ROHDE & SCHWARZ CMS33 Radio Tester, Repair, Teardown & Analysis, Variable RF sig gen level fail.

[@t1d100]

Great call on the problem, during your diagnostics. Maybe add an anti-static cat whisker broom to sweep away any future filings. This type of broom is found in paper copy machines. They make a ground to the paper to drain away static. Similar devices are found in some electric motors. The whiskers are made from conductive plastic and are mounted with simple brackets. Very doable, within the space that you have. You will have to determine if you actually want to tie it to earth ground. Of course, your issue is magnetic. There is also anti-static expanded foam. Just take it against the wheel. Also, there are anti-static sprays. You kind even find it in the grocery/department stores. It is used to stop the static caused by fabrics brushing back and forth on itself. Additionally, you might be able to swap out the encoder for a photo type. Obviously, R&S was trying hard to engineer the encoder robustly, however they actually over did it. Great repair.

[@3dsmaxrocks699]

Seems every electronic repair guy has a cat LOL Me too! Nice work BTW

[@TobiWan18]

I've recently acquired a CMS 33 however it looks like the measured RF power on the TX test section is not correct (looks like its doubled). Would you share the service manual and do you have any hints?

[@rfmanrfman4536]

@@TobiWan18 hi you can download the CMS 52 or CMS54 service manual on the internet, it's basically the same as the 33, however if you look at my CMS 54 video you will see in the rear left there is a module called the RF attenuator, it's gat a silver block with a heatsink, & also a fan plugs into the board too, the solid coax from the Front N socket connects to it, on that PCB there is a Blue potentiometer this is used to calibrate the TX RF power reading, the manual says input 10 Watts 300MHz and adjust for right reading on display. It could be someone has messed with it before you, believe that board is where the problem lay. All the best.

[@renatopicarazzi2186]

Hi, my name is Renato, I wanted to ask you if you have changed the battery on the CMS 50 and if you know where to find the wiring diagram, thanks

[@rfmanrfman4536]

@@renatopicarazzi2186 Hi Renato, I'll be honest I don't ever recall having to replace a battery in them. I assume yours has failed? It's probably located in the control module just behind the display but you must be very careful in removing the module as there is a delicate ribbon cable connecting to the display & there is a little wiring loom also which is tucked in behind it. The battery if fitted is probably a button cell type. As for the service manual these are hard to come by, there is a free on the internet if you do a Google search CMS52 service manual, this is almost the exact same as the one you have, if you search hard enough you will find it. I have some R&S service manuals but not for many models, the other problem is getting spare parts R&S appear to have tightly controlled service info & parts, if you do ask them for prices they will be eye watering, all the best,

[@renatopicarazzi2186]

@@rfmanrfman4536 Grazie mille Thank you very much, very kind