A beginner's beginner...  - Page 1
Forum section: electronics / beginners

author: Pcmaker
author_rank: Regular Contributor
timestamp: October 14, 2017, 04:46:06 pm
content: Hello, guys. I'm a n00b in every sense of the word. I found this site via EEVblog channel on Youtube. I work as a maintenance guy. Jack of all tades from plumbing to welding, but a master of none. I've been watching dozens and dozens of the EEVblog videos on Youtube and I find it fascinating, even though I have no clue as to what's being talked about most of the time.I'm planning on changing that. I want to be able to take something electronic apart, troubleshoot and repair the issue.I have all the tools in the world, and my EEVblog Brymen 235 multimeter I ordered just came in today.I've only worked with 110v and up equipment such as HVAC really. The only times I've worked on low voltage stuff is when I'm working on 24v thermostats and low voltage contactors.Are there any Youtube videos/channels that walk you step by step for the beginning stages of electronics troubleshooting? I think EEVblog is very entertaining, but it's way above my current knowledge of Electronics engineering.When something of mine breaks electronically, I pretty much just toss it in the trash and buy a new one. I have a DeWalt 20v/12v battery charge that does not work and I want it to be my first little repair project. There's 120v going into the board, but no lights. I do not see a fuse, and the contacts are clean. I tried making sense of the board, but I don't see anything loose, burnt, etc...What do you guys think it could be and where should I look first?back side of the board

author: Neilm
author_rank: Super Contributor
timestamp: October 14, 2017, 05:15:19 pm
content: As you say you are a n00b, I would suggest you don't try probing it when it is powered up, and remember that the large capacitor will retain charge for some time after removal of mains.There is a fuse on the board. If you look at the picture of the topside, in the top left just below the wires is a black rectangle. The board Ident says "T2A L/250V". This is a time delay fuse at 2A rated for 250V. It could most likely be a resettable so the fuse opens when there is a fault and closes again when the supply is removed.

author: Pcmaker
author_rank: Regular Contributor
timestamp: October 14, 2017, 05:31:12 pm
content: Quote from: Neilm on October 14, 2017, 05:15:19 pmThanks for respondingIf you don't mind me asking, how would someone know if something is a fuse or not? Through how it's labeled?Without desoldering the fuse, I checked for continuity on the solder joints of the fuse on the back side of the board and I'm getting a beep on my meter. I'm currently double checking again for anything that looks burnt or something loose through my magnifying glass.

author: Twoflower
author_rank: Frequent Contributor
timestamp: October 14, 2017, 07:06:08 pm
content: Not sure if this is due to the way the picture was taken, but the C109 (lower right corner of the first picture) looks bulged. Can you check if the Cap looks OK? If not that's probably one candidate to replace. If that's the case I would replace C110 as well.

author: Pcmaker
author_rank: Regular Contributor
timestamp: October 14, 2017, 08:27:20 pm
content: Quote from: Twoflower on October 14, 2017, 07:06:08 pmIt is slightly bulged! And there's something that came off of the bottom. I checked for uF and it's at 7.6, but the label on the cap is 10uF. C110 and C111 are good. What I'm assuming is C112 on the top is showing 1100 uF, even though it's the same as the other ones.Is it OK to test for uF on a cap if it's still on the board or does it need to be desoldered and taken out for testing?I'm assuming the "C" stands for capacitor when printed on circuit boards?Thanks!

author: Dubbie
author_rank: Unknown
timestamp: October 14, 2017, 08:33:41 pm
content: You need to remove the cap to test it properly.

author: Twoflower
author_rank: Frequent Contributor
timestamp: October 14, 2017, 08:47:51 pm
content: If some strange stuff came out of the button and the top is swollen that cap is definitely dead.Can you post a decent picture of the markings of the C109 (manufacturer, voltage, capacitance and probably some codes)? It might help to provide you information to get a replacement cap. As a Capacitor does not only had a capacitance (e.g. 10uF) and voltage (e.g. 35Volt) but also the ESR. This is the resistance how fast the charge can build up (and can discharged). As this defective capacitor is close to the SMPS (the transformator is an indicator that this is a SMPS) there are probably some requirements regarding this ESR. Unfortunately this ESR rating is usually not written on the device itself. You have to look it up in the specification of the capacitor.Even if you have measured the C110 the capacitance you haven't checked the ESR value. I would replace it as well. they don't cost a fortune. But only this two and eventually C111. Unless you see a similar damage as you see on C109 (bulging and/or the device spitted out the electrolyte).Before you place the new cap you must clean the PCB to prevent further damages to the copper traces. the stuff in the electrolytic caps isn't very friendly to the PCB.EDIT: Yes. C stands for Capacitor, R Resistor, L coil/inductor. Others might not be that standardized, for example Tr could be Transformer or Transistor. It also depends of the age and origin of the PCB. But usually you can see that if you look at the devices to see what it could be.

author: Neilm
author_rank: Super Contributor
timestamp: October 14, 2017, 09:15:29 pm
content: Quote from: Pcmaker on October 14, 2017, 05:31:12 pmIn this case yes. There should be protection on pretty much anything connected to the mains and it should always be as the mains enters the board. Protection components come in all sorts of shapes, not just tubes. In power supplies these tend to be resettable devices such as the "Polyswitch" which is a trade name for some of these. They look a bit like capacitors, either as disc devices or blocks such as the one here.Quote from: Twoflower on October 14, 2017, 08:47:51 pmIntegrated circuits tend to be labelled IC or U, Transformers can also be labelled TX and Diodes are usually labelled D

author: Twoflower
author_rank: Frequent Contributor
timestamp: October 14, 2017, 09:31:04 pm
content: @Neilm: Right; I forgot the Diodes (D). Transistors are often Q. I think Tr is outdated by now.

author: Electro Detective
author_rank: Super Contributor
timestamp: October 14, 2017, 09:47:20 pm
content: FWIW somebeginner's beginnerfast tips:1. Put some electrical tape over the meter's A and mA uA sockets NOW, because that's a NO GO Zone for beginnersYou don't need to mourn over a NICE blown out meter or chase up expensive internal meter fuses for it2. Ensure the meter is set to the correct setting because you have a device with AC and DC inside,AND you will want to measure continuity (aka BEEP!) and capacitance.Wrong settings + random probing= $$$ +Think, Select, then probe.. EVERY TIME or else you may get an unwanted visit from the magic smoke genie3. C109, C110, C111, and C11 near the heatsink need to go in the trash, end of storyGet good replacements and fit properly noting the + and - markings on caps and board4. Now you can charge your drill5. This one was easy, great for a beginnerI was never this fortunate

author: Pcmaker
author_rank: Regular Contributor
timestamp: October 14, 2017, 09:57:11 pm
content: Quote from: Twoflower on October 14, 2017, 08:47:51 pmHere goes:

author: Johncanfield
author_rank: Regular Contributor
timestamp: October 15, 2017, 12:11:32 am
content: 10 microfarads at 50 volt rating (the u is micro.) Amazon has a bunch of electronic parts kits - look for one that has some caps rated for 50 volts. Good for you for taking on a new challenge!

author: Pcmaker
author_rank: Regular Contributor
timestamp: October 15, 2017, 01:09:16 am
content: What about the ESR rating for this cap? That's what I'm looking for right now

author: Dubbie
author_rank: Unknown
timestamp: October 15, 2017, 01:41:59 am
content: The exact esr is probably not important. A good quality new electrolytic cap should be fine.

author: Twoflower
author_rank: Frequent Contributor
timestamp: October 15, 2017, 07:52:27 am
content: I beg to differ. Even if it's not 100% indicator, but the 105°C type indicates this capacitor is obviously under stress.@Dubbie:Why do you think the ESR doesn't matter? From the location of the device it is close to the switching circuit, the cap is 105°C rated low ESR type and oviously is stressed (the reason why it is released the magic smoke). All of this indicates that the device has some specific requirements beyond 10uF/50V.EDIT: That was written before my first coffee so I missed the word 'exact'. Right the exact value doesn't matter. But go for a low ESR type.Funny thing: I looked up the brand to see if there's a datasheet available. The first hit was "badcaps" it looks like they're notorious for failing. But here's the datasheet:http://www.ltec.com.tw/Series/LZG.pdf(search for "ltec capacitor LZG") And it indicates low impediance low resistance. The exact values usually doesn't matter as the manufactures try to reduce these values (they are unwanted). They are usually sorted under "low ESR" types.@Pcmaker: So go for a low ESR type, 105°C, 10uF, 50V. Check the right dimensions (diameter and lead-spacing).

author: Electro Detective
author_rank: Super Contributor
timestamp: October 15, 2017, 08:13:26 am
content: Quote from: Electro Detective on October 14, 2017, 09:47:20 pmLook up that DeWalt charger on the net and see if others have had the same problem

author: Brumby
author_rank: Unknown
timestamp: October 15, 2017, 10:47:10 am
content: Quote from: Pcmaker on October 14, 2017, 05:31:12 pmYepThe one on your board is T2A L/250V> Slow acting> 2 Amp> Low rupture capacity> 250V (up to)

author: Pcmaker
author_rank: Regular Contributor
timestamp: October 15, 2017, 11:24:54 am
content: I was thinking of getting this capacitor kithttps://www.amazon.com/Ocr-Electrolytic-Capacitor-Assortment-0-1uF%EF%BC%8D1000uF/dp/B01MSQOX0Q/ref=sr_1_4?ie=UTF8&qid=1508066659&sr=8-4&keywords=capacitor+kit

author: Twoflower
author_rank: Frequent Contributor
timestamp: October 15, 2017, 11:50:29 am
content: Nothing I would recommend. Probably also not low ESR rated. Unfortunately I can't read the marking on the picture. And you don't know if they deliver that brand or another they can get hands on. the parts will probably be the cheapest stuff found on the planet.I'm not a big fan of such kits. I would rather recommend buy the parts you need plus a few spare. That way you build up your stock with parts you might need later on again. But that's my personal opinion.If you're thinking you'll do more electronics in future you might get used to the component sellers. The problem usually with mouser/digi-key is they charge you for the shipping and some request a minimum order. But usually you can select the quality you want to buy. Selecting the devices is sometimes a bit problematic as you have to filter out the matching devices:Digikey example.

author: Pcmaker
author_rank: Regular Contributor
timestamp: October 15, 2017, 02:30:48 pm
content: Quote from: Twoflower on October 15, 2017, 07:52:27 amHow do I know if a capacitor is low ESR? Are there markings that indicate it? I'm going to Fry's electronics today after work to get a replacement capacitor.Should I also buy a solder sucker tool? I had a hard time pulling out the cap as I was pulling on it at the same time as heating up the solder in the back.

author: Twoflower
author_rank: Frequent Contributor
timestamp: October 15, 2017, 03:25:39 pm
content: Unfortunately that's not written on them directly. You need to look into the datasheet. And Fry's seem to have only one 10uF/50V cap which seems to be a normal type. Maybe they have something not listed online. I don't know that store.A desolder pump is a nice thing to have. Some use this or some de-solder wicked. I've used both and both seem to work reasonable.

author: Pcmaker
author_rank: Regular Contributor
timestamp: October 15, 2017, 07:13:59 pm
content: Quote from: Twoflower on October 15, 2017, 03:25:39 pmAs a general rule of thumb, do I always go for low-ESR caps?

author: Twoflower
author_rank: Frequent Contributor
timestamp: October 15, 2017, 07:20:19 pm
content: In most cases you could do that. But a) they are more expensive and b) some circuits don't like the low ESR type. For example linear voltage regulators might behave unexpected. But in most cases the the you could use them.

author: Pcmaker
author_rank: Regular Contributor
timestamp: October 15, 2017, 10:59:50 pm
content: Bah... well, that didn't work. I replaced 2 of the caps with new ones from Fry's just to see if that was the issue. Still not working.I was very optimistic, too.Hmm..

author: Dubbie
author_rank: Unknown
timestamp: October 15, 2017, 11:43:49 pm
content: Might have to start following the power stage by stage to see where it stops measuring how it should.

author: tautech
author_rank: Super Contributor
timestamp: October 15, 2017, 11:53:43 pm
content: Quote from: Pcmaker on October 15, 2017, 10:59:50 pmNow you want to identify the 8 pin SOIC, it's the SMPS controller so get the datasheet online and check it for Typical Applications where often you can find very close examples used in actual products.When found give us a link so we can follow along and help if needed.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: October 16, 2017, 11:31:48 am
content: This looks like it's a flyback converter (Single input transistor) In which case, the startup resistor is a prime candidate for going o/c or high value. Usual clue is that without the small current this draws, the reservoir cap (big electrolytic center of board, mind your fingers as it can have 350v on it) will remain charged for a long time after power is removed.Likely it's one of the larger resistors stood on end, R3 or its sleeved neighbour. Will have a value somewhere between 47k and 1M. You can't measure it in circuit.The other larger resistor, R17, 0.47 ohm, is likely for current sensing. It's also quite common for resistors of this type to 'dry joint' so check the soldering.Some of the larger connection pins near D11 and L2 on the underside (possibly the transformer) also look a bit dry-jointish.

author: Old Don
author_rank: Regular Contributor
timestamp: October 16, 2017, 12:14:46 pm
content: You can buy high quality capacitors in small quantity from places like Mouser. You want to match the microfarad, voltage and 105 deg ratings. If you select low ESR as a selection you'll end up with only a couple of choices. From google "mouser 10 microfarad 50v low esr radial" (radial = leads at one end) gets you to a chart and Panasonic EEU-FR1H100B is one that they stock and costs $0.33/each. You might want to add solder and other items needed for PCB work that you might not have for general repair work. A 60-40 solder in small dia. with rosin flux (never acid!), PCB flux to help solder in the new components, maybe a low wattage soldering iron and an assortment of tweezers and board cleaning gear and place an order. Also see if the fuse does reset or also needs to be replaced and add a new one to your shopping list.

author: Pcmaker
author_rank: Regular Contributor
timestamp: October 17, 2017, 02:59:28 pm
content: Ok, I tested R3 and the sleeved resistor and they both checked out OK.Then I took out R17 and got this. I did the resistor chart and this should be a 47 ohm resistor +/-5%I cycled through the Range button and the only thing that shows anything is regular ohms. M and K shows 0000I'm thinking this is a bad resistor?

author: odessa
author_rank: Regular Contributor
timestamp: October 17, 2017, 03:07:39 pm
content: Thats 0.47 ohm, so your meters good, and so is the resistor

author: Pcmaker
author_rank: Regular Contributor
timestamp: October 17, 2017, 03:14:18 pm
content: I'll put it back then. The BM235 can't show the next digit after 4?Also, I'm not giving up just yet. One thing I haven't checked is the transformer. I only checked the mains coming in at 120v.