Saturday, May 10, 2014

Repairing the FS-R6B Rx

I had  spare FS-CT6B radio with myself if anything happens to my Spektrum Dx6i.
But when I was trying to make a RC controlled robot using Arduino ,I accidently connected the powersupply to the Rx in the reverse polarity and damaged the Rx.

I was sure that the regulator(LDO) might be the only thing damaged inside the Rx.So I decided to take apart the Rx and diagnose what is the problem.
Damaged Rx

Remove the screws

The PCB and case

Bare PCB - no visible damages

Connected a 5V supply from a BEC and checked the output of the LDO,but it was just 1.21V instead of 3.3V

Now it is confirmed that the LDO is the problem.Now looking at its part number and its datasheet for Pinout.
The LDO is CA33


The datasheet on the internet
The LDO was originally a 3.3 V regulator capable of delivering upto 300mA.Searching for replacements ,I came across the AMS1117-3.3 that I had in my components box.Compared the Pinouts and spec.
The AMS1117 was capable of delivering upto 1A .Its huge when compared to the 0.3A of CA33
Comparing the datasheets



Comparison of the packages

Made a small breakout board for the AMS1117

Connect the AMS1117 to PCB and turn ON power

It works

To make the AMS1117 fit inside the case ,cut the tab on the top of AMS1117

Desoldering SMD components is a hell of a job without SMS rework station
Just cut the legs and pry it

The IC removed 

A clean removal of the CA33

Now attach the AMS1117 in the place of CA33

Testing -It works

'Use hot glue to keep the AMS1117 in place

Put together the case and PCB 
Another Test - working great

Vola! Saves Rs.600 by a Rs.15 replacement and some 15mins time.

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