Fixing a simple AC adapter - Page 1
Forum section: electronics / repair

author: brumbarchris
author_rank: Regular Contributor
timestamp: January 20, 2016, 08:22:20 am
content: So, one of my friends came to me with this AC adapter he purchased for a Nintendo hand-held game console (which came without such an adapter as an accessory). Consequently, he purchased this adapter separately, from an uncontrolled source, and it turns out the adapter is no working at all. I opened it up (pictures below), turns out it is not the lowest quality piece of junk I have ever seen (as I always expect when I open up such things). It is actually quite well built, even with green solder mask! Nevertheless, it is not working, and I am trying to get to the bottom of it. I measured a few of the components and I reversed engineered the schematic (see image below). Fortunately, all of the components are well marked (seems nobody is trying to protect any IP here) and I could even get the datasheets for most of them. The schematic below also contains some comments and some of the measurement results.I have measured and ruled out things like interrupted cable. 220VAC reaches the board, but at the output (measured on the board) I always get 0V. There is no short-circuit between the output pins. I have reinforced all soldering joints on the board.I am not sure about the internal TRAFO wiring, but what I show on the schematic is a best guess (I measured the resistance between pins, without taking the TRAFO off the board).There are a few suspicious things:1. R1 seems to be extremely high value. I am incapable of corroborating the value I measure with the multimeter against the color code on the resistor (the colors on the part are unclear). Also, the value I measure with the multimeter fluctuates slightly between 8.2Meg and 9 Meg, sometimes (but rarely) a bit higher, towards 10 Meg. Could it be broken? I am fairly experienced in electronics, but mostly low voltage DC, and 0 experience with off-line power supplies. Is such a resistor value common on the input? It seems to me that this resistor limits the input peak current to about 30uA (when the 220VAC input waveform is at its peak at 310V), so I doubt that we can ever get 900mA in the secondary winding of the transformer from such a low input current.2. There are a few resistors (R3 and R5 which measure much differently in circuit than when taken out), but I guess that is OK3. The D4 diode measures only 0.18V when measured with a multimeter set on diode measurement. All other diodes measure OK (0.45...0.7V). Is this 0.18V value bad?4. If I measure the output of the TRAFO, I see sometimes 5VAC, sometimes 3.7VAC and most of the time about 10mVAC. But the output (measured between OUT+ and OUT-) is always dead 0 VDC.When I opened it up, I sincerely hoped it would be something simple, like a disconnected wire or something of the sort. So...help!Regards,Cristian

author: mij59
author_rank: Frequent Contributor
timestamp: January 20, 2016, 08:35:06 am
content: Remove R1 and measure it again, its probably open.Check all the the transistors and diodes for shorts ( main suspect is Q1)

author: ElektronikLabor
author_rank: Regular Contributor
timestamp: January 20, 2016, 08:35:23 am
content: I would toss it away.It is a fake chinese cheap Power Supply (look at the fake CE-Symbol). If the transformer is not made propperly, it can kill you.

author: brumbarchris
author_rank: Regular Contributor
timestamp: January 20, 2016, 08:39:13 am
content: Whatever replacement we would buy would have the same transformer quality problem: they could all kill you. In fact, I agree that we risk our lives most of the times when we plug something in the mains, as most adapters are now fake and from China.Measuring R1 outside the circuit would yield just the same, as it is nothing connected to its terminal to the left (in the schematic) except the mains plug, which is floating when I perform the measurement.Regards,Cristian.

author: rob77
author_rank: Super Contributor
timestamp: January 20, 2016, 10:03:29 am
content: if R1 measures 8+ megs, then it's definitely gone.. replace R1 with a new one based on the color code of the broken one.if R5 - the 1meg resistor measures 8ohm in circuit - then Q1 is gone (can't see any other low resistance paths in the schematic than the busted C-B junction of Q1) - and most probably R1 burned through because of the broken down Q1.so probably it would be cheaper and much faster to get a new AC adapter.

author: brumbarchris
author_rank: Regular Contributor
timestamp: January 20, 2016, 11:50:24 am
content: Yes, but getting a new adapter is not really the point. Fixing this is more or less an exercise, not a lucrative activity.I did some more research on it. Q1 is definitely busted, took it off the board, measured it separately: short between each two pins, taken in all combinations.R1 resistor: yeah, busted; problem is, I am not sure what value I should replace it with. The colors on it are not easily distinguishable. I definitely have a first bar brown, then a second bar black. The third bar would look like a silver. Based on the color code, it cannot be grey. But I am not sure it is not a golden bar, the third one. If its silver, the resistor would be 0.1Ohm. If it is gold, the resistor would be 1Ohm. Both are surprisingly low values. It looks like this resistor is there to act as a fuse, which is what it did. So at least the protection mechanism of this adapter worked!R2 resistor: this one also seems to be busted. It measures about 38kOhms. But the color bars on it are: blue (this one is sure), grey (not very clear, but its definitely not red, and the only possible resistor values up to the E24 series starting with 6 are 62 and 68; so it must be grey) and maybe silver or gold. So anyway either 6.8Ohms or 0.68 Ohms. Unfortunately, even if I manage to get my hands on a PA 13003 transistor replacement, I believe the value of R2 is not something I could play with. For R1 I suppose it won't matter too much if I use 1Ohm or 0.1 Ohms, but for R2 it matters if it is 6.8Ohms or 0.68Ohms.Is there anybody so familiar with what seems to be a fairly simple and common off-line PSU design that can advise?Regards,Cristian

author: rob77
author_rank: Super Contributor
timestamp: January 20, 2016, 12:11:46 pm
content: i would go with R1 = 1R and R2 = 6R8 - considering the fact R2's purpose is sensing the current through Q1 and provide current limiting with the help of Q2 (which is part of feedback loop as well). if you use 6R8 then 100mA through Q1 will yield 680mV which about the right voltage to start open Q2 and pull Q1's base down... so 6R8 sems to be a good value for R2 ( 0R68 would start limiting the current at approx 1 amp - and that's too much for such a small PSU)

author: rob77
author_rank: Super Contributor
timestamp: January 20, 2016, 12:16:34 pm
content: and of course check Q2 and the opto-coupler as well - those might be gone as well. these simple circuits are like avalanche - one part breaks and drags all others along.

author: brumbarchris
author_rank: Regular Contributor
timestamp: January 20, 2016, 12:19:06 pm
content: I will see if I can get in the replacements for the active parts. So far I checked the two transistors (anticipating a damage also in Q2), but the component price is 1 EUR (several parts of each) and shipping cost is 5 EUR, could be too much for what my friend is willing to pay.Anyway, good suggestion about the optocoupler, I'll have to check that too.Regards,Cristian

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 20, 2016, 12:55:24 pm
content: What is the point of replacing ANY of the components?If the transformer is shorted (and you won't find a replacement for that)then the circuit will never work again even if all the other parts are perfect.That is why these are disposable, ephemeral gadgets.

author: brumbarchris
author_rank: Regular Contributor
timestamp: January 20, 2016, 12:58:43 pm
content: There is no short circuit between the primary and the secondary winding of the transformer.Cristian

author: Richard Crowley
author_rank: Super Contributor
timestamp: January 20, 2016, 01:22:33 pm
content: Quote from: brumbarchris on January 20, 2016, 12:58:43 pmSorry, I mis-read the description that Q1 was shorted.

author: SL4P
author_rank: Super Contributor
timestamp: January 20, 2016, 01:31:20 pm
content: Obvious suggestion...Since none of the components are mechanically stabilised (with hot snot etc)... literally every solder joint is a suspect for fractures. simple touch testing with a meter won't help in many cases, as the light pressure will push the copper together for the duration of the test.As mentioned - check across and between xfmr windings, opto and ... well everything! At least it has a basic isolation gap between primary and secondary.

author: brumbarchris
author_rank: Regular Contributor
timestamp: January 20, 2016, 02:04:52 pm
content: Well, I have already resoldered all the joints myself, with good old leaded solder paste.And about the isolation gap - as I said, this is not really the cheapest possible junk I have ever seen, it could have been worse!Regards,Cristian

author: brumbarchris
author_rank: Regular Contributor
timestamp: January 20, 2016, 04:37:06 pm
content: While looking for a suitable Q1 transistor replacement I discovered that (unfortunately) you can get equivalent transistors in different pin-out configuration. That would not really be a problem if I know 100% what the pinout of the original Q1 transistor was, but as that measures a short circuit between any two pins, it would be impossible to know.So the only thing this can be inferred from is the reverse engineered schematic I posted in the first post. Does that one look all right? Could the emitter and base of Q1 be switched in-between them, would the schematic make more sense that way? Attached here are two random 13003 transistors datasheets I could find (the one from ST I am planning to buy as a replacement).Regards,Cristian

author: oldway
author_rank: Super Contributor
timestamp: January 20, 2016, 04:46:26 pm
content: I can't understand why you loose your time and your money to try to repair such a dangerous and low quality adapter.It is a true piece of shit. Don't you see it's a very low level technology ?It works on 230V, It can kill you.

author: johnkenyon
author_rank: Regular Contributor
timestamp: January 20, 2016, 06:43:31 pm
content: Quote from: medvedev on January 20, 2016, 08:35:23 amBuy a USB to Nintendo lead, and an existing USB charger.That's what I've done with my whileaway-hours-at-the-airport DSLite. One less item to lug around and/or lose, and none of the 240 vs 110 crap you get with the original Nintendo device.

author: Monkeh
author_rank: Super Contributor
timestamp: January 20, 2016, 06:47:55 pm
content: Quote from: brumbarchris on January 20, 2016, 08:39:13 amUh, no, no they're not. Fake, that is, the vast majority are indeed manufactured in China.

author: rf+tech
author_rank: Frequent Contributor
timestamp: January 20, 2016, 07:08:24 pm
content: Hi brumbarchris,I understand your desire to not only help your friend, but to learn in the process. I agree that the effort to repair this device "is not worth it" but the knowledge gained can be more valuable than the item being repaired. To that end, and with the heeding of others warnings, let's proceed.The two datasheets agree as to the pinout of the 13003 transistor. Further, your schematic shows the E B C connections correctly. However, the lead numbers assigned to the base and emitter in your schematic are reversed. The pinout you show for the 2SC945 is correct.The C4V3 part number for D3 almost certainly indicates this to be a 4,3 Volt zener diode.If possible, please post some closeup photos of the questionable resistors, taken in bright daylight, so we can better assist in the interpretation of their markings.In the interest of safety, it would also be a good idea to use a mains isolation transformer while working on this device.RF+ Tech

author: brumbarchris
author_rank: Regular Contributor
timestamp: January 20, 2016, 09:03:41 pm
content: Thank you for understanding.Not sure why you say the two datasheets agree with respect with the pinout of the 130003 transistor. In the datasheet I see pin 1 being the Base and in the other one I see pin 1 being the Emitter.Except maybe if the views of the transistor in the two datasheets are from the two different sides.I'll try to get the photo camera again tomorrow, to put also some snapshots of the resistors.Regards,Cristian

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 21, 2016, 01:40:17 am
content: FWIW, I have a small handful of 13003 transistors that I've salvaged from old CFL bases. They are all BCE, as shown in the TY datasheet and the OP schematic.There are many transistors you could substitute for the 2sc945. NPN Silicon, 50V 100 mA, ECB pinout in TO-92 package. You could probably even get away with using a 2n3904 (EBC), bending the pins around.

author: rf+tech
author_rank: Frequent Contributor
timestamp: January 21, 2016, 02:09:23 am
content: Gah, I've had a very bad headache all day and now see that it has gotten the better of me.I've downloaded six different manufacturer's datasheets for the 13003 fromhttp://search.datasheetcatalog.net/key/13003. All agree that the base is pin 1, on the left.Motorola was the originator of the MJ13003, so their datasheet can be considered correct and the ordering is BCE for the TO-126 package. With the TY Transistor datasheet in agreement with the others, let's just say that ST got it wrong and disregard this one.The 13003 is also available in a TO-92 package and the pinout for this device is EBC.RF+ Tech

author: brumbarchris
author_rank: Regular Contributor
timestamp: January 21, 2016, 06:55:39 am
content: Well, good to know, as I was planning to buy the ST device as a replacement. I still intend to, presumably they got the different pinout with respect to the other manufacturers, but the datasheet is probably right as to their own transistor. Anyway, I can measure the transistor when it comes in, to find out the actual pinout. If I now have the certainty that the schematic is correct, I can place the transistor the other way around, if needed.I'll try with the pictures "in broad daylight" today, although it looks like it is going to be overcast.Regards,Cristian

author: brumbarchris
author_rank: Regular Contributor
timestamp: January 23, 2016, 03:45:53 pm
content: Tried today to get some decent pictures of the burnt out resistors, no success, unfortunately (it is rather day even in broad daylight, due to the cloudy weather we are getting for about a week now). But the good news: my friend bought a new adapter (hopefully identical) and he is willing to allow me to open it up and have a sniff around it. I'll get my hands on it on Monday.So I will be able to measure the actual resistors, and I am also planning a purchase from Farnell for the active parts (but I need to bundle it with some other order we will need to make these days, otherwise shipping cost will make it totally unworthy).Regards,Cristian