[Premium-Rx] Racal 1792

[GandalfG8 at aol.com]

Hi Chris

The 1792 is a great receiver but things to watch out for...

CPU batteries, if not changed, can leak and cause damage to the CPU board. 
This can range from mild surface corrosion, if caught early, to really severe 
damage if not.

The LCD displays deteriorate with time. This can range from a slight bleeding 
of the smaller characters to a total mess.
Slight bleeding is usable but, once started, it is lilkely to get worse 
although slightly bleeding displays can remain usable for quite a long time. New 
displays are still available but not cheap and getting harder to find. 

There are two main version of the RX. Early ones do not have backlighting or 
BITE, later ones do. Later sets will usually sell for quite a bit more.

Make sure the "correct" filters are fitted. Some sets were supplied from new, 
in the UK at least, with a set of narrowband filters and just LSB. Sometimes 
filters get removed or changed later.
Unlike the 6790 the 1792 does not auto detect the filters, so what the 
display tells you may not be true. I think this applies to the later sets, with 
BITE, too but not quite sure on that, 

The set may, or may not, have an interface card fitted. These plug into the 
end of the CPU card. If the card isn't fitted it won't affect the operation of 
the receiver so long as the correct ROMs are fitted. Fitting a card later may 
need a new set of ROMs. I have heard, but again haven't confirmed for myself, 
that an RX with a ROM set for the IEEE interface, for example, won't function 
if the interface is removed.

The tantalum capacitors, used throughout the RX, are known to be unreliable 
and can fail at random, usually going short circuit. Some users recommend 
changing all the tantalum capacitors in the set as a precautionary measure. That's 
quite a lot of work, and perhaps overkill, but they do give problems and 
failure of one capacitor can shut down the RX completely if it pulls down the power 
feeds.
Don't let this put you off too much. Other sets share this problem, I know of 
6790 owners here who've complained of the same thing, and many sets seem to 
work ok for years without it being an issue.

If you can get to look at the set, or get hold of some decent photos, the 
three most important things to check for are that the CPU board is clear of 
corrosion, and the battery not leaking excessively, that a decent set of filters 
are fitted, and that the dsiplays are sharp and clear.
And, of course, that no modules are missing but that should be fairly 
obvious:-)
There's no cover over the filters as in the 6790 and, with crystal filters 
anyway, the marking should be clear on top.
Mechanical filters are harder to identify. The sets sold here, with narrow 
passbands only, had all Collins mechanical filters except for one crystal unit 
in the 100Hz position. The other clue on these is that there's no USB filter 
fitted.

It will be obvious from the front panel/display if its backlit and with BITE, 
or not, and if the three points above are ok, and all seems to be working 
well, then it should be a nice receiver.

Unlike the 6790, the 1792 always had the RF preamp fitted. Internal links 
enable the preamp to be bypassed if required but this is rarely done.
There are a couple of other options, ISB and a 100KHz IF output that are 
sometimes fitted, but lack of these don't affect normal operation.

I think that's about it for now:-)

Nigel
G8PZR








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