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January 28, 2012

Fixing Old Speakers – The Common Woofer Foam Rot Problem

Audio Research freebie speakers

Audio Research freebie speakers


Got an old pair of speakers that don’t bark as well at the low end as they did in their younger days? You might be suffering from the dreaded woofer foam rot. Recently, I had been hunting for a good, cheap pair of speakers to partner with my newly repaired Hitachi receiver. I luckily found some free on Craigslist; someone just 2 blocks from me was giving away a great pair of 4-way Audio Research speakers with massive 12″ woofers, probably 1980’s vintage. They were “great”, that is, except that the suspension foam surrounding the woofers had almost completely decayed away.
Foam Rot

Woofer Foam Rot


This is the well-known “foam rot” problem seen in woofers and other high-compliance drivers of similar age. A few decades ago, speaker manufacturers started using a glued-on ring of shaped foam in place of the concentric corrugated cardboard surround on hifi speaker woofers, presumably to reduce distortion, especially at high excursion amplitudes. Unfortunately, the use of this foam has a recomplicating effect; it tends to decay away in 20 or so years, rendering the woofers useless. (The foam is apparently far from stable, which is good reason also to wear gloves when doing this repair; I don’t know the composition or the decay products.) Fortunately, there is an easy solution; there are many vendors of new, precise-fitting woofer foam, and the repair can be done quickly. (more…)

January 26, 2012

Most Repairs are Easy – Fixing an Old Hitachi Receiver

Filed under: repair,Uncategorized — Tags: , , , , — admin @ 1:34 pm

As you can see throughout this blog, I do a lot of repairs of durable goods ranging from cars to electronics. I’m writing a book on closely related topics now (stay tuned here for publication news). One of my contentions is that most repairs are quite easily accomplished with only a small set of tools and rudimentary expertise. In addition, often, the source of the problem can be found by simple visual inspection. Here is one such example.

The Failed Switch

The Failed Switch


I had in my electronic “junk pile” an old Hitachi SR-5150 stereo receiver that a neighbour had discarded in the fertile back lanes of Vancouver, BC. The SR-5150 is roughly early 1970’s vintage; it is all solid state and has all discrete transistors (the power transistors are even Hitachi’s own), and an analog FM tuner driven mechanically with pulleys and a flywheel. Nothing high end, maybe 20-30W per channel judging from the power supply. The receiver was dead to the world; it would not show any signs of life when turned on. I was motivated to fix the thing because I was looking for a decent amp to use as part of a new sound system centred on a home computer. (more…)

January 15, 2012

How To Fix A Toaster That Isn't Designed To Be Fixed

Filed under: Uncategorized — admin @ 3:26 pm

The Patient, pre-operative state

The Patient, pre-operative state


One half of our 4-slice Black and Decker toaster hadn’t been working for several months. I finally decided to take a crack at fixing it, as I so often do with broken products. The hardship of insufficient independent toaster ports had become unbearable (or more accurately, I couldn’t resist tinkering with the thing.) I suspected a broken filament from the outset. Here’s what I did for this repair. (more…)

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