hifi engine


I have a Hitachi 8300 amp that only turns on and that's it
...any ideas why it crapped out?

krokkor's picture

Hitachi HMA8300 failure


did you heard for a a "click" sound after few seconds from power on ?
If not may be the amp is under protection 'cause DC in the output stage that could damage the speaker (that's the reason you can't heard the output load relay switch-on).

Download the service manual from HFE library

With power switched off check if fuses F701L/R and F702L/R aren't blowed up (don't exctract fuses from his socket if the amp is powered and left the power supply capacitors discharging for a couple of minutes from power off, before check these fuses). If they're OK switch power on and with a multimeter in DC (100 V range at least) check on R731L/R (both channels) if a DC is present; in normal condition no voltage should be present between ground and this component (use negative output speaker socket for GND).
In case a DC is present on R731 shout down power, left electrolytic capacitors of power supply to discharge for few minutes, then check with the ohm-meter the fuse resistors in the driver circuit (R704,R710,R711,R714 and R716) in both channels; test these components disconnecting one pin from the PCB in order to have a correct measurement. If wrong value occurs during the test replace the component with same type and power fuse resistor or in alternative with a 2 W carbon film resistor.
If after this fixing the DC is still present on R731 may be the end stage is damaged (driver or end stage transistors short) so you need to check all semiconductors on circuit in order to find the damaged one.
Otherwise if after the initial check on R731 no DC is present this means that the protection circuit is defective so check power supply of the relay S3 and or the relay's driver semiconductors (Q501,Q502,Q503,Q504) ad associated components.

HMA8300 is a complex circuit; if you're not deep inside electronics repair pls. refer to an Hitachi service in order to fix the problem.
If you try the repair by yourself be careful to end stage high tension (+ - 100 V) and wait for the power supply electrolityc capacitors to discharge before attempt measurement or working on the PCB. If Electrolytic capacitors requires too much time for discharging don't short it with a tools but use a 125 V bulb lamp for discharge the capacitors.

Hope this can help you