SM Desks

[sandall]

At the start of our Panto run our GDS desk suddenly appeared to be (at least partially) shorting out the external Tecpro 725 Master station's +24V - the problem only appeared when the desk was powered-up for final rehearsals. The quick-fix was to disconnect the external Tecpro from the desk & give the DSM a belt-pack.

 

Has anyone met a similar problem, or have access to circuit diagrams of the audio side of these desks? Trying to get technical help out of GDS has so far made getting blood out of a stone seem child's-play (Zero88 they ain't).

 

I assume (but can't get confirmation) that the internal Tecpro card gets its +24V from the desk, for use as a stand-alone system, & that this is hopefully diode-isolated from the +24V from any external master-station. Lots of possible scenarios for the problem, but knowing how the system is meant to work in the first place would help :(

[Jevans]

I don't know anything about the GDS desk internals (though can sympathise about recent problems with GDS tech support - lots of quality issues with ArcSystem kit recently!) but I do know the Techpro units.

 

I'm going to presume it's a 745 not a 725? I don't think they've made anything with that code - If the master station is not providing the power supply for the network (sounds like it isn't if you've replaced it with a beltpack) have you checked if termination is turned off on the master station? There should be a pair of pins soldered together on the expansion connector on the back if it's being used with an external PSU. It sounds awful if you get it wrong - previously I've just soldered a pair of pins together on a connector and plugged it in so it's possible this has fallen out if it's been done like this?

Re-reading though maybe I've misunderstood, is the master station within the desk or another bit of kit?

[sandall]

I'm going to presume it's a 745 not a 725? I don't think they've made anything with that code - If the master station is not providing the power supply for the network (sounds like it isn't if you've replaced it with a beltpack) have you checked if termination is turned off on the master station? There should be a pair of pins soldered together on the expansion connector on the back if it's being used with an external PSU. It sounds awful if you get it wrong - previously I've just soldered a pair of pins together on a connector and plugged it in so it's possible this has fallen out if it's been done like this?

Re-reading though maybe I've misunderstood, is the master station within the desk or another bit of kit?

Well spotted - it' is indeed a 745, but the manual doesn't show an expansion connector or any termination pins (or am I misunderstanding you?). This is a permanently-powered external unit (so comms doesn't rely on the SM desk being in use), but the desk itself contains what the schematic shows as 2 single-channel "Tecpro intercom" units (presumably belt-pack PCBs or, more likely, a 2-channel PCB). I would assume the card(s) get a +24V from within the desk, but it could equally be relying on external power from the comms ring; with no circuit diagrams forthcoming it's a bit hard to tell..........

 

We previously had a 15-year old NL desk whose show-relay side was beginning to fail (lots of little low-power amp cards), so somebody had the bright idea of spending an obscene amount of money replacing the rest of the desk, which was working fine, with the GDS, assuming that someone else would put in new comms & a stand-alone show-relay amp. TBF it's worked quite happily for 5 years, with the internal unit feeding the DSM headset & everything else powered from the 745, until late in the panto rehearsals, when someone decided it was time to start using the desk. Horrible noise in headsets & current overload LEDs lit on both rings. The Lx guys pulled the XLRs to the desk out of the 745, which solved their problem, but isolated the desk from the comms rings; hence the need to rig a belt-pack for the DSM.

 

When we tried re-plugging the XLRs & powering the desk the mains fuse on the 745 promptly blew (a bit alarming just before a run, when you don't have a spare master-station, but it seems to have survived), which suggests that something in the desk is putting a pretty hefty short across the incoming 24V. I don't really want to touch anything till the run has finished, so in the meantime I'm hoping for inspiration.

[A.Russell]

This is an excerpt from the Orbital website (here). Section F says that a power supply can be integrated. Is it possible that your desk has one and that the two power supplies are shorting each other out?:

 

Intercom

• All intercom systems can be integrated in the GDS SM desk system.
• 19" Third party units can be installed if required.
• Standard intercom facilities can be integrated in the panel design when using case types that don't support third party 19" rack equipment. This isparticularly useful when using the fibre glass lightweight case type 'A' as this low back to front profile is suited to prop corners or control rooms that are tight on space.
• Functions such as
  • Ring select
  • Mic control
  • Volume control
  • Aux control
  • Headset paging interface

  [*]GDS provide a custom intercom card that is designed for use with the standard analogue intercom systems such as tecpro, metro, asl etc. This approach allows a standard panel layout using standardised buttons etc.[*]Intercom power supplies can be integrated into the SM desk system if no master station exists.

 

Note: Edited as I had made two posts and the first one was superseded by the second one.

[Jevans]

My apologies - I had the 741 in my head, which does have what I described - I've just checked the 745 and it doesn't...

 

So I presume the 745 is powering your whole system? I suppose the key question then is what exactly has changed since it was working. I don't quite understand when you say the desk was just powering the DSM headset - surely there must have been an interconnect between the desk and the rest of the world?

 

Or do you mean the DSM was using the front panel headset on the 745 and has just now moved to using the GDS built bit in the desk? If so then I'd say, yes, they've put a PSU in the desk, at a guess.

 

I'm surprised that the Canford based power supply fused as the Tecpro PSUs are usually pretty bomb proof in my experience and just start working again as soon as a short or other problem is removed.

[sandall]

This is an excerpt from the Orbital website. Section F says that a power supply can be integrated. Is it possible that your desk has one and that the two power supplies are shorting each other out?:

Alex, thanks for that. Yes, that seemed a possibility, but if GDS desks normally rely on an external master station for comms power that looks less likely.

 

John - Sorry, I wasn't making myself clear. The theatre is unusual in that because Lx & Sound traditionally take their own cues, rather than being called from the corner, there is not a great use of comms, & the SM desk may not get powered-up until the Dress, & even then only be used for cue-lights & dressing-room calls.

 

In the current case, because the desk had to be disconnected from the Tecpro rings (to enable the LX Op to call spots) the desk headset became redundant, so the DSM was given a belt-pack plugged into the nearest comms wall-box (though unless any of the ASMs were on cans this may not have been needed).

[Jevans]

Okay - so what's powering the comms ring when the desk is unplugged? The 745 which is external to the desk? Or is there another PSU somewhere?

[sandall]

Okay - so what's powering the comms ring when the desk is unplugged? The 745 which is external to the desk? Or is there another PSU somewhere?

Yes, just the 745, which lives in a separate rack & is permanently powered (apparently it forgets the routing of show-relay onto one of the rings if you switch it off). The only schematic I've been able to get my hands on appears to show that the pre-amp for the paging mic is fed from the incoming Tecpro power, which suggests they have had to run the show without calls :(

[sandall]

Postscript: Finally got access to the desk yesterday & discovered a new (at least to me) form of enemy action. There were 3 video BNC cables hanging out of the bottom of the desk (curious, as there are only 2 monitors). A bit of wiggling & one of the cables dropped out. What it dropped out of was one of the 3-pin male XLR comms outputs :huh:. The locking-ring of the BNC connector had been shorting out all 3 pins of the XLR, & the bayonet slots must have been gripping pins 1 & 2 enough to hold the weight of the cable. Cursed, & re-plugged the master-station to the desk. Surprisingly all was well again, despite the load on the +24V having being enough to blow the master-station's mains fuse (tough, these Tecpros).

 

The cameras are patched in the control-room direct to a wall-box near the SM desk. Camera 1 also feeds a video DA for control-room monitors, etc. Someone had apparently thought it a good idea to unplug the SM's feed from camera 2 & stuff camera 2 into a spare output of camera 1's DA instead. Some other bright spark obviously thought the best way to find the missing camera feed to the wing was to plug random cables into random sockets until they got bored & went off to find something else to wreck. Nobody of course thought to make any record of what they had done, or why .

[sunray]

We once total silence just after the 'house keeping pre-amble' had started. Unfortunately we were frontending the house system and the shout went up 'It's gone again'. It took several minutes of rebooting the house kit (as had cured the problem previously) before we looked at ours and found a jack plug jammed in the second XLR output on the back of the mixer where someone had tried to to get audio to record the event.