:my mk5 90 12v supply failed when switched on after a long rest during covid pandemic.1N4007 diodes and 12V regulator needed replacing. After that heater supply returned but no drive t v7 grids. Tried replacingJ175 M1 and M4 without improvement. Boogie suggests using 1N5392 diodes instead of 1N4007 but how would that improve relay operation ? Any advice / help , please.