After having my Altec Lansing MX5021 desktop speakers for the past 9 years and put up with the increasingly loud standby hum for ages I decided to take the unit apart and have a look and see what was the cause.
The Altecs are looking a bit sorry for themselves now, they’ve fallen off my desk countless times, survived about 5 house moves but still sound incredible.
However, there’s always been a low hum from the amp/subwoofer box so I took the unit apart on Tuesday night and tried to find out what was causing it.
As soon as the unit was apart the cause of the hum was dramatically easy to locate, it’s the transformer.
I detached the transformer from the casing (its screwed and glued) and re-mounted it on a thick bed of silicone to try and damp the humming.
The windings themselves were really hot despite the unit not being driven for some time before the strip down, the same was true for the heat sink on the amplifier board, it was still very hot about 35 minutes after power down.
One thing I didn’t like the look of was that the sub casing was filled with fibreglass insulation which actually covered the transformer and the heat sink. Strange build choice.
Put the whole unit back together and tested, the hum is still there. Bummer.