Need help identifying components

[Venturebrowser]

Hello everyone. I am trying to repair a DVD player that got hit by lightning and no longer has power at all. I've found what I think is two fuses right where the AC comes into the board, but I need help ensuring that they are in fact fuses and if so, find a good replacement for them. They are pictured below (the black rectangular components). There is no continuity on either one of them. Thanks in advance for any help.

 

[Harald Kapp]

Welcome to the forum.

Sorry, but those are capacitors as can be seen from the labeling C101 and C102 next to the components. Capacitors are meant to show no continuity.

Look for any components that show signs of damage (changed color, cracks in the case etc.).
Look for burnt copper traces on the PCB.
Is there a component near the power input that's labeled F...? That would be a fuse.


What experience and which instruments do you have? We may be able to guide you along in locating the fault but for this we need to know what we can expect.

 

[Jagtech]

If it took a voltage spike, I would check the fuse (F101) first, of course, but also check the blue varistor that's right beside the fuse; it should have infinite (no conductivity) resistance. If it shows any low resistance, its shot. It is meant to short out to protect the unit against voltage spikes, and subsequently blow the fuse.

 

[(*steve*)]

but also check the blue varistor that's right beside the fuse; it should have infinite (no conductivity) resistance.

This is true, but if you get a reading other than open circuit, you'd be best off removing the device to test it as there may be other things in the circuit that you're actually measuring.

Having said that, varistors usually fail open circuit, usually with damage. A varistor that shows significant conduction to a low voltage multimeter (we're talking only a couple of volts typically) is almost certainly going to fail rapidly if mains is connected.

 

[Venturebrowser]

Thanks Harald for your reply.

Feeling pretty silly about not noticing the printing on the board. There is a F101 fuse which I checked, and it was a dead short, so, good. I also checked the varistor as Jagtech suggested and it had no resistance at all. The varistor is a new one for me, but by following Jagtech suggestion, it appears to be good also.

I've inspected the board closely, and can't seem to find any other obvious physical indications of a fault. To your question of competency, I know the basics of DC theory and can use a multimeter pretty well. So, if you are generous enough to give me some direction, I'll do my best to follow it.

Thanks again!

 

[Harald Kapp]

First, please show us an image of the complete power supply board, so we get an idea what it is about.

But without visible traces of damage it is going to be difficult to locate the fault(s).

Do you feel confident enough to measure voltages in the circuit while it is on live power (mains)?

 

[Venturebrowser]

Good evening Harald. Yes, I feel confident enough to check it live. I've include 4 images in the link below. Thanks again for the help!

https://drive.google.com/folderview?id=0B6VxF8abqzzFQjZfcHVXbjhPTDg&usp=sharing

 

[Harald Kapp]

O.K., that is a switch mode power supply.
Looking at your photo 3, input is to the right, filtered (capacitors and choke), rectified (diodes D121...) and smoothed (big electrolytic capacitor in the center). The smoothed voltage is then chopped and transformed (IC, transformer). The transformed voltage is rectified (big diode at lower left and smothed again.

Check the diodes (4 diodes in the mains part, lower right of the picture, one in the secondary part (lower left). Do they behave as expected?

When you apply power to the mains input, is there a voltaeg across the first smoothing capacitor (center)? Be careful, there can be up tp 300 V (DC) on this capacitor, depending on your mains voltage.

You may have to put a load across the secondary output (e.g. 100 Ohm). Some switch mode power supplies do not operate without a minimum load.

Be careful, the capacitors in this circuit can hold dangerous voltages for some time even if mains power has been removed!

 

[Venturebrowser]

Thanks again Harald. I plan to try these tests you've suggested, I've just gotta find the time. I'll let you know what I come up with.

 

[Venturebrowser]

Would it be best to remove the diodes from the board to accurately check them?

 

[Harald Kapp]

Electrically it is sufficient to lift one pin off the PCB. This excludes the influence of any other component when measuring the diode - or any other component for that.
MEchanically handling may be easier if you remove the component completely.

Take care to note the position of polarity dependent components (diodes, elelctrolytic cpaacitors etc.) so you can re-insert the in the correct way.

 

[Venturebrowser]

I finally had a chance to check the diodes but nothing beyond that. 4 of the diodes showed around 600, 1 at 500, and 1 at 510. Are those 500 values considered in tolerance?

 

[Harald Kapp]

Those numbers show the forward voltage as seen by your multimeter at the meter's current. These numbers are fine.

What about the tests I suggested?

 

[shrtrnd]

Just lift one leg, high resistance in one direction with an ohmeter, low resistance in the other direction.