• HD Dimmers Overview

    HD dimmers predated RD dimmers, and were manufactured by LMI in the early 80's.  ETC still stocks some parts for this rack. ETC can also perform board level repairs on the clock cards and dimmers.  As each of these touring racks and installation racks were custom built, there are no manuals.

    HD Touring Rack

    Figure 1

    Rear of Dimmer Module

    Figure 2

    Front of Dimmer Module

    Figure 3

    Looking from the top of the dimmer module down: (Figure 3)

    1. Recessed output trim screw to set top-end level.
    2. A 10 segment LED that will move in correspondence with incoming signal level.  Incoming signal was 0-10Vdc -- there are no other control options.
    3. A three position switch, this switch will set the dimmers into one of three modes: 
      - Off:  No output 
      - Dim: Will dim from an incoming signal 
      - Full On: Will stay on regardless of incoming signal (spring loaded bump)
    4. Load neon. This will illuminate when a load is attached. This can be a handy way to see when you have a blown lamp.
    5. Plug-in jack to meter dimmer output.
    6. Neon lamp that illuminates when the module has power.
    7. Circuit Breaker.
    8. FuseThe modules are not SCR based dimming is done with a triac.

    Backside of dimmer (Figure 2)

    If you remove a module, you will see a small toggle switch on the PCB. This switch is to determine whether the slot has a dual 1.2kW or a single 2.4kW module in it. The rack pictured is a 1.2kW.  You should not change this, as it may damage the modules.

    Rack (Figure 1)

    The chokes for the dimmers are in the rack -not on the dimmer module. On the rack assembly for each row of dimmers (each row is a phase) is a control section. This section has test points for the Neutral, Line voltage, Clock signal, and control common.  There is also an LED that indicates power to the clock card.   The fuse provides protection for the clock card behind the small screw panel. This clock card takes the 0-10Vdc control signal and modifies it to a pulse-width signal based on the voltage zero-crossing per phase.
    On the back side of the Rack are breakers and output connectors; generally Socapex.

    Common Failures:

    • The connectors between the dimmer and the enclosure are prone to burning out.
    • Breakers and fuses can go.
    • The clock card can be damaged by voltage surges (but can be repaired at the factory).

    Part Numbers:

    Note: Most of the below parts are not currently in stock and the availability is limited.

    J313  CON 10M TERM BLK SOC EV Male (module) small stock available
    J312  CON 10P STRIP Female (rack) none in stock

    Other parts

    1050A1002  ASSY;DIMMER MODULE, 1K  none in stock
    Q107    TRIAC; Q6025P 25A 600V
    F101     FUSE 10 AMP  SC-10
    CB102   CIR.BREAK;SP,  SLOW, 10A
    1050A1001  ASSY;DIMMER MODULE, 2K
    Q109    SCR; 63A PACK
    F106    FUSE 20 AMP SC-20

    Note: Most of the parts are not currently in stock and the availability is limited.

    Additional information about HD Dimmers 

    HD Dimmers are analog dimmers. 
    Originally they had a digital patch built into them but the patch was removed on all of them. 
    Some may have been retrofitted with either EC-24 cards or a Response 96 out card (most likely the former). 

    There were two versions of the rack. One had the ramp/trigger cards on the side panel, the other version had them behind in a little door to the right or left of the modules (there were left and right had units)  They both worked the same.

    There were three versions of the trigger cards.  All interchangeable but some had better trigger/zero crossing circuits.

    There were both dual 1K and single 2K modules. There were two version of these too. Basically the same but the driver that controlled the bar graph went obsolete so it was changed to a different circuit.

    The biggest problem they had was that they would slip out of the tray during shipping and have to be pushed back in at each sited. Version II had a retaining bar.