Mark:

Read the manual. There is a list of 11 operator traps and you've identified
one of them- the trace shift in the opposite way you'd think.

The 491 uses an I.F. of 100-200Mhz so what you see are all the local FM
stations leaking through. You can get rid of the stuff by using a low pass
filter that cuts off at 80mhz or use a high pass filter that passes all
above 108Mhz.

If you don't have a manual you'll be lost as some of the mixer inputs relied
on harmonics. Companies like W7GU have manuals

Ralph
"Mark Aren" wrote in message
m...
Hi,

Wonder if anyone can help.

Q1. Fresh off of eBay, this SA is having terrible problems with input RF
leaking straight through to the IF on the lowest RF range. I assume
that the input mixer is shot (441-0671-03).

If I remove the LO feed to this mixer, the expected signal goes away,
but the crud remains. I assume that the IF on the lowest RF range is
close to one of the broadcast bands (TV or FM).

The mixer assy has two diodes which look like they should be easy to
replace. Does anyone have a schematic for this assy or maybe just tell
me what these devices are and some idea where I might get
replacements.

Q2. I feed in 144 Mhz and crank the SA centre frequency lower (130MHz) and
the trace shifts left (I rather expected it to shift right). I assume
that this could be connected with the busted mixer ?

Q3. This one is definatly operator error. The mid range 'B' has two scales
270 - 900 and 800 - 2000MHz. How do I switch between these two ranges
(!)

Thanks in advance.

Mark.