A standard Quad 405 service includes: •Fault diagnosis & rectification. •Replacement of all out-of-tolerance (OT) components including all decoupling electrolytics. •Sensible modifications*. •Performance test (frequency response, distortion test, listening test)•Soak test (running for a prolonged period of six to 8 hours into a dummy load to locate any short term failures). •Safety test (Earth leakage and insulation breakdown test).The standard 'from' price does not include replacement of faulty mains transformers.
This particular Quad 405 shown in the images above has just been fully serviced in our lab. The main fault in this case, was blown LH output transistors and drivers. The probable cause of failure was the crowbar circuit operating due to a dried out AC shunt capacitor C17. On the early 405s this particular pair of capacitors is located on a tiny PCB behind the loudspeaker terminals. It is often overlooked by the would be ‘service guy’ as too much trouble to ‘get at’. Our full service includes replacing the following ;•All out of tolerance (OT) parts discovered during the diagnostics check•Replace full complement of electrolytic capacitors (unless very recently changed).•Smoothing capacitors. If the ESR, value, or physical condition is below standard (we now use the latest ,high grade 10000uF 100V screw terminal capacitors). These fit the original large clamps and offer a superior performance.•L & R IC1 301 changed to a low noise counterpart. •L&R +ve feed resistors R7 replaced with 1W types•On early 405s, the LS Zobel network earthing point is corrected to go to the output ground. Also the incorrectly shorted stand-off resistor R2 is reinstated in circuit by removing the erroneous input ground to chassis s/c.•Finally we carry out a listening test followed by a soak test for several hours, followed by a Portable Appliance safety Test. (PAT). The smoothing capacitorsQuad 405 full service & LS and DIN socket Upgrade (Q405FSSU)On older 405s, for a nominal extra charge, we can fit RCA (phono) sockets in parallel with the DIN socket and fit professional loudspeaker binding posts in place of the push to connect types. * What we call ‘sensible modifications’ involves changing certain components for higher performance types where a genuine improvement in functionality and/or performance is achievable. Where necessary we may also re-route wires/cables. For example, we move the left & right Zobel network on earlier boards to the correct output earth plane.