Harman Kardon AVR 158 (2011)


State of preservation and error analysis

I received the Harman Kardon receiver with the error description that the sound is very quiet. After resetting the settings and performing a reset, the audio playback was flawless again. The device, which is more than 10 years old, is otherwise in good condition optically and with regard to the soldering points. Nevertheless, the device was disassembled, cleaned and the main, display and transformer PCBs were re-soldered.


Repairs recording

  • Check and resolder solder joints
  • Perform a microprocessor reset
  • Check ESR of capacitors
  • Check voltage sources
  • Clean the inside and outside of the housing
  • Test the device over a longer period of time
Picture 1 Harman Kardon AVR 158 (2011)
After a long test in home use over several weeks, it has been shown that there is obviously another problem. - Namely, a noise occurs. The problem was most noticeable on a source via HDMI connection.

Cause of the noise

Picture 2 Harman Kardon AVR 158 (2011)
According to the error findings, it was likely that the problem was caused by the HDMI PCB. - This must also be transmitted to the amplifier stage (main PCB) via a power supply that is shared among the PCBs. After extensive analyzes and measurements, it has been shown that the noise from the DC-DC converter (step-down) circuit part on the HDMI PCB is fed back to the +15 V supply voltage, which, as suspected, also transmits the interference signal back to the audio stage (Main-PCB).
Picture 3 Harman Kardon AVR 158 (2011)
It turned out that a solder joint of an SMD resistor "R924" (circled in red in the picture) that had become cold over time caused a loose contact. Because after pressing the component, the interference signal has increased significantly. After resoldering the resistor, the cause (trigger) of the problem could be eliminated. However, the IC "IC812" has probably also been affected by the loose contact, because a background noise is still present. The IC will now be replaced...