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2) Checking the speaker protection:
- Mount IC5 type LM324 in its socket with the notch in the direction of fuses
F1 and F2.
- Once again connect the mains voltage to the transformer. Normally, relay
RY1 should energize after a few seconds.
- Connect a 1.5V battery with its + pole to LS+ and its - pole to LS-. Normally,
the relay should de-energize and LED LD30 should light up. This means
that the protection against positive voltages is alright.
- Connect the + pole of the 1.5V battery to LS- and the - pole to LS+.
Normally, the relay should de-energize and LED LD29 should light up. This
means that the protection against negative voltages is alright.
NOTE: When testing with the battery the relay will once again become
energized after 2 seconds and will then de-energize immediately. This is
normal.
- Remove the mains voltage and wait 5 minutes before carrying out the next
test.
3) Checking the output stage:
- Mount IC6 type TL071in its socket with the notch in the direction of IC5.
- Mount IC7 type TL061 in its socket with the notch in the direction of IC5.
- Mount IC8 and IC9 type TL072 in their sockets with the notch in the
direction of the relay.
- Connect transistors T10 and T11 (IRFP9140 or equivalent) and T12 and
T13 (IRFP140 or equivalent) to their corresponding print pin connections on
the pcb.
- Short-circuit the amplifier input using a short-circuited CINCH or RCA plug.
- Connect the mains voltage to the transformer.
- Measure the voltage across resistors R78, R79, R80 and R81, respectively.
NOTE: Since one connection of these resistors is hard to reach (the connection
against the heat sink), the jumper to the LEFT of each resistor may also be
used.
The voltage across these resistors must be about 35mV (0.035V). If the
voltage across one or more resistors is higher than 60mV, the amplifier should
be switched off immediately and the fitted components should be checked.
Once again disconnect the transformer connections from the amplifier block.
Now the other amplifier block is tested in the same way.
H4020-ED2-31
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