laptop power adapter repair, need help identifying board component

[swampcat]

I am in the process of restoring a vintage laptop. The power adapter is no longer functioning and I would like to attempt to repair it. The adapter converts 120 AC to 18 DC.

I have opened the adapter, and the only sign of visible damage is an orange/brownish residue coming out of a yellow transformer(?) -- see attached image



On the side of the transformer(?) is written:

129601-001
DET9217 HI-POTTED
E115982 MP-130C​

It is soldered to the PCB via 12 points, 6 on one side and 5 on the other.

All of the resistors, capacitors and other components appear to be in pristine condition. There is no dust, water damage, sketchy solder, rotting plastic/rubber, or anything else visible. There is a slight metallic smell but not a burning smell.

My questions are:

1. Is the yellow component I am referring to a transformer?
2. Am I right to initially assume that this is the likely culprit given the gooey substance on its surface?
3. How would I go about locating a replacement transformer that matches the specifications for this power adapter? I have tried searching for variations of the numbers. E115982 leads to Si-Steel transformers-- some similar looking pictures on google, but none of the same apparent size or number of pins.

I would be grateful if you can help me in the right direction. Thank you!

 

[Les Jones]

It is very unlikely that the transformer is faulty. I think the "gooey" substance is just transformer varnish. What LOGICAL steps have you taken so far to identify the faulty component ? The most likely components to fail in switch mode power supplies are electrolytic capacitors, the switching device, (Power transistor or mosfet.) or the controller chip.

Les.

 

[alec_t]

I agree with Les. Even if the transformer were faulty, it is most unlikely you could find an exact replacement one new. You might strike lucky with a pre-used one from an online source.

 

[DerStrom8]

I agree with the others, the transformer is probably the least likely part to have failed. That's not to say it definitely didn't, but I would troubleshoot elsewhere first.

You say the power supply is "no longer functioning". Could you elaborate please? Is there no output at all? Is the voltage just too low? Have you tested voltages at different points around the board to try to identify if and where there may be a discontinuity?

Matt

 

[JimB]

The transformer looks like a normal varnished transformer, and is most unlikely to be faulty.

If I were faultfinding this unit, one of the first thing that I would suspect is the cable which connects to the laptop.
With many years of bending and flexing, they are prone to breaking the conductors near the ends of the cable.

Use your multimeter to check the resistance of the wires in the cable.
Measure from the solder pads on the PSU circuit board to the pins on the plug which connects to the laptop.

Also use the multimeter to check the PSU output voltage at the solder pads on the PSU circuit board.

JimB

 

[swampcat]

Thanks for your replies!

That is good to know about the transformer, to my untrained eye it looked fishy.

By non functioning it appears to have no power output on the laptop-cable end. The laptop-end has 3 holes, pos neg and ground that I was testing by inserting multi-meter probes. That is a good idea-- I will test the solder pads for that to see if its a cable issue.

I will also test points around the board and consider capacitors as potential culprits. I will reply with my findings. Thanks again

 

[tomizett]

At the risk of stating the obvious... but it sounds like you may be new to this, so **please be careful**!

Half of that power supply is connected to the mains and will possibly hold enough charge to be dangerous for several minutes after it's been unplugged. Charge will be stored in the big cylindrical black capacitor on the lower-right of your photo. After unplugging the board, and before handling it, measure between the leads of this with a meter set for DC volts, and check that there is no more than about 20V present.

Good luck with the repair!

 

[swampcat]

At the risk of stating the obvious... but it sounds like you may be new to this, so **please be careful**!

Half of that power supply is connected to the mains and will possibly hold enough charge to be dangerous for several minutes after it's been unplugged. Charge will be stored in the big cylindrical black capacitor on the lower-right of your photo. After unplugging the board, and before handling it, measure between the leads of this with a meter set for DC volts, and check that there is no more than about 20V present.

Good luck with the repair!

Thanks for the good advice Tom

I am taking this slow, starting with some multimeter and breadboard stuff-- with resistors and capacitors at low voltage.

I have heard about the dangers of capacitors, but I will remember to let it cooldown and check it with the multimeter first

 

[Les Jones]

A switch mode power supply is not the right thing to start learning on. Wait until you have a GOOD UNDERSTANDING of electronics before attempting to repair them.

Les.