Need help finding correct serial number for capacitors - Page 1
Forum section: electronics / beginners

author: sysv
author_rank: Newbie
timestamp: April 09, 2018, 07:15:29 pm
content: Dear EEVBlog Forum. First time poster, long time watcher of the youtube channel. Feels great to be hereI'm an electronics hobbyist trying to debug a faulty dryer machine (drying clothes). I (think) I've narrowed the issue down to three faulty capacitors on the logic board but I'm having great trouble identifying exactly what capacitors I need to buy. Here are close-ups of the faulty caps:Cap 1:https://drive.google.com/file/d/1tEFpZdHDATOCBZDevyfvVijM7V78XglX/view?usp=sharingCap 2:https://drive.google.com/file/d/10kEpqdvh7-1lWNKCwlQAn8_NhjdiLPT8/view?usp=sharingCap 3:https://drive.google.com/file/d/1Oji7gTeDDQECb92MmTOsJGAn2KgjKDUt/view?usp=sharingGoogling Cap 1, I managed to find this data sheet:https://www.vishay.com/doc?22206.This data sheet seems to describe one of the caps I need to replace. So, now to my questions:Question 1: How can I identify the correct part number? The data sheet lists several different parts (WKPXXX#CP###KR). If someone could offer guidance how to read this I would greatly appreciate it! Like, are there some industry conversions used on these caps that's good to know? What does 4n7K mean for example? And what does the X1, Y1 and "C RUus" mean?Question 2: How would I identify cap 3 (smallest one) if I couldn't assume it's a cap from the same manufacturer like in this case? I can't seem to google cap 3Question 3: Where do/would you buy three separate, single capacitors from? The only site I found that carries these capacitors are mouser.de. Are there any alternatives or other recommendations that I should check out?Thank you!

author: meeko
author_rank: Contributor
timestamp: April 09, 2018, 07:39:07 pm
content: 4n7K means 4.7 nF, +/- 10%.http://www.dummies.com/programming/electronics/capacitor-tolerance-code/X1 and Y1 are safety ratings:https://www.allaboutcircuits.com/technical-articles/safety-capacitor-class-x-and-class-y-capacitors/The backwards "R" joined onto a "U" is Underwriters Laboratories' "Recognized Component" mark, and indicates that it meets Canadian (the c at the front) and American (the us at the end) safety standards.https://www.ul.com/marks/ul-listing-and-classification-marks/appearance-and-significance/marks-for-north-america/.

author: helius
author_rank: Super Contributor
timestamp: April 09, 2018, 07:42:32 pm
content: How did you determine they are faulty?Quote from: sysv on April 09, 2018, 07:15:29 pm4n7, K, are the value of the capacitor—its capacitance—and the tolerance for that value. "n" means nano and the letter is placed at the position of the decimal point. So 4n7 means 4.7 x 10-9and the value is in farads. Another way to write the value would be 4.7nF. K as the tolerance means ±10%. Seehttp://www.robotoid.com/appnotes/electronics-capacitor-markings.htmlThe part number, on the other hand, typically follows the "two digits, then multiplier" convention based on picofarad units. 4.7nF is equal to 47 + 2 zeros pF, so the part number will contain 472. WKP472KCPEH0KR is the full part number. In this case, "EH0" means that the leads are spaced 12.5mm apart and are 10mm long and 0.8mm in diameter. This is primarily important for automatic insertion machines and you don't have to worry too much about that for manual repairs.X1 and Y1 are special categories for capacitors that are used across the line voltage: Radio Frequency Interference suppression caps. They are safety ratings to prevent fires, and replacements should also be rated appropriately. "C (Underwriters Laboratories logo) US" means that UL has listed this part and its Canadian counterpart has also. It's a good bet that other nations testing labs have also listed the part but there isn't room to print them all on the package.Your second cap is very similar, it's a WYO472MCMCD0KR (or "CF0KR", doesn't make much difference). Tolerance class M ±20%.QuoteThe logo is that of TDK EPCOS. This is a MOV, not a capacitor: part B72207S0271K101. Seehttps://en.tdk.eu/inf/70/db/var_11/SIOV_Leaded_StandarD.pdfQuoteDigikey, Farnell, Arrow, Jameco, etc

author: sysv
author_rank: Newbie
timestamp: April 11, 2018, 05:54:56 pm
content: Quote from: helius on April 09, 2018, 07:42:32 pmI set my multimeter to 2K Ohm resistance measurement and probed the components (making sure to switch the pins to make sure polarization was correct) and I looked at the numbers in the display. These three components measured infinite resistance. However, I realized that when I measured these components they were mounted on the PCB which was a little bit of a warning to me. After measuring these components de-soldered, they now show resistance which is a little bit of a let down. Seems like they are fine and not the problem.Quote from: helius on April 09, 2018, 07:42:32 pmAha, sort of like how voltages are written like 3v3 for 3.3V sometimes.Quote from: helius on April 09, 2018, 07:42:32 pmThank you. It's always nice to pick up on these conventions!Quote from: helius on April 09, 2018, 07:42:32 pmIf I understand correctly, a radio frequency interference capacitor (in this case) is used on the high voltage lines to "slow down" the rapid change in AC current in an effort to reduce the noise produced by having high voltage on the PCB?Quote from: helius on April 09, 2018, 07:42:32 pmSo in this case you had to know the company logo to identify the part? Or is there anything else that would give it away? How would you identify this as a MOV? (MOV is a varistor, right?)

author: james_s
author_rank: Super Contributor
timestamp: April 11, 2018, 06:04:26 pm
content: The impedance of a capacitor drops with frequency, so the RFI suppression caps across the AC line appear as an (almost) open circuit to mains frequency but to high frequency noise they appear as a low impedance and shunt it to ground. Those do fail from time to time but normally won't cause the device to malfunction.Let's take a step back and look at the actual problem here, what exactly is the symptom of the device you're trying to repair?

author: helius
author_rank: Super Contributor
timestamp: April 11, 2018, 07:01:56 pm
content: Quote from: sysv on April 11, 2018, 05:54:56 pmI'm not really sure what you expect to find by measuring capacitors with an ohmmeter? Given a DC voltage across them, a functioning capacitor should appear as an open circuit, with only minimal leakage (< 1 uA), which is a near infinite DC resistance. DMMs often use pulses and not DC test voltages, so the indicated "resistance" depends on the waveform the DMM uses. In general it's a terrible idea to test capacitors this way as it gives you very little useful information.The measurements that you would do to measure capacitor health are: first, obviously, capacitance: this is a separate setting on a DMM measuring in farads. Ceramic caps can change their value depending on the voltage so they don't always read as you would expect even if workingsecond, leakage: this is the current that "leaks through" a capacitor biased at DC, which is often more of a problem than capacitance loss. The test setup to measure it is a bench DC supply with an ammeter (DMM set to milliamps) in series with the capacitor.third, dielectric loss or ESR: this is the amount the capacitor heats up when AC current passes through it, a big issue for power supply capacitors. You can use an ESR meter or make your own setup with a function generator and an oscilloscope. There should be threads about that here.QuoteYou get to recognize the way certain parts are packaged (as well as common logos). Blue or green epoxy-dipped discs are often MOVs. It also helps to know the standard capacitance and resistance values:http://www.rfcafe.com/references/electrical/capacitor-values.htmhttp://www.rfcafe.com/references/electrical/resistor-values.htm"275" could mean 2.7uF, but that isn't a common value for a disc capacitor. It's closer to tantalum or MLCC territory, but those have different shapes (thru-hole tantalums are bead-shaped like a jellybean, and thru-hole MLCC are square chiclet shaped).

author: sysv
author_rank: Newbie
timestamp: April 12, 2018, 03:52:45 pm
content: Quote from: james_s on April 11, 2018, 06:04:26 pmThank you for that explanation, this increased my understanding of capacitors by a great deal!The problem is, when the power button is pushed, the "on" led doesn't light up. I thought it might be something simple, like a fuse or maybe a broken cap so the main CPU wouldn't function. I measured the caps as described in the original post. I know my method of measuring caps are horrible but my multimeter doesn't have a capacitor testing setting, so my thought process was: Let's try to determine if some caps are broken or not.

author: sysv
author_rank: Newbie
timestamp: April 12, 2018, 04:03:52 pm
content: Quote from: helius on April 11, 2018, 07:01:56 pmThe "problem" is that electronics are a smaller hobby of mine and I don't have as much time to spend on it as I wished I had. My multimeter is a cheap one where you can't do proper capacitance tests and I don't have an oscilloscope or a bench power supply yet (I have an oscilloscope at work I use in cases I really need it but so far I haven't needed it much yet). So my idea was to simply determine: Does it look like any capacitors are broken? That's the level of troubleshooting I'm doing. I see this whole repair project as a way to just learn while doing.Thank you for summarizing how to measure capacitors properly, I'm going to save your description for future use!QuoteAha, thanks for the clarification

author: james_s
author_rank: Super Contributor
timestamp: April 12, 2018, 05:36:42 pm
content: It may well be something simple, could you post a picture of the board? With some experience you'll start to recognize subsystems like the power supply and that will give you clues on troubleshooting. There are two common arrangements in this sort of thing, one is a power supply with an iron mains frequency transformer to step down the voltage, the other used for low current devices is a transformerless power supply using a capacitor to limit the current followed by a shunt regulator. More complex switching power supplies using a high frequency ferrite transformer are possible but rarely seen in appliances.

author: sysv
author_rank: Newbie
timestamp: April 15, 2018, 02:24:54 pm
content: Quote from: james_s on April 12, 2018, 05:36:42 pmHere are two pictures of the boardhttps://drive.google.com/open?id=13Zi9OdnqVzjkb_o8Z8rZK-xB0zReX_0hhttps://drive.google.com/open?id=1x5sSPL_JZcOEj6qcF-SPguGyrz52d9cENote that the three desoldered passive components are missing from this board. Two of the caps are supposed to be located on the lower right side of the board (first picture) and the varistor was located in the middle of the board.As far as I can tell, the mains input is on the top right of the first picture. The other, similar looking sockets seems to be output power for the various motors in the dryer (the black boxes are relays?) and the top of the board carry control signals.On the back of the board is an 8-bit micro controller. Any input on what I could look for here is greatly appreciated.