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R&S CMT82 service tips

Rohde & Schwarz CMT82 service tips

These may, or may not apply to other R&S CMTxx models.

Change the noisy 24V fan to a stack of two 12V DC PC PSU cooling fans connected electrically in series. Enclosure top and bottom opens up by removing the 4 screws from 2 blue plastic pieces in the rear corners. Fan connector in on the bottom side. Mark how it is plugged before disconnecting anything though it's not necessary here.

Replace blown LCD backlight lamps; 3 mm diameter 6 V 120 mA miniature dial lamps (H101 to H108). For this, loosen Volume and VAR knobs (different size of hex screws) and remove knobs, remove also front metal face plate's 4 screw at corners, 2 small ones between LCDs in the middle and fold mask plate off. Next unscrew two M2.4 screws by the N- RF input connector, the ones holding the unit (see picture: marked with red squares), until it also folds out from top. If possible, do the lamp soldering without unplugging the 3 flat cables, the blue socket's pins are a bit fragile. If the front panel keys do not work after units is reassembled, you probably have accidentally pulled out (partially) one of the flat cable sockets, possibly from under (rear) the unit at the other end of the cable. They have no locking mechanism.

No monitor speaker audio? Replace H100 lamp on the front panel just besides INPUT 2. This lamp is inside a black heat shrinking tube (it does not light up anything, so is it as hour counter for service?). Exact value is so far unknown, but audio works and the 24 V 20 mA lamp glows very faintly - find out the proper voltage and current, or use what lamp you have -  at your own risk!

If you wish to clear user programming settings from memory, hit "9" "9" "SPEC": the CMT re-boots with factory settings.

If power supply fails or does not work properly, replace fried electrolytic capacitors.


Rev. 2010-10-24
© I. Yrjölä, 1999... 2011