SMIQ03B Frequency offset

[Aleksandar]

Hello to everyone,

On my SG I noticed that in the frequency range from 0.3MHz to exactly 450.000MHz I have a frequency shift plus 133.570MHz, plus/minus error of the counter.
450.001MHz and up to 3GHz is true, but at 450MHz, the counter shows 583.570MHz! And all below that frequency.
Or for example for 100MHz, I read 233.570MHz on the counter.
I also checked everything on the TEK 492 spectrum analyzer. The amplitude is OK.
Does anyone have any advice where there may be an error?
Thanks
Aleksandar

[Qw3rtzuiop]

Take a look at the IQ-Modulator board.
The block diagram and schematics for that board are available here:
http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=Rohde_Schwarz
The board is described in service manual vol.2 page 185ff

[Aleksandar]

Thanks for starting the problem search.
Although I would like to get some more concrete advice?

[Qw3rtzuiop]

There are troubleshooting checklists.
Check everything around the 2.4 GHz LO.
Checklist items 7.4.4.7 and 7.4.4.8

[Aleksandar]

Thank you very much.
I solved the "malfunction".
A very banal thing. The last time I changed the battery, I somehow disconnected the cable coming from the Reference / step synthesis module. I marked with a red circle. Now I opened the SMIQ from the bottom, intending to start fixing it and immediately saw what happened.
Thanks again for the help. Without her, I wouldn't have started repairing.

[Qw3rtzuiop]

Nice! Always good to see test equipment working again.

[Aleksandar]

Yes, that's right. But at that time I was doing something on 1296MHz and it was all good.
Maybe this will be useful for someone!
Thanks again.