Quad 34 faulty channel

[Elliotaw]

Hi. I have emailed this question directly to Quad but maybe someone on here can help me a little quicker ??

I have owned a few 34's, my most recent one I bought 2nd hand in an unworking condition. I bought an upgrade kit from Dada electronics. I have very little circuitry knowledge but am reasonably skilled at electronic assembly so managed to successfully fit the kit to my 34 and also to my 405-2 amp. This upgrade appeared to fix the faults apart from the 'tape' function would not work on the pre amp (pressing the tape button just had no effect whatsoever) however since I only use the CD input, I never chased the problem. Apart from that, both amp and pre amp have been working perfectly.
Over the past few months I have noticed the depth of the sound on one channel to be lower than the other. At first it was barely noticeable, but most recently, it has gotten much worse, now I have full volume and clarity on one channel, the other is now almost silent. If I put the balance control fully to the bad channel, it is still working, but at maybe 1% volume. When I adjust the volume control, there are loud clicks as it goes through each volume level. The tape function remains unselectable.

I have swapped leads to check if the fault lay in my cd player, pre amp, amp or speakers and I'm 99% sure it is within the pre amp.

I have also replaced all of the original input and output connection terminals to RCA's and unfortunately my positioning meant I have removed the serial number (oops)

Any ideas ?

Elliot