Advertisement
* T3, BR2, BR3, REG1, REG2 establish the low voltage rails +24V, ±15V.
* Q3 circuit delays switching of RLY1 until the oscillator formed as part of U1 has started.
* Drive signals for the IGBT switching transistors are from U1 PINS11 and 14 via isolator
transformer T2.
* The IGBTs form a resonant push/pull circuit with C14-15, L3 and T1 primary.
* T4 is a sensing transformer for control circuits.
* The secondary of T1 is rectified and smoothed to form the high voltage rails for the power
amplifiers.
* RLY2 and RLY3 switch the rails if the amplifier temperature exceeds certain limits.
* T4 and D15 to D18 develop a d.c. voltage relative to the current drawn through T1. This is
used via U3b, U2b to switch off the drive to the IGBTs by shutting down U1 if the current
drawn through T1 exceeds certain limits. U2b comparator latches once triggered.
* U3a buffers the output from the attack/decay circuit formed by D11, R33, R34, C37. This
voltage passes to the limiter control circuits via CONN1 PIN5 to PCB700, U3a where it acts
upon the limiter threshold voltage 'V-threshold' at VR1.
* U2a compares the high voltage rail 'Vcc' with a reference voltage from the +15V rail. If
'Vcc' exceeds certain limits, U2a via D10 shuts down the IGBT drive. This is non-latching.
* Q4 drives the relays RLY2 and RLY3, which step down the 'Vcc/Vss' rails. The base of Q4 is
driven from PCB700 via CONN1 PIN4.
* NTC4 senses the IGBT heatsink temperature within the power supply. D12 adds a small d.c.
voltage to that on C37 to also control the limiter circuit as above.
SAFETY COMPONENTS
* FS1 is a 1AT fuse to protect the low voltage circuits.
* Th Trip1 is the main unit thermal trip fitted to the rear panel. (240V version = 20A)
* PTC1 protects the switch circuit if something prevents RLY1 operating at switch-on.
WARNING: LETHAL VOLTAGES ARE PRESENT ON THIS POWER SUPPLY.
ENSURE VOLTAGES HAVE DISCHARGED BEFORE REMOVING
PCB712 (PSU).
DIS-ASSEMBLY (See equipment list for tools - Appendix 1)
Access to the circuitry is via the top panel which is retained by 12 x Pozi-head (PZ1 and PZ2) set
screws. Side panels can be removed for access if necessary. (6 x Pozi-head PZ2)
Most servicing can be carried out without removing the main PCB since it is double sided and
component side soldering/de-soldering is normally possible. However, when necessary the PCBs
can be removed as follows:
a. INPUT PCB PCB701
* Remove connectors J103, J203, CONN5 and CONN6. (Cut tie wraps as necessary.)
* Remove 8 x POZI head screws from XLR connectors. Note position of screws with
spring washers (2).
* Remove 2 x POZI head screws holding PCB to main PCB.
* Carefully raise PCB to gain access to J105, J205 underneath linking PCB701 to PCB710.
Remove cables from J105, J205.
* PCB701 can now be removed completely.
6
Hide quick links:
Advertisement
