PROEL HP-X series, Service Manual

Page: 11 / 24

11
6.2 Malfunction Analysis on Amplified Part
Sequence
No.
Circuit Function Failure
1
Class AB Power
Output
‐ Power supply protection: Any of the short circuits of power output
transistor (CH1/Q2, Q3, Q10, Q11, CH2/Q19, Q20, Q24, Q25) will cause
the high current and power supply protection;
‐ Amplifier protection: +15 V/ ‐ 15V is derived from the current limiting
of R31, R40 and D3, D4, if the power supply is abnormal it will lead to
the DC output, amplifier will go into protect status;
‐ Clip limit doesn’t work – check whether the devices of D7, D8, D9,
D40, LED1, R22 is damaged or not;
‐ Amplifier self ‐ excitation – check whether the device of C3, C7, C8,
C10, C14 was turn bad.
‐ Crossover distortion : check whether the BE voltage of the
negative ‐ positive half ‐ wave power transistor is <0.2V or not, then check
the value of temperature compensation transistor Q and resistance
(R25, R26, R13) is changed;
‐ IC/5532 damaged, unbalanced of the of positive and negative bias
voltage, has DC output and power amplifier goes into protection.
2
Overload/
Short ‐ circuit
Protection
‐ Output short ‐ circuit and no protection,
‐ Start–up protection
3
Clip Limit
Circuit
‐ No clip limit, check whether the D7 is on;
‐ Clip limit delayed, check the D9 and R19;
‐ Wave form jitter when in clip limit;
‐ No volume gradually increase function after start ‐ up.
4
Over ‐ temperature
Protection and
Delay Circuit
‐ The delay circuit protect is a collection of VHF, short circuit,
over ‐ temperature, DC ‐ protection, as well as start ‐ up delay.
‐ When the Protection function and start ‐ up delay is abnormal please
check this circuit.
5 DC Protect Circuit
‐ No output ‐ relay does not pull ‐ in, first check whether it is normal for
24V power supply, Q6 base is a high level.
‐ On / off has the sound of shock ‐ a long pull ‐ in on the relay;
Repairing Guide:
1) When repairing the amplifier, please series connect a 100W—200W lamp to start the equipment in
order to avoid the damage of related device;
2) The circuit of CH1 and CH2 is the same but the sequence No. of device is different, all the testing
parameter can be shared;
3) Power amplifier protection means the power supply and protection indicator on the panel are lit;