Looks like someone in the past has had a go, notice the replaced capacitor and the odd pair of series resistors in position 570 on the left channel. looking at the values of both resistors (one at 170 ohm and the other at 180 ohm) they have been used to replace the original 330 ohm component. I don't see any outward signs of frying or damage.....however I have contacted Martin and requested a full capacitor kit and a recommended set of components for this rogue channel......I will post pics as things develop.

Ok...

Been a while but I've finally got my hands on an old dual beam oscilloscope! its a vintage CRT job that lacks lots of modern day refinements but I'm hoping to use it to follow the incoming signal on the functioning right channel and compare this at the same points on the failed left channel. Tested the scope with its own 1v ptp square wave test signal and both channels work ok...however it came without a probe so I have ordered one up.....should be interesting ;¬)

Craig wrote:

Ok...

Been a while but I've finally got my hands on an old dual beam oscilloscope! its a vintage CRT job that lacks lots of modern day refinements but I'm hoping to use it to follow the incoming signal on the functioning right channel and compare this at the same points on the failed left channel. Tested the scope with its own 1v ptp square wave test signal and both channels work ok...however it came without a probe so I have ordered one up.....should be interesting ;¬)

Real dual beam scopes are a treat to use. My Philips scope is it's (heavy) weight worth in gold when checking for faults or anomalities 🤒

I'm wondering now if I should buy a signal generator too in order to trace this fault.....

Just had a look on the internet, seems there are some free signal generator software packages available to download.....does anyone know if they are any good?

I assume you are talking about signal generator software that runs on a regular computer? I suppose all of them do what it says on the tin, but there are a few caveats:

• Computer audio outputs are typically not galvanically isolated, which may result in ground loops and hum
• If the output is a combined headphone / line level socket, the output impedance can be pretty much anything
• Because of the unknown impedance and "0-100" volume settings, you won't have much idea of the real output level into a given external device unless you just try and measure it. If the device you're troubleshooting is dead, test & set the output level with some other similar device/input that works.

Keeping these in mind, they can be just as useful for troubleshooting as a "real" signal generator.

Thanks Mike

Is there any reason I cannot hook the computer audio output to my oscilloscope and set the signal up prior to injecting into the amp? maybe .5 volt 1khz ?

I was playing around with

Ok.....got my scope up and running