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Sony Ericsson CST-60 Charger

Discussion in 'Troubleshooting and Repair' started by TimeManx, May 11, 2010.

  1. Tesla

    Tesla

    165
    2
    May 10, 2010
    Good work. You might list the parts replaced and there exact specs. (and what you crossed the transistors to) for the next person.

    If I recall correctly, (for the first attempt) you got one of those transistors from an old board. It might have been bad.

    There was some question as to the proper polarity on the 5vDC output. Just double check with DMM before soldering in the wires. I documented the connector pinout earlier in the thread (and it was doubled checked against my working one).

    Feels good to fix something, yes? :)
     
    Last edited: May 17, 2010
  2. TimeManx

    TimeManx

    31
    0
    May 11, 2010
    Yeah, it feels awesome.

    Here's what I replaced (I had replaced the same parts in my first attempt too).
    R1 - 0.5 Ω
    R2 - 10 Ω
    R3 - 2.7 kΩ
    Q1 - 13001
    Q2 - C945

    Although I had said that I had Q1 from an old board but I still put in a new one just to be safe. And yes the output voltages are reverse to what is printed on the board.

    Just tested this with a phone. Working flawlessly.

    Thank you everyone for all the help.
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,192
    2,694
    Jan 21, 2010
    One important little detail, Resqueline suggested that the 0.5 Ω resistor was probably a fuseable resistor. Whilst nobody can be sure, if it is, and you replace it with a normal resistor, you may be removing some critical protection. The next time you short it out (let's hope there isn't a next time) the pyrotechnics may be a little more impressive.

    It might be worth keeping an eye on this thread for Mitchejk's findings when he takes apart a new one. I'm certainly interested and I would not be surprised if this thread continues to discuss this power supply for some time.

    But good job fixing it. :)
     
  4. Mitchekj

    Mitchekj

    288
    0
    Jan 24, 2010
    Well...

    Got the CST-60 today. First off, if the case was the same, congrats on getting the thing apart, timemanx! This was the most solid sonic weld I've ever met, I do believe. I ended up using a dremel.

    Bad news is, this is a completely different design. I had half way expected that, but was hopeful anyway. The nameplate says 4.9Vdc 450mA out, 120-240Vac in. So it looks like they may have gone to a different vendor for newer chargers, or at least a major new revision. (With good reason, perhaps.) This particular one was made by a Finnish company: Salcomp PLC. Looked up by UL file # E135498. The PCB has #E128280, which is Yue Wah Circuits CO LTD of China.

    At first glance, this has a bridge (of four discrete diodes,) and a much more sophisticated regulation/feedback circuit. Edit: (And definitely a fusible resistor, a large white wirewound with a dot on it.)

    Good news is, it looks like a flyback yet still no controller IC! They're using two BJTs to switch this thing. So at least part of my curiosity may be sated. Problem is, I need to capture a new schematic, so much more work may be in order. Hopefully I can figure out what the little semiconductor packages are. (There is a 13003 transistor, the other looks like a SOT-23 w/ "SKX" on the top... any ideas? The SKX may be way off... will have to get it under a microscope tomorrow.)

    I'll get pics tomorrow, since I have no camera here at home.

    Nice job on getting yours working again, btw. :) And yes, definitely need to figure out if that was a fusible resistor though, fire hazard and such.
     
    Last edited: May 19, 2010
  5. Mitchekj

    Mitchekj

    288
    0
    Jan 24, 2010
    I'll split this into two posts... this one has the schematic I captured (hopefully accurate!) and pics of the PCB / case. Edit: Oh, wires and pen marks are added by myself, btw.

    Next post I'll post some screen caps (actually photos of my scope's screen... sorry if some are blurry a bit.) and what I could find out about it.
     

    Attached Files:

    Last edited: May 22, 2010
  6. Mitchekj

    Mitchekj

    288
    0
    Jan 24, 2010
    Well I didn't get all the captures I'd have liked. When I tested the "short circuit protection" by shorting the output, the fusible resistor opened, (I'd assume other components did as well.) So now I need to repair it before continuing. I should've left that test for the veeeery last. Hindsight, eh?

    Some basic stats:
    Load: 20W 16 Ohm non-inductive load resistor. (What I had handy for the output range, I really need a programmable load.)
    Vout: 5.331Vdc
    Iout: 330mA
    Pout: 1.76W
    Vopen(no load): 5.40Vdc
    Vin: 120Vac
    Iin: 42.5mA
    Pin: 2.95W (real power)
    Pin: 5.1VA (apparent power)
    PwrFactor: 0.578
    Efficiency: 59.66%
    SwtchFreq: ~64kHz

    I had expected a bit more efficiency from this thing... but, 60% sounds reasonable. (Edit: under full load, it may be better, I'd need to check that.)

    Anyhow! You can see how the AC input is being turned into Vbulk through the bridge and the caps. The inductor does nothing to smooth the ripple on top of Vbulk, since the Vbulk ripple is identical on both sides of it. I don't know if their intent was to try to smooth this ripple (like an LC PI filter?) or as a means to some type of DCM EMI filtering? (Though that would be on the other side of the bridge, yeah?) Seems pretty extraneous though.

    That Vbulk is turning Q1 on through the divider R9, R10, R11 and getting the switching started, (see Startup_Q1_base.) As the aux coil charges, he pulls Q1's base low through the RC network R7, C5 at ~64kHz (a very common switching frequency.) and the cycle repeats itself in a steady state. (see Q1_base.)

    Primary current was measured across current sense resistor R4 (252mVpk, for a 115mApk primary current, see Primary_Current.) The rapid drop off of current leads me to believe the snubber is working overtime, but I didn't want to try to measure that without an HV probe. If I'm thinking right, we can see something like 600-800V+ spikes if the primary suddenly ceases all current flow, right? I don't want to replace my scope's front end just yet. Edit: Just sitting here and it popped in my head that I was reading across the current sense resistor for the primary current measurement... of course it drops off sharply, it's below the switch. When the switch opens, all current (through the resistor) ceases very rapidly. The current through the primary winding will ramp down at a normal rate, through the snubber... ugh, I'm losing it. :)

    Anyway, when the primary collapses each cycle we get that energy induced into the secondary (see Vsecondary, which is the voltage directly across the secondary winding.) Notice it's ~24Vpp, most of which is negative, that's normal and familiar. Now normally, you'd see the catch diode (D9) first thing, right on the secondary output (pin 6 here.) They've put another catch diode on the negative side, D8, to allow C8 to act as the output bulk cap while still being west of D9. I've not seen this scheme before, and it's exact purpose eludes me... but it does appear to work. I contend that they could've saved themselves a diode by doing it the normal way. :) Any thoughts?

    R14,15,18,20 are forming a current sense resistor for the output (~2.02 Ohms) which is sensed by R19. This will bias Q3 to start turning the opto on when the current starts to get too high. That brings your duty cycle of Q1 down (lowering the output) via Q2. Though the fabled short-circuit protection still doesn't work, obviously, since I managed to smoke it. In any case, R21 and D7 form an OVP circuit, which DOES work quite well. Otherwise, everytime you unplugged your phone the supply would blow up. With no load, the supply's open voltage would raise quite a bit. I'm not sure what the zener's voltage is, it's a little SOD-323, so I can't even see the markings... (deduced he's a zener by measuring the voltage across it w/ load and without) but he starts to conduct whenever the voltage goes too high, which turns the duty cycle down through Q3, the opto, and Q2. This works quite well, as it limits the output to 5.4Vdc. I didn't get scope caps of that, but I did take a peek at the waveforms, and yes, Q1's duty cycle went down when I removed the load.

    Now that's all well and dandy, that's a basic flyback. What still trips me up is the whole interaction between Q1, Q2 and the aux coil. I'll throw some guesses out there and see what you guys think:

    I get that Q1 and Q2 form a current control scheme, that's pretty basic. R7 and C5 switch Q1 based on the TC, got that. D6 and R12 are shunting the negative spikes from the aux coil (like a snubber,) right? I guess my only confusion is R8. So is it some kind of pull-down for Q2? I take it it's weak enough to not disrupt Q1/Q2's steady state operation, but what purpose does it serve if it doesn't actively pull-down? (Actually I may have answered my own question... does it act as a divider for the opto, to establish the postive ~17Vdc coming from pin 4?) That may make sense, actually. I like it. I need to read up on the detailed operation inside the off-line controller ICs, to get a better feel of how exactly they are switching these things.

    Ok, I've typed too much. I'm sure I've made some mistakes / assumptions which are untrue, but please do comment. Learning is my goal here, afterall. :)
     

    Attached Files:

    Last edited: May 26, 2010
  7. Shaio

    Shaio

    1
    0
    May 28, 2010
    Hello! After googling for quite a while, to find technical specifications of this charger, i've finally found this forum. And i'm very happy to see, that you have the same charger as mine (the second version, with detailed analysis).

    So i'll get to my question :)

    I am in need of a mains charger for my USB devices, and i've found that one of my chargers is 4.9V/450mA as specified on the box (the same as Mitchekj's). According to wikipedia:
    From that numbers, it seems that everything is ok. When i checked my cellphone with the charger, it was drawing 470 mA actually, so i'm not so worried about the 50 or so mA. But after researching a bit (my electronics knowledge is not that great), and found that i need a regulated supply, so i don't damage the devices i'll be charging.

    So here come my questions :)

    1. Do you think, the 5V output is stable enough, to trust that the devices being charged, will not be fried, and;

    2. Do you think, that the 450mA vs 500mA as specified in the standard, should be potential risk?

    To sum up: do you think, that i can safely put my iPod Touch in the hands of this charger? :D

    P.S. I know, that i can buy a charger, but they are pricey, and if could skip this expense, i'll be quite happy. Also, i know that i have to put a couple of resistors on the D+/D- pins, to get the device to charge.
     
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