Logitech R-5 Speakers Repair

Yesterday I bought a pair of salvaged speakers at Pasar Loak Jembatan Item. Logitech R-5 speakers, bought them salvaged/used for cheap. I can’t seem to find an official Logitech product page for these, but according to an article these speakers were from 2008, and these were cheapies back then too, about 10 USD.

When I bought them the stereo cable was missing the 3.5mm aux stereo plug, they were dirty, and one of the speaker drivers had scratches on the membrane. The stereo cable was cut at the end and had the insulation removed, exposing the inner conductor. The conductor for ground and left channel was twisted together for some reason. Soldering a 3.5mm aux stereo plug should be a simple thing, I tought to myself. Spoiler: no.

After I brought them home I tried plugging the mains cable and pressed the power button. The LED indicator lights up, always a good sign. I proceed to measure the stereo cable’s exposed conductors for AC and DC voltage. The purpose was to make sure nothing dangerous was going on before I connected them to my computer or phone.

After that I reused the 3.5mm aux stereo plug from one of my previous post for this cable.

TRS Plug Stereo Cable Channel
Tip White Left
Ring Red Right
Sleeve Shield Ground

I then plugged that to my computer and played some music. It works! But the left channel sounded much weaker than the right channel, and the volume potentiometer adjustment was very scratchy and sometimes turned off one of the channels.

So I opened the right speaker unit and sprayed contact cleaner to the volume potentiometer and spin them a bit. That did nothing. I desoldered the potentiometer and opened its case. Turned out some of the wiper in the potentiometer had bent/twisted. I bent them in the correct orientation, sprayed more contact cleaner, put the potentiometer back together again, soldered it back, and tried playing music again. Much better this time: the channels now only occasionally turned off, and the scratchiness were much reduced. To completely fix these I would need to buy a replacement potentiometer. Not now though.

Thinking that I had fixed what mattered the most, I cleaned up and shrunk the heatshrink tubes that I put on the stereo cable beforehand.

Now the left channel is completely silent. I turned the volume potentiometer up and down but the left channel is still silent. I tweaked the 3.5mm aux stereo plug that was still connected to the PC, still nothing. After troubleshooting using a multimeter, reopening the case, and desoldering the stereo cable from the circuit board, I found out that the left channel and ground was shorted in the cable. Did that happened because I was using hot-air station at too high temperature to shrink the heatshrinks? No idea.

I cut off the heatshrink and a small portion of the cable and resoldered the connections inside the 3.5mm aux stereo plug, but the short circuit persisted. Now I think the Tip and Sleeve of the plug itself is also short-circuited, perhaps the insulator inside the plug melted because of the high temperature of the soldering iron. Anyway I cut the plug off and threw it away.

Good thing I already have other plugs on hand, better quality too: supposedly gold plated, also the casing and the strain relief was made of metal. So I redid everything and this time there was no drama. The left channel worked again. I now have a pair of working speakers, albeit with somewhat scratchy volume adjustment that very occasionally turned off one channel.

See ya folks.

Note: The amplifier chip is TEA2025B from STMicroelectronics. The product page and datasheet never mentioned which class amplifier this is.

  • 2023-08-04 Update: I had just replaced the potentiometer with a cheap, generic, no-name, stereo 10KΩ. As expected the volume adjustment now functions smoothly. No scratchiness and no more occasionally-turned-off-one-channel.