Film-Tech Forum ARCHIVE: CAT745 - battery low + security tamper

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Posted by Carsten Kurz (Member # 5396) on 03-11-2015, 06:59 PM:

A CAT745 in a friend's Christie 2230 stopped mid-show, and the touchpanel displays two critical security events:

IMB LowBattery
IMB Security Tamper

I read in a Dolby technote that this combo typically means the IMBs certificate is wiped.

Seems there have been no warnings before regarding the battery voltage. The system is about 2 years old (220/745 combo), so, a very early CAT745.

Could this be a glitch with a chance to recover on-site?

- Carsten

Posted by Mike Renlund (Member # 4675) on 03-11-2015, 08:17 PM:

If the CAT745 battery has died, been tampered with, or removed, then the board will need replacing. In earlier versions of the CAT745, the battery low status would not be reported but that was fixed a few versions back.

Mike Renlund
Dolby Laboratories

Posted by Steve Guttag (Member # 268) on 03-11-2015, 09:42 PM:

So what is the life-cycle of the battery on the CAT745. That is, what is the safe time between battery changes? Naturally, one would want a time that ensures that it NEVER dies.

Posted by Carsten Kurz (Member # 5396) on 03-12-2015, 07:09 AM:

There certainly was no tampering with the system, it started playing a night show, and stopped after playing for about 20min. I assume that the anti-tamper system is also dependent on the backup battery, so a failed battery will not only reset the clock, but also trigger a security tamper event. I am not sure wether there was never a low battery warning before, but at least the owner/operator never was hinted towards a problem.

2 years with a spontaneous failure seems a bit short for such an important backup battery. Is it really only one on the CAT745, or two?

Of course it could be caused by other defects as well, maybe a spontaneous very high drain caused by some of the circuit, emptying an otherwise working battery.

- Carsten

Posted by Leo Enticknap (Member # 534) on 03-12-2015, 11:23 AM:

So under normal circumstances (i.e. assuming that the low battery isn't symptomatic of another fault, e.g. a bad capacitor causing battery drain), the low battery log alert should give you enough time to get it replaced by a service company before the 745 fails altogether?

Posted by Mike Renlund (Member # 4675) on 03-12-2015, 11:56 AM:

This does sound odd, especially failing during a show...when the projector is supplying the power for the security circuit and not the battery.

There is only one main battery on the CAT745 (CR2477N). There is a small coin battery slot (empty) next to the main battery to carry the load during the replacement of the main cell (you would use a CR2032 coin battery for this).

Total lifetime of the battery will vary on usage. On a 12/12 duty cycle (12 hours of use, 12 hours of projector off) the battery should last a little more than 8 years. Current software will give you a warning if the battery is low, there is also a line in Show Manager's Theatre Devices tab that shows if the battery is low or not.

Mike Renlund
Dolby Laboratories

Posted by Sam D. Chavez (Member # 1841) on 03-12-2015, 02:21 PM:

Thanks Mike.

Great to have someone from Dolby tech services on this forum.

Posted by Carsten Kurz (Member # 5396) on 03-12-2015, 02:59 PM:

The Christie says:

'IMB Low Battery - Critical' - is that really a 'dead' battery, or a 'low battery warning'?

It is followed by 'IMB security tamper'. And yes, it occured mid show. I'd say that normally this should not actually occur while the IMB is powered by the projector, but maybe it was an earlier event that led to it.
It was the second show of that night, so the IMB certainly was powered up for 3-4 hours before it happened.

Technically, there is a difference between a dead battery actually causing clock loss, security tamper, and a detection circuit only complaining about a weak/dead battery. An actual clock reset can be detected by reading it's value or another indicator. A low voltage is just an A/D or comparator reading.

I didn't reach the guy today, guess he is busy getting his integrator to fix it.

@Leo: A Dolby document says:

'Do not remove the main battery on the IMB without having a good backup battery in place; this will case a tamper event and the subsequent loss of the IMB’s private key. Do not place the IMB on a conductive surface.'

If I got Mike right, you can insert your own backup battery during the change into a second socket.

Mike - when you say early versions did not report battery status - was that a hardware issue on the first CAT 745 units, or a Dolby software issue that was later fixed for all installed units (e.g. with 4.7.x..)?

And yes, it is very nice to have someone from Dolby on the forum.

- Carsten

Posted by Carsten Kurz (Member # 5396) on 03-13-2015, 09:17 AM:

The CAT745 has been replaced. The guy measured the battery in the old CAT 745 and found it to have full voltage, at least unloaded.

- Carsten

Posted by Mike Renlund (Member # 4675) on 03-13-2015, 10:46 AM:

Yes you can use the small coin battery to allow you to change the main battery on the unit. We do recommend that you wear a rubber/nitrile glove during the change to prevent your finger oils from shorting the battery during the swap.

In this case, it really doesn't sound like a plain battery failure. Perhaps something else went wrong with the IMB. I am not sure what that would be though.

As to when the alerting was fixed, it was a software issue and taken care of in 4.8.2. From the release notes:

DC-12604
Corrected the behavior of the CAT745 IMB low battery alert.

Mike Renlund
Dolby Laboratories