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Looking For Clues To Resolve Electrical Problem — Parallax Forums

Looking For Clues To Resolve Electrical Problem

idbruceidbruce Posts: 6,197
edited 2011-04-13 06:17 in Propeller 1
Hello Everyone

I realize this is probably pretty useless, but I am looking for a few fresh ideas.

I have an intermittment electrical problem :( It appears to be a brownout, but I imagine that it could also be a short or open circuit. A project description and a problem description are included below.
Brief Project Description
The project is an automated piece of machinery and it includes, two propeller proto boards, eight stepper drivers, numerous pushbutton switches, 2 X 20 LCD screen, standard hobby servo, and numerous miscellaneous items. All the electronics are mounted inside or to the cover of a NEMA Type 1 4X4X24 enclosure. A 7.5VDC 1.4A wall wart supplies power to the two proto boards, LCD screen, and servo. Additionally, there are five different voltages inside the enclosure, which are, 3VDC, 5VDC, 7VDC, 12VDC, and 50VDC.

Brief Problem Description
Everything was working fine until a couple days ago when one of my cables began hitting a cooling fan. After removing the cover and rerouting the cable, that is when all my trouble began. Since then, the proto boards are having trouble booting, and the LCD screen flickers or doesn't light up at all. I have tried to find any obvious shorts, opens, pinched wires, etc... but so far, I have been unable to find the guilty culprit. I additionally switched the power supply with an exact spare duplicate. It is worth noting that the problem disappears when the enclosure cover is removed and the cables attached to the cover are extended away from the main enclosure. Another item worth noting is that it affects both proto boards instead of just one.
I realize it is virtually impossible to troubeshoot this problem without being here to inspect the project, but I am just looking for a few fresh ideas from the information that I have provided. Any input will be greatly appreciated.

Bruce

Comments

  • Graham StablerGraham Stabler Posts: 2,510
    edited 2011-04-12 16:06
    When you say the LCD does not light up at all, does this mean the back-light isn't even operating? That would suggest a PSU issue. You should probably just start unplugging things, start with just the proto-board, then add the lcd etc.

    Graham
  • lonesocklonesock Posts: 917
    edited 2011-04-12 16:09
    Shots in the dark:
    * are your grounds all tied together?
    * if not, is it possible that the cover, when in place, is connecting 2 ground planes better left separate?
    * with the cover off, can you re-create the problem by jumpering any 2 of the sockets used to mount the cover?

    Jonathan
  • idbruceidbruce Posts: 6,197
    edited 2011-04-12 16:27
    @Graham - Yea, sometimes the backlight does not come on at all or it struggles back and forth. I agree that it is a power supply issue, however, unplugging and replugging everything would be unrealistic for testing considering the cover. I personally suspect, that either the 3.3VDC, 5VDC, or 7.5VDC is going to ground and causing a brownout. My next intention is to extend two wires from the enclosure and perform a load test with the cover off and then on.

    @Jonathan - The 3.3VDC, 5VDC, and 7.5VDC have a common ground plane, the 50VDC and 12VDC are completely seperate. The cover is attached to the same ground plane as the protoboards.

    Thanks for your replies
  • kwinnkwinn Posts: 8,697
    edited 2011-04-12 17:43
    A prop, 8 channel adc chip, sd card, and a bit of software make a great troubleshooting tool.
  • idbruceidbruce Posts: 6,197
    edited 2011-04-12 17:49
    @kwin - And your response helps me how?
  • Mike GMike G Posts: 2,702
    edited 2011-04-12 18:54
    Idbruce, hard to say... I have no visual...
    It is worth noting that the problem disappears when the enclosure cover is removed and the cables attached to the cover are extended away from the main enclosure.
    Sounds like a grounding issue. Again I have no frame of reference of what this thing looks like or what the cables carry. Break out your DMM and start looking for an unexpected electrical potential. I'd start with the case then cables.
  • idbruceidbruce Posts: 6,197
    edited 2011-04-12 19:19
    @Mike G - Thanks for responding. I am an electrician by trade and this is kind of like people asking me to troubleshoot their electrical problems by phone.

    I am still formulating my plan of attack to find this problem. However, it definitely has nothing to do with the LCD, which has been unplugged and the problem still remained.

    I also forgot to mention that there is also 24VDC in the enclosure.

    As I previously mentioned, I intend to perform a load test on the power supply. Additionally, the 50VDC, 24VDC, and 12VDC are easily unplugged with banana jacks from the exterior of the enclosure, which should limit the search parameters.
  • kwinnkwinn Posts: 8,697
    edited 2011-04-12 20:07
    idbruce wrote: »
    @kwin - And your response helps me how?

    You build equipment using the prop and other electronics so assembling a prop with an adc to monitor and record analog voltages and digital signals should not be a problem. The obex has objects for reading the adc and logging data to sd cards. With some spin to tie the objects together you can narrow down or possibly pinpoint the problem. With battery backup the sd card may not even be needed. I have a serial data logger that was assembled for a very intermittent problem. It started as a kluge, and has gotten worse as things were added but it has saved me many hours of troubleshooting time.
  • kwinnkwinn Posts: 8,697
    edited 2011-04-12 20:42
    idbruce wrote: »

    Everything was working fine until a couple days ago when one of my cables began hitting a cooling fan. After removing the cover and rerouting the cable, that is when all my trouble began.
    This would be a good area to start. Possibly a wire with the copper conductors broken inside the insulation but making contact unless disturbed by being moved or from vibration. Try flexing and gently pulling on the wires in that area. The connectors or connection points are the other stress points on cables and should also be checked. Most often I find breaks rather than shorts here but both are possible.
    Since then, the proto boards are having trouble booting, and the LCD screen flickers or doesn't light up at all.
    Do all these boards have a common power supply? Is the same unregulated input voltage powering all these items?
    . I have tried to find any obvious shorts, opens, pinched wires, etc... but so far, I have been unable to find the guilty culprit. I additionally switched the power supply with an exact spare duplicate. It is worth noting that the problem disappears when the enclosure cover is removed and the cables attached to the cover are extended away from the main enclosure. Another item worth noting is that it affects both proto boards instead of just one.
    These are all indications that it is a broken wire kept in intermittent contact by the surrounding insulation. Any flexing or vibration will cause a momentary break. Check any power and ground wires that are common to the LCD and protoboards first, then signal wires if those are good.
  • prof_brainoprof_braino Posts: 4,313
    edited 2011-04-13 06:17
    idbruce wrote: »
    one of my cables began hitting a cooling fan. After removing the cover and rerouting the cable, that is when all my trouble began.

    the problem disappears when the enclosure cover is removed and the cables attached to the cover are extended away from the main enclosure.

    1) What caused the cable to start hitting the fan?
    2) The cover removed and wires straightened:
    3) is the cover electrically isolated from the enclosure or is it grounded?
    4) can you add a jumper to duplicate each wire in turn to see it it affects anything?

    In my case, a stray mounting screw fell beneath the board and was wedged between the solderside and the mounting post. It did not fall out unitl I removed the board.
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