FRsky Rx died - need help identifying SMD component - Page 1
Forum section: electronics / repair

author: enut11
author_rank: Super Contributor
timestamp: December 18, 2024, 08:12:51 pm
content: This FRsky RC receiver died after connecting it to a variable power supply. It is rated for 5-10vDC. I believe I did not apply more than this but the power supply (Korad 3005) may have spiked when adjusting the rotary output.Anyway, there is now a short between the +pins and ground and it may be due to U2 (33942) 4-pin device. I need help in identifying what U2 is and the chip pin assignments.enut11

author: fzabkar
author_rank: Super Contributor
timestamp: December 18, 2024, 08:26:16 pm
content: I suspect that it's a 3.3V LDO regulator. The datasheets for the other two ICs may give you a clue (Vcc).

author: u666sa
author_rank: Frequent Contributor
timestamp: December 18, 2024, 08:45:14 pm
content: Linear voltage regular, 4 volts, 400 mah

author: adam7
author_rank: Newbie
timestamp: December 19, 2024, 12:05:32 am
content: It is LDK320ADU33R SOT-89-3

author: fzabkar
author_rank: Super Contributor
timestamp: December 19, 2024, 12:29:09 am
content: https://es.aliexpress.com/w/wholesale-LDK320ADU33R.html(photos)https://www.st.com/resource/en/datasheet/ldk320.pdf(datasheet)

author: enut11
author_rank: Super Contributor
timestamp: December 19, 2024, 01:51:31 am
content: @adam7 and @fzabkar: Thanks for the tips.I have worked out the most likely pinout version (below). It is feeding an STM32 micro so should be 3.3v LDO. Will place order today.enut11PSAny tips on removing the old one. Seems like I need 2 soldering irons?

author: linux-works
author_rank: Super Contributor
timestamp: December 19, 2024, 02:18:29 am
content: its a sign from the gods. they want you to convert to ELRS.

author: DaJMasta
author_rank: Super Contributor
timestamp: December 19, 2024, 03:34:09 am
content: A little solder blob on the tab and some soak time should do with a reasonable iron, but of course with SMD, hot air is king. The combination of both can make for shorter work/less chance of board damage.

author: linux-works
author_rank: Super Contributor
timestamp: December 19, 2024, 05:53:43 am
content: but frsky rf tech is years out of date compared to the open source elrs protocol and product set. you can get plugins for your tx (jr bay) that will talk elrs and rx's are $20 and less. they are far more reliable and have much better range and telemetry options. just not worth repairing frsky rx's when you get down to it.

author: enut11
author_rank: Super Contributor
timestamp: December 19, 2024, 07:18:07 pm
content: Thanks for your input. The type of models I fly (mainly old timer aeroplanes) do not need the capabilities of ELRS.enut11

author: enut11
author_rank: Super Contributor
timestamp: December 19, 2024, 07:44:56 pm
content: ProblemThe 3.3v SOT89 version shown in the data sheet above has the wrong pinout for the PCB.I am certain that power- in is as per Reply #5 so am back to searching for a suitable device

author: fzabkar
author_rank: Super Contributor
timestamp: December 19, 2024, 08:13:17 pm
content: Quote from: enut11 on December 19, 2024, 07:44:56 pmAI gave me this:https://www.lrc.cn/Upload/PDF/Product/IC/LDO/LR8558.pdf

author: linux-works
author_rank: Super Contributor
timestamp: December 20, 2024, 04:32:53 am
content: I'm not talking about features. I'm talking about rf reach, reliability and signal loss re-acq.but hey, everyone should be free to use old, outdated proprietary link protocols that cost twice as much as modern open ones.people can do all kinds of non-logical things.enjoy your old tech.

author: linux-works
author_rank: Super Contributor
timestamp: December 20, 2024, 03:45:48 pm
content: there's a discord forum for elrs, if anyone wants to read up more about it:https://discord.gg/FcJKZKnathe long form is 'express LRS' if you want to search on it.if you need a remote control rf system, this can do some things that others cant so even for non-rc stuff, it might be useful.

author: linux-works
author_rank: Super Contributor
timestamp: December 20, 2024, 04:12:05 pm
content: $13 for a tiny rx:https://www.amazon.com/HGLRC-ELRS-2-4G-Receiver-Omni-Directional/dp/B0CNRX33V6that's about half the price of what frsky charges for their 10 year old tech. btw, frsky has at least 2 (maybe 3?) different protocols and its a nightmare if you have the wrong versions and want to inter-connect.elrs even has a web interface if you need to change things (it can join your wifi network or be an AP and you connect to it).its like comparing fortran to python. things have progressed quite a lot in rf remote control. just the richness of telemetry, alone, should make people consider converting.and now, you have 'gemini' which is a pair of 900/2.4ghz diversity tx/rx pairs. so you can do really long range and also have a backup channel.frsky is dead dead dead and they know it.note, you used to need both a tx and rx line to run elrs (frsky needs only one serial line, usually). but now they added half duplex mode to elrs so if you must, you can get by with a single uart line, but its better if you have both tx/rx lines on your spare uart (on the plane).finally, you probably need pwm outputs rather than 'serial' and you can find elrs rx's that break out directly into pwm servo ports. or you can use a single board to take elrs serial out (from its rx) and then that 2nd board will do the elrs_serial -> pwm for you. either way. you can get lots of pwms if you want. (also battery voltage telem, which is important!)

author: linux-works
author_rank: Super Contributor
timestamp: December 21, 2024, 04:29:13 pm
content: btw, we're in the middle of a complexity change in ELRS. they just added some new modes and that kind of confuses a lot, tbh.dual band (800/900 for one and 2.4ghz for the other) makes things complex and single-band antenna vs dual band antennas. and switch diversity vs full chipset diversity. and compat of this new series vs the previous one that was in place for years.I'm staying with the previous gen of elrs until the new 'gemini' stuff proves itself. there's enough in the SX chipset that I dont need to add the complexity of the new series.but some may really need the low freq support (8/900mhz) and for long range planes, that would make sense. still, that freq is also there on the older elrs SX chips.

author: 005
author_rank: Newbie
timestamp: December 29, 2024, 12:31:28 am
content: Six years ago, I successfully repaired an XR8 with this LDO: XC6201P332PRPlease also check for a burnt trace as shown in this video from RCModelReviews: