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debug prop hardware — Parallax Forums

debug prop hardware

s2jesses2jesse Posts: 62
edited 2009-02-28 23:42 in Propeller 1
Ok ill keep this short to start.. ive recently started making my own prop boards.. i jsut made a cool tiny one with smd parts.. does anyone know off hand the possible causes of a prop outputing like 1.5 - 2ish volts on all the io pins could be.. Fried prop?· Its a pretty simple board, similar to the schematic for a prop proto board.. The first one i soldered up worked fine.. Wierd thign is i was·even more carefully when soldering this one.. It seems to download and detect the prop fine from the propller tool. I can even write the program to ram(f10) or so it seems(not getting correct voltages out of the chip). But if i try write it to the eprom (f11) it gives me an error. ive checked the Smile out of the board all seems fine no solder bridges etc all resistors in check...getting·3.28v on vdd... ·anyway i thought id toss it out see if anyone had any insight.


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Comments

  • CannibalRoboticsCannibalRobotics Posts: 535
    edited 2009-02-26 03:18
    On the first attempt, populate the board in stages.
    I've learned that the next step after ohming out the board as well as you can on ground and power is to make sure all data paths do not have a short to either. Next, install the regulators and power up. Look at current, if it's high then turn off and start over. If current seems right, (very LOW) then put a pulldown resistor (1K ohm) somewhere on the output side of power path and check all of the power pads. I've used a resistor actually tied to the tip of the probe from the VOM and ground.
    Jim-

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  • s2jesses2jesse Posts: 62
    edited 2009-02-26 04:14
    thanks for the tips ill give it a shot
  • s2jesses2jesse Posts: 62
    edited 2009-02-28 04:15
    man i dont know what to do next... ive wasted probably about 100+ bux on boards and props...

    I·just built from scratch another board. I did it incementally...

    first thing i tired was just the prop by itself. no crystal no eprom etc just the vreg and checked it im geting 3.28 volts at the vdd and vss pins of the prop.... prop tool detects the propeller fine.. even downloads code into it it seems... however again even with this second board im getting like 1.5ish volts out of all the i/o pins.. i wrote a litlte test blinker which will slowly pulse a pin. it downloads if i dont try two write it to epromm but it doesnt seem·toggle the pin it just puts out a·constant 1.5ish out of all pins.. theres no shorts and current draw seems normal.. There has to be something im totally missing..· i built 3 boards.. first one pretty much works perfectly... these second two are doing the same thing.. they are all from the same batch of pcbs and same parts,·im about to cry [noparse]:)[/noparse]

    so at this piont i have a very cleanly soldered very quick short solder times on each pin.· prop, eprom, vregulator, xtal and 10k resistor. i left caps out for now.

    I dont know what to do next.[noparse]:([/noparse]




    Post Edited (s2jesse) : 2/28/2009 4:21:44 AM GMT
  • PropabilityPropability Posts: 142
    edited 2009-02-28 05:09
    Don't know where you are located but sometimes it may help to have a second set of eyes looking at what you have done. Maybe there is a 'prophead' in your area. Just spent a 'few' hours myself working on why something wasn't right but it was just software not hardware.
  • s2jesses2jesse Posts: 62
    edited 2009-02-28 05:42
    think i randomly found it ill post in a bit just fun what it is if its it [noparse]:)[/noparse]
  • s2jesses2jesse Posts: 62
    edited 2009-02-28 20:42
    i think maybe its the flux conducting some small current..·how do you clean it properly this is a tiny board with all smd parts
    ·
  • KokovecKokovec Posts: 14
    edited 2009-02-28 21:07
    Make sure that you don't have any excessive noise on the voltage rails.
    Try placing a 1uF cap across the Prop voltage pins.
  • s2jesses2jesse Posts: 62
    edited 2009-02-28 21:14
    i have caps everywhere.. i really think its the flux cause it will work then ill solder another small component on using flux and it wont work again then later after more soldering , cleanig and burning off exess flux it works ... i did a test and put a little flux on a my desk and checked it with a multimeter even when it dried it was like 100k ohm resistnace
  • KokovecKokovec Posts: 14
    edited 2009-02-28 22:17
    That's strange. Flux is usually non-conductive when it's dry.
  • mctriviamctrivia Posts: 3,772
    edited 2009-02-28 22:20
    isopropel alcohol and a brush

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    Need to make your prop design easier or secure? Get a PropMod $50CAN has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module.
  • mctriviamctrivia Posts: 3,772
    edited 2009-02-28 22:28
    but 100k should not effect voltage.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Need to make your prop design easier or secure? Get a PropMod $50CAN has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module.
  • s2jesses2jesse Posts: 62
    edited 2009-02-28 23:42
    i have everythign packed very tightly on this board so any conducting flux is allowing small currents to flow to random pins·... im almost positive now because 2 of the boards started wroking after i really cleaned them well with one of those cans of electonic board cleaner and let it dry very well.

    ·
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