QSC CX Series, Service Manual

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CX Series
CX6/6T & CX
1
2/12T Possible Causes:
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AMPLIFIER DOES NOT COME OUT OF PROTECT
1. Check speaker bus for DC; if over 3VDC present, the protection circuit is operating normally
to hold of operation. See DC FAULT WITHOUT CURRENT DRAW section to fix this DC
fault.
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RELAY WON’T TURN ON WITH NORMAL OPERATING AMPLIFIER:
1 .Check Relay power voltage. With relay off, voltage at C516 should measure about 47VDC.
With relay on, C516 should measure about 27V. if not check D516, R531, C516, D515.
2. If relay power voltage OK; check voltage on the timing capacitor C515. Should rise to
12-15VDC, in three seconds, which triggers Q513. If not check R528, R530, C515 polarity
3
.
Timing voltage OK; check relay transistor Q512. If good, RN501
B
-C resistors from base to
speaker bus should activate relay.
4. Relay driver Q512 OK, check driver Q513 and LD
1 01.
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NO RED “PROTECT” LED
1.
Check LED voltage, If over -2V, LED is defective. If OV with relay off (no negative voltage to
LED), there is no “protect” power (open or missing R534), which defeats shutdown circuits.
Be sure to correct before proceeding.
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NO MUTING DELAY (be sure “protect” LED works)
ALSO WITHOUT THERMAL OR DC PROTECT: relay or circuit is “stuck on’!
1, Relay Q512 shorted or wrongly mounted. Check by jumping base to emitter, should turn it
Off.
2. Relay Q513 shorted or wrongly mounted. Check by jumping base to emitter, should turn it
Off.
NO MUTING DELAY ONLY (all else OK):
1. D518 reversed
(
charges timing capacitor C515 immediately)
2. R528 low (fast C515 charge)
3. R29 low (low voltage on E7 turns Q513 on too soon), missing or high R30 (no off current).
EXCESS MUTING DELAY:
1. Check timing capacitor E515 voltage, If it rises normally but circuit is slow to turn on, check
D517 (lift temporarily), LD501 bad or intermittent, RN501 D too low.
2. Timing capacitor voltage wrong; determine cause (R528, R530, reversed C515, reversed or
wrong Q511.
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NO THERMAL SHUTOFF
Short the amplifier load with full signal to raise heatsink temperature and put voltmeter across PTC
R516 &
R616
(yellow or gray sensor on the output transistor), looking for voltage to rise from 0.7V
cold to 5.5V at shut down.
1.
No Red “Protect”, may have no R531, which defeats whole thermal circuit (no voltage across
PTC). Also check D517 high/missing, or relay drive circuit stuck on.
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NO DC PROTECT:
I.
R532 missing or very high.
2, BR502 defective/wrongly stuffed
3. Q511 defective/wrong
4, D518 reversed (also no muting delay)
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