Logitech R-5 Speakers Repair

Joshua R. T. Purba

2023-03-13

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.

I misarranged the units. The unit with button and knob should be the right channel, the one without should be the left channel. In general the units were dirty. — Front view of the salvaged speakers.

Not too much damage on the casing itself, just scratches, dirt, white paint particles. — Side view of the salvaged speakers.

Just like the sides, the back didn't have much damage. — Back view of the salvaged speakers.

Manufacturer's labels at the bottom of the right channel unit. — Labels of the salvaged speakers.

The end of the stereo cable had the 3.5mm aux plug cut off, and the conductors were exposed. — The cut off stereo cable.

The conductors of the left channel (white insulation) and ground (uninsulated shield) were twisted together. — Close-up of the cut off stereo cable.

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.

Preparing to solder the 3.5mm stereo aux plug.

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.

Aside from the speaker driver, there really was nothing inside this enclosure. — Inside the left channel unit.

Other than the speaker driver, there were the amplifier board and the power transformer. No wonder this unit was heavier. — Inside the right channel unit.

This all-in-one board contains the power supply (discrete diodes for rectification from the power transformer and capacitor for smoothing), amplifier, LED indicator, power button, volume adjustment potentiometer, and headphone socket. — The power supply and amplifier circuit board.

Close-up of the board showing the amplifier chip.

The wiper inside the potentiometer was bent.

I bent the wiper back into its position. Good enough. — The wiper was fixed.

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.

Because I tought that I was nearly done I cleaned the front face. A scratch can be seen on the reflective surface of the membrane of the speaker driver of the right unit. — The front face of the case had been cleaned.

I used heatshrink tubes as extra strain relief and heated them using hot-air station. Looks nice, right? Too bad the left channel then didn't work anymore. — Heatshrunk tube on the 3.5mm aux stereo plug.

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 plug off and threw it away.

Good thing I already have other plugs on hand, better quality too: (supposedly) gold plated, also the “handle” 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.

The metal 3.5mm aux stereo plug felt much nicer than the plastic one it replaced. The left channel worked again. — The replacement 3.5mm aux stereo plug.

See ya folks.

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