SL70/RD218 not showing targets

[cowbayalbin]

Hi everyone -

new to the forum, thought I'd post this question here after finding a lot of useful advice in the archives:

My new old boat came with an old Raytheon SL70 unit and a RD218 radome. It powers up, the scanner rotates but shows no targets/shoreline/whatever. If I turn gain way up to 93%, it displays some speckles and an obvious rotation pattern, black screen with rotation pattern above that.

From other posts in this forum I've learned to run the debug and self test programs - the debug screen shows S 50 G 207 in the first line, then C140 F55 S0 in the second line

The self test window shows 447 hours on the heater, reset count 0, and a pass on everything EXCEPT 2 values:
These are Receiver supply 5v FAIL and Receiver supply 12v FAIL.
Modulator Current SP, MP, LP readings are 113, 120, 131 respectively
Rotation time 2458, STC preset max 149

As I'm unfamiliar with these units, can anybody help suggest where to start troubleshooting regarding the two FAIL readings? I'm a bit confused as to why there seems to be power to both units, cable passes self test, magnetron heater, tuning, heading etc. pass self test, but the power readings indicate some issue. I'm grateful for your suggestions!

Paul