Rohde & Schwarz SMS

[Repairman]

I'm sure my topic has been discussed at length before but nowhere can I see a solution.
My SMS signal generator arrived with a blown fuse and a bad on/off switch
I recapped the PSU and fitted a new switch but found the display to be (still) garbled with keys unresponsive.
I ended up blaming the (apparently dead) P8049 microprocessor but eventually found I could get its 6MHz oscillator running by adding 470 ohms from Pin 3 to 5 volts.
I tested the display board on my working SMS2 and its fine.
With the pull up resistor I can now see 6MHz at the crystal pins but no microprocessor activity
When I fitted an unprogrammed P8742 (without the 470 ohm resistor) to test the oscillator circuit it was OK.

I'm wondering if an on-board PSU on the P8049 chip has failed which prevented the oscillator running and killed the internal logic.
I can't find a detailed schematic for a 8049 to see if it has an internal regulated supply
Has anyone got a solution?
Allan