Modify output voltage of a Dell power brick

[RCKadath]

Hi,

I'd like to modify the voltage of a spare 65W Dell power brick that I have to around 17V (instead of the nominal 19.5V unloaded).

I think that I identified the SMPS controller but it's only a partial part number on the marking. If someone could help me get the full part number and/or datasheet I could handle the rest.

The chip is a SO-8 and the marking is 103AIW on the first line and EK713 on the 2nd.

I still tried a few things without the datasheet. I found a 15 k resistor between Vout and a 2.5V pin on the IC. That looked like part of the voltage feedback divider so I replaced it with a pot. That didn't work. I also tried the same thing with a 75k resistor that I found between Vout and a ~2.25V pin. Didn't work either.

Thanks for any pointers!

[budm]

Re: Modify output voltage of a Dell power brick

Pictures of the board? You may be able to change the value of the feedback resistor network around the Optoisolator and the Vref Diode (such as TL431).
http://www.alldatasheet.com/datashee.../TSM103AI.html

[RCKadath]

Re: Modify output voltage of a Dell power brick

Here's the picture. Sorry that's the best I could do with my point and shoot.

[rogfanther]

Re: Modify output voltage of a Dell power brick

Post a picture of the other side also, please

[budm]

Re: Modify output voltage of a Dell power brick

That is good picture, but take another section of the board also so I can see how the traces are connected, and yes, top side also needed.
The Opto and the ref diode will be in the DC output section of the board.
This is an example of typical power supply.

[RCKadath]

Re: Modify output voltage of a Dell power brick

Thanks budm for the diagram. Here are two more pictures that should help.

I just thought about something. I had to replace the DC jack for a smaller one. The cord going to the DC jack has 3 conductors, coax style. I left the center conductor unconnected as it didn't have any voltage on it when probing. Now I just realized that there is the word "sense" silk screened on the PCB next to where that wire connects. Could it be a voltage sense feedback that I need to short to the positive connection on the DC jack? I don't think so though, is appears to be for communication between the power brick and laptop...

[tom66]

Re: Modify output voltage of a Dell power brick

The SENSE pin is so the laptop can tell the charger is a genuine one, and what output power it is rated to. Dell sold 65W, 90W and I think 130W, so the SENSE, connected to a small chip, tells the laptop what power and rating the adapter is.

[budm]

Re: Modify output voltage of a Dell power brick

See what the P/N of that IC3 is.

[RCKadath]

Re: Modify output voltage of a Dell power brick

See what the P/N of that IC3 is.

It's a TO92 package

DALLAS
2501
0714D3
+058AA

Thanks for the explanation on the sense signal.

[budm]

Re: Modify output voltage of a Dell power brick

OK that is the IC Dallas 2501 is the 1-wire memory chip for the telling the laptop what kind of power supply it is being fed with.
I have to locate that feedback network on the board.

[RCKadath]

Re: Modify output voltage of a Dell power brick

I probed the board and identified any point directly connected to Vout, in case that helps out. I'm guessing that the voltage divider will be connected to one of these points.

The p/n of IC32 is very hard to read. I think it's LA1 and there's a symbol on the left of it that looks like a backward N.

[budm]

Re: Modify output voltage of a Dell power brick

Can you read the P/N of that Dual Opto isolator?

[RCKadath]

Re: Modify output voltage of a Dell power brick

You mean the 4-pin thru-hole parts on the top side?

NEC
2561
LK641

Both are the same.

Thanks for trying to figure this out with me, it's much appreciated!

[budm]

Re: Modify output voltage of a Dell power brick

OK here is the spec sheet. We just have to find how the LED inside the Opto is being driven, it has to be connected to circuit some where which I cannot really easily see from the pictures, it will be real easy once we figure out the connection.
By the way what is the model of this DELL power supply? I have lots of Dell power supply around, I am willing to open it up.

[RCKadath]

Re: Modify output voltage of a Dell power brick

Attached is the result of some more probing.

Here's what's written on the outside:

65W AC ADAPTER
Model HA65NS1-00 Rev : A01
Output 19.5 V, 3.34 A
PA-12 Family

Thanks for the offer to open yours up but I'm more than willing to simply probe mine with your instructions.

[RCKadath]

Re: Modify output voltage of a Dell power brick

Ok, here's some partial reverse engineering of some of the traces. I concentrated on one optocoupler to start with.

I drew it to ressemble the "typical" circuit posted earlier. I think that I have everything I need. I'll try to tweak R25 and R26.

[tom66]

Re: Modify output voltage of a Dell power brick

I think that decreasing the 69.8k resistor will decrease the output voltage.

[RCKadath]

Re: Modify output voltage of a Dell power brick

Bingo! Tweaking R25 and R26 did the trick! Now I just need to replace the pot I used for testing with a fixed resistor. Or maybe leave the pot there to create an adjustable power supply.

Any idea what voltage range I could expect?

Thanks everyone for your help on this, especially budm!

Now that I found this nice forum I could maybe try to fix an old massive 13.8V, 270W supply that I got. It's even got the schematics inside of it so I'm sure I could fix it with you guys help.

[budm]

Re: Modify output voltage of a Dell power brick

Well I am glad you are able to trace out the diagram, looks just as I expect it to be.
Good to see that it does what you need, just be careful not to let that connection of the 68K go open then it will not have feedback to keep the voltage down.

[RCKadath]

Re: Modify output voltage of a Dell power brick

Well if anyone is still following this thread, the success was short lived. I reassembled the brick and it actually worked to power my battery charger (my intended application) and charge one battery yesterday. Today I tried to plug it into another charger and it only worked for a few seconds. After that the voltage started slowly decreasing and goes to near 0 within maybe 5-10 seconds. I disassembled it again and everything seems intact but yet not working.