Replace a blown electrolytic capacitor - Page 1
Forum section: electronics / repair

author: sdancer75
author_rank: Frequent Contributor
timestamp: March 09, 2020, 07:25:12 pm
content: I have a faulty Mpeg decoder (Edition triton T2) with a blown electrolytic capacitor (EC7) near the led display controller (FD650B-S). The PCB marking is YJ-DVB_2S-V06, 2010-01-14,www.yaojinkeji.comIs there any way to find the capacity/voltage of the electrolytic?Regards,

author: DaJMasta
author_rank: Super Contributor
timestamp: March 09, 2020, 07:56:02 pm
content: What evidence do you have that suggests it's blown? Looks like it wasn't fitted in assembly intentionally to me.You could try determining its function, and if another capacitor is fitted with a similar function and footprint, it could be a good choice. You can also look for app notes for the devices it attaches to, to get an idea of what likely would work in that place, and you can measure the voltage across it in circuit to deduce a safe (at least safeish) minimum voltage rating. Alternatively, you can look for pictures of the same device that have it fitted and try to determine from that.I still think it was never fitted to the board, though.

author: greenpossum
author_rank: Frequent Contributor
timestamp: March 09, 2020, 07:56:42 pm
content: Here are some ideas for consideration:See if you can find any schematics or tear down videos that show the value.What is the supply voltage of the circuit? Usually 5 or 12V. Maybe 15. Then add some margin.Put in a capacitor of higher voltage (say 25V) then measure the voltage and reduce if you want to.Assuming it's a supply filter capacitor put the largest μF that will fit the footprint.PS: I agree with DaJMasta. Did you actually find debris from the "blown" capacitor? I thought you had desoldered it cleanly.

author: Gyro
author_rank: Super Contributor
timestamp: March 09, 2020, 08:30:14 pm
content: There arethreefour other empty footprints, what makes you single out that one?

author: sdancer75
author_rank: Frequent Contributor
timestamp: March 09, 2020, 09:15:43 pm
content: I blew the capacitor trying to desolder a neighboring part with my air gun station....Unfortunately I didn't get any image shoots before. 🤫

author: SpecialK
author_rank: Regular Contributor
timestamp: March 09, 2020, 09:33:23 pm
content: it looks to be associated with U6. Probably a buck converter. Look up the datatsheet for U6 and look at the sample circuit for the otput smoothing capacitor value.

author: Bud
author_rank: Super Contributor
timestamp: March 09, 2020, 10:28:04 pm
content: Just use a 25V rated cap, the big ass chip to which the cap connected to is using certainly much lower bus voltage.Or temporarily solder a 10uF 25V cap , power the board up and measure the actual voltage across the cap.

author: sdancer75
author_rank: Frequent Contributor
timestamp: March 10, 2020, 06:52:31 am
content: Quote from: Bud on March 09, 2020, 10:28:04 pmThanks, but unfortunately I have also a short circuit problem somewhere, that's why I tried to desolder some parts next to the mentioned capacitor.But anyway I will try 10uF/16v (power of the decoder is 9V so I doubt it's bigger than 16v).

author: SpecialK
author_rank: Regular Contributor
timestamp: March 10, 2020, 09:36:56 pm
content: What is the chunky connector on the front? SCART?Anyway check U6. Let me know what the marking says. It clearly is some sort of switching regulator as evidenced by the smoothing 4R7 coil and EC7.

author: Gyro
author_rank: Super Contributor
timestamp: March 10, 2020, 09:44:08 pm
content: Yes it's a SCART.

author: SpecialK
author_rank: Regular Contributor
timestamp: March 10, 2020, 10:06:15 pm
content: Is this the unit?

author: sdancer75
author_rank: Frequent Contributor
timestamp: March 11, 2020, 09:19:48 am
content: Quote from: SpecialK on March 10, 2020, 10:06:15 pmYep, that's it...After all, it's 5V input my mistake!

author: sdancer75
author_rank: Frequent Contributor
timestamp: March 11, 2020, 09:45:14 am
content: Quote from: SpecialK on March 10, 2020, 09:36:56 pmYou probably have right about the switching regulator, but U6 seems to be ok. I initially found the other switching regulator U8 on the rightmost side of the bigger image I attached (I had a shortcut between positive and ground). I replace it with a replacement part (not the same) of dubious quality (ebay -store) but the shortcut fixed. The original part marking is KV7RF which is actually an SY8089AAAC (https://datasheet.lcsc.com/szlcsc/Silergy-Corp-SY8089AAAC_C78988.pdf). The replacement part was KV5IU (not exactly sure right now, since I am out of the office right currently). I ordered some pieces of the original SY8089AAAC to check it out once again.Anyway, testing the decoder I could feel the heat on the sink of the main IC, but the LED display was off. Measuring the LED controller (FD650B-S) on the board I found a shortcut between VCC and GND. I desoldered the IC but out of the circuit was ok. Νext, I continued with the SMD capacitor C351 that is beside the electrolytic I blew.That's the way somewhere in the road I evaporated the capacitor :-(PS: From the schematics of the SY8089AAAC I cansee its a 22uF!