Thanks for the great advice, as you say with this advice and a bit of
common sense I should stand a good chance of fixing it. When it first
happened I just assumed it was a capacitor problem considering it's age
and so was just going to abandon it but when it responded to a tap I
thought it might be too soon to give up on it. The only difficulty at the
moment is that the problem has settled down a lot, so I will have to wait
till it gets more flakey as the act of taking the cover off will probably
be enough to get it going again and at this stage it can keep going for
quite sometime before it flakes out again which makes faultfinding
difficult.


Just go for it, when you start poking around, it's very likely the problem
will occur once you start flexing and tapping things.