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  1. #1
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    Faulty squzeebox touch burned u25

    I have burned U25 on sbt and can not read what this is.

    Can anyone help me ?

    Is this power-supply controller or low voltage detector?
    Thanks
    AnekeleaName:  11.jpg
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    Last edited by Anekelea; 2017-05-26 at 22:16.

  2. #2
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    U25 has short on 5/4 legs (Vout/bypass)
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    What to look for? Any ideas?

    Can anyone give me the correct voltage on pin5 (vout) on working sbt ?
    Last edited by Anekelea; 2017-06-01 at 07:59.

  3. #3
    Member JoeMuc2009's Avatar
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    Recently got a Touch with the very same issue. Now I'm looking for the spare part as well, however, it's hard as usual to find what part this actually is. The print reads something like 4B40R according to the images from my very shitty USB microscope:

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    Google does not reveal anything that makes sens when I look for 4B40R. However, digging through the results of "4B40" brought me to this page:

    http://bbs.ic37.com/TOREX/XC6204B40_datasheet_336701/

    According to the PDF, the SMT marking code 4B40R would mean:

    4 = indicator of product line XC6204
    B = Voltage 3.1~6.0V at 100mV steps
    4 = 3.5V output
    0R = production lot number / date

    The product name for this combination would be (I believe) one of these:

    XC6204B351MR
    XC6204B351ML
    XC6204B352MR
    XC6204B352ML

    where the red digit is for the accuracy (1 means 1%, 2 means 2% accuracy). It might not be this critical in the Touch so both could work.
    The red letter at the end is for the pick-and-place feeder direction and is meaningless for hand-soldering

    It seems close enough. Let's see where we can purchase this part. DigiKey and Mouser both state no stock and minimum order quantity of 3000. argh. Alibaba might be a change though. I found one seller (Shenzhen Wanxinwei Technology Co.) who offers XC6204B352DP which unfortunately is the wrong pin configuration. It's still the closest I found. I filed a request for the exact model numbers stated above. Let's see how that turns out.

    Cheers
    Joe


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  4. #4
    Member JoeMuc2009's Avatar
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    Well, I found a replacement but it seems that does not fully do it:

    PMIC - Linear (LDO) Texas Instruments LP2985IM5-3.5/NOPB

    This has basically the same data on its datasheet as the original Torex part. Both are designed for 150mA but to me it looks like the circuitry behind the regulator actually draws considerably more. After doing the replacement, I found that this poor little chip heats up beyond 100░C in any operation mode. Might be something else wrong in the circuitry but the good news here is that the Touch actually powers up and is usable for the first time since I got it. Besides a half-defective line in the lower region of the display, everything appears to work. I assume this wouldn't last long though. Once the unit is assembled back together, and with the display right on top of it, there is no way for that heat to escape so it will build up until the chip blows. Maybe something else on the board took damage when U25 was blown. I found evidence of somebody meddling with the EEPROM, it was apparently resoldered. Also looks like the CPU was reflowed. While all this was done with care and no obvious screw-ups, something must have gone wrong later.
    I took some pictures with my IR camera and superimposed photos of the actual board manually. It's not a perfect result by any means but indicates the hot spots (white) pretty well. I wish I had one of these FLIR E8 cameras, they do this on the fly.

    Front with U25, I measured 108░C peak:
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    Back side, here is another hotspot in the WiFi controller area but "only" around 60░C:
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    Basically all voltage regulators (there are some more, I counted at least 10) are driven pretty hot. The U25 replacement definitely runs out of spec so I'll try to find out what is wrong there. Maybe it needs to be replaced by something more beefy that does not fit the SOT23-5 footprint. On the other hand, if more than 150mA are drawn, another component may wait to blow up next. Damn...

    I measured around U25 and found that it gets a stable input of 5V. The output however struggles to exceed 2.5V and rarely comes close to its designed 3.5V output. This can't be good. The recorded output waveform (~10seconds) shows a lot of noise.

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    I'll still have to do the same measurements with a fully intact Touch. Will be back soon.


    PN me if your Boom / Classic / Transporter display has issues!

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  5. #5
    Member KeBul's Avatar
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    My goodness Joe, I admire your skills and tenacity...

    Interesting work you are doing on this, but I would have been on eBay buying a replacement by now!

    Good luck with your further investigations, look forward to reading the next chapter.

    Kev

  6. #6
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    Quote Originally Posted by JoeMuc2009 View Post
    Well....

    I measured around U25 and found that it gets a stable input of 5V. The output however struggles to exceed 2.5V and rarely comes close to its designed 3.5V output. This can't be good. The recorded output waveform (~10seconds) shows a lot of noise.

    I'll still have to do the same measurements with a fully intact Touch. Will be back soon.
    It looks like the regulator ic keeps trying to shutdown. Something killed the original voltage regulator. Perhaps there is a short on the output of the regulator, e.g., shorted filter capacitor?

    Regards,

    Rob
    Regards,

    Rob

  7. #7
    Member JoeMuc2009's Avatar
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    Yeah I think the designed current threshold of the chip is exceeded by the circuitry it supports (which I assume is the CPU because of its proximity). The chip is designed for 150mA and the data sheet states a maximum current of 500mA whatever that means. The waveform is a hot ride though. I would expect a repetitive pattern if the chip consistently restarts which it does not seem to do either.
    Anyway, I'll try to solder in a new CPU. Guess whoever was at it before me probably screwed up the reflow job. Hard to say because without x-ray it won't become visible. Just ordered a few CPUs with Alibaba now. May take some weeks until they arrive. Wish me luck

    Oh, and about the capacitors. I did some measurements of the CPU caps (the ones on the other side of the board "behind" the CPU). No shorts there at least. This is so tricky without a circuit diagram.
    Once the original CPU is off the board, I will first see whether the voltage regulator is still getting that hot. If it stays calm, it might be the right track I am on. Soldering in a new CPU is still a real challenge. Let's see how that turns out.
    Last edited by JoeMuc2009; 2017-09-08 at 11:20.


    PN me if your Boom / Classic / Transporter display has issues!

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  8. #8
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    Quote Originally Posted by Anekelea View Post
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    Hi,

    Long time guest/lurker, hoping that you might be able to help.

    I've been repairing my Touch, but I have damaged resistor R4. It's right in the middle of the board, on the same side as U25.

    Would someone be able to measure the value of R4 for me please?


    Many thanks and best wishes,
    Chris.

  9. #9
    Member JoeMuc2009's Avatar
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    Hi Chris,

    just desoldered and measured it, and found that R4 is a 1k resistor.
    Good luck with your repair!

    Regards,
    Joe

    Quote Originally Posted by hnb2907 View Post
    Hi,

    Long time guest/lurker, hoping that you might be able to help.

    I've been repairing my Touch, but I have damaged resistor R4. It's right in the middle of the board, on the same side as U25.

    Would someone be able to measure the value of R4 for me please?


    Many thanks and best wishes,
    Chris.


    PN me if your Boom / Classic / Transporter display has issues!

    LMS 7.9.0 on Windows Server 2012
    1x Squezeebox Classic SB2
    7x Squeezebox Classic SB3 (one waiting for repair)
    7x Squeezebox Boom (two waiting for repair)
    1x Transporter
    2x Controller (one waiting for repair)
    3x Touch (two waiting for repair)
    1x Radio

  10. #10
    Member JoeMuc2009's Avatar
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    Sorry to inform you that I'm going to give up on this Touch. Soldered in a new CPU, no improvement. Quite the opposite in fact, the Touch no longer boots. And U25 still goes beyond 110░C.
    This is so frustrating. I think the result is that besides the IR sensor and replacement screens (currently got two working screens from defective units), I cannot offer any Touch-related services. That thing is just not made to be repaired. Sigh.


    PN me if your Boom / Classic / Transporter display has issues!

    LMS 7.9.0 on Windows Server 2012
    1x Squezeebox Classic SB2
    7x Squeezebox Classic SB3 (one waiting for repair)
    7x Squeezebox Boom (two waiting for repair)
    1x Transporter
    2x Controller (one waiting for repair)
    3x Touch (two waiting for repair)
    1x Radio

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