SCA-14 (C4) MMIC Amplifier replacement for CMU200 ??? - Page 1
Forum section: electronics / testgear

author: eb4eqa
author_rank: Regular Contributor
timestamp: November 08, 2016, 11:00:44 pm
content: Hi,I found the RF3 output on my CMU200 to be unexpectedly low. It did not take long to find the final amplifier in the RF3 was damaged, attenuating instead of amplifiying. For now, I've removed the IC and bridged intput to output. By setting a 18dB attenuation in RF3 in the CONNECT CONTROL screen, I get perfectly correct output levels but only to -5dBm instead of +13. It would be nice to leave he instrument as it should be anyway.I've got a few "similar" MMICs and I was tempted to replace it but I noticed that this SCA-14 is specified as SINGLE SUPPLY, and the MMIC I had (SFH-0189) requires a negative bias to the input pin.I can't find a SCA-14 original part or similar replacement. Someone knows where to get one, or an alternative?Thank you,Roberto EB4EQA

author: hafrse
author_rank: Regular Contributor
timestamp: November 09, 2016, 07:11:01 pm
content: Hi Roberto,I have used SBW-5089 and worked fine for me on RF4 and RF1 (both were blown) , RF tests passed after that.See eBay item 350671554073 selling 5pcs for 20.99 USD.Good luck!Hani-GeorgeSM5TAO

author: eb4eqa
author_rank: Regular Contributor
timestamp: November 09, 2016, 08:50:29 pm
content: Hi Hani-George,Yes, that one seems a perfect replacement!I just ordered them, I'll come back one I check it.Thank you !!!Roberto EB4EQA

author: MaartenH
author_rank: Newbie
timestamp: October 17, 2017, 07:09:16 am
content: I have the same problem (RF3-OUT MMIC).I'm very scared to ruin my CMU200, as it was a lot of money.Is it possible to write in a few lines the steps I need to do, and what are the things to avoid ? And how to avoid the module start to leak or crosstalk RF ?need to take out the complete FE ?Where to open the FE to access the MMIC ?etc73's Maarten

author: capt bullshot
author_rank: Super Contributor
timestamp: October 17, 2017, 07:29:45 am
content: I had replaced both SCA-14 in my CMU200 RF frontend:You'll have to remove the FE from the CMU and completely take it apart to get access to the MMICs.Lots of screws to remove, desolder the center pins of the N and SMA connectors, unscrew and remove them, remove all the screws that fix the PCB inside the case. They have some kind of seal in their heads, I've heated the screwdriver with the soldering iron to deal with that.Replace the MMIC, put everything back together - works, self tests pass.Be careful not to bend the hardlines between the FE and the RX/TX module.Edit: There's the 50W power attenuator mounted on the bottom of the enclosure and soldered to the board, you must desolder and carefully bend the two copper bands to remove the PCB, be careful not to break or twist them.Edit 2: I've found a picture inside the RF FE. You see the attenuator (white block), the sealed screw heads, and to the left hand side one of the MMICs ("C4"). This one is for RF3 output connector, so you should be able to replace the MMIC without removing the PCB from the enclosure. This is from what I remember, better check yourself again.

author: MaartenH
author_rank: Newbie
timestamp: October 17, 2017, 06:44:55 pm
content: Okay thanks a lot !!!!So the MMIC is on the far left of your photo, vertical roughly in the middle.This means that the repair is far less risky, I ordered a SBW-5089 from Ebay.