Digitech QM1523 - Page 1
Forum section: electronics / beginners

author: benjzet
author_rank: Contributor
timestamp: January 20, 2015, 01:08:46 am
content: Good Morning Forum,I am new to this electronic stuff... For years, I have paid someone else to fix my stuff, well, no more!!At least in theory.I am good at soldering and have 4 solder tools, plus flux, wick and a ton of solder (two scope products and a solder gun (non-gas) and one other that has no label).Anyway, back to the problem at hand. I have a Digitech QM1523 that I brought for $15 at my local Jaycar (photo's pending). I also have an old HP Pavilion Compaq monitor I ripped apart to test (also photo's pending). I am trying to read voltage, the instruction's make no sense and was wondering if I could gain some insider knowledge from here?.If I am reading the cap's correctly and I like to think I am, the big brown one's are 16v rated and the little brown is 10v rated.Yet, when I use the multimeter on the upside down U thing on 20k the big brown guy's reach up to 18.27 before I move on (buy they are still climbing) and the little guy reaches 67.9.Am I doing this correctly? I just want to find something wrong, pat myself on the back, replace it and see if it worksAgain, that's the theory.So, what does everyone else here think?

author: retiredcaps
author_rank: Super Contributor
timestamp: January 20, 2015, 03:52:33 am
content: I suggest you watch this 5 minute multimeter tutorial video first followed by Martin's videos. After some practice measuring some AA, 9V batteries, learn the difference between the hot side and cold side on the SMPS before measuring your Compaq monitor.

author: retiredcaps
author_rank: Super Contributor
timestamp: January 20, 2015, 04:25:40 am
content: Another tutorial using a manual range meter.https://learn.sparkfun.com/tutorials/how-to-use-a-multimeter

author: benjzet
author_rank: Contributor
timestamp: January 20, 2015, 06:54:28 am
content: Thank you for the tutorial's.I followed the advice, I got my 1.54 from my AA battery, I have it set to DC 20v for my 16v caps and 10v for the little cap, all 5 of them.However, with no power to the board.2 caps give a reading of 0.02 and 3 give a reading of 0.00 and the little cap gives a reading of 0.00Is there something wrong with all the caps? or is it because I have no power going into the board?Thank You.

author: sleemanj
author_rank: Super Contributor
timestamp: January 20, 2015, 07:33:39 am
content: You have a fundamental (and large) hole in your understanding about1. what a capacitor is2. how a capacitor works3. what the values printed on a capacitor mean4. how to measure various features of a capacitor5. how to decide if a capacitor is bad or notI feel that filling in this hole in your knowledge is beyond the scope of a forum thread really.No offence, but you need to learn to crawl before you can walk and from your posts in this thread, I don't think you're at the crawling stage yet.https://www.google.co.nz/search?q=electronics+for+beginnersEdit to add: You might want to try and get hold of "Make: Electronics" by Charles Platt, I think it's rather a good primer (introduction) to the world of electronics.

author: benjzet
author_rank: Contributor
timestamp: January 20, 2015, 07:54:42 am
content: Good Evening Forum!Please disregard my previous post.I have tested all according to their own rating.Audio Board:c202 13.45 (16v), c201 13.45 (16v), c207 0.00 (16v), c205 0.00 (16v), c208 0.00 (16v), c210 4.62 (10v)Display Board:Cap1 13.45 (25v), Cap2 0.00 (16v), Cap3 0.00 (16v), Cap4 0.00 (16v), Cap5 0.00 (16v), Cap6 3.28 (16v)Power Boardc811 13.45 (25v), c927 5.01 (16v), c932 5.01 (16v), c923 13.45 (16v), c922 13.45 (16v), c925 13.45 (25v), c805 13.45 (25v), big 344 (unknown, covered by glue v)To explain, the 'c' code is the individual capacitor on my board.The 5.01 or 13.45 is what my multimeter detected with power flowing.The '(' ')' is the voltage rating written on the capacitor.All those 0.00, would they need replacing? are they the non-functional parts?Thank You.

author: Wytnucls
author_rank: Super Contributor
timestamp: January 20, 2015, 07:57:41 am
content: Read Sleemanj's good advice again.

author: benjzet
author_rank: Contributor
timestamp: January 20, 2015, 08:55:17 am
content: Okay,So if all my reading and studying is correct, you read the uF of the capacitor, not the v.Is that correct?If yes, I will retest correctly.Thank You.

author: Wytnucls
author_rank: Super Contributor
timestamp: January 20, 2015, 10:01:57 am
content: All you wanted to know about capacitors:http://en.wikibooks.org/wiki/Electronics/CapacitorsThe "rated capacitance" CR or "nominal capacitance" CN is the value for which the capacitor has been designed. Actual capacitance depends on the measured frequency and ambient temperature. Standard measuring conditions are a low-voltage AC measuring method at a temperature of 20 °C with frequencies of100 kHz, 1 MHz (preferred) or 10 MHz for non-electrolytic capacitors with CR ? 1 nF:1 kHz or 10 kHz for non-electrolytic capacitors with 1 nF < CR ? 10 ?F100/120 Hz for electrolytic capacitors50/60 Hz or 100/120 Hz for non-electrolytic capacitors with CR > 10 ?F

author: Riotpack
author_rank: Regular Contributor
timestamp: January 20, 2015, 10:03:54 am
content: The voltage written on the side of the capacitor is the MAXIMUM voltage you can use the capacitor for in a circuit. Think of it like a tire with a maximum inflation pressure of 30psi. You cannot go above this, but you can inflate to less.So in your circuit, they have used some capacitors which can handle a maximum of 16V. The capacitors store their charge from the voltage provided by the circuit. If you measure 0.00v it does not mean the capacitor is faulty. It may not be getting power from the circuit before it, or it may be used in a way where you will not measure a DC voltage at all!I would not go around probing this monitor with the power turned on! If you are interested in electronics and looking to learn more, start with some battery powered kits and watch videos like those posted.Its a big dangerous leap to jump into a live monitor without having knowing exactly what you're dealing with. I really recommend pushing the monitor to the side and getting a few electronic kits and playing around with them.There's enough videos and people here to help.

author: benjzet
author_rank: Contributor
timestamp: January 20, 2015, 11:29:31 pm
content: I thank everyone for their reply.I have been reading and watching all the video's.I don't have the cash to get 'kits' that's the whole reason I am doing it this way.I am still being told off regarding or advised purely over DC Voltage.I understand the details of the capacitor now. I am just wanting to confirm 100% if spending a whole day/night reading/watching and taking notes is correct, I measure the uF of the capacitors and not the DC voltage?If I don't measure the uF and I dont measure the DC Voltage, as they are the only two things written on the capacitor, what do I measure then? and please, no more lessons, videos, wiki or referring to anyone else post, just a quick answer and it'll be good...Please!!Thank You,- Benjamin D

author: VK5RC
author_rank: Unknown
timestamp: January 21, 2015, 12:05:06 am
content: The big problem is that the value on the capacitor is not necessarily what you should find, often the act of connecting a Multimeter will alter the electrical properties circuit, also voltages are relative, so the two points that you measure it between are very critical. I would add a comment that switch mode power supplies are quite complex electronically, they would not be a good starting point to begin an exploration of electronics.Exploration of a linear type power supply eg an old transformer type 'wall wart' with great care near mains voltage ( and a ground leakage safety switch) looking at how transformers, diodes and capacitors I think may be more helpful.

author: benjzet
author_rank: Contributor
timestamp: January 21, 2015, 12:13:02 am
content: Okay.What should I find then?If uF and Voltage are not what I look for.All my research state I search for the uF with a +/- 10% either way.So I have done that, I have 2 capacitors working.Rated for 470uF and testing are discharging, apparently a good thing.3 1000uF capacitors testing 0 or error code 1 with nothing else happening.2 470uF capacitors also testing at 0 or error code 1.I have my multi-meter set to 2k uF for testing purposes, something all this reading and research told me I should do.So, can I please gain a relatively simple answer? I just want to know if I am on the right track, if I am testing these capacitors correctly!!Please just answer!Please do not tell me what I should start with or test, I have this unit to test, nothing else!Please no more telling me what to watch or read, I've been doing that for two days and following along in their test's!I am just after an answer after 2 days of asking!

author: benjzet
author_rank: Contributor
timestamp: January 21, 2015, 03:05:34 am
content: NVM forum!I worked it out.I was right, those three caps that were reading 1 or 0 and nothing else,Just replaced them, the board now has power (I tested the 5v out, both of them),Before replacing those caps, they were zero. After replacing the caps, they are now 5.05v and working.I have 1 cap on the main board right next to the two 5v in connections that reads 1 only so now I am replacing it and will keep you up to dateThank You.

author: Wytnucls
author_rank: Super Contributor
timestamp: January 21, 2015, 04:13:37 am
content: No, you're not right. You don't have a clue about what you're doing. Your crappy multimeter doesn't measure capacitance. Replacing most of the caps on the board may fix your problem, if you're lucky, but that is not learning to fix electronics.You need an LCR meter or at least an ESR meter to troubleshoot caps properly. Google those up as you probably have never heard of them.

author: benjzet
author_rank: Contributor
timestamp: January 21, 2015, 04:27:13 am
content: I have heard of both of them, but I live in a country town, I don't often get into the city and my only electronic store is more interested in selling radio's and solar panels than testing equipment. So, again, I am doing the best with what I have. I do have a clue about what I am doing, I understand enough, I was just seeking clarification. I realize completely that my first post was waaaay off and I am really thankful for the youtube vid's and websites posted, which I have printed off completely...I tested and retested as per everything I have read, I even unsoldered to test as well which another article/book suggested doing as a third test using a multimeter if nothing else was available. I have ordered 4 caps and replaced 2.6 in total.The power board after all my testing works now 100% my mainboard/logic board has 1 cap and the other 3 are on the audio board. as the unit uses the majority of the same caps. I have swapped some off the audio board and got my mainboard working 100%... Therefore it's all about the audio board now.So, my monitor is turning on, thankful for that. Once I have the audio reconnected I will post some photo's of my working monitor.I wish to thank you all who in turn posted those photo's and video's.With time and more practice, I naturally will get far better.Thank You.