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ARRI SRI Main Board & Gate / S16 Question


Ryland Bouchard
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Hello,

I purchased an ARRI SRI, with German eleectronics, with the hopes of improved registration over my Bolex H16 EL. It was sold to me as "functional" from a camera broker. Of course this functional camera arrived with both of the main fuses blown - and after I replaced the fuses and applied power the camera motor runs immediately even with the main switch in the off position. I had planned to have the camera serviced anyway, but I am now debating whether this particular camera is just not worth the potential repair costs and should be returned to the seller. In addition to the potential electrical/main board issue it looks as though the camera has been through an "upgrade" to S16, with a widened gate and viewfinder that says SR3, but has not been recentered. Attached are photos of the widened gate. I'm really not interested in S16, as I prefer R16, but was hoping someone experienced with the SRI could let me know if the work done on this gate looks like a DIY job that would scratch the film or be problematic in any way. I assume recentering the viewfinder/lenses is an expensive change which is why it was not performed?

Also, has anyone had a similar issue with applying power and the camera running immediately? No LEDs light up, the camera motor just stars spinning as soon as the power cable is inserted regardless of the main switch position. There is continuity, or extremely low resistance (3 ohms) between the two power pins, which would seem to imply a faulty capacitor or other shorted component inside the camera body, unless I'm missing something. With the main board removed from the connector the short is no longer present, and I did not find any shorted tantalum capacitors in my quick check on the main board assembly. I've discussed sending the camera off to a few repair shops, which I'm happy to do, but I'd like to know what I'm getting into with the S16 work that's been performed.

Thank you in advance for any help/insight you can provide.

Ryland

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normally one tries to leave a tiny piece of "guide rail" on the left side of the gate to support the film from the other side. This is not possible with all gates but milling that part completely off often results in localised scratching of the frame edge. Can't see clearly if there is anything left of the left side rail but I'm guessing it is pretty much gone

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as for the low resistance, I'm guessing the 3ohm reading was when power was completely off and battery removed? 

transistors and fets can short to "closed" position if overheated which might be something happening here. Just guessing because not being very familiar with the SR electronics but in cameras like this, whether with a brushed or brushless motor, the motor speed is controlled using one or more FETs or transistors in series with the motor winding(s). If the transistor/fet would short the power would go though the motor winding all the time which in brushed motor would lead the motor to run continously at full speed and with brushless leading to the motor overheating and burning.

caps can of course short easily too and if a design has varistors they are common suspects too.

That is one possible explanation but someone more familiar with SR electronics can guess better 🙂

Edited by aapo lettinen
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Hi aapo and Mark,

Thanks so much for the feedback!

aapo: Yes the 3 ohm reading was with the power off and battery removed. Your analysis of the fault makes sense to me and it did seem to me like there was likely an open transistor/FET on the main board (or elsewhere) if there wasn't a failed capacitor hidden somewhere in the chassis. As for the guide rail on the left side of the gate - yes, it looks like it's pretty much gone. That's very helpful to know, and I'll make sure to keep an eye out for this in the future.

Mark: I agree it doesn't feel like a keeper. The seller should have accurately disclosed the faults and gate modifications - so I'll likely send it back. I like the lens choices and simplicity of the older cameras but finding one in good shape is such a challenge.

Thanks again!

 

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That gate modification doesn’t look good, normally there should be a thin support rail left at the side of the expanded aperture. Ideally also the entire left side support rail should be machined back so that no part of the exposed film area is in contact with the gate. For this reason the early SR I Gates with inset support rails are not really suitable for S16 conversion, see this post where I attached some photos of proper SR2 and SR3 S16 gates for comparison:

 

I would also be concerned that whoever did this modification didn’t do all the other things that need doing. The mirror shutter needs to be enlarged for instance to cover the expanded gate (the shutter angle was typically reduced from 180 to 172.8 degrees), the mount and viewfinder need to be shifted across, the mags need to be modified. Does the camera have a S16 fibre screen (ground glass)?

If none of these things have been done I guess you could still use it as is and crop to R16, but there is the risk of emulsion dust build up from possible scratching where that gate support rail is missing, or the possibility that the gate was not re-fitted properly after being modified.

With the added problem of faulty electronics I would be sending this camera back and asking for a full refund. Or you could ask the seller to cover the cost of a professional check/repair.

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