How to remove glue holding down capacitors? - Page 1
Forum section: electronics / repair

author: AZImmortal
author_rank: Contributor
timestamp: May 11, 2018, 08:27:51 am
content: My friend has a TV that's having problems powering on, so I decided to open it up to see how the capacitors are doing. However, I discovered that all of the capacitors that are mounted at 90 degree angles are held down by some kind of white glue. Are there any common methods or solvents that can be used to remove the glue? Here's a picture of the board.https://imgur.com/a/hyeAeVb

author: wraper
author_rank: Unknown
timestamp: May 11, 2018, 08:41:48 am
content: Cut with a small knife/scalpel.

author: tautech
author_rank: Super Contributor
timestamp: May 11, 2018, 09:00:36 am
content: Quote from: wraper on May 11, 2018, 08:41:48 amYep, it's white RTV silicone. Do what wraper said.

author: Electro Detective
author_rank: Super Contributor
timestamp: May 11, 2018, 10:25:10 am
content: This is where an ESR tester may save you chopping away on caps that are okUse a hair dryer first to soften things up and use plastic/covered tools, glovesand or tape up any exposed metal handles on knives, pliers, tweezers etcWith the heat the white stuff may just pull off, depending on the silicone gradeand don't forget the glasses to protect your eyes... and look cool on the job

author: wraper
author_rank: Unknown
timestamp: May 11, 2018, 10:32:57 am
content: I'd also say check the ESR in circuit or solder new capacitors in parallel for testing to avoid wrecking the PCB needlessly.

author: wraper
author_rank: Unknown
timestamp: May 11, 2018, 10:40:48 am
content: BTW does it not power on at all? Did you check fuses, voltages. My gut feeling tells there is nothing wrong with capacitors in this case.

author: AZImmortal
author_rank: Contributor
timestamp: May 12, 2018, 04:27:13 am
content: Thanks for all the answers, everyone. Unfortunately, I'm not an engineer, so all I know from previous experience and reading about other people's problems with their TVs with similar issues is that failing capacitors is a likely culprit. Iamgood with a soldering iron, so my plan was to just take a shotgun approach and replace all of the capacitors and hope for the best, which is what I did with my own TV that was having power issues. I was hoping that when I looked at the capacitors that I would find at least a few that were bulging/leaking/etc for obvious visual confirmation that they were done, but all of them are visually intact.Quote from: wraper on May 11, 2018, 10:40:48 amAccording to my friend, the TV will sporadically turn on. I'm not sure how often it will actually turn on, but he says he just tries to keep turning it on over and over again until it finally does turn on. Once it does turn on, he claims that it will stay on indefinitely.When it doesn't turn on, the TV will still initially react to the press of the power button by briefly turning off the red power LED, but then after a few seconds, the power LED will change back to red to indicate that it's in the off state again. Unfortunately, like I mentioned above, testing things like fuses, voltages, etc, is beyond my limited knowledge.

author: tautech
author_rank: Super Contributor
timestamp: May 12, 2018, 05:40:15 am
content: Quote from: AZImmortal on May 12, 2018, 04:27:13 amDefinitely sounds like crook caps but unlikely to be the 82uF more so the LV output caps and their current draw is shutting down the SMPS. Do replace the 2 little radials near the controller IC as they're for its VCC supply.Good rule of thumb is any 10% low to labeled value...in the bin!

author: AZImmortal
author_rank: Contributor
timestamp: May 12, 2018, 08:41:28 am
content: Thanks, when you say the 2 little radials near the controller IC, do you mean C5802 and the one to the right of it next to the HOT text? Are those the ones that you would replace first based on the limited information that I've provided? Should I just do all the upright radials, including the two on the left side of the picture?QuoteForgive my newbness, but can you elaborate on what you mean by this? Thanks again.

author: tautech
author_rank: Super Contributor
timestamp: May 12, 2018, 09:09:06 am
content: Quote from: AZImmortal on May 12, 2018, 08:41:28 amYes those 2 along with the LV ones below the white line on the silkscreen that marks the border between HV and LV circuits.QuoteUp to you on those two but I don't consider them to be where the action is ....or isn't.For the sake of a couple of $, why not.Quote from: AZImmortal on May 12, 2018, 08:41:28 amSay they are marked 1000uF and only measure 900uF....bin them.Now this is just a quick and easy recommendation if you haven't got access to an ESR tester and they tell another set of parameters however for the price of a few caps there's no need to go there.Typically you want to get low ESR caps for the secondary (LV) side of SMPS and they commonly have ESR specs in the tens of milli ohms. Stuffed low ESR caps might measure into ohms and that high series resistance prevents then from doing their job properly and hence high output ripple. When you get brave (I am sometimes) you might wander a finger over LV output caps to check if any are getting hot....a sure sign they're stuffed but for the novice with limited electronic experience be careful, bloody careful......one hand in your back pocket...that sort of careful !I'd be pulling output caps and measuring first then the 2 by the IC.Good luck come back with your findings.

author: wraper
author_rank: Unknown
timestamp: May 12, 2018, 10:19:47 am
content: Quote from: tautech on May 12, 2018, 09:09:06 amMost electrolytic capacitors are rated for ±20%, and usually land on the low side. 900uF is what many brand new capacitors will measure. Not to say it's only valid when measuring properly at 120 Hz AC and not multimeter with square, sawtooth or whatever waveform. Multimeter is only useful for checking completely dead capacitors. Capacitance starts dropping significantly only when ESR already gone up through the roof and there is almost no electrolyte left.

author: AZImmortal
author_rank: Contributor
timestamp: May 13, 2018, 06:56:55 am
content: QuoteBy white line, do you mean the thick white one that runs pretty much across the middle of the board? And if so, do you mean all six of the caps that are below that line? The ones that are mounted at 90 degrees? I see the following:C5855CM875CM858CM851C9118C9218QuoteI definitely plan to! Thanks for the help so far.

author: tautech
author_rank: Super Contributor
timestamp: May 13, 2018, 07:49:50 am
content: Quote from: AZImmortal on May 13, 2018, 06:56:55 amYep, all those.They're likely marked Low ESR but not always however I'd be checking their values one by one and if they all seem to be true to label then the problem's likely somewhere else.What wraper said is worth taking note of and if you find something you don't understand come back with further questions.

author: kripton2035
author_rank: Super Contributor
timestamp: May 13, 2018, 07:57:00 am
content: if you plan to do some repair on things like this, an esr meter is definitely a must have.please take a look at my esr repository, there are many to build (or buy) easy.

author: AZImmortal
author_rank: Contributor
timestamp: May 14, 2018, 05:16:18 am
content: Quote from: tautech on May 13, 2018, 07:49:50 amThanks, it's very much appreciated.Quote from: kripton2035 on May 13, 2018, 07:57:00 amThanks, I didn't know that ESR meters were something that could be relatively easy to make from common parts. It's very likely that my dad (who has passed away but was an EE) has an ESR meter among his old things, so I might be able to find one if I dig around (hopefully it'll say something obvious like "ESR meter"). Otherwise, I'll definitely consider making one since capacitor replacements is one of the things that I do most commonly.

author: kripton2035
author_rank: Super Contributor
timestamp: May 14, 2018, 05:56:28 am
content: only people that repair electronic appliances need (and build or buy) an esr meterengineers generally conceive things, and don't have a need for esr meters ...don't know what kind of people your dad was, but hope you will find any useful devices in his old things.

author: AZImmortal
author_rank: Contributor
timestamp: May 14, 2018, 07:33:03 am
content: My dad was very much the type to build/repair just about anything that he could (he built his own multimeter from scratch when he was pretty young) and he had a workbench with a bunch of different tools/meters/etc, but I never really bothered to go through them. However, I do remember replacing all the caps on a motherboard with him when I was younger and I don't remember him testing any of the caps before we replaced them, so maybe he didn't have one.

author: tautech
author_rank: Super Contributor
timestamp: May 14, 2018, 08:49:00 am
content: Quote from: AZImmortal on May 14, 2018, 07:33:03 amA 'shotgun' cap replacement approach was quite normal up until the last few years when ESR testers became affordable. Most of us have done it.But now we have better tools we do check them but that doesn't mean those that don't do regular repair work must have one. For years I just measured basic capacitance and set myself -10% as a threshold for old caps. It's quite true that new ones have some variance in measurement but that's not what this is about. Measure a few, compare and compare and get a feel for what your DMM measures then somewhat trust it as providing arepresentativemeasurement you can make decisions on.Without spending $$$ on gear that you'd use only 'once in a blue moon' the hobbyist can get by with bugger all and a bit of learned experience.Everyone offers their kind and thoughtful advice based on their needs and when I ventured into SMD I got some USD $300 ST3 Smart Tweezers that give me more than good enough indication of uF and ESR in an instant so I've never needed anything else. Previously I made do with a cheap VC99 DMM and that was OK but only just OK.You'll work it out.

author: AZImmortal
author_rank: Contributor
timestamp: May 14, 2018, 09:25:48 am
content: QuoteYeah, this is definitely me up to this point, haha. There's a lot of equipment that I know would make my life easier but I can't justify the cost most of the time, so I just do what I can and hope for the best. I do like to make my own equipment when it's cheap though, and an ESR meter sounds like it fits that criteria. Hopefully I can figure out the schematics easily enough.QuoteThanks for the pep talk!

author: Shock
author_rank: Super Contributor
timestamp: May 14, 2018, 11:49:59 am
content: Powering on issues from cold is a capacitor ESR symptom. As the capacitors warm ESR is lowered, so a marginal capacitor can become operational when the TV is warm.If marginal, warming the capsgentlywith a hot air gun/hair dryer aimed at the caps can prove it, the fault will appear to go away if so and allow you to power cycle.Warning though 400V to 1000V+ can be present in a lot of LCD TVs so make sure you do nothing silly like coming into contact with the PCBs with your hands or a tool with the panel off while testing.The low voltage and start cap come to a few dollars in most cases. The TV will normally be a few years old and have cheap caps so therefore it's an easy decision. But an ESR along with capacity test is more definitive.

author: AZImmortal
author_rank: Contributor
timestamp: May 14, 2018, 10:44:22 pm
content: Thanks. Since the TV turns on eventually with enough effort, it would seem to fit the marginal criteria, although the high voltage warning definitely gives me pause in trying it, haha. How gently is "gently" when it comes to warming caps? A few minutes on low heat before trying to turn on the TV?

author: Shock
author_rank: Super Contributor
timestamp: May 15, 2018, 06:15:12 am
content: Quote from: AZImmortal on May 14, 2018, 10:44:22 pmJust make sure not to make contact, stay back a couple of inches, consider anything on a PCB dangerous to touch unless you know better. Hair drier with an attachment can work well to direct the air a bit, without the attachment if you have no options.When the unit is cold and faulty constantly blow hot air on the suspect cap (not the whole PCB). Plug in power up and test. Hit a few times and if you have if no luck try another cap.The caps are temp rated, you're going nowhere near that, you're aiming for radiant heat warm, not burning warm. Practice on a metal spoon or something and just get it warm.You can use the same method to troubleshoot cold start issues on the video/processor board as well.Unplug from the wall blow a cool fan onto the PCB for a while to reset it. Make sure you always know if it's plugged in and switched on at the wall. Working on capacitors or old PCBs wear eyewear as occasionally they blow and you don't want it in your eyes.Some remote controls send a signal but the batteries are too flat to send the proper power on. If you have manual controls on the TV try that as well when it's not working or change the batteries if unsure.

author: Gregg
author_rank: Super Contributor
timestamp: May 16, 2018, 12:04:55 am
content: To expand on Shock’s excellent recommendations, a can of so called compressed air turned upside down will very quickly cool components. It is basically refrigerant in a can; you only need a tiny amount of the liquid to hit the component and evaporate. This may save you lots of time and potentially point out soon to fail caps. There may be some slight oil residue from using a lot of it, but alcohol will clean it away quickly.A cheap hot air soldering station, look up the 858D thread here:https://www.eevblog.com/forum/reviews/youyue-858d-some-reverse-engineering-custom-firmware/]https://www.eevblog.com/forum/reviews/youyue-858d-some-reverse-engineering-custom-firmware/] https://www.eevblog.com/forum/reviews/youyue-858d-some-reverse-engineering-custom-firmware/They come with a few different nozzle sizes and are perfect for slow heating of individual components as the temperature can be turned way down and the air regulated. For the price it may be a nice addition to your tools. One would also be ideal for warming up the silicone holding the caps to make it cut easier