A quick video I threw together using the free version of VSDC video editor. It shows how to restore the troublesome push selector switches fitted to the Quad 33 Pre-amp.This is not to be carried out by people with no manual dexterity as it can be very tricky at times. I have not attempted to show how to dismantle or reassemble the unit. There are many videos on the web that show that. This is just to show that using a suitable solder work station the switches can be carefully removed from the circuit board, taken apart and cleaned.
The problem with these switches would seem to be that although silver plated, after many years the silver oxidises. This can be seen on the external pins of the switch. The internals will be the same. Sometimes switch cleaner may cure the problem. My unit had so many faults, but then it had come from a skip, it was difficult to know where to start !
Being an experienced engineer I have an old Pace solder rework station and can do reasonable soldering. Now 67 years old my eyes are not as good as they were so need glasses etc.
Using the solder sucker all the switches can be removed from the circuit boards, removing the upper small board too. After removing the solder a small quantity may remain that causes the pins not to release from the board. Flexing the pin at the pcb pad will normally release it.
I started with the smallest switch before deciding to produce this video. That is also why the battery failed shortly after starting to record the process, I was mentally in repair mode, not video record mode !!
Having removed the switch it is most important to take care when raising the little tab that holds the switch together. If you break that, the switch will not stay together. The shammy leather sticks I used in the video are sold as Video Recorder video head cleaning sticks. They were better than the cotton buds as they tended to leave cotton fluff inside the switch. The shammy leather also gave a nice burnishing or polishing action. We do not want to use any abrasive as that would destroy any plating as it is probably only microns thick.
Take great care not to dislodge the sprung contact pads on the push part of the switch. My first one ended up on the floor and I was lucky to find the contacts never mind the tiny springs.
After reassembly I checked each switch with a multimeter for continuity in pushed in and out modes.
As they say, reassembly is the reversal of disassembly, and after several hours work the Quad 33 worked fine. Well not quite...there are still some audio quality issues, probably dried out caps, but at least the signal is now constant and getting better as it is left running. Probably capacitors reforming. I have already changed the 2 in the PSU and the 2 connected to the balance pot. I might be ordering the capacitor overhaul kit available off the web but first need to look at the Quad 303 power amp as that is suffering non symmetrical clipping and there is a general bass distortion at higher sound levels.
21 авг 2024
