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  • Proper multimeter specs for fixing capacitors on your motherboard?

    - by Xeoncross
    When our motherboards or LCD's go out it is possible that the capacitors are at fault and can be easily replaced by removing and replacing the bad caps rather than buying new screens or computers. After all, replacing a cap is much faster than building a new PC. Along those lines some of the capacitors I see on my boards are over 900µF. What is the bare minimum you need in a multimeter to test for bad capacitors (or good capacitance?)

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  • What type of Multimeter is safe to use on computers?

    - by Ssvarc
    In "Upgrading and Repairing PC's - 18th edition" by Scott Mueller on pg. 1278 he discusses multimeters. "You should only use a DMM (digital multimeter) instead of the older needle-type multimeters because the older meters work by injecting 9V into the circuit when measuring resistance, which damages most computer circuits. A DMM uses a much smaller voltage (usually 1.5V) when making resistance measurements, which is safe for electronic equipment." Most DMM's that I've looked at have 9V batteries. Are they internally stepping down the voltage used when making these measurements? Wouldn't the concern of injecting 9V be true when measuring continuity as well? A little off topic, there is a fascinating way to test for laptop screen inverter failure, (http://www.fonerbooks.com/test.htm), is anyone aware of a safe DMM that is capable of this as well?

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  • How to find polarity of a power supply that's lacking the customary markings

    - by Nosredna
    If I have a power supply (not a computer power supply, just a battery-replacing wall wart) and it doesn't have the usual polarity marking, how to I know if the tip is positive or negative? Update: I couldn't find my multimeter. I did find a model number on the power supply and typed it into Google. Some guy selling a bunch of power supplies on eBay had checked it and found that it was tip positive, which is what I needed!

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  • What could be causing Windows to randomnly reset the system time to a random time?

    - by Jonathan Dumaine
    My Windows 7 machine infuriates me. It cannot hold a date. At one point it all worked fine, but now it will decide that it needs to change the system time to a random time and date either in the future or past. There seems to be no correlation or set interval of when it happens. To remedy it I have: Correctly set the time in bios. Replaced the motherboard battery with a new CR2032 (even checked it with a multimeter). Tried disabling automatic internet synchronizing via "Date and Time" dialog. Stopped, restarted, left disabled the Windows Time service. Yet with all of these actions, the time will continue to change. Any ideas?

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  • What could be causing Windows to randomly reset the system time to a random time?

    - by Jonathan Dumaine
    My Windows 7 machine infuriates me. It cannot hold a date. At one point it all worked fine, but now it will decide that it needs to change the system time to a random time and date, either in the future or past. There seems to be no correlation or set interval of when it happens. In attempt to remedy this, I have: Correctly set the time in BIOS. Replaced the motherboard battery with a new CR2032 (even checked it with a multimeter). Tried disabling automatic internet synchronizing via "Date and Time" dialog. Stopped, restarted, left disabled the Windows Time service. Yet with all of these actions, the time will continue to change. Any ideas?

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  • How Can I Test My Computer’s Power Supply?

    - by Jason Fitzpatrick
    You’re concerned your computer troubles stem from a failing (or outright fried) power supply unit. How can you test the unit to be sure that it’s the source of your hardware headaches? Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites. The Question SuperUser reader Sam Hoice has some PSU concerns: My computer powered off the other day on its own, and now when I push the power button, nothing happens. My assumption would naturally be that the power supply is done (possibly well done) but is there any good way to test this before I buy a new one? How can Sam test things without damaging his current computer or other hardware?   The Answer SuperUser contributor Grant writes: Unplug the power supply from any of the components inside the computer (or just remove it from the computer completely). USE CAUTION HERE (Though you’d only be shocked with a max of 24 volts) Plug the power supply into the wall. Find the big 24-ish pin connector that connects to the motherboard. Connect the GREEN wire with the adjacent BLACK wire. The power supply’s fan should start up. If it doesn’t then it’s dead. If the fan starts up, then it could be the motherboard that’s dead. You can use a multimeter to check if there is power output from the power supply. Adrien offers a solution for readers who may not be comfortable jamming wires into their power supply unit’s MOBO connector: Most well-stocked geek-stores sell a “power-supply tester” that has all the appropriate connectors to plug each part of your PSU into, with spiffy LEDs indicating status of the various rails, connectors for IDE/SATA/floppy power cables, etc. They run ~$20 US. With a little careful shopping you can even find a highly-rated PSU tester for a measly $6. Have something to add to the explanation? Sound off in the the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.     

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  • laptop motherboard "shorts" when connected to adapter

    - by Bash
    Disclaimer: I'm sort of a noob, and this is a long post. Thank you all in advance! summary: completely dead laptop with no signs of life whatsoever (suddenly, for no apparent reason) Here's the deal: Lenovo Y470 (only a few months old with no water or shock damage). It stopped working suddenly (no lights, no sound, even when connecting adapter with or without battery). I tried a different adapter (same electrical rating), but no luck. I disassembled the thing completely, and tried plugging in the adapter and looking for signs of life with all different combinations of components installed (tried all combinations of RAM, CPU, USB power cords, screen, etc plugged in). no luck. Then, I noticed (as I was plugging in the adapter to try for the millionth time) that there was a "spark" for an instant when I first connect the adapter to the power jack. The adapter's LED would then flash (indicating it isn't working or charging). So, I thought the power jack has a short of some sort (due to bad soldering or something). Scanned virtually every single component on the motherboard, and tested the power jack connections with a multimeter. No shorts or damage to anything on the entire motherboard. Now I'm thinking I need to replace the motherboard. But, my actual question: What does this "shorting" when connecting the adapter signify? (btw, the voltage across the power connections and current through it drop to virtually zero when the adapter is connected and "sparks", and they stay that way). The bewildering thing is that there are no damaged components, and the voltage across adapter terminals returns to normal after I disconnect it (so it's not damaged). Please take a look at the pictures (of the motherboard's power connection and nearby components) and see if I'm missing something completely obvious... Links to pictures and laptop and motherboard model: pictures on DropBox Motherboard model: LA-6881P Laptop model: Lenovo IdeaPad Y470

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  • charging light on in laptop with battery removed.

    - by Jus12
    I hope this is the right place for this question. I have an LG R310 laptop. Recently the adapter connector started playing up, so I got a second hand replacement adapter of the same rating. The adapter was a cheap type (I know I made a mistake) and faulty.. it made a low buzzing sound when plugged in and not connected to the laptop. It didn't make the noise when connected to the laptop. Foolishly I used this adapter for several weeks. One day the adapter stopped working. The led didnt work and it was not charging. It had also drained the laptop's battery to 0%. I then got an original replacement adapter. Now I can use the laptop on power but the battery does not charge. The charging light does not come on. The interesting thing is that when I remove the battery the charging light comes on and stays on after I insert the battery back (the battery still does not charge). I need to know if the faulty adapter damaged the motherboard or if its just a problem with the battery. I have a multimeter and I prefer not to open the laptop. Thanks in advance.

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  • Melting plastic around DC-in jack in laptop

    - by Ove
    I recently noticed that the plastic around the DC-in jack of my laptop was warped (melted) a little bit. Since I noticed, I have done some experiments, and saw that the metal tip of the charger heats up very much when I am gaming, or performing CPU-intensive work (it's so hot that i can't hold it between my fingers). When I am using Windows normally (web browsing, music, video), the tip is not hot. I tried using another charger from a compatible laptop, but its metal tip overheated as well, so the problem is not caused by the charger. I have been using this laptop for gaming for 1.5 years and I never had this problem. When gaming I always use a laptop cooler. Dust is not the problem (i cleaned out the dust), and the CPU and GPU temperatures are not higher than when I got the laptop. The only thing that is excessively hot is the charger tip. Because I bought my laptop from the USA, sending it to warranty and back would cost more than the laptop's value, so I need to fix it myself. I have googled around, and I saw that the problem might be the DC-in jack that is located on the motherboard of the laptop. I plan to take the laptop apart and see if it has become loose, and soldering it in place if it has. My questions for you are: Did anyone deal with this problem in the past? Did anyone manage to fix it? Is the DC-in jack the culprit in this case? Or is it possible for the problem to be caused by another part on the motherboard? Is there any way I can check the DC-in jack with a multimeter? What should I measure (resistance, etc)? EDIT: My laptop is a Sager NP5135 (aka Clevo B5130M). I also posted on NBR, including some pictures: link

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  • How to send from my Z88 to my PC

    - by Bevan
    I've got a Cambridge Z88 that I want to get working with my PC. Around 6 years ago - in 2004 - I made heavy use of my Z88 to do a whole bunch of writing on the train while commuting to and from work. The Z88 is solid state, lightweight and has a full size silent keyboard, so it works very well as a writing instrument. I still have the serial cable I soldered up back then and used successfully in 2004. It has these connections: Z88 9 pin ----- ------- 2 TxD ------> RxD 2 3 RxD <------ TxD 3 7 GND <-----> GND 5 4 RTS ------> CTS 8 5 CTS <-+ RTS 7 8 DCD <-+---- DTR 4 9 DTR ----+-> DCD 1 +-> DSR 6 Unfortunately, I haven't been able to find my notes from 2004 that describe how I got it to work back then. I've spent several hours trying to Google a result, but to no avail. I'm pretty sure the cable is fine - after all, it's what I used successfully six years ago, and I've checked it out with a multimeter - so I'm focusing on the PC end of things, which is where I'd like some assistance. Q1: In my recent attempts, I've been using both Hyperterminal (as built into Windows XP) and the command line (copy com2: con:), but with no success. What's a good (better!) serial communications application to use? Is there one that allows me to see as deep as the signalling that's occurring on the wire? Q2: If you have a Z88 that works correctly with your PC, what software do you use on the PC end, and what's the pinout of your cable? I'm pretty sure that the Z88 itself is working properly: When using the built in Import/Export tool to send a file, I see different behaviour when my serial cable is connected compared to disconnected. When disconnected, the transmission appears to work, with a progress meter counting up and then finishing; when connected, nothing happens 'cept a timeout if I wait long enough.

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  • Does anyone know where I could find a 2 input USB voltage meter?

    - by John O
    What we really need is a tiny UPS, of sorts. We'll be hooking up a solar cell and a battery to a single board computer. Currently, that SBC is a custom Pic32 device, and it does it's own UPS and voltage monitoring duties. I've been tasked with trying to replicate all of its features with off the shelf products... and for the most part I've succeeded. But I don't currently have any way to switch between two sources of juice, or monitor when they're getting low. These guys have something: http://www.mini-box.com/picoUPS-100-12V-DC-micro-UPS-system-battery-backup-system I really like it, the price is well within the budget. We might even work it in though it does 12V and I'll probably be using 5V... there are enough engineers on hand to figure out something. But I'd still have no idea what the voltage was for the PV or battery. I was hoping that there was some simple little USB multimeter thing that I could use to monitor this with, but I can't seem to come up with anything. I've found all sorts of cool hardware, but nothing that will help us. Does anyone know of anything?

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  • Parallel port with C#

    - by Michael S.
    Hello, I am trying to send data to LPT1 port with a C# program, unfortunately with no success.. I am using windows 7 x64. I tried both x86 and x64 (inpoutx64.dll) dll's.. With the x64 dll when I send: Output(888, 255); It just continues the program as everything went ok, but i can't see anything on my multimeter (only the static 0.02V).. I also tried the following with C++: int main () { int val = 0; printf("Enter a value\n"); scanf("%d", &val); _outp(0x378, val); getchar(); _outp(0x378, 0); return 0; } But it throws an exception: Unhandled exception at 0x01281428 in ppac.exe: 0xC0000096: Privileged instruction. I remember once I made something like this work on xp, I hope it's possible on win7 too.. Please help me with this. Thanks.

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  • Why are my hard drives failing?

    - by WishCow
    I have a small Ubuntu server running at home, with 2 HDDs. There are two software raids (raid1) on the disks, managed by mdadm, which I believe is irrelevant, but mentioning it anyway. Both of the HDDs are Western Digital, and have been used for around 2 years, when one of them started making clicking noises, and died. I figured that maybe it's natural after 2 years, so I bought a new one, and resynced the raid arrays. After about a month, the other drive also died. I didn't get suspicious, since both drives have been bought at the same time, it's not that surprising to see both of them near each other, so I bought another one. So far, 2 old drives failed, and 2 brand new in the system. After one month, one of the new drives died. This is when it started getting suspicious. Since the PC was put together from some really old parts (think AthlonXP), I figured that maybe the motherboard's SATA controller is the culprit. Of course you can't switch parts easily in an old PC like this, so I bought a whole system, new MB, new CPU, new RAM. Took the just failed drive back, since it was under warranty, and got it replaced. So it is up to 2 failed drives from the old ones, and 1 failed drive from the new ones. No problems, for 1 month. After that errors were creeping up again in /var/log/messages, and mdadm was reporting raid array failures. I started tearing my hair out. Everything is new in the system, it's up to the third brand new HDD, it's simply not possible that all of the new drives that I bought were faulty. Let's see what is still common... the cables. Okay, long shot, let's replace the SATA cables. Take HDD back, smile to the guy at the counter and say that I'm really unlucky. He replaces the HDD. I come home, one month passes and one of HDDs fails, again. I'm not joking. Two of the brand new HDDs have failed. Maybe it's a bug in the OS. Let's see what the manufacturer's testing tool says. Download testing tool, burn it to a CD, reboot, leave HDD testing overnight. Test says that the drive is faulty, and I should back up everything, if I still can. I don't know what's happening, but it does not look like a software problem, something is definitely thrashing the HDDs. I should mention now, that the whole system is in a shoebox. Since there are a load of "build your own ikea case" stuff, I thought there shouldn't be any problems throwing the thing in a box, and stuffing it away somewhere. The box is well ventilated, but I thought that just maybe the drives were overheating. There is no other possible answer to this. So I took the HDD back, and got it replaced (for the 3rd time), and bought HDD coolers. And just now, I have heard the sound of doom. click click whizzzzzzzzz. SSH into the box: You have new mail! mail r 1 DegradedArrayEvent on /dev/md0 ... dmesg output: [47128.000051] ata3: lost interrupt (Status 0x50) [47128.000097] end_request: I/O error, dev sda, sector 58588863 [47128.000134] md: super_written gets error=-5, uptodate=0 [48043.976054] ata3: lost interrupt (Status 0x50) [48043.976086] ata3.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen [48043.976132] ata3.00: cmd c8/00:18:bf:40:52/00:00:00:00:00/e1 tag 0 dma 12288 in [48043.976135] res 40/00:00:00:4f:c2/00:00:00:00:00/00 Emask 0x4 (timeout) [48043.976208] ata3.00: status: { DRDY } [48043.976241] ata3: soft resetting link [48044.148446] ata3.00: configured for UDMA/133 [48044.148457] ata3.00: device reported invalid CHS sector 0 [48044.148477] ata3: EH complete Recap: No possibility of overheating 6 drives have failed, 4 of those have been brand new. I'm not sure now that the original two have been faulty, or suffered the same thing that the new ones. There is nothing common in the system, apart from the OS which is Ubuntu Karmic now (started with Jaunty). New MB, new CPU, new RAM, new SATA cables. No, the little holes on the HDD are not covered I'm crying. Really. I don't have the face to return to the store now, it's not possible for 4 drives to fail under 4 months. A few ideas that I have been thinking: Is it possible that I fuck up something when I partition and resync the drives? Can it be so bad that it physicaly wrecks the drive? (since the vendor supplied tool says that the drive is damaged) I do the partitoning with fdisk, and use the same block size for the raid1 partitions (I check the exact block sizes with fdisk -lu) Is it possible that the linux kernel or mdadm, or something is not compatible with this exact brand of HDDs, and thrashes them? Is it possible that it may be the shoebox? Try placing it somewhere else? It's under a shelf now, so humidity is not a problem either. Is it possible that a normal PC case will solve my problem (I'm going to shoot myself then)? I will get a picture tomorrow. Am I just simply cursed? Any help or speculation is greatly appreciated. Edit: The power strip is guarded against overvoltage. Edit2: I have moved inbetween these 4 months, so the possibility of the cause being "dirty" electricity in both places, is very low. Edit3: I have checked the voltages in the BIOS (couldn't borrow a multimeter), and they are all seem correct, the biggest discrepancy is in the 12V, because it's supplying 11.3. Should I be worried about that? Edit4: I put my desktop PC's PSU into the server. The BIOS reported much more accurate voltage readings, and also it has successfully rebuilt the raid1 array, which took some 3-4 hours, so I feel a little positive now. Will get a new PSU tomorrow to test with that. Also, attaching the picture about the box: (disregard the 3rd drive)

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