DVD power supply repair tips

bridge-rectifier-repair

This demonstration fixes the power supply of a DVD player, but the skills transcend this one application. [Alan] walks us through the process of repairing a power supply (translated) on a simple consumer electronics unit.

Obviously this starts by cracking open the dead device and verifying that the culprit is the power supply. [Alan] then removes that board from the chassis and gets down to work with a visual inspection. He’s got several images which illustrate things to look for; blistered electrolytic capacitors, cracked solder joins, scorch marks, etc. In his case there’s obviously a burnt out fuse, but that merely protects the hardware from further damage, it’s not the cause. Next he examines the diodes of the bridge rectifier. These need to be removed from the system to do so, which he accomplishes by clipping one end of each as seen above. He found that two diodes on one side of the bridge had broken down. After replacing them he tries a new fuse which immediately burns out. But a quick swap of the capacitors and he gets the thing back up and running.

We perk up every time we see this type of repair hack. We figure if we can build our own hobby electronics we should be able to fix the cheap devices like this one.

Comments

  1. mrsayao says:

    Can someone explain how to test those diodes? Is he using the meter in continuity mode? Also, black dots on caps = blown or leaky correct? I know this is pretty basic stuff, but I got lost in translation. Thanks!

    • John says:

      A diode can be tested with a meter by placing the leads across it, noting the reading, then reversing the leads. It should read much higher in one direction than the other (this is the readers digest description!!). As for the cap in the picture, it looks like a pen mark. If they’re bulged up etc – that’s a visual sign of death.

    • Anonymous says:

      > Is he using the meter in continuity mode?
      Yes, checking continuity in both sides only one side should work. Two sides working or none = bad diode.
      >Also, black dots on caps = blown or leaky correct?
      It probably had a bad smell as it “just smoked”.

      I´m not an expert so I could be wrong.

    • mrsayao says:

      Edit… I’m dumb… my multi has a diode function that I’ve never used… brain fart. Happy Friday!

      • yeah, diode mode, it should read ~0.7 if its good.

      • aztraph says:

        not dumb, but let me lend you some experience, testing diodes can be simple, but you have to check them both ways, make sure they haven’t shorted out. and on rare occasions it’s necessary to remove them for testing. On caps? It’s best to remove them if you want to check them for accuracy, but if the top scoring is ruptured, or there is ANY kind of bulge, it’s best to go ahead and replace them. I find electronics with mismatched voltage all the time, and when I replace those, I make sure to get all the same voltage and matched to the cap with the highest voltage rating.

        • mrsayao says:

          Thanks for all the tips!

          Wait a sec, I’ve seen mismatched voltage caps before, is it because they’re skirting the bottom line or a design consideration??

          • datagon says:

            It’s a design consideration. Consumer electronics often have a few different supply rails at different voltages. The physical size and cost of the capacitor is usually directly related to its voltage, so capacitors only just high enough in voltage will often be chosen in order to reduce board footprint and cost. That’s why you might find, say, 6.3V and 16V and 35V and 400V capacitors in the same design – 6.3 for 3.3/5V rails, 16 for 12V rails, 35V for intermediate rails sometimes (24V or so), 400V for autoranging rectified AC input. To make all the caps 400V (or even 35V) at the same capacitance would increase the size of the device dramatically – as well as the cost of the components themselves.

          • aztraph says:

            Well when I see 3 different voltages for caps run in parallel, and the smallest voltage has blown, I don’t care if its a design consideration or not, I replace them with all the same voltage, usually the higher of the set. since the function of these caps are typically to even out the dc after the rectifier, and have a voltage regulator after the caps, the only way you can go wrong is with too small of a cap, but I usually keep it in the 25v to 35v range as a limit

    • cde says:

      Most DMMs have a diode mode. That’s the mode he used. And the Cap with the dot smoked out. Not exploded, but functionally, still dead.

    • Justin says:

      Please remember when testing that even if the device is unplugged, Capacitors still hold a charge for a long time and can cause serious injury. Don’t be dumb.

      Diodes are one way check valves for current. When they are bad they allow current in both directions. When good they permit the flow in one direction but stop it in the oposite direction.

      Set your multi-meter to either a diode test, a continuity test, or an Ohms test. (all 3 tests are fundamentally the same)

      You have to isolate at least one leg of the diode to prevent you from getting a false reading from the rest of the circuit.

      Using the probes on either side of the diode should result in an open circuit in one direction and a closed circuit in the oposite. So touch the black probe to one side and the red to the other side. Record the finding. Then repeat with black on the other side of the diode and red where the black was. If it shows that it not connected (just like if the probes in the air). And connected (beeps, shows a nominal resistance, or gives a 0000) The diode is MOST likely fine.

      In the circuit shown was using 4 desecrate diodes but there are some 4 in 1 diode bridges that exist and may require you to replace the full bridge. Luckily they are relatively inexpensive even from Radio Shack.

      Hope this helps. Stay Safe.

  2. Niru says:

    Is there a howto for the extremely expensive and very fragile apple powerbook power supplies?

    I know that it’s usually flaky connector wiring, (or dirt on the magsafe connector) – but sometimes, it seems like it’s inside the white-box-transformer. (IMO – least value for the money consumer-product out there, today; magsafe is cool, but these power supplies don’t stand up to day-to-day use.)

  3. GenesisOfMoY says:

    I read through briefly, and would like to point out a couple of ideas. But before I do, I would like to say this is a nice write up. Many good tips!

    First, I’m not opposed to snipping the leads of a component, but solder should not be used to hold anything together. Solder is soft, and prone to breaking from temperature and vibration stresses. Components should be secured in place, then solder is used to make the connection. Besides, in this example, one should just replace all 4 diodes. Their cost is negligible, and they could have been weakened by whatever damaged the other two. (as a side note, I can usually test bridge diodes in circuit)

    Second, before trying a new fuse, a quick test with the meter would have saved you the cost of the fuse.

    Third, fuses are not really there to protect the ‘device’ (there are a few exceptions), but generally, fuses are there to protect everything else FROM the device (like your house on fire). Most of the time, the device is already damaged when the fuse blows.

  4. Sven says:

    I have repaired quite a few switching psus and i have some pointers to add to this.

    100% of the time (in my experience, and after eliminating such obvious faults as broken cords and broken connectors) the fault will be one of these:

    Bad capacitors on the secondary side (low voltage), 50% of the time

    Bad capacitors on the primary side (high voltage), 5%

    Broken rectifier or transistor on the primary side, 45%. This is however often caused by:
    Broken switchmode controller (it’s usually very hard to find a new one without putting in way too much work)

    • Rodders says:

      I used to repair lots of switch mode supplies from arcade games. About 75% of the time the fault for a dead psu was a high value resistor (100k or more) in the primary side feeding the kick start circuit.
      I have seen this same fault in many other supplies and is now usually the first thing I will check.

  5. Drone says:

    I knew it even before I started reading… Bad Chinese caps – planned obsolescence.

    • polossatik says:

      Indeed, any monitor/tv/cdplayer/etc that does not power on or only power up after repeated attempts chould be checked first for cheap/bad caps.
      DO realise there are different types of capacitors, in the power supply part you typically want caps with a low ESR/ impedance , if you replace those with an other cheapo “standard” capacitor it might even not work (or not for long).
      They cost a little bit more, but it’s worth to use low ESR/ impedance if you’re trying to resurrect power supplies.

  6. defaultex says:

    I’m surprised more hardware hackers don’t repair their devices. It’s how I got started with electronics, repair CB radios, TVs, VCRs, and various small kitchen appliances. I’d really suggest anyone looking to expand their skillset to begin with kitchen appliances since they tend to be the simplest but have a wide range of techniques depending on vendor and function of the circuits found inside.

  7. ejonesss says:

    http://badcaps.net/ is a good place to go for info.

  8. Marlon says:

    what are the value/s of those 2 resistors beside the power IC of the DVD player.. i cant read it anymore coz it burns… pls reply … thanks and more power!!!

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