I mentioned previously that i found some insulation tubing but wasn't sure which capacitor it should be fitted to. I ended up fitting insulation to BOTH of the capacitors I thought it could be but this didn't fix the problem.
I also briefly removed c404 and c411 from circuit to see if it made any difference but it didn't.
I'm not really sure where else to go with this....
The ic401 thermal pad looked a little dodgy when I last saw it, so perhaps there is intermittent electrical conductivity with the heatsink? I'll order a replacement pad and see what happens.
Also, I'm tempted to buy a new lm379 and replace the one that's there in case the IC is at fault.
The insulation would only come into play to prevent any long(ish) leads from actually shorting out against something else. If nothing was touching the bare wires on the capacitors, then the insulation serves no useful purpose (apart from future preventative issues).
I was looking for potential low impedance paths to ground on the output of IC401. Apart from a faulty IC401 - these components are the only ones that could pass a higher-than-normal current sufficient to blow the fuse.
I will suggest checking the following components:
Y deflection drive:
R412 (1.5 Ohm resistor in series with C408 to GND).
R413 (0.22 Ohm resistor to GND).
C408 (0.1 uF capacitor in series with R412 to GND).
X deflection drive:
R405 (1.5 Ohm resistor in series with C407 to GND).
R406 (0.22 Ohm resistor to GND).
C407 (0.1 uF capacitor in series with R405 to GND).
You might also try disconnecting the X and Y deflection yokes.
Look for overheating of the resistors and potential low impedance path through the capacitors. However, the problem with the capacitor (if there is a problem) may only appear when the machine is switched on.
My component references are from my schematic diagram. We already know that this diagram is not 100% correct with your particular machine. Just check the component values out and check the PCB tracking to IC401 to make sure you have identified the correct components.
The datasheet for IC401 states that the maximum current is 600 mA (for maximum power output).
If you have disconnected the +9V and -9V rails from IC401, you could put two (2) multimeters in series with the supply rails (+9V and -9V) and see what the low voltage current is at switch on and whether it increases as the machine warms up or not; and whether the increase in current is on both supply rails or just one (i.e. the current flows from one supply rail to GND).
This might give us a bit more information on the manifestation of the fault.