Re removing the back panel of the Tannoy Reveal 6D or 8D, take out the 6 screws with a 3mm hex driver first, then simply but gently pull, wobble and ease the whole heat sink and metal back panel out of the recessed back board of the speaker cabinet. It's a tight fit but will start to move. Be careful to brace as you pull, to avoid overshooting - the back panel has all of the electronics attached on its inner surface and there are three sets of cables connecting between the boards and the speaker box, for the woofer, tweeter and front switch. The link in a post above to badcaps is useful. Schematics are available there - or PM me for a copy.
Prepare yourself for the ugly sight of the boards being drizzled with vibration management goop, which is a pain to clear away to enable diagnosis or repair.
I have one of my 6Ds in surgery at the moment, trying to hunt down an intermittent fault, which I think could be the thermoswitch or some component in that loop. Might seek help from the experts here soon.
These nice sounding monitors are easily repairable. It's usually something insignificant that's stopped working. A blown track or capacitor. Be encouraged and get into it. Make it work again!