My neighbor asked me if I have another power supply he can use to charge his wife's portable O2 generator. Little about this guy: He uses tape to fix everything. Nevertheless, he's not familiar with good electronics terms. Told me he can't get the light to light unless he wiggles the cord.

I have the PS in my possession. Here's my observations BEFORE DOING ANYTHING: First, when I plug the supply in the green light comes on what appears to be fully lit. Over the course of about 10 seconds the LED slowly extinguishes. Wiggling everything does nothing for the light. Before I break the seal on the plastic body of the PS I wanted to hear your thoughts.

The unit:

 

I would suspect the battery being the victim of charger abuse before I would take the supply apart. I would also advise against getting involved with this guy because he sounds like he will blame you for ANYTHING that goes wrong.

 

Did you measure the output voltage?
Fixing that supply could be problematic.

That voltage and current rating is similar to those used with many laptops.
Perhaps one of those could be substituted.

 

The reason why I don't expect the battery to be the issue is because he has a 12V plug in charger that works. Apparently the 12V has a booster that ups the voltage to charge the battery properly. My mother-in-law has the same sort of machine. Only her PS will not work with his wife's generator.

As for trust, I've known this guy for 17 years. I've helped him out of many jambs in the past. Successfully. He trusts me and I know I can trust him. Already told him he may very likely need a new charger, which is the optimal approach. But this guy has National Geographic magazines from the 1970's that he's holding on because they're valuable. Yes, he's a hoarder. Can't let go of anything. Over the years I've tried to help him but that's like trying to sweep rain water up a steep hill.

 

Did you measure the output voltage?

Difficult to do without risking shorting pins. And I don't have any sockets I can plug into the pins to be able to read voltages.

 

To be sure, it's likely a broken wire at the PS. Those two are known to be rough on cords. I've fixed many other cords for them in years gone by.

I'm about to open the box. Just a few more cuts along the seam and it will pop open. Even if I ruin it - in its current state it's not useable. So if it's a lost cause then there's no more significant loss. If I fix it and it stops working then they're back in the same boat they're in today. Besides, she has plenty of oxygen bottles.

 

1. With nothing connected to the supply output, does it do the same 10-second fade?

2. If you bounce power to the supply (10 seconds off), does the LED reset to the start of the 10 second pattern, or does itgo off much more quickly?

3. What is the output voltage doing during the 10-second fade?

4. How heavy is the supply? This is to determine if it is linear ow switching.

A 10-second fade out pattern doesn't sound like a broken wire. Maybe something is getting hot, and it takes 10 seconds for that heat to do something to something else. Maybe a current limiter is kicking in, or the switching frequency is changing to the point that it cannot operate, or . . . . .

ak

 

So far there is continuity between Pin 1 (V+), Pin 2 (A) (sense circuit), Pin 3 (B) (sense circuit) and Pin 4 (V-). These continuities are from the plug shown below. Pin 1 is the top right pin, pin 2 is just below pin 1, pin 3 is left bottom and pin 4 is top left. Wiggling the wires revealed no intermittent connections. There are no shorts between any of the pins. And the metal ring of the connector appears to be not connected to anything. No ground, no shielding.

Visual examination: The blue (V-) shows broken insulation exposing wires (no danger of shorting) but does not show a break in the wiring.

I will now turn my attention to troubleshooting the power connector and power cord. The cord itself looks in decent condition, but who knows without testing. Maybe I should have started there before opening the PS.

 

1. With nothing connected to the supply output, does it do the same 10-second fade?

After waiting several minutes the 10 second rule applies. (unpowered during that time)
After shorting the pins together (unpowered) the 10 second rule applies

2. If you bounce power to the supply (10 seconds off), does the LED reset to the start of the 10 second pattern, or does it go off much more quickly?

See answer #1

3. What is the output voltage doing during the 10-second fade?

Starts at 19V and fades.

4. How heavy is the supply? This is to determine if it is linear ow switching.

Well, I hate to admit this but I found the issue: The stupid power cord. It has an open wire when wiggled. Intermittent. I didn't have to do all that work opening it up. But I did so based on the observations of my neighbor. That should have been the first thing I checked. It's been a while since I've done failure analysis.

Lesson learned. Different power cord and the light stays lit at full brightness. Testing now for 2 minutes to rule out any other issues.
{shaking his head}

 

Thanks for the input everyone. Sadly I feel somewhat foolish. Next time someone tells me they have a flat front right tire I'm going to check ALL the tires before I start looking for a nail.

I hate myself right now. This was way too easy a fix. Now I have to close up the box.

 

Sadly I feel somewhat foolish.

Don't beat yourself up too much.
We've all had those slap-your-head moments, where we've missed the obvious.

 

Thanks for the input everyone. Sadly I feel somewhat foolish. Next time someone tells me they have a flat front right tire I'm going to check ALL the tires before I start looking for a nail.

I hate myself right now. This was way too easy a fix. Now I have to close up the box.

Hey - I was wrong as well. So that should absorb some of the heat.

 

Thanks all. They are happy to have a working charger again. And I didn't even have to heat up the iron.