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Page updated: 12-Feb-2022

Technics Crossover Repair

This SB-CS90 3-way speaker system was a 2nd-hand freebie, but both speakers sounded very dull. The speaker units and crossovers are all wired using spade terminals so it was fairly easy to measure and swap sections around to narrow down the faults to the crossover boards.
Blown capacitors seems to be a common problem with crossover circuits, and one of the originals looked like it had already been replaced in the past, so plan A was to identify and just replace the faulty component(s).

However, the original capacitors were packed very tightly and the values not commonly available (at least, not for a price I was prepared to pay!). There was also some doubt about how much abuse the crossovers had seen so I decided to replace them all and make some new boards.

The original resistors were removed and the values confirmed ok with  a multi-meter. The inductors were also removed. I didn't have an inductance meter but the coils showed continuity so I assumed these were ok.

The circuit was traced and transferred into a PCB design tool.

The 'hard-to-get' capacitor values were replaced by multiple capacitors in parallel, and extra capacitors were purchased so they could be hand-picked to achieve the closest value.

Additional spaces are available on the new boards to allow for different parallel combinations if they ever need replacing in the future.

The new layout is spaced out more than the original, with the power resistors mounted near the top & side edges of the board to reduce the amount of heat reaching the capacitors.

The spade terminal connections were replaced with soldered cables.

Disclaimer: I know very little about loudspeaker crossover design so there may well be some schoolboy errors, but to my ears they seem to work ok.

I had to buy a minimum of 5 boards so there are 3 spare if anyone wants them for the price of postage and packing.