Film-Tech Forum ARCHIVE: Smart MOD 4 Backplane Schematic Needed

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Posted by Mitchell Dvoskin (Member # 751) on 07-14-2008, 11:49 AM:

I need a schematic for the backplane of the Smart MOD 4 Processor. If anyone can help, please contact me.

Posted by Steve Guttag (Member # 268) on 07-14-2008, 08:42 PM:

Why not just contact SMART? They are STILL in business and seem more than ready to help. They may not be manufacturing new but they are still servicing what they did sell as well as distributing other products.

Steve

Posted by Mitchell Dvoskin (Member # 751) on 07-15-2008, 08:25 AM:

We already contacted Smart and they said they had no schematic for the backplane. Hard to believe perhaps, but that was the answer from Norm at Smart: "We do not have a schematic on this part from the 25 year old processor".

Posted by Robert Minichino (Member # 3495) on 07-15-2008, 09:16 AM:

What do you need the backplane schematic for? The manual has schematics for the individual cards with the pinouts labeled (circled letters), so that might help depending on your purpose. If it's not installed I could have a look at it and map it out, too.

Posted by Mitchell Dvoskin (Member # 751) on 07-15-2008, 09:58 AM:

The processor has a problem with the Surround channel. It was working fine, and simply stopped working one day. The signal has been traced from it's generation point on the matrix card to the Delay/Surround Generator card, where it leaves the card on Pin "R" (to the SURR BUSS). It is being held LOW for some reason at this point. It you lift pin 9 of U2 from the socket, the signal is still OK at this point, so the IC is working. Only when connected back to pin R is it being clamped. Possible a short to ground somewhere, or wherever the signal goes next there is a problem at the input stage on the next card or cards.

That is why the schematic of the backplane is needed. All we know is the signal leaves this card on pin R, but where does it go next? The "SURR BUSS" could go to many points, all need to be checked. Having schematics of all the cards is good, but without the backplane schematic, the signal paths are a guess. It's a sizable job to remove the backplane for a visual inspection. We'd rather have the schematic so that is unnecessary to pull the backplane until all other signal point checks have been exhausted.

Posted by Robert Minichino (Member # 3495) on 07-15-2008, 11:27 AM:

Well, it looks like from there it goes to pin D on the Sub/Option 345 card, and goes out on pin R. There's a mistake in the schematic on sheet 1 for the 345 around U2. U2 is an analog switch that connects the digital surround input to the Surr Bus. If U2 went bad it would be likely to short out the surround bus; I'd try pulling TL185 U2 on the 345 card and see if that fixes things.

From 345 pin R it continues on to the output card 330, pin 4 I think, into quad VCA U3. It also looks like the mag input is connected to the surround bus at this point too; check the connector to make sure it's not shorted out there.

Oh, and instead of visually inspecting the backplane, I'd just hook on to the backplane at the output of surround gen card and the rake a test probe across the edge connectors. [Smile]

[ 07-15-2008, 12:41 PM: Message edited by: Robert Minichino ]

Posted by Gordon McLeod (Member # 33) on 07-16-2008, 09:57 PM:

I don't have the mod 4 as we bypassed it directly to the mod5 in our installs but on the mod5 there was some switching done on the mother board of the busses
Is there any external mag or digital hooked up as it is possible that it is swamping the bus

Posted by Mitchell Dvoskin (Member # 751) on 07-17-2008, 07:35 PM:

The problem turned out to be from human error. A while ago the magnetic surround channel was disconnected. Rather than leave Mag-S connected to the preamp output, it was disconnected and placed it on the G terminal (ground) so that there wouldn't have any noise or hum on the surround channel when using mag.

The problem is, the way the processor is designed, the inputs from the mag preamp go directly to the respective MAIN BUSSES for each channel. When the Mag-S input wire was placed on ground, it shorted the surround buss to ground, in all modes. Removing the wire from the ground terminal restored operation.

Posted by Gordon McLeod (Member # 33) on 07-17-2008, 08:24 PM:

All the Smart processors use bussing and as such it is important that external devices must disconnect from the bus when not required to prevent bus loading