My most successful posting to date (measured by the amount of comments) is my tutorial for fixing the Harman/Kardon AVR 35RDS receiver. In the comments section I thought about an English version of the tutorial, as surely the receiver was sold internationally as well. Below is the translation of my original post. Please notify me (or simply write a comment), if my explanations are not coherent.
Lately our receiver lost its adjustment for volume, radio stations, and digital input, after switching it off. Unfortunately the default volume is „20“ on a scale of „0“ (very loud) to „64“ (nearly silent). Thus „20“ does not blow our speakers, but is much louder than our average volume of around „45“ („30“ is very, very loud).
suspected the storage battery that is used for saving adjustments was faulty. Yesterday (07-07-07) I searched the net and found a thread in the HiFi-Forum (German language) about the receiver forgetting its adjustments (Vergessen der Einstellungen). In this thread several courageous men described their attempt to fix the storage capacitor.
Yes, a capacitor. H/K did not use a battery but a supercapacitor, a high energy density capacitor. This capacitor seemed to have conked out. Unfortunately this capacitor is located behind the display which is located on the board behind the cover.
Tools resp. material required:
- a middle sized crosstip screwdriver
- a small side cutter or pincer
- a small needle-nose plier
- a soldering iron (and solder)
- a replacement capacitor (supercapacitor, 5,5 V, 0.1 F)
- cable ties
Steps to be taken:
- Pull the plug. Don’t forget! Don’t skip!
- Unscrew the receiver. I recommend separating the different screws from each other in order not to mix different sizes.
- Detach the cover so you are able to unscrew the board from the cover. In order to do so, you have to cut several cable ties and possibly disconnect some plug-and-socket connections.
- Detach the board from the cover, remove the bass knobs, and the volume knob as well, unscrew the nut of the volume potentiometer.
- Bend the display until you can see the malfunctioning capacitor.
- Pinch off the faulty capacitor, solder the new capacitor (pay attention to polarity, and constructional depth, the display has to fit in afterwards; see remark at the end of posting)
- screw the board down and connect all(!) disconnected cables
- screw the cover down, screw the receiver down, finished
It is good to have somebody around to help and reassure you who also looks out for loose cables. Below there are several pictures to illustrate the aforementioned steps.
Some advice from Maschbauer in the comments of the original posting: I found a clever tip in another blog: instead of soldering the capacitor directly, just solder two cables in order to place the capacitor at another, better accessible place. Now you only have to unscrew the receiver in order to replace the capacitor.