Tuesday, May 10, 2011

Some questions that were asked.

A few individuals have asked questions direct, and I wish to clarify some items.  It is best when you post on the blog that way it can also answer several hundred other readers questions.


Question  1: 
How do you check the (brown) ceramic caps.
Answer: 
Simple, I use a standard Ohm meter in the Resistance mode.  Since the biggest problems with caps when they fail is the become either a direct short, or they will never store capacitance (open).  The meter reads in the ohm mode by sending a small amount of electricity through resistors and report the difference in Ohms. Test with leads RED on one side and Black on the other.  One direction will give you a high resistance ~2000Ω and then reverse the leads on the meter and the other direction should give you Infinity. This is an OK capacitor. If you have a very low resistance or 0 (zero) Ohms, the cap is shorted.


Why?:  I started small just repairing for friends and family, after a number of common repairs I saw the need for a shop, so when I opened the shop I was looking at the prices of equipment (oscilloscopes, digital probes, professional hot air guns, and all the high tech test hardware) and the prices were too high for the amount of work I was doing. So as I grew, I got comfortable with what I had, and never changed.  If it works why change it?.  The success rate would could not be improved enough to justify the high dollar purchases.



Question 2: What are the soldering tools you use.Answer:  Ordinary hobby tools for the most part.  The soldering pencil is a 40w medium tip Weller type with base.

Then there is a soldering station that was purchased from Radio Shack with a small pencil tip, for the very small parts.
The key to a good solder joint is heat management, and flux.  When you are soldering large items, you should have a larger tip. Flux also assists in distributing heat as well as removing oxidation from the solder pads.  



The desoldering iron is a simple Radio Shack that cost about $12. Though it should be cleaned often, unplugged when not used. (the tips don't last long)




A scope would be nice (any donations?)  just kidding.


Other Tools do include a combination Hot Air and Soldering station (collecting dust) I just use it when I get into tight situations or the need for speed or controlled heat arises.

9 comments:

  1. Yep, our most important tools are: using your brain and building experience.

    Everything else is just toys :-)

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  2. Forgot to answer a common question that was asked. Why did you put a DONATE button on the page?

    Someone suggested it. So I did.

    Believe me, I am not and will not get rich blogging. Some may donate a dollar, if it helped them, though not required and any donations will go to the bigger site/forum when it's started.

    I think it's like begging, but I'm just trying to accomodate requests. Peace

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  3. Just writing to clear up a couple of technical issues:

    1) A capacitor (ceramic or electrolytic) will exhibit an extremely large resistance no matter how you measure it (reversing the leads should make no difference). If you get a 2K resistance, then that cap is faulty. I assume you remove these caps from the mobo before measuring. There's no way to make an accurate in-circuit measurement with a multimeter.

    2) You certainly can charge a laptop battery fully with a 65W charger (on a laptop that normally uses a 90W adapter). The 65W charger can handle the battery charging current just fine. Get a "Kill-a-Watt" and measure this current some time. It's not that large.

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  4. Glen:
    1: Since we are testing for short, and not measuring, the method described is only to find if a CAP is shorted, not it's uF rating. If it shorted it will be shorted in either direction.

    2: You CANNOT fully charge a battery with 65w adapter when it requires a 90w. Li-ION batteries do not work the same as Ni-CAD batteries. Modern laptops use power controller IC's and will toggle MOSFETs if the wattage is correct and will not if it is too low. Example are the MAXIM MAX8734 and the ISL Charge/Battery controllers.

    The DELL's have an additional signal pin in the center to identify which charger is connected. Sometimes the voltage on the center pin is 3v, 3.5, or less. One method of identifying on Dell is that the white tipped triaxial plugs are 4.74A and the black tips are usually 3.42A so you do have to have the correct adapters even for the BIOS to indicate that the correct adapter is being used. That test could also be done on Toshiba, or Gateway laptops.

    There is no one way for a tech to find a solution, you can only find a solution that works for you. Other techs have benches full costly test equipment and may spend hours on a single repair, but getting back to basics sometimes is the most cost effective. Consider that the audience is worldwide, and not just some major cities, they may not have the equipment that you might have.

    A suggestion to verify your above post:
    Try your comment with a DELL laptop... say a Inspiron e1705 and it's original battery. Charge it fully as you can with a 3.42A charger and check the dots on the battery for 5 leds. Then run the unit on battery only. Write down the time the laptop stays on. or using the indicator in the taskbar and see it's percentage before it shuts down from low batt signal.

    Try the same thing with the 4.72A charger.
    and find the difference. You'll see how fast the charge is depleted with the 3.42A charge vs the 4.74A charge. This is one of the major problems that happens when people buy the wrong charger. The battery don't last long, then they go buy another battery with the same results. Wasting money.

    Also I only deal with OEM batteries and chargers because I know the defects of the $9.99 chargers that are on eBay. And how long the chargers last. Poorly rated wires and parts are not worth the 'savings'.

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  5. Additional note: On the HP DV 6K/9K series the tip of the adapter is smaller on the end, and it will not fit into a 65w jack. But a 90w will fit into a 65w jack.

    Early DV6K/9K (such as 6003/9002) would take either, and though the 65w would fit, it would not fully charge the battery.

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  6. As luck would have it, I have an old E1705, so I'll try that experiment. It's interesting to note (I think) that I can charge that laptop fully by attaching a cut-off charger cable to my bench power supply, with no voltage being provided to the center pin.

    With regard to the capacitor you said that if it exhibits 2K resistance in one direction then it is "OK". This is absolutely not true. Even an electrolytic will show 1M of resistance. A 2K reading is a faulty cap, not a good one.

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  7. I think we may be arguing different things with regard to the chargers. You mention Dell's 3rd pin (one-wire ID) and HP's adapter barrel sizes as
    barriers to using 65W chargers. I believe your argument is more practical, while mine is theory (correct me if I'm wrong).

    The power difference between the two adapters would only come into play if the charge current exceeded the max. to keep the voltage in regulation. I've never seen a laptop draw 3.5A charging (not even close). Are you saying the control circuitry will purposely not charge the battery fully? Why?

    BTW, I can't agree more about the quality of eBay adapters. I recently ordered a 90W adapter for a client and it died a week later. They sent another and I decided to put it on my "stress-tester", which is a rig I built with a bunch of power resistors. The adapter lasted to about 70W, then ... pop!

    It's definitely a trade-off -- many of my clients still choose the cheaper adapter.

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  8. You are correct on the 2K value reading of the Cap... That was an oversight, it should have been more like 2Meg Ohm- very high resistance. Though it will still only be one direction. Caps do block DC but not AC (or signal waveform will pass through). I'll change this error in post)

    RE: circuit protection vs draw current. Many of the modern laptops use this method. I am not sure if it is to sell more adapters or just shrewd business practice.

    I have had a number of experiences with the early DV series when they went from 65w to 90w and they still appear the same but would not fully charge the battery. Even though the draw is low. That is the charge draw. But for example. If the Dual Core CPU uses 35w alone, that does not provide current for the rest of the LCD, HDD, DVD so it is not really overkill. Add in a nVidia GO7600 and then you may not have enough to use a 65w Power supply.

    I have seen them run on 65w, but while running they would not charge, and the battery level would stay the same.

    This I assume so that you will have to buy a $12 power supply instead of a $9. I won't say that they are crooks for doing this, but ...

    On the front end of the Power section, the MOSFETS too have changed. You not have to account for the Drain value but also the surge value. Since current coming in does bounce higher than running current when initially plugged in.

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  9. RE: Dell e1705, you may be able to charge it, but the POST may tell you "Incorrect Adapter Detected" and will not charge the battery. And the BIOS may report "No Adapter".

    ReplyDelete

I cannot repair laptops for you via the internet, I can only answer questions related to posts. This is because I have not had experience on every motherboard that is out there. Bear with me.

If you do need it repaired. Contact me for quote (US/CDN Only)

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