akira HTS-797AS, Service Manual

Page: 9 / 20

- 9 -
Model No.: HTS-797AS
Version: 1.0
Over current protection check:
In the moment of being electrified and before this unit enters the protection mode, use the volts DC of
multi meter to test the collector voltage of L/R over current protection tubes Q515 or Q530.The
normal volt should be approximately equal to the one of the amplifier positive power supply. If it
declines heavily to cause the Q405 through and this unit will enter the over currency protection mode.
At this mode we can further check whether the problem is in the right or the left channel. The way is
to check the transmitter voltage of the over currency protection tube. It shows that the channel has
entered the over currency protection mode if the voltage is over 0.6v. Then you should place emphasis
on checking if there is some apparatus in this channel that has been punctured and whether the output
resistance of the amplifier tube transmitter is at the open state.
Trouble shooting way of the protection circuit itself having problems:
After confirming the over current and voltage circuit both work normally but the problem cannot
solved, this time we need to consider the protection circuit may have problems. The checking steps
can be conducted as the following pane chart.
Whether Q404 (55151) base is below 0.6v
YES
NO
YES
NO
YES
YES
NO
YES
NO
NO
Whether the CPU U001 (39) is high level
Electrify the units and turning on protection
Whether Q001 (5401) base is high level 5v
Q001 (5401) or
Q005 (5551) NG
Whether the Q407 (5551)
collector is high
level
Q407 is punctured or the amplifier’s over
voltage protection has problems
Q004 (5551) is
punctured
Q405 is punctured or the problem of
amplifier’s over current protection
The machine circuit has no problems. The default is
due to the CPU program
CPU U001 NG
Whether Q405 (5401) collector is low
level