[Premium-Rx] Racal RA177x display board -- manual error

[John Nelson]

In case anyone is restoring either a Racal RA1772 or RA1778, there seems to
be a long-standing error in the manual for both receivers in respect of the
PM692 display-board supply. Both manuals indicate on the schematic and in
the write-up that the display board is powered from the auxiliary AF/memory
regulator (PS427/1) at pin 10, but this is definitely not the case. Pin 23
on the display board is the supply input, fed via a connection to the PM419
meter board. The latter receives a +5V feed at pin 6 from the main PM370
power supply. The PS427/1 board is not involved. 

There are several other errors in the 1778 manual, notably that in the VCO
alignment instructions it inverts L4 and L6. It states that L5 is adjusted
with Channel 5 (17.999) set, which makes sense, but that L6 is adjusted with
Channel 4 (7.999) set. This should presumably be Channel 3 (29.999). The
manual also does not specify the channel setting for L4, which should
presumably be Channel 4 (7.999). A similar error exists in the 1772 manual.
Both fail to mention that there is a convenient test point available for
making the VCO voltage measurement instead of rather unhelpfully referring
to the inaccessible junction of a resistor and diode. 

Many thanks to Nature's gentlemen G3NCR and G3YFK for invaluable assistance
in getting to the bottom of these issues. 

73 John
GW4FRX