sicelo | Looking at page 4 of N900 schematics, and testing my broken USB n900, where the USB Vcc/Vbus pin shows a short to ground | 17:13 |
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sicelo | The curious thing is, there's no such short to ground when I put multimeter on F5300 | 17:14 |
sicelo | F5300 itself isn't blown. Now I'm wondering - can I 'safely' ignore the mysterious short to ground on the actual usb pad and instead solder a new port's vbus pin to F5300? Unless I'm missing something here, at least schematic and my F5300 findings suggest it should be safe | 17:17 |
sicelo | joerg, and others, ^ | 17:17 |
joerg | how did you detect that "short"? | 17:19 |
joerg | and where's my N900 schematics? | 17:19 |
sicelo | If i place multimeter on pads that correspond to 1 and 5 on microusb, it shows continuity | 17:24 |
joerg | well, that's what is supposed to happen since this is a power-in rail, no? :-) | 17:26 |
sicelo | There was a previous failed attempt to re-solder the usb port back on. That said, I really can't understand how it could lead to this short, and more weirdly,why it isn't 'visible' on f5300 | 17:26 |
joerg | measure true ohms | 17:27 |
sicelo | Hehe, well, if i place dmm on 1 and ground, i have continuity. Exactly same thing with pin 5 and gnd | 17:27 |
sicelo | Wi test ohms now | 17:27 |
joerg | or duh, just connect a USB charger and measure voltage from F5300 to GND | 17:27 |
sicelo | True ohms between 1 & 5 is exactly 0 | 17:29 |
sicelo | Found your schematics? | 17:31 |
joerg | sure :-) | 17:39 |
joerg | you say you don't find that short from F5300 to GND? smells like a failure in probing | 17:40 |
joerg | or you soldered VBUS pin to ... sleeve? instead of PCB pad | 17:41 |
joerg | measure ohms between both sides of F5300. When you are confident to always get a proper contact and instant result (~0 ... 1 ohms), measure again F5300 (either side) to GND or pin2 of batt connector | 17:44 |
sicelo | New port isn't soldered in yet ... i won't do it right away | 17:44 |
joerg | so what is it you're measuring? USB PCB pad to F5300? | 17:46 |
joerg | an what's >>between 1 & 5<<? | 17:47 |
sicelo | Usb pad 1 and pad 5 | 17:51 |
joerg | according to schematics there is absolutely nothing other than a plain simple trace from VBUS pad of USB socket footprint to F5300. I don't see how that could possibly have a short to GND at one end and none one the other | 17:51 |
sicelo | Yes, beats me | 17:51 |
joerg | there must be a glitch in probing somewhere | 17:52 |
joerg | measure continuity from pad to F5300 | 17:53 |
joerg | what means >>F5300 itself isn't blown<<? | 17:53 |
sicelo | Pad to f5300 = 47kOhm | 17:55 |
sicelo | F5300 not blown means i get 0 ohm when dmm leads are on each side of f5300 | 17:56 |
joerg | you actually managed to damage PCB so the trace from USB,pin1 to F5300 is cut and instead shorted to GND. Congrats :-) | 17:57 |
sicelo | :-p | 17:57 |
joerg | you of course can connect USB receptacle pin1 VBUS "free air" yellow wire to "right hand" pin of F5300. Make sure the receptacle pin1 does never touch the PCB footprint pad | 17:59 |
sicelo | Right hand pin of f5300 means? | 17:59 |
joerg | however carefully check the other 4 footprint pads before you proceed | 17:59 |
joerg | "right hand" in schematics, the one supposed to connect to USB | 18:00 |
joerg | the fuse can't be 0 Ohms, must be at least fraction of an Ohm | 18:00 |
sicelo | D+, D- are intact. Continuity seems okay. Only the vbus is borked | 18:00 |
sicelo | 0.5ohm | 18:01 |
joerg | check for short to GND too | 18:01 |
joerg | on D+- | 18:01 |
sicelo | I did. They're okay | 18:01 |
joerg | 0.5R sounds absolutely correct. So you can determine which end of Fuse is real 0 ohms to N|L|C 5300 | 18:02 |
joerg | to the other end you may solder some thin wire and run that to the "aired" pin1 of receptacle | 18:03 |
sicelo | NLC means? :-) | 18:03 |
joerg | N5300 diode, L5300 coil, Capacitor | 18:04 |
sicelo | Right. Let me locate those | 18:04 |
joerg | C5300 is a 4pin capacitor, prolly looks odd | 18:04 |
joerg | N5300 diode also looks like it's supposed to be 4pin | 18:05 |
sicelo | Yes, so i can't probe that. Even the cap is a weird 4 pin thing :-p | 18:09 |
sicelo | At least all are accessible. The diode's pins are underneath (balled is the term?) | 18:09 |
joerg | sicelo: the capacitor like the diode have 2 connected pins that are VBUS and 2 connected that are GND | 18:10 |
joerg | BGA package, yes | 18:11 |
sicelo | I guess my T235H dmm's resolution isn't the most accurate around. But looks like the vbus side of f5300 is the one on left when camera module is on top | 18:11 |
joerg | can't duplicate that now. you could send a 1A current through the "short" from F5300 to L5300 and measure the voltage across F5300. If there are something like 0.5V its ok, if there's 0.00V then you feed the current to the wrong side of F5300 | 18:13 |
sicelo | Makes sense. I'll try that | 18:15 |
joerg | when you use a lab PSU, watch out for damn output buffer capacitors that defeat current limit completely for a curent surge on making contact! | 18:26 |
joerg | keeping that probelm in mind, you may just get away with two tips and lab PSU: adjust current limit to a few 100mA; connect L5300 and "wrong" (L5300) side of F5300; ramp up voltage until PSU signals current limited mode, add a 50 or 100mV on top ; now switch off PSU and short output to discharge buffer capacitor inside PSU; connect to "right side" of F5300 and L5300 and switch on PSU, current limit shouldn't kick in thanks to the 0.5R of fuse you have now in | 18:30 |
joerg | current path | 18:30 |
sicelo | Unfortunately I don't have it (lab psu) | 18:34 |
sicelo | But can do that test later at a friend's | 18:35 |
joerg | good luck! | 18:41 |
joerg | and happy new year, better than damn 2021 | 18:42 |
joerg | to all of you | 18:42 |
joerg | *sigh* topic is vasty meaningless without infobot :-/ | 18:43 |
joerg | maybe I could find infobot factoids for ~lf (or ~tabletsdev ~combined ~emmc ~flasher) sdk: ~sb in my chanlogs and set up an autoresponder for them | 18:46 |
joerg | http://reisenweber.net/irclogs/libera/_maemo/_maemo.2021-01-17.log.html#t2021-01-17T13:24:06 etc | 18:48 |
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