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  1. #121  
    Hmm, looking more closely at the bottom pair of resistors, there appears to be a circular dark spot, indicating perhaps a via? That should link the area in between the resistors on the bottom to the D- pin. If you have a multimeter, you can check for continuity from there to the data pins.
    I don't believe that the disconnecting the bottom pair would suddenly cause the charger to no longer function, since the data lines use the 5V charging power, and you said that it's signaling just fine (lightning bolt appears). Is this an Apple charger? That second pair should just be there to change the voltage on one of the data lines, and since the ones on the touchpad are shorted out, there shouldn't be a need for it.
    Just to be certain, you did not connect the newly vacated solder pads of the second pair to anything, did you? Try checking the outside power pins with a multimeter to make sure there is still 5V coming through without the touchpad plugged in. Or maybe there's an accidental short somewhere? When you get around to it, post photos and maybe we can help spot something in your new setup.

    (Also, completely irrelevant, but I just noticed the big(ish) black 6V smoothing capacitor at the bottom of your character's board. That doesn't give much leeway for a 5V output. Sloppy. :P)
    Last edited by wilywyrm; 10/17/2011 at 12:14 AM.
  2. #122  
    I did pay attention to not reconnect any pathways after removing the SMTs. Does not mean nothing happened though. I'll post pics tomorrow.

    As for the capacitor...
    Sloppy... Sure. But more over china cheap...
  3. #123  
    Quote Originally Posted by RICKV View Post
    I think I may have part of the issue...

    In my first mod, I have removed all 4 resistors to replace them with a 250k and a 300k.

    However looking closer at the pics I took yesterday, tell me if you see the same, but the top pair of resistor are linked to the D+ circuit. At this point I have also linked the D+ and D- without success.

    Click to view quoted image

    Look carefully at the lower pair of resistors... the circuit pathway does not seem similar. There does not seem to be a link to the D+...

    Maybe I need to only remove the top one and replace with the 240/300. Removing the lower pair may have broken the actual charging pathway, explaining why I don't have any current anymore even though now the lightning appears...

    I'll try and scratch the white markings to have a better look at the circuit pathway.

    Comments?
    Rickv,
    Some Technobabble:

    The Resistors marked 68C are 49,900Ohm and the 85C is 75,000Ohm
    This makes the Voltage at the D+ 2.1V and D-2.8V

    Your 250/300 Resistors would give you 2.36V at the D+D- Bridge which is as near as damnit the same as you would get by simply bridging the D+D- terminals with the original resistors in place (albeit at lower impedance).
    Last edited by Wheel_nut; 12/17/2011 at 07:58 PM.
  4. #124  
    Quote Originally Posted by Wheel_nut View Post
    Rickv,
    Some Technobabble:

    The Resistors marked 68C are 49,900Ohm and the 85C is 75,000Ohm
    This makes the Voltage at the D- 2.1V and D+2.8V

    Your 250/300 Resistors would give you 2.36V at the D+D- Bridge which is as near as damnit the same as you would get by simply bridging the D+D- terminals with the original resistors in place (albeit at lower impedance).
    Oh, darn. Yeah, Wheel_nut is right. Just bridging the data pins should give you the same voltage if it's an iDevice charger. Might want to make a note of that in the thread's first post for posterity. Sorry for all the hassle.
    Last edited by wilywyrm; 10/17/2011 at 12:32 PM. Reason: Dumb typo. data -> iDevice.
  5. #125  
    Quote Originally Posted by wilywyrm View Post
    Oh, darn. Yeah, Wheel_nut is right. Just bridging the data pins should give you the same voltage if it's a data charger. Might want to make a note of that in the thread's first post for posterity. Sorry for all the hassle.
    I like what's been going on here! Been having similar ideas but am not as clued up as you guys seem to be.

    Are you saying bridge the two centre USB pins on most 'iPad' style 12v-->5v chargers to get the TP to 'see it' and pull a full 2A?

    I bought this (pic) double USB unit (as I want to charge both the TP and a Wifi Modem from automotive 12v DC) for a few $'s and pulled it open.

    I think it was rated at 1A & 0.5A for each respective USB socket..
    There is an 8 pin chip: MC34063 800. Whatever that does..
    The visible capacitors are 6.3v 470uf.
    The USB pin resistors are looking like:

    R20 = 753.
    R21 = 513.
    R22 = 433.
    R23 = 513.

    What's my next move please!
    Bin it?
    Solder it?



    Thanks!

    PS. Someone could probably offer a good service here 'adapting' cheap existing charger units to suit TP owners with cars!
    Attached Images Attached Images
    Last edited by Mutoidi; 10/17/2011 at 12:37 PM.
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  6. #126  
    Quote Originally Posted by wilywyrm View Post
    Oh, darn. Yeah, Wheel_nut is right. Just bridging the data pins should give you the same voltage if it's a data charger. Might want to make a note of that in the thread's first post for posterity. Sorry for all the hassle.
    See my edit to my post on previous page. Sorry for erroneous report that it is working with the TouchPad. IT DOESN'T! Not only do I get the low power warning but the Touchscreen becomes erratic.

    I think I need to remove all four resistors and replace with the 250K Pull-up and 300K Pull-down as found by Wilywrm.

    Mutoidi, DO NOTHING just now, we haven't found the solution yet.
    Last edited by Wheel_nut; 12/06/2011 at 12:26 PM. Reason: Edit: Corrected Resistor values
  7. #127  
    Quote Originally Posted by Wheel_nut View Post
    See my edit to my post on previous page. Sorry for erroneous report that it is working with the TouchPad. IT DOESN'T! Not only do I get the low power warning but the Touchscreen becomes erratic.

    I think I need to remove all four resistors and replace with the 300K Pull-up and 250K Pull-down as found by Wilywrm.

    Mutoidi, DO NOTHING just now, we haven't found the solution yet.
    OK.. "Copy that Houston".. Holding!

    Back to the drawing board Eh!

    Daemon likes this.
  8. #128  
    Well, I guess in that case I'll go back and edit my other posts. I only tested the circuit I showed with a breadboard and made my own on some perfboard, so I haven't tried bridging an iDevice charger (Don't own any iDevices).

    Here's a possible explanation for the discrepancy. The resistors labeled 753 and 433 (75K and 43KOhms) are attached to the 5V pin and D+ or D- pins. Bridging the data lines makes them essentially parallel resistors, so we can calculate their combined impedance to be about 27K. Doing the same for the resistors connected to ground (51K and 51K) gives 25.5K.
    A resistor divider with those values at a voltage of 5V would give about 2.4V, compared to 2.727V with the official charger. Maybe that's what makes the difference, or maybe the impedance instead.

    In any case, here's a picture with what I would do in your case, but just to be safe, wait until others confirm or work it out if you have the time. Try to get SMD resistors in the size on your board (0805 or maybe even 0603?), but if you're new to soldering or can't get ahold of the tiny little buggers, you can try to use through hole resistors like RICKV is. It'll be hard to fit them into that space, maybe you can try attaching it to the respective pins directly? Don't mess with the MC34063 chip or the board that it's on.
    Last edited by wilywyrm; 10/17/2011 at 01:07 PM.
  9. #129  
    My second take at it will be later tonight (Canada Eastern time).

    However reading the latest posts here is a thought you can chew on.
    On my second PSU, if bridging D+D- parallels the resistors, it definitely modifies the impedence to a level out of range.

    Here is an idea, Bridge D+D-, remove only the appropriate resistors to remain with proper values, and bridge the connections left by the removed resistors.

    I have a feeling this might solve all of the issues we are experiencing and simplify the mod on any existing PSU. In some cases you could only bridge over the resistor without even removing them... you just bypass the resistor without removing it.

    Now since I'm no electronics engineer, I might need help in calculating which of the resistors to remove and which to bridge. (For now on my second PSU as I'm not sure the 1st one is still correctly functioning).

    This community is absolutely awesome... try getting this kind of help in the Andro´d or IOS community... or windows even...

    Thank's to all for the help.

    BTW Once we get it figured out I will suggest a Mod to close this thread and we can create a sticky with the proper information right at the top of the post, alleviating some pain and grief for the newcomers...
    HP Touchpad, Palm Pre2.

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  10. #130  
    Quote Originally Posted by wilywyrm View Post
    Well, I guess in that case I'll go back and edit my other posts. I only tested the circuit I showed with a breadboard and made my own on some perfboard, so I haven't tried bridging an iDevice charger (Don't own any iDevices).

    Here's a possible explanation for the discrepancy. The resistors labeled 753 and 433 (75K and 43KOhms) are attached to the 5V pin and D+ or D- pins. Bridging the data lines makes them essentially parallel resistors, so we can calculate their combined impedance to be about 27K. Doing the same for the resistors connected to ground (51K and 51K) gives 25.5K.
    A resistor divider with those values at a voltage of 5V would give about 2.4V, compared to 2.727V with the official charger. Maybe that's what makes the difference, or maybe the impedance instead.

    In any case, here's a picture with what I would do in your case, but just to be safe, wait until others confirm or work it out if you have the time. Try to get SMD resistors in the size on your board (0805 or maybe even 0603?), but if you're new to soldering or can't get ahold of the tiny little buggers, you can try to use through hole resistors like RICKV is. It'll be hard to fit them into that space, maybe you can try attaching it to the respective pins directly? Don't mess with the MC34063 chip or the board that it's on.
    OK.. & thanks for the Pic too.. I'll hang on in before grabbing resistors of those values, whilst you guys reserach it all a bit more more fully?
    In the light of RICKV's post above, in my case do you feel R22 & R23 should actually be removed.. or instead bridged?

    What does an MC34063 800 do anyway.. is it a 'regulator'?

    This is not a specific 'iDevice' unit.. but a generic Asian thing, found in my local Supermarket, but you can bet they had a few million 'i's in mind!

    Do you think the erratic TP Touchscreen behaviour may be due to changed voltage differentials or perhaps a grounding/leakage via the charger, causing loss of effective capacitance?

    Yeah RICKV.. WebOS - 'No Surrender!'

    Last edited by Mutoidi; 10/17/2011 at 03:11 PM.
  11. #131  
    NONONONONONONONONO don't bridge anything except the data pins on top. There's no need, and if you bypass(bridge) the resistors, you will make a short circuit from the 5V supply to ground, diverting all the power and scaring the magic smoke out of the charger and maybe your touchpad! Maybe the problem you're experiencing has something to do with which resistors you removed? When you get to take a second whack at it, we could probably help more.

    Mutoidi, remove them all and pick either R20 and 21 or R22 and 23 as the place for the new resistors. The MC34063 is a switching regulator, essentially, it just turns some voltage into another, probably 12 to 5 in your case. As for the erratic touchscreen behavior, it could be anything causing anything.
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  12. #132  
    Wilywyrm,

    Edit: I agree with your diagram - the Pull-Up Resistor is 250K and the Pull-Down 300K


    I await Rickv's findings .... no point in butchering my cheapo psu as well!

    Rickv, Note that the existing Potential dividers produce ~2.4V and ~2.8 volts respectively so you could create both voltages using the SMD Resistors.
    Last edited by Wheel_nut; 10/20/2011 at 08:19 PM. Reason: Agree with Wilywyrm findings
  13. #133  
    "..Mutoidi, remove them all and pick either R20 and 21 or R22 and 23 as the place for the new resistors. The MC34063 is a switching regulator, essentially, it just turns some voltage into another, probably 12 to 5 in your case. As for the erratic touchscreen behavior, it could be anything causing anything.."


    Thanks 'wilywyrm' - was your attached pic meant for me? If so, it is not actually my unit.. so I wonder whether to remove all resistors and then replace (with 300K & 250K?) @ ONLY R20 & R21.. as PCB layouts are in fact different? Re-attaching your orig. pic to me (of mine!) for your kind re-checking anyway.

    Yep.. reg. would be from 12v --->5v DC.

    Cheers!
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    Last edited by Mutoidi; 10/17/2011 at 06:28 PM.
  14. #134  
    Thanks for pointing that out, Wheel-nut, and I'm absolutely certain. I've used the same little perfboard with that exact resistor setup on both my computer's 5V supply and a regulated 5V solar panel setup I built. It works fine.
    However, since you brought it up, I should confirm that the Barrel outputs 2.48V. I did measure that before tearing into mine. I hadn't mentioned this before because it works fine without this and thus appeared to me as useless, but there is a 1K resistor by the USB connector pulling 5V to ground. It really does work without this, but for safety of mind, I guess you could add it.
    Also, if you can get to the data pins somehow, you should see that there is a 135.6K resistance between the data pins and ground, which is not really what works in the circuit! I initially tried a 135/135 split, but it didn't work despite the voltage being the same. HP is a sly one; I still don't know why it appears as 135.6K, but it does.

    If anyone wants, I can post pictures of the board in question.
  15. #135  
    Oops, sorry for the ambiguity there, and don't mention it. The image which you attached was meant for you; the one in my last post for RICKV. Thanks for pointing that out.
    Yes, the advice still stands. Replace R20 with 250K and R21 with 300K. Remove R22 and R23, and leave the spaces empty
  16. #136  
    Quote Originally Posted by wilywyrm View Post
    Oops, sorry for the ambiguity there, and don't mention it. The image which you attached was meant for you; the one in my last post for RICKV. Thanks for pointing that out.
    Yes, the advice still stands. Replace R20 with 250K and R21 with 300K. Remove R22 and R23, and leave the spaces empty
    No worries.. now it's probably my turn to cover ambiguities by asking you to bear in mind that this unit has a double USB output.. only one of which needs to be 'TP modified'.. the other is for a lower current draw Wifi modem. My first pic is probably of the 'secondary' (lower current) USB.

    SO, here now finally I hope, are 2 more pics, one of what is presumably the 'primary' (higher current by design) 'TP' USB, in which I hope you can make out the PCB tracks more clearly.. and also see the thinner wires running off to feed the 'secondary' lower current USB, they seem to be wired in parallel.. and a second pic where both USBs are visible. Does this change things regarding power to the secondary, if I then remove R22 & R23 here on the 'primary' instead?

    Hope that's clear-ish?
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    Last edited by Mutoidi; 10/17/2011 at 07:21 PM.
  17. #137  
    It appears that the thinner wires are just there to provide the second port with power, so the resistor modifications should not affect the second port since there is also an independent set of resistors on the second board. Even if that weren't the case, no significant amount of power goes through the resistors anyway, so no worries on breaking any parallel power circuitry.

    tl;dr, I think you'll be fine.
  18. #138  
    Quote Originally Posted by wilywyrm View Post
    Thanks for pointing that out, Wheel-nut, and I'm absolutely certain. I've used the same little perfboard with that exact resistor setup on both my computer's 5V supply and a regulated 5V solar panel setup I built. It works fine.
    However, since you brought it up, I should confirm that the Barrel outputs 2.48V. I did measure that before tearing into mine. I hadn't mentioned this before because it works fine without this and thus appeared to me as useless, but there is a 1K resistor by the USB connector pulling 5V to ground. It really does work without this, but for safety of mind, I guess you could add it.
    Also, if you can get to the data pins somehow, you should see that there is a 135.6K resistance between the data pins and ground, which is not really what works in the circuit! I initially tried a 135/135 split, but it didn't work despite the voltage being the same. HP is a sly one; I still don't know why it appears as 135.6K, but it does.

    If anyone wants, I can post pictures of the board in question.
    WilyWyrm, I can explain the reading of 135.6K between the D+- pins and the Ground or +5 pins.

    If you consider that the impedance between the +5 & Ground is < 1K then the equivalent impedance looking into the D+- to Ground is 300K in parallel with 250K+1K which is ~= 136K

    Similarly, the impedance betwwwn D+- and +5 is 250K in Parallel with 300k+1K ~= 136K

    When I measure these, The impedance from D+- to Ground measures slightly LESS than that from D+- to +5V. This supports my hypothesis that the resistors are 250K to Ground and 300K to +5v.

    I would appreciate a picture of the Barrel PSU board just to satisfy my obsession with understanding anomalies

    It is now 01:10 in the morning here so I will butcher my PSU tomorrow (by which time we should have the results of Rickv's efforts).
  19. #139  
    Quote Originally Posted by wilywyrm View Post
    It appears that the thinner wires are just there to provide the second port with power, so the resistor modifications should not affect the second port since there is also an independent set of resistors on the second board. Even if that weren't the case, no significant amount of power goes through the resistors anyway, so no worries on breaking any parallel power circuitry.

    tl;dr, I think you'll be fine.
    Good.. so it's OK to modify the first board without then affecting the second.
    (Except possibly with Wheel_nut's 300K to +5V instead of to ground, as I think is indicated in your first pic?). I'll hang on until that hypothesis is ascertained anyway!

    Thanks for all your guidance.. no point in having a TP that isn't fully MOBILE and charged, is there!. I'll keep my eyes on this good thread for any further developments!

    Good luck and steer clear of any actual 'Smoking' tests!

    Last edited by Mutoidi; 10/17/2011 at 08:00 PM.
  20. #140  
    OK so I'm the culprit for some sloppy work... But I won slap myself too hard on the hands as I was working in space smaller than a dime fitting 2 elephants on the boat! (see here to understand the reference).

    Brushing up on my Macro photography skills for the audience, I have found a very minor overlap of the solder creating a bridge (short) in my assembly. Scrubbing it out and cleaning with a wirebrush and some compressed air did the job and now I'm getting +1000mA while streaming video from Youtube connected to my car PSU.

    wilywyrm's original assumption is OK. The setup I have in the attached picture is pull-up 240k 1/4watt and pull-down 300k 1/4 watt.


    So I can confirm the numbers and schematics originally posted by wilywyrm supported by some great calculus from Wheel_nut.

    Now on to My next challenge... getting Navit to recognize my BT GPS receiver... That would make it a nice 10" GPS setup wouldn't it! When I get it working I'll post pics of the whole setup...

    Thank you again to all who helped and handholded me.

    PS my multimeter's battery is dead and I don't have a replacement handy so I could not verify. However I tested the setup for 30 minutes with Govnah and Dr Battery and have not had any glitches or missbehaviours from the TP.
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