Please help to fix this PA-1151-03HS-ROHS power adapter

[tmhobadcap]

The power adapter is for my HP 600-1390 Touch Smart All-In-One Desktop which could not be turned on recently. I found that the power indicator led light on the power adapter was not on and so I think something wrong with the power adapter.

When I opened it, I found that the capacitor close to the led indicator light was with a bulged top. After replacing the capacitor, I still have trouble in getting 19V from the power adapter in order to turn on the computer. When I plug in the power, sometimes, the led (also the computer) does not turn on. But sometimes, the led (also the computer) turns on for a certain amount of time, which may be just a few seconds or as long as a few minutes.

Because of my very limited electronics knowledge, I would like suggestions on checking which component first, since there is a lot of "glue" (the white color stuff) covering a lot the components and it is very difficult to clear/clean them before checking each component. Also, suggestions on how to clear/clean the "glue" easily are also welcome.

[CapLeaker]

Re: Please help to fix this power adapter

I’d run the PSU with the covers off upside down. This way you can measure things to isolate the problem. For example, when the power goes off, what voltage do you have on the main filter capacitor on the primary side? Does the led on the power supply come back on when you unplug the cord from the laptop?
Basically you got a few failure points. The laptop power jack, the secondary low voltage side or the primary high voltage side of the power supply and the DC power cable. Question is if the led goes out, because there is no high voltage DC on the primary, or there is an intermittent short or open on the secondary dc side. The white silicone… just pick it off.

[tmhobadcap]

Re: Please help to fix this power adapter

I’d run the PSU with the covers off upside down. This way you can measure things to isolate the problem. For example, when the power goes off, what voltage do you have on the main filter capacitor on the primary side? Does the led on the power supply come back on when you unplug the cord from the laptop?
Basically you got a few failure points. The laptop power jack, the secondary low voltage side or the primary high voltage side of the power supply and the DC power cable. Question is if the led goes out, because there is no high voltage DC on the primary, or there is an intermittent short or open on the secondary dc side. The white silicone… just pick it off.

Thanks for your comments.

I followed your suggestion and ran the PSU with the covers off upside down. I tried four times to measure the voltage on the main filter capacitor (I think it is the biggest one which is 400V, 150 micro Faradays) with results as follows:

First time
I plugged in the ac power. The dc plug was not connect to the computer. The led did not light up. No voltage output. The voltage on the main filter capacitor was 170V.

Second time
I plugged in the ac power. The dc plug was not connect to the computer. The led light up. There was 19V dc output. The voltage on the main filter capacitor was 290V. I plugged in the dc plug to the computer. The computer turned on and ran for about 9 minutes and turned off. The led light turned off. The voltage on the main filter capacitor became 170V. I unplugged the dc plug from the computer. The led still did not light up.

Third & Fourth times
Same as First time.

ps: The DC output cable was from a Dell power adapter. The is because at first I thought something wrong with the original dc cable and I cut it. I have checked that there is no continuity problem with the Dell cable. I have checked that there is no continuity problem with the AC power cable. Also, I have resoldered some of the suspected cold solder joints on the pcb.

[Per Hansson]

Re: Please help to fix this power adapter

The 290v is not an expected reading: with a line voltage of 120VAC you should see: √2 x 120 = 170VDC like you measure.
However normally this voltage should be going through a voltage doubler: to get more useful energy storage in the big bulk filtering capacitor.
That would bring the expected voltage to 340VDC (this is why it is rated to 400v).
However you don't see that in any of your readings so I'm wondering if maybe the capacitor is bad.
It would be good to have a capacitance meter and measure that it really is 150uF like the print says...

[CapLeaker]

Re: Please help to fix this PA-1151-03HS-ROHS power adapter

So the problem is indeed inside the power supply. The 290V reading is indeed funny. Did you have both probes on the capacitor? The grounds are different in the primary vs secondary. You can’t use the same ground point. Almost sounds like a cracked solder joint. Resolder everything that is mounted to the heat sink or is large like the transformer. Unfortunately all the silicone on the back side has to come off.

[tmhobadcap]

Re: Please help to fix this power adapter

The 290v is not an expected reading: with a line voltage of 120VAC you should see: √2 x 120 = 170VDC like you measure.
However normally this voltage should be going through a voltage doubler: to get more useful energy storage in the big bulk filtering capacitor.
That would bring the expected voltage to 340VDC (this is why it is rated to 400v).
However you don't see that in any of your readings so I'm wondering if maybe the capacitor is bad.
It would be good to have a capacitance meter and measure that it really is 150uF like the print says...

Thanks for your comments.
I will check on that capacitor. I do not have a capacitance meter. May be I will replace it if I have one. But I have to remove the silicone first.

[tmhobadcap]

Re: Please help to fix this PA-1151-03HS-ROHS power adapter

So the problem is indeed inside the power supply. The 290V reading is indeed funny. Did you have both probes on the capacitor? The grounds are different in the primary vs secondary. You can't use the same ground point. Almost sounds like a cracked solder joint. Resolder everything that is mounted to the heat sink or is large like the transformer. Unfortunately all the silicone on the back side has to come off.

I have both probes on the capacitor on the underside of the pcb. Will do more resoldering as per your suggestion after removing the silicone. Since the silicone has been hardened, it will take a lot of time and patient. Anyways, I will try to do so.

[tmhobadcap]

Re: Please help to fix this PA-1151-03HS-ROHS power adapter

I have both probes on the capacitor on the underside of the pcb. Will do more resoldering as per your suggestion after removing the silicone. Since the silicone has been hardened, it will take a lot of time and patient. Anyways, I will try to do so.

I removed the silicone covering one of the components with heat sink. And then I resoldered the joints. Then I powered up the PS for the 5th time, the result is just like the 1st time.

I will do more later.

[CapLeaker]

Re: Please help to fix this PA-1151-03HS-ROHS power adapter

Resolder everything that’s heavy or gets hot. Sometimes you need a microscope of some sort to see the rings on solder joints. It may look good to the naked eye, but yet it’s not. While you are at it, maybe your DMM has a min-max function. Put your meter to the output of the psu and let the DMM record what happens. I wonder if the output gets a bit unstable and the PSU in protection mode?
What PWM does it use in the primary?

[tmhobadcap]

Re: Please help to fix this power adapter

Thanks for your comments.
I will check on that capacitor. I do not have a capacitance meter. May be I will replace it if I have one. But I have to remove the silicone first.

I think of a quicker way to test relating to the capacitor. I have a 220uF 400V capacitor. I connected it in parallel with the existing 150uF 400V capacitor so that I do not need to remove the 150uF (removing it needs to remove some of the silicone first). In such case, the total capacitance will just be higher. So if the 220uF is correct in term of capacitance, then I can know if the problem is from the existing 150uF capacitor. Am I correct?

Anyway, I have added the 220uF 400V capacitor and done the 6th and 7th time of powering up the PS and have the following results.

6th time
Just like the first time.

7th time
I waited the voltage across the 150uF capacitor to drop to 0V and then plugged in the ac power. The dc plug was not connect to the computer. The led light up. There was 19V dc output. The voltage on the main filter capacitor was 290V. I plugged in the dc plug to the computer. The computer turned on and running. So far up to this moment, it has been running for about an hour. I will keep it running to see if it will turn off by itself. Also, I will turn the computer off before going to bed and see if I can turn it on again tomorrow.

[tmhobadcap]

Re: Please help to fix this PA-1151-03HS-ROHS power adapter

Thanks for your comments.
I will check on that capacitor. I do not have a capacitance meter. May be I will replace it if I have one. But I have to remove the silicone first.

Resolder everything that's heavy or gets hot. Sometimes you need a microscope of some sort to see the rings on solder joints. It may look good to the naked eye, but yet it's not. While you are at it, maybe your DMM has a min-max function. Put your meter to the output of the psu and let the DMM record what happens. I wonder if the output gets a bit unstable and the PSU in protection mode?
What PWM does it use in the primary?

Yes, I will do resoldering on all the joints after removing all the silicone on the bottom of the pcb. May I know why they add silicone? Just for gluing? It seems to me that no gluing is needed on the bottom of the pcb covering some of the soldering joints.
Yes, next time I will check if there is any sudden change on the output voltage.
Sorry, I do not know what PWM means.

[CapLeaker]

Re: Please help to fix this PA-1151-03HS-ROHS power adapter

Congrats you may have found your problem! The PWM is an IC that switches the mosfet of and on in the primary. Look at the mosfet and follow back the gate drive circuit to that PWM.
They use silicone not only for glueing certain parts, also to keep dirt from accumulating between the high voltage pins which may create a short. But in this case it’s more to glue things so it doesn’t move one way or the other.

[tmhobadcap]

Re: Please help to fix this power adapter

I think of a quicker way to test relating to the capacitor. I have a 220uF 400V capacitor. I connected it in parallel with the existing 150uF 400V capacitor so that I do not need to remove the 150uF (removing it needs to remove some of the silicone first). In such case, the total capacitance will just be higher. So if the 220uF is correct in term of capacitance, then I can know if the problem is from the existing 150uF capacitor. Am I correct?

Anyway, I have added the 220uF 400V capacitor and done the 6th and 7th time of powering up the PS and have the following results.

6th time
Just like the first time.

7th time
I waited the voltage across the 150uF capacitor to drop to 0V and then plugged in the ac power. The dc plug was not connect to the computer. The led light up. There was 19V dc output. The voltage on the main filter capacitor was 290V. I plugged in the dc plug to the computer. The computer turned on and running. So far up to this moment, it has been running for about an hour. I will keep it running to see if it will turn off by itself. Also, I will turn the computer off before going to bed and see if I can turn it on again tomorrow.

Last night, after the computer running for 7.5 hours, I turned off the computer and uplugged the power adapter. This morning, I tried several times to turn on the computer. Details as follows.

8th time
I disconnected the 220uF 400V capacitor. Turned on the PS but the computer could not be turned on.

9th time
I connected back the 220uF 400V capacitor. Turned on the PS and then the computer was able to turn on. But after running for 45 minutes, the computer turned off by itself. No DC power from the PS.

10th to 13th times
Powered on the PS. I could see that the led light up and then died out in a few seconds. The computer could not be turned on.

[tmhobadcap]

Re: Please help to fix this PA-1151-03HS-ROHS power adapter

14 time
I powered on the PS. The computer could be turned on. Lets see how long it can run this time.

[tmhobadcap]

Re: Please help to fix this PA-1151-03HS-ROHS power adapter

14 time
The computer continuously ran for 9 hours. Then I turned it off.

[CapLeaker]

Re: Please help to fix this PA-1151-03HS-ROHS power adapter

Oh boy, that’s a tough nut. In one way it doesn’t run for long or at all, the other way you got like 10 hrs run time. I don’t think it’s the cap, but maybe something else around there. Did you get that glue off. Look if there is a small cap next to the pwm. It’s called a start up capacitor. Change it.
It almost sounds like when the PSU a is cold it doesn’t want to run. Try heating it up a bit with a hair dryer, then plug it in.

[Per Hansson]

Re: Please help to fix this PA-1151-03HS-ROHS power adapter

Look if there is a small cap next to the pwm. It’s called a start up capacitor. Change it.
It almost sounds like when the PSU a is cold it doesn’t want to run. Try heating it up a bit with a hair dryer, then plug it in.

I second this, try changing the two small caps next to the large 400v capacitor.

[tmhobadcap]

Re: Please help to fix this PA-1151-03HS-ROHS power adapter

15th time
The computer continuously ran for 9 hours before I turned it off.

This morning, I started to remove the silicone around the two small capacitors next to the large 400V capacitor so as to replace them. But I found that there are some other small components underneath the silicone. If not careful, I may damage them. Therefore, I will wait for another not powering up before going to replace the two small capacitors.

I just started the 16th time today.

[tmhobadcap]

Re: Please help to fix this PA-1151-03HS-ROHS power adapter

On the 20th time of turning on the computer, I got the power adapter no power out again after running for about 8 hours. I will proceed to removing the silicone and replacing the two small capacitors.

[tmhobadcap]

Re: Please help to fix this PA-1151-03HS-ROHS power adapter

Today, I removed the silicone and replaced the two small capacitors. One is 50V 22uF and one is 50V 47uF. I do not have 50V 47uF and so I used 100V 47uF.
After that the computer was turned on. But unluckily, after running for about 3 hours, the computer turned off (the power supply light went off).