it’s always the capacitors – Logitech SB3 one channel low audio fix

It’s always the capacitors¹ causing trouble these days, and if it’s not them it’s the connectors 😉

When I started work decades back, in Test, on units that had a Z80 microprocessor I kept a Z80 spare. When a faulty unit came in, I always tried swapping the microprocessor. Never in my time there did that clear the fault, it was always something else.

ICs are surprisingly resilient, and after some decades of experience trying to fix things, there’s one suspect that seems to be the #1 troublemaker – the humble electrolytic capacitor, and particularly in its SMD form. I’ve repaired gear from the 1970s and 80s and often the fault is an overstressed transistor, they were more rubbish in those days. Often the electrolytic capacitors are still OK after decades, it’s the more recent ones that seem to fail earlier. Nowadays we just don’t seem to know how to make electrolytic capacitors that last. Or nobody expects modern electronics to be in service for more than five years 🙁

It’s not always the connectors and capacitors, but they seem to be the bad guys most of the time!

First suspect connectors, then electrolytic capacitors

I had a Logitech SB3 network player, and when I powered it up after a year it sounded tinny with low output on one side. I blamed the tinniness on the cheap and nasty headphones I used, but fiddling with the 3.5mm jack didn’t change anything. Tried the headphones on something else, they were OK, switched headphones, fault persists.

The usual suspect would be the connector, these are often mechanical in some way and prone to damage. However, there was actually something coming out of the low channel. Connector faults are usually honest all or nothing intermittency, or nothing at all.

A couple of months in the laboratory can frequently save a couple of hours in the library², so before I get this on the bench I enquired of Google, which came up with this thread, and this one . Both mention capacitors as the likely culprit. I took this SB3 apart

I identified the output capacitors by buzzing out continuity between the jack connector and the negative sides of C35 and C32. If you look really hard at C32 you can see some gunk, but it wasn’t obvious at first glance, and there is some funky hand-soldering on the board connectors anyway. I determined that this board was made after the end of June 2005, by the original Slim Devices startup that Logitech bought out. So it’s 20 years old at most.

SMD caps were bastards to desolder – you can’t really use solder tweezers on them, but let’s hear it from Mr Carlson, just twist them off

This worked fine for me³ – the secret is in the construction of a SMD capacitor, which you can see from the wreckage

What you can also see is that C32 has leaked a lot. I was tempted to solder to the remaining posts after cleaning the gunk a little bit, but they didn’t take solder. I guess the clue is in the name – aluminium electrolytic, and ally doesn’t take solder.

What’s standing up is some sort of riveted connection to the leads/SMD contacts, so I snipped these as flush as I could with sidecutters to lift the plastic to show the full horror of the leak.

This construction seems to be a particular weakness in SMD capacitors. Look at the top of the replacement leaded electrolytics I fitted, and you’ll see they had to score the can, so if you fit these backwards or otherwise cause leakage it can break out the top of the cap. That implies the seal at the bottom is pretty damn good. While I’ve seem electroytics detonate when you wired them in backwards on a power supply, it it true, sometimes the top breaches explosively.

There was a problem with electrolytics made in the late Nineties/early 2000s and the Wikipedia article shows leaded electrolytics bulging at the top. SMDs just seem to leak at the base.

I had some 220uF 16V electrolytics I had bought at some radio rally. From what I know now I wouldn’t buy NOS electrolytics again, but I tested the replacements with a Chinese tester widget

I decided I can live with that, and soldered a couple in place, forming the leads to make contact with the pads.

Not so fast. Reassembled unit and listened. Nothing on one channel. Eh? Then I observed the headphone jack was recessed – C35 was standing proud and fouled the curved back of the case somewhat. Solution was to replace it and lay it down.

Great. Sorted – back fits on OK and the socket is flush. Socket is slightly cruddy so it needs a clean, but signal quality is fine. I did take a look over the other electrolytics particularly the 220uF 16V ones with a magnifier, but they looked OK. I didn’t want to recap everything given I don’t have the right SMD caps, so I took the First Do No Harm approach.

There’s gonzo startup-ery written throughout the weird construction of this, from the uncleared flux on the hand soldered connectors and board interpass connection, though the main PCB looks properly made. And what’s up with that whopping great big 3300 uF 16V Nichicon cap jumped across at the top of the board, and another one patched in closer to the connectors?

In all fairness, however, their work has stood the test of time in that it is still supported, and this unit now works OK. Lyrion Music Server is the server end, which you can run on a Raspberry Pi using PiCorePlayer (which has a server offering). I couldn’t get NFS to work on that but a large-ish USB stick on the pi itself works fine. You can scp files to that to add new music.

1. More specifically electrolytic capacitors, unlike in days gone by non-polarised caps seem to last fine ↩︎
2. Frank Westheimer ↩︎
3. This guy pushes back on the twist idea and says hot air is a better way. Twisting worked for me this time, I may try it on some scrap gear to see if it is a general solution or only works soemtimes ↩︎