[Premium-Rx] RACAL 1771, 1772 SERIES FAULTS

[Dan Rae]

Royce, Alan (AS) wrote:
> What are some of the known problems and their repairs for the RA1771,
> 1772?
> Al 
> ______________________________________________________________
>   

Al, most of these will have been mentioned in the recent discussion of 
these radios but here we go again, and if anyone is contemplating the 
nice looking 1772 and 1778 currently on eBay UK; remedies are as expected: 

1/  Power supply wiring.  The PVC insulation loses it's plasticizer from 
heat over the years, the insulation gets brittle and the wires corrode 
badly.  Problems can occur on the power supply PCB due to heat over the 
years.  PTFE / Teflon wire is your friend.

2/  Other wiring gets fragile from some other mystery chemical cause; 
where there are fine screened wires with rubber sleeves on the ends the 
wires can break easily.

3/ The group of up to 6 big power supply capacitors if original will 
almost certainly have dried out and should be replaced.

4/ Possibly a lot of the 150 µF Philips blue capacitors on the IF/AF 
card  as well as the two 470 µF caps on the chassis will have dried out 
also.  Test them! 

5/  The axial tantalums on the IF card may have changed value, replacing 
them will then give correct AGC timing action again.

6/ Reed relays in  the preselector can die.

7/ the two 2N3866s on the first mixer card and fit as big heat sinks as 
possible..

8/ The quad FETs in the first mixer can be replaced by an SD5000, 
perhaps an improvement over the original.

Any PC board rework should be done very carefully, bearing in mind the 
the copper traces lose adhesion very easily.  In particular #7 above; I 
have seen these where the transistors are hanging off the board attached 
only by loose copper traces.

Most of the above with the exception perhaps of the chemistry stuff is 
what is found in any 30 plus year old electronics.

I'm sure there are other common faults that I have missed, but the above 
is a good start :^)
73
Dan
ac6ao / g3ncr