[Hammarlund] SP-600 RF illness cured

[James A. (Andy) Moorer]

> ... and the resistors measured within tolerance  -- until I got to R6 
> which comes off the send side of the send/receive switch line.  It 
> measured 1 MEG. It should be 1K.  The reason for its unduly high 
> resistance became obvious under the gaze of my Optivisor magnifier. The 
> little resistor was charred and split along its longitudinal axis  -- just 
> like the many BBODs this receiver once sported
> Once this resistor was replaced and the RF module wired back in, the radio 
> played beautifully --better than ever, actually.
>
> I am, of course, curious as to how or why this resistor might have burst 
> into flames at some point (or why -- after doing so -- it clung to life 
> for awhile, at least).  I've done extensive voltage checks and find 
> nothing terribly amiss.
>


R5 and R6 (and R15/R16 on 2nd RF) are underpowered. They are spec'ed at 1/2
watt, but more often than not, I find them obviously charred. I believe if
you put the receiver into manual and run the RF gain to max, they will get
quite hot. I routinely replace them with 1 watt resistors.

Glad to hear you brought it back to life! Good job.

James A. (Andy) Moorer
www.jamminpower.com