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Thread: Boss gt1 dead :(

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    Boss gt1 dead :(

    Hello everyone, I have a dead BOSS GT1 because power adapters got mixed and connected the following adapter AC 9v 2.1amp that belongs to a digitech genesis 3.

    The BOSS GT1 needs a DC 9v but I don't know how many amps it needs, I guess less than 600ma

    After connecting there was a "clack" sound and you know the smell.

    Opened the thing and found a hole on some chip close to the power input, it reads something like J04 or JD4, even the J can be an L o I because the hole is right under lol

    Anyone know what kind of chip it is? maybe a diode?

    Can it be replaced? I have done some soldering but this thing is really small.

    Attached an image, chip is on the red square and you can see the hole if you zoom.

    Click image for larger version. 

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    Lifetime Member Enzo's Avatar
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    The amps was never the issue, putting AC in where DC belonged means that 60 times a second, reverse voltage was feeding into the poor thing. I don't doubt the top blew off an IC, or even ruined them all.

    I don't know what the IC type is, but a schematic would answer that.

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    Supporting Member The Dude's Avatar
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    Similar scenario, but I looked at the supplies. The Boss supply is 9VDC negative tip. The Digitech supply is 9VDC positive tip. The wrong polarity supply was hooked up. And, yes, I agree. The OP is going to need a schematic.

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    Lifetime Member Enzo's Avatar
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    I thought he said the wrong one was a 9vAC adaptor. Says 9VAC on the rear of the unit in photos I see.

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    Supporting Member The Dude's Avatar
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    Yep you are correct. I just looked at some pics of the Digitech piece. It does say AC. It was the damn Chinese that confused me. I looked up this:

    https://www.ebay.com/itm/AC-Power-Ad...o/371446168454

    and it shows a polarity diagram, which made me think it was DC. Why they have a polarity diagram on an AC adapter is beyond me. Anyway, sorry for the confusion. It does also say AC/AC adapter on the sticker. My bad.

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    Thanks for your responses, the problem was connecting a 9V AC into a 9V DC, from now on I am going to place some sticker to avoid this.

    The chip that exploded maybe saved the rest of the components or maybe the entire board is dead, is hard to know but the rest of the components look fine.

    Suppose I am able to get a replacement for the chip that exploded and somehow get the schematic, soldering the new one is even possible?

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    Lifetime Member Enzo's Avatar
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    Surely possible, I do it. This is what we call surface mount soldering. There is a product called Chip Quik, or something like that, that works very well for this.

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    Thanks for the tip, checked some video about Chip Quik and its amazing.

    Going to try to find the schematic, otherwise will have to send it to BOSS, any idea on how much money they will want to fix it?

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    I suggest desoldering the chip with Chip Quick and drawing a schematic of this part of the circuit. Looking at the symbol of the component Q2 - I would say that this is transistor, most probably MOSFET and most probably with channel P. If you desolder it, it will be easier to tell. Don't forget to post photos of the PC board.

    Mark

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    I guess the exploded component is an LD4, it looks like JD4 because of the hole under it.

    Found that in the market they have developed chips called LDO regulators, they are supposed to regulate voltage variations and reduce noice output, this make sense because BOSS needs this thing to reduce hum or noices on sound output and at the same time provides steady voltage.

    So my next step will be to send an email to a LDO manufacturer and ask if he knows the damaged chip, I guess is going to be related to china.

    If I am right this information will help others because this LDO chips might be used for most BOSS stuff, usually a good LDO will fry itself to protect the rest of the feed.

    You guys familiar with this?

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    It is possible but I doubt that this is LDO chip. Still suggest to desolder the chip and check the tracks below it. This would clarify whether this is MOSFET, or LDO. Are pins 1,2 and 3 shorted on the board? Are pins 5,6,7 and 8 shorted on the board? This would indicate a MOSFET.
    Also your description of LDO is slightly incorrect :-).

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    Chip under question is the QS8J4 dual mid-power MOSFET.
    https://www.rohm.co.jp/datasheet/QS8J4/qs8j4tr-j
    Attached Files Attached Files

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    Lifetime Member Enzo's Avatar
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    LDO = low drop out

    Any simple voltage regulator needs a higher input voltage than the output will be. If your product is battery operated, then you don;t want a regulator that needs 3 or 4 volts of headroom. A low dropout regulator can regulate with just a very small extra input.

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