GENERAL RULES IN TROUBLESHOOTING

[marcialnasi]

  Some of my rules of troubleshooting

1.  Safety first - know the hazards associated with the equipment you
    are troubleshooting.  Take all safety precautions.  Expect the
    unexpected.  Take your time.

2.  Always think 'what if'. This applies both to the analytic procedures
    as well as to precautions with respect to probing the equipment.
    When probing, insulate all but the last 1/8" of the probe tip to
    prevent costly shorts.   (If I had a nickel for every time I have been
    screwed not following this advice...)

3.  Learn from your mistakes.  We all make mistakes - some of them can
    be quite costly.  A simple problem can turn into an expensive one
    due to a slip of the probe or being over eager to try something before
    thinking it through.  While stating that your experience in these
    endeavors is measured by the number of scars you have may be stretching
    the point, expect to screwup - we all can point to that disaster
    due to inexperience or carelessness.  Just make it a point not to
    make the same mistake again.

4.  Don't start with the electronic test equipment, start with some analytical
    thinking.  Many problems associated with consumer electronic equipment
    do not require a schematic (though one may be useful).  The majority
    of problems with VCRs, CD players, tape decks, and answering machines,
    are mechanical and can be dealt with using nothing more than a good
    set of precision hand tools; some alcohol, degreaser, contact cleaner,
    light oil and grease; and your powers of observation (and a little
    experience).  Your built in senses and that stuff between your ears
    represents the most important test equipment you have.

5.  If you get stuck, sleep on it.  Sometimes, just letting the problem
    bounce around in your head will lead to a different more successful
    approach or solution.  Don't work when you are really tired - it is both
    dangerous and mostly non-productive (or possibly destructive).

6.  Many problems have simple solutions.  Don't immediately assume that
    your problem is some combination of esoteric complex convoluted
    failures.  For a TV, it may just be a bad connection or failed diode.
    For a VCR, it may just be a bad belt or idler tire - or an experiment
    in rock placement by your 3-year old.  For a CD player, a dirty lens
    or need for lubrication.  Try to remember that the problems with the most
    catastrophic impact on operation - a dead TV or a VCR that eats tapes -
    usually have the simplest solutions.  The kind of problems we would like
    to avoid at all costs are the ones that are intermittent or difficult
    to reproduce: subtle color noise, the occasional interference, or the
    dreaded horizontal output transistor blowing out every 3 months syndrome.

7.  Whenever possible, try to substitute a working unit.  With modular
    systems like component stereos and computers, narrowing down a
    problem to a single unit should be the first priority.  This is usually
    safe to do in such cases and will quickly identify which unit needs work.
    This same principle applies at the electronic or mechanical parts level.
    Note that there is the possibility of damaging the known good part by
    putting it into a non-working device or vice versa.   This risk is most
    likely with the power circuitry in amplifiers, TVs and monitors, power
    supplies, etc.  With appropriate precautions (like the series light bulb)
    the risk can be minimized.

8.  Don't blindly trust your instruments.  If your get readings that don't
    make sense, you may be using your equipment in a way which is confusing it.
    DMMs are not good at checking semiconductors in-circuit or the power
    transistor you are testing may have a built in damper diode and/or base
    resistor.   Your scope may be picking up interference which is swamping
    the low level signal you are searching for (TVs and Monitors, or low
    level circuits in VCRs and CD players).  Your frequency counter may be
    double triggering due to noise or imperfect signal shape.

9.  Realize that coincidences do happen but are relatively rare.  Usually,
    there is a common cause.  For example, if a TV has no vertical deflection
    and no picture, it is much more likely that a common power supply output
    has failed than for parts in both the deflection and video subsystems to
    be bad.  In other words, first look for a common root cause rather than
    trying to locate bad parts in separate circuits.

    Exceptions include lightning, power surge, dropped, water, or previous
    repair person damaged equipment.  However, multiple electrolytic capacitors
    in older equipment may be degrading resulting in failures of unrelated
    circuits.  Determine if all the problems you are troubleshooting have just
    appeared - see below. It is very common to be given a device to repair
    which has now died totally but prior to this had some behavior which you
    consider marginal but that was not noticed by the owner.

10. Confirm the problem before diving into the repair.  It is amazing how
    many complaints turn out to be impossible to reproduce or are simple
    cockpit error.  It also makes sense to identify exactly what is and is not
    working so that you will know whether some fault that just appeared
    was actually a preexisting problem or was caused by your poking.  Try to
    get as much information as possible about the problem from the owner.  If
    you are the owner, try to reconstruct the exact sequence of events that led
    to the failure.  For example, did the TV just not work when turned on or
    were there some preliminary symptoms like a jittery or squished picture
    prior to total failure?  Did the problem come and go before finally staying
    bad for good?

11. Get used to the idea of working without a schematic.  While service info
    for TVs is nearly always available in the form of Sams' Photofacts, this
    is hardly ever true of other types of equipment.  Sams VCRfacts exist
    for less than 10 percent of VCR models and only the older ones include
    anything beyond (obvious) mechanical information.  While a service
    manual may be available from the manufacturer of your equipment or another
    Sams-like source, it may not include the information you really need.
    Furthermore, there may be no way to justify the cost for a one time repair.
    With a basic understanding of how the equipment works, many problems can be
    dealt with without a schematic.  Not every one but quite a few.

12. Whenever working on precision equipment, make copious notes and diagrams.
    You will be eternally grateful when the time comes to reassemble the unit.
    Most connectors are keyed against incorrect insertion or interchange
    of cables, but not always.  Apparently identical screws may be of differing
    lengths or have slightly different thread types.  Little parts may fit in
    more than one place or orientation.  Etc.  Etc.

13. Pill bottles, film canisters, and plastic ice cube trays come in handy for
    sorting and storing screws and other small parts after disassembly.  This
    is particularly true if you have repairs on multiple pieces of equipment
    under way simultaneously.

14. Select a work area which is wide open, well lighted, and where dropped
    parts can be located - not on a deep pile shag rug.  The best location will
    also be relatively dust free and allow you to suspend your troubleshooting
    to eat or sleep or think without having to pile everything into a cardboard
    box for storage.

15. Understand the risk of ESD - Electro-Static Discharge.  Some components
    (like ICs) in solid state electronic devices are vulnerable to ESD.  There
    is no need to go overboard but taking reasonable precautions such as
    getting into the habit of touching a **safe** ground point first.

    WARNING: even with an isolation transformer, a live chassis should **not**
    be considered a safe ground point.  This applies mostly to TVs, computer
    and video monitors, some AC operated strobe lights, and other line
    connected devices.  You shouldn't be touching components with the device
    powered and plugged in (at least, not until you really know what you are
    doing!).  Once unplugged, sheet metal shields or other ground points
    should be safe and effective.

[marcialnasi]

   Some quick tips or rules of thumb

* Problems that are erratic or intermittent - that come and go suddenly -
  are almost always due to bad connections - cold solder joints or internal
  or external connectors that need to be cleaned and reseated.  It is amazing
  what a large percentage of common problems fall into the category.

* Problems that change gradually - usually they decrease or disappear - as
  the equipment warms up are often due to dried up electrolytic capacitors.

* Problems that result in a totally dead unit or affect multiple functions
  are generally power supply related.  These are usually easy to fix.

* Catastrophic failures often result in burnt, scorched, cracked, exploded,
  or melted components, or similar catastrophic consequences.  Use your senses
  of sight and smell for the preliminary search for such evidence.

* Listen for signs of arcing or corona - snapping or sizzling sounds.  A
  component on the brink of failing due to overheating may provide similar
  audible clues.

* Many CD player problems are mechanical - dirty lens, worn or oily drawer
  belts, dirt/gummed up grease on sled tracks/gears, bad/partially shorted
  spindle or sled motor.  Power problems with portables seem to be common as
  well.  No matter what the symptoms, always make it a habit to clean the lens
  first - many peculiar failure modes are simply due to a dirty lens.  Actual
  laser failure is relatively uncommon despite what the typical service shop
  may claim.  CD players are also remarkably robust.  Optical alignment should
  never be needed under normal conditions of operation.

* TV and monitor problems are very often power supply or deflection related.
  These tend to have obvious causes - blown posistor, rectifier diodes, filter
  capacitor, HOT, or chopper.  Flyback with shorted windings or shorts between
  windings or in the voltage multiplier (if used) or screen/focus divider
  network are also common.  Where the HOT or chopper is involved, operation
  should be observed after the repair as components in the vicinity may cause
  the new parts to fail.  HOTs should generally not run hot.  If they do,
  check for weak drive, exfess B+, etc.

* Microwave oven problems are almost always power related.  Faulty components
  in the microwave generator - magnetron, HV diode, HV capacitor, HV
  transformer - are relatively easy to identify.  Sometimes, components on
  the primary side can cause baffling symptoms like the misaligned interlock
  switches that blow fuses or the weak triac that causes the oven to blow the
  main fuse only when the cycle *ends*.  Control problems may be due to a
  spill in the touchpad or failure due to a power surge.

* Ink-jet printers are extremely reliable electrically.  Look for simple
  problems such as caked ink in the 'service station' area, misaligned
  print-head contacts, or a nearly empty cartridge when erratic printing
  problems develop.

* Laser printers tend to develop problems in the fuser, scanner, or power
  control modules.  These are often simple like a burned out lamp, bad
  motor, or bad connections.
* Problems with audio tape decks like VCRs are mostly mechanical.  Similar
  solutions apply.  Where one channel is out, suspect a broken wire at the
  tape head before a bad chip.

* Telephone line connected equipment like modems and phones are susceptible
  to phone like surges.  Where a device seems to respond to user commands but
  does not dial or pickup, suspect a blown part near the phone line connector.

* Sam's Magic Spit(tm).  This approach - using a moistened finger to probe
  LOW VOLTAGE CIRCUITS has come to the rescue many times.  Touching various
  parts of a circuit from the solder side of the board in an attempt to evoke
  some sort of response can work wonders.  Once an suspect area has been
  identified, use a metal probe or nail to narrow it down to a specific pin.

  The reason this works is that the reduced resistance of your moist skin and
  your body capacitance will change the signal shape and/or introduce some
  slight signal of its own.

  - Logic circuits - marginal timing or signal levels will result in a
    dramatic change in behavior with a slight 'body' load.  It has been
    possible to locate a race condition or glitchy signal on a 305 pin PGA
    chip using this approach in less time than it would have taken to roll
    the logic analyzer over to the system under test.  Signals which have
    proper levels and timing are gnerally remarkebly immune to this sort of
    torture.

  - Analog circuits - behavior can again be altered.  In the case of audio
    amps, probing with a finger is just as effective as the use of a signal
    injector - which is what you are doing - and the equipment is always
    handy.  By evoking hum, buzz, clicks, and pops, locating the live or dead
    parts of a circuit is rapid and effective.

  - Unknown circuits - where no schematics are available, it may be possible
    to get the device to do something or locate an area that is sensitive to
    probing.  The function of a section of circuitry can often be identified
    by observing the effects of touching the components in that area.

    For example, I was able to quickly identify the trigger transistor of in a
    wireless door bell by using my finger to locate the point that caused the
    chimes to sound.  This quickly confirmed that the problem was in the RF
    front end or decoder and not the audio circuitry.

  - Bad bypass capacitors - touching the power/signal side of a good bypass cap
    should result in little or no effect.  However, a cap with high ESR and/or
    reduced uF will not be doing its job bypassing the pickup from your finger
    to ground - there will be a dramatic effect in audio or video systems.

  Don't get carried away - too much moisture may have unforeseen consequences.

  Depending on the condition of your skin, a tingle may be felt even on low
  voltage circuits under the right conditions.  However, this is pretty safe
  for most battery operated devices, TTL/CMOS logic, audio equipment (not high
  power amps), CD players, VCRs (not switching power supply), etc.

  WARNING: Make sure you do this only with LOW VOLTAGE circuitry.  You can
  easily fry yourself if you attempt to troubleshoot your TV, computer monitor,
  photoflash, or microwave oven in this manner!

[Born2BeWired]

If it ain't broken, don't fix it!
 

[_basura_man()]

pag nagfafailure analysis ako sinisira ko talaga yung unit para alam ko kung saan nagfail,reverse engineering hehehe.

[Born2BeWired]

pag nagfafailure analysis ako sinisira ko talaga yung unit para alam ko kung saan nagfail,reverse engineering hehehe.

Kids, don't try this at home.

Seriously, at times, if you want to get to the bottom of something, you may have to destroy it. I also do this once in a while. It is sensible sa production line. Pero sa "out-patient" repair jobs, I guess this will be a very bad thing to do.

[spoco]

 Noted po mga masters!! thank you po sa tips!!

[_basura_man()]

Pero sa "out-patient" repair jobs, I guess this will be a very bad thing to do. 

madami kasi akong sisiraing unit ngayon,up to now di ko pa din alam kung saan ang sira 

[comtronixs]

dapat alam mo kung papano gumagana ang isang unit... may idea ka sa section..  and marunong kang mag analyze ng flow ng circuit hehehe

[_basura_man()]

dapat alam mo kung papano gumagana ang isang unit... may idea ka sa section..  and marunong kang mag analyze ng flow ng circuit hehehe

off topic:

namaster ko na ang bawat section(dito kasi nabuild yung first proto hanggang namasspro,the rest factory na),ok lang kapag iisa ang pyesa,pero in realworld to become manufacturability,we need to have at least three alternate part para sa prime part,the sad story here is kapag nagpalit kana ng pyesa,ayun dun na lumalabas ang problems(halimbawa ang optoisolator na ginagamit sa UART,ok sa isang part pero sa ibang pyesa ayaw na hehehe),halos parehong specs,gagana minsan,minsan hindi na,nagiging marginal,kahit na nasimulate na sa MonteCarlo analysis na alam na ok sa worst case scenario,kapag napalitan na ayun dun lumalabas na ang problema  .
Another problem is kung iyon nalang talaga ang pyesa na available(katulad nitong nangyari sa Japan,naapektuhan masyado ang mga E-caps kasi karamihan ng capacitor players ay Japanese,hirap maghanap ng alternates na ayoko kumuha sa Taiwan or China to meet the original specs).Hirap din ako gumawa ng root cause analysis kasi we need proofs and testing to prove na yun talaga ang sira,isa pang problem even the original designer di rin alam kung bakit nagfafail sa ibang pyesa 
Kaya ginagawa ko sinisira ko to replicate the problems experienced by customer