[TonyDuell]

A bit more on this machine.

I thought it had a problem with the autorevese system in that if I turned that feature on, then pressed the left-to-right button the appropriate solenoids would engage. Grounding the guide would then flip it to go right-to-left, but grounding the guide again did not stop the tape.

I checked the 5 transistors and 2 electrolytics on the autoreverse module, they are all good. And then I realised that when it reverses, it waits for the tape to stop (no voltage from the reel motors) before it engages the other solenoid. During that time the tape is not moving, so the guide would remain grounded via the tape foil in normal operation. So I tried it like that, holding my ground wire on until the other pinch roller engaged. And it works fine.

So human error on my part...

As for the audio problem, it's another silly fault. I fed my test oscillator into both channels of the tuner input, set the controls appropriately selected AMP mode and pushed up the recording level slider. One meter registered, the other didn't. Tapping the slider got both to register to the same level. And my 'scope showed signals of the same amplitude at the monitor outputs and speaker sockets (after pushing up the volume slider), including when test speakers are connected.

So I suspect it's nothing more than dirty pots. Although the user interface is a slider, they're normal rotary pots with rack and skew gearing (well, it is a Philips!), so getting replacements is not going to be too hard I think. But I will try cleaning them first.