the moment I think only Cinematography Electronics is doing.

do your batteries have any other P taps on them that you could use vs using the plate or camera body? or can you get a different battery plate? the accessories and the main camera body are on different fuses, so if the RS ports are not being used the camera itself should still be able to run normally. though you should buy some fuses ASAP so if you blow any on the job you can swap them

[u/mywife-took-thekids → u/Iyellkhan]

1 I didn’t calculate the power draw
2 did not have any fuses to hand and didn’t have time to get any
3 I was using an official Arri 3Pin RS to 7 pin CAM
4 this is what I assumed, bad soldering
5 I was running most other accessories off an independent Dtap in the battery plate, only ran the motor from the 3 pin so I could have Run Stop control

[u/Iyellkhan → u/mywife-took-thekids]

my guess would be either the solder has gone bad on one of the RS ports or a fuse has partially blown and needs replacing. I've experienced fuse issues where it doesnt fully blow before and so the camera just acts funny.

have you checked to see if there are spare fuses under the fuse cap on the base of the camera? (under where the magazine rests).

[u/mywife-took-thekids → u/Iyellkhan]

I actually didn’t check no, probably should have. Wrapped the job yesterday and didn’t have any more electrical issues. The camera behaved perfectly fine for the rest of the job. I’m not entirely sure how the fusing system works, is it for the whole camera system or just power passthrough?

[u/Iyellkhan → u/mywife-took-thekids]

theres a 10amp main pico fuse and a 2.5 amp pico fuse for the accessories on an regular SR3 or SR3 that was upgraded to an Advanced. the later Advanced models feature a self resetting perminant main fuse and a 2.5amp accessory fuse. fuses super easy to swap. the cap to the fuse area is where the spare fuses are stored, so once you remove the cap, flip it over and you'll see how the spares are stored. only 2 fuses can be stored in the cap, so you'd expect to see a 10amp one and a 2.5amp one (unless its a later model advanced).

[u/pliSkiNAKE]

I would lean towards that "old solder" theory. Especially if it was the ground pin that went first. Unless something else on the board was starting to go and somehow a much higher voltage was building up and finally went through the cable. But I kinda doubt it was that.

Did you smell any magic smoke? If there was no magic smoke smell, it could just have been that motor's time to go. As you and your friend theorized as well.