Control/Dimming Hub Electric Architectural Dimmers

JD

Well-Known Member
Joined
Jan 1, 2005
Location
North Wales PA
I'm going to start this thread to provide reference information for some future poor soul who may have to service one of these systems. Hub is no longer around, and information about these systems and dimmer modules does not exist. As such, over the next few months I am going to have to reverse engineer the equipment and create my own schematics. The system consists of an analog controler mounted in a wall. It has seven dimmers and a master, as well as an up/down motor controler for the bulk of the building's lights. Up in the hot attic is a cabinet containing 18 modules, each 3.6Kw. (and a tiny little motor attached to a pot!) It has been in use for 28 years 24/7. Amazingly, it still works pretty well, although the curves are trash at this point. I am suspecting this will involve massive capacitor replacement.
Today I started with the controler and had my first surprise! The controler outputs 0 to -24 vdc! Yes, Negative!
I will post back as the project continues.
 

Mac Hosehead

Well-Known Member
Joined
Sep 10, 2014
Location
Shark Tank
Going way-back, negative control voltages were not uncommon. My college had a Century Strand Cue Card system that had a negative control voltage. I believe the original Edkotron (gray) packs were negative control. The next generation (greenish brown) had a positive control. You could mix the two since they had the same control connector but something usually blew up.
 

microstar

Well-Known Member
Joined
Jan 19, 2014
Location
Lawton, OK
I worked with a Century Edkotron system (greenish brown version) at the Penthouse Theatre at the Univ. of Washington in 1971 or 1972.
Don't believe it was very old at the time. Interesting units, named after Edward Kook, one of Century's founders.
 

JD

Well-Known Member
Joined
Jan 1, 2005
Location
North Wales PA
First bit of reverse engineering was the wall controler. No surprises there, and couldn't be simpler! Well, maybe one surprise: The up/down motor switch actually has line voltage on it! Almost no current so I suspect it goes right to the little motor. I suspect there are a couple of phase shift capacitors involved for reversing as when you push the switch up or down, the opposing contact jumps to 196 Vac measured to ground. So, if you are working on one of these, beware that not all wires are low voltage!
nave_panel_s.jpg

control.jpg

One other note: It is mounted in a steel box in the wall with a dedicated conduit that goes straight to the rack. All appear to be #14 THHN.
 
Last edited:
  • Like
Reactions: microstar

JD

Well-Known Member
Joined
Jan 1, 2005
Location
North Wales PA
So, here are some pics. 14 mods, not 18. Stands about 6 foot tall. "Open Architecture" kind of reminds of the old hub autotransformer units! The modules are robust, using two 80 amp SCR's back-to-back for a 160 amp bridge on a 3k dimmer! (No wonder they've lasted so long!) Next week, I am going to reconstruct the actual dimmer schematics.

d1.jpg

d2.jpg

d3.jpg

d4.jpg

d5.jpg
 
  • Like
Reactions: microstar

JD

Well-Known Member
Joined
Jan 1, 2005
Location
North Wales PA
Worked out the motor control (apparently common for Hub) and frame wiring of the Dimmers.

motor_dimmer_frame_s.png


The power supply for the -24 vdc controls appears to be an off-the-shelf 24 Volt DC supply. Again, pretty simple.
power_supply.jpg
 

ship

Senior Team Emeritus
Premium Member
Joined
Mar 29, 2003
Location
Illinois
Hub still does exist and Ken is a friend of mine (current retired owner / tech person of the company). He still does repairs on the gear, and someone like you he would want to chat with in training. Believe he is a member of this website, but I will email him directly in chiming in.
 

JD

Well-Known Member
Joined
Jan 1, 2005
Location
North Wales PA
Hub still does exist and Ken is a friend of mine (current retired owner / tech person of the company). He still does repairs on the gear, and someone like you he would want to chat with in training. Believe he is a member of this website, but I will email him directly in chiming in.
That would be great! Refer him over to this thread. Already began working on the pulse-drive card. All generic parts that are still commonly available. Very basic firing circuit using a MOC3010 photo-triac. There are reasons this thing is still working after 28 years of continuous use!
Before starting the reverse-engineering project, I did some extensive searches for any data or even cut-sheets. Like many things that were built before the internet, it is like none of it ever existed.
 
  • Like
Reactions: RonHebbard

JD

Well-Known Member
Joined
Jan 1, 2005
Location
North Wales PA
I am dividing the dimmer module between the Line Voltage section and the low voltage section as it adds clarity. One thing I don't like about this design is that the heat sink is at line voltage. Once again, the wiring layout is beautiful in it's simplicity.
Line_mod_s.jpg

One note about Pin #1, which is shown as a N/C.
This is connected through an isolation diode to the negative rail. I would suspect it may be used if a single module were being used as you could connect a remote pot across pins 1, 2, 1 and 3 and have a stand-alone dimmer.
 
Last edited:
  • Like
Reactions: microstar

JD

Well-Known Member
Joined
Jan 1, 2005
Location
North Wales PA
Interesting! Where as most analog driving boards use a ramp generator and a comparator, this one actually works by the control voltage modifying the ramp! One resistor is left unlabled as I am reading it as Red-Orange-Gray, but that would be 23 followed by eight zeros! Going to have to climb into the loft and take another look!
The heart of this circuit is the 0.15mfd 100 volt capacitor which governs the ramp. The 1mfd 63 volt cap simply filters noise from the control signal and helps slow down inrush by delaying an instant "full on." Zero Voltage Cross is detected in the usual fashion by throwing a diode in series with the bridge rectifier and then amplifying the pulse (two transistors at the bottom.) Interesting using the biased Unijunction as the primary switch! Reminds me a bit of the old super-strobe controllers.
Remember, in a unijunction transistor, it is the Anode/Gate voltage that fires the device, the opposite of an SCR.
LV_driver.jpg

I am expecting that after 28 years being on, the main 100mdf power supply caps have dried out and plummeted in value, allowing massive ripple on the + buss. I think I will be changing the 680 ohm resistor and zener diode on all units simply because of the thermal evidence.

And, what they all look like mounted on the board:
LV_driver_board.jpg
 
Last edited:
  • Like
Reactions: microstar