ROHDE & SCHWARZ SML01/02/03 SG ATTENUATOR Repairs

[shashitej]

Hello ALL,

This is my first post on this blog, knowingly or unknowingly if I make a mistake pls help me to rectify it

I have got Rohde & Schwarz SML03 Signal Generators - 3nos with problems
one of the problem is horizontal lines on the displays ->LCD's to be replaced
second problem is all the 3 attenuators behaving erratically like,
(1) at 0 dbm output is -17dbm, in one module,
(2) at 0dbm working fine but on negative side behaving erratically like-7dbm=-24dbm, -22dbm=-50 dbm so on 2nd module
(3) difference of -12 to -15 dbm at all levels 3rd module

does anyone have the component layout and schematics for this attenuator module or where can i purchase the same
The module consists of GaAs MMIC SPDT RF switches

Any help is highly appreciated .

[shashitej]

[shashitej]

[shashitej]

[Brandy]

Most likely it's the little white smd parts, which are "P35-4227-C06-300" high performance Gallium Arsenide single pole double throw broadband RF switches.
I have the same problem, my device makes jumps in 5dB steps, depending on the attenuation settings.
You may shorten the required pins and see if it helps. Surely you will skip the steps of the shorted witch.
See the attachment for the switches.
Unfortunately it seems that the parts are not available anymore, at least I cannot find them in the net...
Maybe you can take them from another SML as you have more than one 

[ardiesse]

You can identify which switches are at fault using a multimeter. 

Take the shields off the attenuator, and temporarily re-install the attenuator in position without shields.  Turn the signal generator on and probe switch pins 6 and 7 with a multimeter, as you vary the output level (1 dB steps are handy).

Normal voltages at pins 6 and 7 are about +1.0 V "high" and about -7 V "low".  When a switch goes bad the voltage swing at pins 6 and 7 is much less.  Start troubleshooting from the RF input and follow the PC traces through to the output.  You don't need schematics.

That's how to troubleshoot the bad switches.  Replacement is a different matter.  I'm using SSW124 as replacements, but these are old lab stock.  I don't know whether anybody makes pin-compatible replacements.  The Mini-Circuits KSWA-2-46 has a different pinout.

Rob