Before fault rectification and refurbishment: right channel defunct, crackling on left channel, two main smoothing capacitors leaking and there are numerous faulty & out of tolerance components. Rs, Cs, and semiconductors.

New Nichicon or EPCOS 100V 105 oC smoothing and output capacitors are fitted in place of the old style bracket mounting types. here. The bridge stack was also replaced with a 35A 600V bridge rectifier

On older 303s with the crude diode bias arrangement we can fit a tiny BIAS modification board. This provides a more precise adjustment of the output transistor bias. Incidentally on all Quad 303 repairs we carefully set the bias to the sweet spot for minimum harmonic distortion. Too much and THD increases, to little, ditto.

We mount the smoothing/output capacitors using our specially designed capacitor PCB. This correctly mounts the modern capacitors in place. It also conveniently allows the inclusion of L & R +rail fuses. In the event of a blown output device,etc. or shorted LS, a fuse blows rather than a vaporised PCB track. In the above image, you can also see the replacement bridge rectifier.

Some 3O3s we receive for service are in a very poor state. e.g., rusty case, bottom plate and front panel. We can restore the overall look, for an additional cost, by stripping and re-spraying these parts with primer and top coat. The re-sprayed sections, (cover and bottom panel) will be in two tone colours, that are close to the original colours. We can only carry out resprays when the warmer and drier weather prevails.