SONY TA-AX330 faults and fixes
When I moved in to Warsaw at the end of Spring, I felt the need to set up a proper Hi-Fi setup. I already had a pair of Tonsil speakers from the 90s (produced shortly after they split from the ever so famous UNITRA), but I lacked a nice amplifier. Previously I've used those speakers with a home-made amp based on two 32W TDA chips soldered onto a tiny perfboard, but it broke a long time ago, so I needed a replacement. I got the TA-AX330 from a friend (<-- warning: flashing imagery and loud .MOD tunes) for the low low price of FREE, but the amp had immediately shown some problems.The unit, in all of its blurry glory. (click to enlarge - JPG, 688KB)
The unit is quite fancy for what it's worth - it has a nice equalizer, five satisfyingly clicky input selector buttons, balance slider and two speaker outputs (sadly, only one can be active at a time). The sound is clear, with a lot of bass and treble, and the EQ allows for even better sound reproduction - it's especially useful for content with quiet/muddy vocals.
Remember how I mentioned those cool input selectors? They were the first offender. Sound would fade in and out, or would be missing altogether unless you mashed the button a few times. I planned to disassemble the unit and spray some deoxidizer on the button contacts, but the problem went away after around a week of continuous use.
Second problem was a lot worse. For some reason, Sony decided that it would be a good idea to insert a repeater into the audio path, that would be engaged only when the device is fully operational - this adds a delay of 3-4 seconds every time you turn it on, presumably to make sure that the capacitors are charged before the device outputs any audio. All was fine until that repeater started acting strangily - at random moments it would start disengaging and engaging again, emitting an annoying clicky sound. I decided to disassemble the unit to get a look at the internals.
DisassemblyThe internals; important screws marked (click to enlarge - JPG, 2.8MB)
I started by unscrewing the top cover. The mainboard was on the right, with the repeater being more or less in the center. I plugged the speakers back in and tried to play some audio - a gentle tap on the repeater's case was enough to disrupt the signal.Bottom, left and back of the case; important screws marked
While disassembling the unit, be very careful about the part with big heatsinks - they're being held only by a few flimsy wires, and you wouldn't want to break any of those. Also, before flipping the board, you'll need to cut two zipties that hold the cables to the case.The PCB, flipped upside down (click to enlarge - JPG, 1.7MB)
I desoldered the repeater and by checking the pinout underneath, I concluded that it's just a standard part - not something specifically designed for audio gear. Unfortunately, I couldn't find a replacement in my shop; Mostly for fun I tried to disassemble it and see what went wrong - the part was old enough that it had a slide-in plastic case instead of a sealed plastic case, so it could be disassembled with just a screwdriver prying it open.
To my surprise, inside it looked almost brand-new. No corrosion on the contacts, the electromagnet worked like a charm. This meant that a weak contact on the PCB was to blame, so I soldered the repeater back in, making sure to use a lot of solder. So far, the fix was pretty successful - tapping the component doesn't change the audio level at all. A better solution in the long run might be to replace the repeater, but as the part was almost brand-new inside, I don't see a reason to.
For future readers
Even though this amp is from a well-known brand and has quite a lot of high-quality components (for example nichicon caps), if you're reading this post more than a few years in the future from 2020 - make yourself a favour, replace all caps inside with new ones. When I'm writing this, most of those amplifiers probably don't need their capacitors changed just yet, but components tend to deteriorate quicker the older they are.