[Premium-Rx] Racal 6793 problem

[Dan Rae]

On 5/21/2016 8:57 AM, C. van Ravenswaaij wrote:
> Hi all,
>
> I have a Racal RA6793-2C with a problem.
> A while ago I switch the receiver on and within a few second I smelled 
> a burning odor. Quickly turned the receiver off.
> After opening the receiver, tried another startup, same smell, but now 
> with smoke coming off of board A4. It looked like tantalum C93 was the 
> culprit.
> To be sure, I replaced all tantalum and regular electrolytic C's on 
> board A4.
> Then checked all supply voltages, they were ok.
>
> Another start of the receiver gave the same smell again. Coil L4 was 
> becoming very hot. This coil is in the 15 V line and seems to draw too 
> much current.
Cornel, if you have replaced all the Cs (which may not have been 
strictly necessary) and C93 /is/ really good now there must be a short 
somewhere else in the +15V rail.  An Ohmmeter will help you find it with 
the board not powered.  The 15V supply to the board is divided into two 
by a 10 Ohm R (R133), lifting this will cut the search in half.

That burnt choke L4 should probably also now be replaced.

Good luck,

Dan  ac6ao / g3ncr