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narf
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Last Activity: Yesterday, 10:52 AM
Joined: 06-16-2024
Location: munich
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  • ok, seems like i can't edit my posts - so post #3 in a row

    i fiiiinally managed to get the buck converter out. really, i have to work on my solder skills. in videos, those kind of chips are out in 5 seconds and i held my gun on this 3x3mm chip for like 10 minutes on 420°C (tried 380 first), swimming in flux, until it went out. board might be dead now, i don't know

    buuuut i've got no more short on the caps... so i should've trusted the thermal foil (post #7)

    --> Texas Instruments TPS54335 - [URL]https://www.ti.com/lit/ds/slusck3/slusck3.pdf[/URL]​...
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  • update:
    i checked all of the marked caps without success. and from all the coils i see, just the one below the big chip marked as L3000 is shorted to ground. so this must be the power rail that's affected. what else can i check before i have to accept that the short is coming from the big chip?
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  • here's a quick update because i haven't written in a while...

    i'm uploading pics (front, back) with all the caps with <= 1 ohms. some i desoldered and re-soldered because they were not faulty and the short was readable on the bare board. and yes, they are looking ugly i might have to check some more videos on hot air solder guns or buy better flux - i dunno.
    marked in red are all caps that i've identified. a green marker on the side means, i have desoldered and checked them.

    they are basically all around the big chip. do you have any better ideas for me than...
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  • thanks again for your replies...

    ok, i was stupid. the current drop to zero when i pressed the board was because my ground connection during injection is not sitting too well on the board.

    unfortunately, i don't know anything about the projector's history. i just bought it to repair

    and i checked once more to see if something heats up. i may have found 2 caps where one might get warmer than the other. i'm gonna take this one out the next time i'm at home. but from the looks of it, all caps look ok. there are no explosion marks or cracks on any cap anywhere...
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  • Thank you for your reply.

    I've seen this video already (and many more ).. interestingly enough, this guy only measures 12V at the PSU, too, even though he reads 17V written on the board.

    I must have destroyed something during voltage injection or the existing short got worse because the caps i've identified before are now down to 0,3 ohms shorted to ground but from the looks of it, i couldn't find any cap that was exploded or damaged. i desoldered one that looked suspicious but it was ok.
    and during that voltage injection, the only thing that gets hot is that...
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  • thanks for the reply, diah. as i said: i'm a newbie, but i'm eager to learn

    i'm uploading pics of the PSU + a pic of the 5 opto couplers with labels "731 P785F 4GR"

    i also saw that a label on the power connector saying 17V (not 12V that i'm getting). i saw this in one of the videos but i think, the guy just changed the PSU altogether....
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  • when the connector is unplugged, i can only measure some very irratic voltage that's jumping in between -1V and +1V. maybe the ground that i'm using for measurement doesn't work as long as the board is not plugged in?! (i tried different screws, metal from the housing and the actual ground wire that later goes to the mainboard.)

    ok, well... i've injected some voltage into the board (1,5V max, limited to 2A) and the only thing that got hot was one buck converter IC (Texas Instruments TPS54335 - [url]https://www.ti.com/lit/ds/slusck3/slusck3.pdf[/url]). i saw that pin 3 (source of the...
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  • i did that part and found that pins 5+8 are leading to ground. but i can't check if the connector would show 12V on one of those pins if it's not connected. that would be the confirmation that something got shorted.
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  • thanks for the reply, CapLeaker.

    i found 2 pins that are connected to ground (pins 5+8 from the left). but i wasn't able to measure the voltage on the connector while it is disconnected. when it's connected, pins 6+7 show 12V. when it's disconnected, i get irratic readings between -1V and +1V on all pins. that's probably some standby mode of the PSU (the internet said). I'm not sure how i can verify if one of the ground pins is actually no ground when i can't measure the connector unplugged.
    btw: unplugged, there's no connection between ground and the potential ground pins (or...
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  • Epson EB-U42 projector / Caps with 0.7 ohms ?!

    hi all,

    first of all: i'm a (motivated) newbie, so please forgive me any stupid question i may or may not ask

    i'm currently repairing a projector: Epson EB-U42 that doesn't start (no lights, nothing).

    what i've found so far:
    - the PSU does its job and supplies 12V to the mainboard via the connector.
    - shortly thereafter, there is a mosfet (TS420-600B) where i can test 12V on the one side (in the data sheet this side is called Anode), Gate 0V, Kathode shorted to ground
    - not far away, there's the first cap with a resistance of 0.7 ohms....
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  • hi all,
    i'm narf from germany. i have an IT background but not too much electronics knowledge but still i try to repair everything

    cheers,
    narf
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