Dolby Cat 745 battery replacement procedure

[David Ferguson]

I have come into possession of a Dolby Cat. 745 card, that I assumed was dead and the battery drained. However, upon checking it the voltage measures 2.83v - which to me, optimistically sounds like it could still have some life in it, and the key not be wiped. But looking at the datasheet of the CR2477N battery, it also looks like it's on the edge of the drop of the curve, where it will soon exponentially lose voltage over time. My Cat 745 has the two battery holders, so not the newer soldered on single battery.

I don't know the full history of the card, so it's more than possible that the key has been lost and someone has put a working batter in in the hope it may work, or that the card has failed in some other way (I read they often had issues?). I don't have access to a working series 2 projector to put it in and try right at this moment, but I thought that for the cost of a battery, it's worth replacing in the hope that it hasn't wiped, and that maybe it can be used in the future. However I have also read that the Dolby considered the Cat. 745 battery to be non field-replaceable, and that when attempted, the replacement procedure was fraught with issues, and often not successful. So I am keen to try and work out what the best method is for a chance of success.

My current plan is to:

1. Solder wires on to the vacant battery holder
2. Connect these to a bench PSU, suppling 3v
3. Replace the battery, knowing that the soldered on wires are providing 3v with a good connection

For those out there who have done this before - any other tips? Or are there issues with these steps that could cause a loss of the key, if it's still there?

[Steve Guttag]

Before I would spend too much time with it, I would try putting it into an S2 projector and see if you can clear the marriage tamper. If the certificate is still good, the marriage will clear. If not, you won't be able to clear the tamper (you don't need a server connected).

I'm sure that soldering in batteries will be best chance of surviving the battery change. I don't believe the problem was with the CR-2032 temporary battery holder, it was with the CR2477N that they ran into problems with the low current not always making it through the contacts.

I know that when Dolby did their mods, they killed the original certificate and just removed both battery holders, soldered in their replacement battery and put in a new (different) certificate.

[David Ferguson]

Before I would spend too much time with it, I would try putting it into an S2 projector and see if you can clear the marriage tamper. If the certificate is still good, the marriage will clear. If not, you won't be able to clear the tamper (you don't need a server connected).

I sadly don't have access to a working S2 projector at the moment... in the unlikely event that anyone in Scotland has one they will let me try it with, let me know!

I wasn't actually proposing to solder in the battery, I was proposing that I solder to the CR2032 backup slot to power it from a bench PSU whilst I did the swap. But if the connection on the CR2477N holder is the weak point, then perhaps I should give it a spray of contact cleaner, make sure there is no corrosion or anything that could cause a voltage drop and limit the current.

Of course, this is all quite academic as I am sure that the likelihood that this card has still has its key, and is still in working order is low... but it feels like I should give it a try as I have nothing to lose.

[Leo Enticknap]

Not only will you need someone in Scotland who has a S2 projector that they are willing to let you experiment with, but it has to be of a make that matches the faceplate of your cat745 (Barco, Christie, or NEC).