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Sci.Electronics.Basics -> troubleshooting method for micro-controller board ?
There are 103 messages in this thread.
You are currently looking at messages 20 to 40.
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Author: robbDate: 17:14 06-11-07
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"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in
message news:4730D28D.30812E35@hotmail.com...
>
>
> robb wrote:
>
> > Thanks Tom,
> > i really appreciate any comments and help
> >
> > i unsoldered one of the L298 and it has no shorts so now the
next
> > then i will do a trace of the 5V lines until i can learn
> > something usefull about the interconnections.
> >
> > i hate working blind and re-tracing things when i could just
look
> > on a schemat.
>
> I suggest you remove the 5V voltage regulator.. That'll remove
the connection
> from the power supply to the digital section and NOW check for
a short across
> the 5V and ground.
>
> The regulator chip may have an internal short you see and it is
at least easy to
> remove from the pcb.
>
> Graham
>
ah ha the L387, i only know this because i looked through the
datasheets i downloaded for all the ICs until i crossed the L387
(5v regulator)
well that just makes too much sense ... start with 5v related ICs
first, i tried to trace the transformer output but had not made
it that far yet
situated next to the L298s (hmm big surprise) i guess i should
have surmised this since all the power regulation for stepper
motors and such is bolted to that heat sink.
i will report results when done, hopefully find some joy
thanks,
robb
that will be next Graham.
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Author: JamieDate: 18:29 06-11-07
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John Tserkezis wrote:
> Jamie wrote:
>
>> You may want to look at capacitors. Especially
>> tantalums, they short very nicely many times leaving
>> nothing but ash.
>
>
> Or worse. I find many times they go short with no visible evidence at
> all.
>
> I was pushing the boss for a thermal imaging camera for this very
> purpose, just apply power till things get warm enough in the right spots
> to tell what is shorted.
>
> I thought I had put forward a very good argument for saving time during
> repairs that are relatively rare where we were, but he still sadly
> didn't go for it... Oh well, I tried.
>
I use a IR Laser guided Temp probe. that works nicely.
--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
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Author: sparkyDate: 21:03 06-11-07
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On Nov 5, 5:14 pm, "robb" <s...@where.on.net> wrote:
> i have a micro-controller board with 3 big 40DIP ICs, 10 or so 16
> DIP support ICs. with 32v/8v/5v transformer supply that connects
> to two bridge rectifiers {32v, 8v}a fuse links sit between
> transformer and rectifiers, no schematic.
>
> i believe the 32v shorted with 5V line and it blew one fuse
> link. the fuse link was replaced with same and when powered all
> three fuses blown.
>
> So....where does one start to diagnose such a *big* problem ?
>
> .
> Only thing working is transformer outputs and it seems like i get
> continuity hits everywhere i check
> the board was built about 1985 (no SMT) it is about 14" x 5" has
> 3 x 40 DIP ICs and 10 or so 16 DIP support ICs, handful of
> transistors many resistors,diodes etc,
>
> ideas and help would be greatly appreciated :)
> robb
A couple years ago I had a PCB with about 30 TTL chips on it that the
5 volt line had been shorted to the 12 volt line. I started out
removing the chips carefully but after I had taken out around 10 that
were shorted I just made a mass extraction and replaced them all.
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Author: James SweetDate: 01:09 07-11-07
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"robb" <some@where.on.net> wrote in message
news:13j1g43faippaa9@corp.supernews.com...
>
> "Tom2000" <abuse@earthlink.net> wrote in message
> news:hjq0j3ttim1dq12u961artuai80l3ou2cm@4ax.com...
>> On Tue, 6 Nov 2007 07:34:53 -0500, "robb" <some@where.on.net>
> wrote:
>>
>>
>> >
>> >there was no obvious visual evidence of any smoked parts that
> i
>> >could see , only the middle busman fuse was blown after the
> short
>> >
>> >and that seemed to be related to power going to the L298
>> >
>> >thanks for all the help,
>> >robb
>> >
>>
>> Tough problem with all the ICs soldered in.
>>
>> Chances are that the 32 volt supply is only used for the L298s,
> as you
>> suggest. It also appears that you can unsolder these without
> damaging
>> any other parts on the board. (Even if you have to cut them
> out,
>> they're still available and easy to replace.)
>>
>> If your short doesn't disappear after pulling the 298s, try
>> unsoldering any of the caps near those chips.
>>
>> Leave unsoldering any ICs as your very last resort.
>>
>> I'm now bowing out of this discussion and leaving it to the
> experts.
>>
>
> Thanks Tom,
> i really appreciate any comments and help
>
> i unsoldered one of the L298 and it has no shorts so now the next
> then i will do a trace of the 5V lines until i can learn
> something usefull about the interconnections.
>
> i hate working blind and re-tracing things when i could just look
> on a schemat.
>
> so thank you ,
> robb
>
>
While normally a very bad idea, a trick I've used with success once or twice
was to bypass the fuse and feed a few volts with reasonably high current
capability into the thing while feeling what gets hot. This needs to be used
with great care though, you can burn traces off the board or in some cases
do further damage, but if 32V got put into the 5V rail, you've got little to
lose in trying.
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Author: Tom2000Date: 01:34 07-11-07
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On Tue, 6 Nov 2007 13:03:40 -0500, "Michael Kennedy"
<Mikek400@remthis.comcast.net> wrote:
>
>"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
>news:47307813.81A767B1@hotmail.com...
>>
>>
>> Tom2000 wrote:
>>
>>> Leave unsoldering any ICs as your very last resort.
>>
>> Funny. That's where I'd START !
>>
>> Graham
>>
>
>He probably means to avoid damaging them by poor soldering skills, but who
>knows.
>
Yep. I'm projecting my own skills (or lack thereof, when it comes
to desoldering ICs) to the op. :-)
Tom
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Author: Arfa DailyDate: 04:20 07-11-07
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"robb" <some@where.on.net> wrote in message
news:13j1g43faippaa9@corp.supernews.com...
>
> "Tom2000" <abuse@earthlink.net> wrote in message
> news:hjq0j3ttim1dq12u961artuai80l3ou2cm@4ax.com...
>> On Tue, 6 Nov 2007 07:34:53 -0500, "robb" <some@where.on.net>
> wrote:
>>
>>
>> >
>> >there was no obvious visual evidence of any smoked parts that
> i
>> >could see , only the middle busman fuse was blown after the
> short
>> >
>> >and that seemed to be related to power going to the L298
>> >
>> >thanks for all the help,
>> >robb
>> >
>>
>> Tough problem with all the ICs soldered in.
>>
>> Chances are that the 32 volt supply is only used for the L298s,
> as you
>> suggest. It also appears that you can unsolder these without
> damaging
>> any other parts on the board. (Even if you have to cut them
> out,
>> they're still available and easy to replace.)
>>
>> If your short doesn't disappear after pulling the 298s, try
>> unsoldering any of the caps near those chips.
>>
>> Leave unsoldering any ICs as your very last resort.
>>
>> I'm now bowing out of this discussion and leaving it to the
> experts.
>>
>
> Thanks Tom,
> i really appreciate any comments and help
>
> i unsoldered one of the L298 and it has no shorts so now the next
> then i will do a trace of the 5V lines until i can learn
> something usefull about the interconnections.
>
> i hate working blind and re-tracing things when i could just look
> on a schemat.
>
> so thank you ,
> robb
>
>
If you have a photocopier or flatbed scanner available to you, and the board
is not too big, I sometimes find it helpful, where no schematics are
available, to scan and print out the underside of the board, then take a few
minutes to draw on an overlay of the major components. Coloured felt tip
pens or highlighters can then be used to trace round critical signal and
power tracks. Makes it a lot easier then when metering for the problem. I
have found a digital ESR meter - such as the Dick Smith - which is capable
of accurately measuring and displaying very low ohms, can be useful for
tracking down dead shorts on rails that go all over a board.
Arfa
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Author: Arfa DailyDate: 04:27 07-11-07
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"James Sweet" <jamessweet@hotmail.com> wrote in message
news:Y8RXi.2719$bm.1189@trndny08...
>
>>
>> First thing you should do is check for shorts across the various power
>> rails. If a short is found, using a sufficient resolution low-ohms
>> meter might let you located the offending component. Sometimes the
>> bypass caps can go short on order gear like this, replace them all if
>> needed.
>>
>> Dave.
>>
>
> Second that on the caps, I recently repaired a Volkswagen ECU that had a
> shorted electrolytic capacitor, I think that was the first time I'd seen a
> lytic shorted, regulator was getting hot which clued me in. I've found
> shorted tantalums in several things.
>
Thirded (thirded ?!) on the caps. A few years back, Panasonic used to use
some purple 10u's in everything they made, and they were swines for going
short. Often used as decouplers around signal processing ICs, so you can
imagine what it was like with whole signal processing stages stopping
working, because a cap on an IC pin, decoupling some internal bias rail or
whatever, had failed ...
These days, I see a lot of shorted electrolytics of all manufacture, on
supply rails in amps and home cinema rigs, and so on.
Arfa
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Author: robbDate: 06:20 07-11-07
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"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:DrfYi.36284$9Y3.746@newsfe1-win.ntli.net...
>
> "robb" <some@where.on.net> wrote in message
> news:13j1g43faippaa9@corp.supernews.com...
> >
> > "Tom2000" <abuse@earthlink.net> wrote in message
> > news:hjq0j3ttim1dq12u961artuai80l3ou2cm@4ax.com...
> >> On Tue, 6 Nov 2007 07:34:53 -0500, "robb"
<some@where.on.net>
> > wrote:
> >>
> >>
> >> >
> >> >there was no obvious visual evidence of any smoked parts
that
> > i
> >> >could see , only the middle busman fuse was blown after the
> > short
> >> >
> >> >and that seemed to be related to power going to the L298
> >> >
> >> >thanks for all the help,
> >> >robb
> >> >
> >>
> >> Tough problem with all the ICs soldered in.
> >>
> >> Chances are that the 32 volt supply is only used for the
L298s,
> > as you
> >> suggest. It also appears that you can unsolder these
without
> > damaging
> >> any other parts on the board. (Even if you have to cut them
> > out,
> >> they're still available and easy to replace.)
> >>
> >> If your short doesn't disappear after pulling the 298s, try
> >> unsoldering any of the caps near those chips.
> >>
> >> Leave unsoldering any ICs as your very last resort.
> >>
> >> I'm now bowing out of this discussion and leaving it to the
> > experts.
> >>
> >
> > Thanks Tom,
> > i really appreciate any comments and help
> >
> > i unsoldered one of the L298 and it has no shorts so now the
next
> > then i will do a trace of the 5V lines until i can learn
> > something usefull about the interconnections.
> >
> > i hate working blind and re-tracing things when i could just
look
> > on a schemat.
> >
> > so thank you ,
> > robb
> >
> >
> If you have a photocopier or flatbed scanner available to you,
and the board
> is not too big, I sometimes find it helpful, where no
schematics are
> available, to scan and print out the underside of the board,
then take a few
> minutes to draw on an overlay of the major components. Coloured
felt tip
> pens or highlighters can then be used to trace round critical
signal and
> power tracks. Makes it a lot easier then when metering for the
problem. I
> have found a digital ESR meter - such as the Dick Smith - which
is capable
> of accurately measuring and displaying very low ohms, can be
useful for
> tracking down dead shorts on rails that go all over a board.
>
> Arfa
>
thanks Arfa,
for helpful ideas.
i used a slightly cruder method last night.
i used a green fine tip sharpie to draw directly on top of the
PCB resist 5V tracks because they zig-zag back and forth accross
the board front to back and i kept loosing track (pun intended)
of where i was testing
the green sharpie about same color as resist shows up as shiny
line an dnot to unsightly
i like your idea as it will help keep track of test points tried
as i can record the test values next to points
thanks again for the ideas/help
robb
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Author: robbDate: 07:46 07-11-07
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"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in
message news:4730D28D.30812E35@hotmail.com...
>
>
> robb wrote:
>
> > Thanks Tom,
> > i really appreciate any comments and help
> >
> > i unsoldered one of the L298 and it has no shorts so now the
next
> > then i will do a trace of the 5V lines until i can learn
> > something usefull about the interconnections.
> >
> > i hate working blind and re-tracing things when i could just
look
> > on a schemat.
>
> I suggest you remove the 5V voltage regulator.. That'll remove
the connection
> from the power supply to the digital section and NOW check for
a short across
> the 5V and ground.
>
> The regulator chip may have an internal short you see and it is
at least easy to
> remove from the pcb.
>
> Graham
>
hello graham,
no shorts on any of the power regulator chips 5v L387 or the
L298s
and still get 76 ohm continuity between 5v an 0v ref.
there is only one place i get a 619 ohm continuity check 5v-0v
test but every where else is 69/63/73
thanks for help graham iguess i just need to keep looking for the
bad components
my de-soldering bulb / iron makes clean quick work of it.
robb
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On Nov 7, 7:46 am, "robb" <s...@where.on.net> wrote:
> no shorts on any of the power regulator chips 5v L387 or the
> L298s
>
> and still get 76 ohm continuity between 5v an 0v ref.
Ummm, what's wrong with that? I = E/R: 66mA. This
(static) current isn't blowing the fuse.
TM
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Author: robbDate: 12:57 07-11-07
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<tonym924@gmail.com> wrote in message
news:1194453785.463668.239090@19g2000hsx.googlegroups.com...
> On Nov 7, 7:46 am, "robb" <s...@where.on.net> wrote:
> > no shorts on any of the power regulator chips 5v L387 or the
> > L298s
> >
> > and still get 76 ohm continuity between 5v an 0v ref.
>
> Ummm, what's wrong with that? I = E/R: 66mA. This
> (static) current isn't blowing the fuse.
>
> TM
>
oh yes the fuses blow.
ther were 3 bussman fuses on different lines and such and they
are all blown
right now i am trying to track down the short(S) so i ca do
better static tests on various components without removing and
then try and power the board back up and look for other problems
at least according to the advice i have recieved etc.
thanks for taking time to look and offer some help , i sorely
need it,
robb
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On Nov 7, 12:57 pm, "robb" <s...@where.on.net> wrote:
> <tonym...@gmail.com> wrote in message
>
> news:1194453785.463668.239090@19g2000hsx.googlegroups.com...> On Nov 7, 7:46 am,
"robb" <s...@where.on.net> wrote:
> > > no shorts on any of the power regulator chips 5v L387 or the
> > > L298s
>
> > > and still get 76 ohm continuity between 5v an 0v ref.
>
> > Ummm, what's wrong with that? I = E/R: 66mA. This
> > (static) current isn't blowing the fuse.
>
> > TM
>
> oh yes the fuses blow.
>
> ther were 3 bussman fuses on different lines and such and they
> are all blown
>
> right now i am trying to track down the short(S) so i ca do
> better static tests on various components without removing and
> then try and power the board back up and look for other problems
I wasn't denying that the fuses are blowing - I was pointing out that
76 ohms is not a short (for most any low voltage power supply), and
that the fuses aren't blowing due to that (not so low) resistance
across
5V.
What resistance do you get on the other rails?
TM
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Author: robbDate: 14:40 07-11-07
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<tonym924@gmail.com> wrote in message
news:1194462545.578813.284170@z9g2000hsf.googlegroups.com...
> On Nov 7, 12:57 pm, "robb" <s...@where.on.net> wrote:
> > <tonym...@gmail.com> wrote in message
> >
> > news:1194453785.463668.239090@19g2000hsx.googlegroups.com...>
On Nov 7, 7:46 am, "robb" <s...@where.on.net> wrote:
> > > > no shorts on any of the power regulator chips 5v L387 or
the
> > > > L298s
> >
> > > > and still get 76 ohm continuity between 5v an 0v ref.
> >
> > > Ummm, what's wrong with that? I = E/R: 66mA. This
> > > (static) current isn't blowing the fuse.
> >
> > > TM
> >
> > oh yes the fuses blow.
> >
> > ther were 3 bussman fuses on different lines and such and
they
> > are all blown
> >
> > right now i am trying to track down the short(S) so i ca do
> > better static tests on various components without removing
and
> > then try and power the board back up and look for other
problems
>
> I wasn't denying that the fuses are blowing - I was pointing
out that
> 76 ohms is not a short (for most any low voltage power supply),
and
> that the fuses aren't blowing due to that (not so low)
resistance
> across
> 5V.
>
> What resistance do you get on the other rails?
>
apologies, i did notintend to come across as snippity :(
i wasn't sure if i forgot to mention the fuses
i am a bit perturbed by this event and am not looking forward to
removing all ICs and then i have to worry with ROMs too
although i am an amateur i understand your point. but, i do not
realize the significance due to my lack of experience
so 73 Ohms is not a short where 0 Ohms would be
but my amateur question would be... is 73 Ohms good value between
5V and 0v reference ? i had presumed not good
thanks for your help and ideas,
robb
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On 7 Nov, 20:40, "robb" <s...@where.on.net> wrote:
...
>
> i am a bit perturbed by this event and am not looking forward to
> removing all ICs and then i have to worry with ROMs too
>
> although i am an amateur i understand your point. but, i do not
> realize the significance due to my lack of experience
>
> so 73 Ohms is not a short where 0 Ohms would be
> but my amateur question would be... is 73 Ohms good value between
> 5V and 0v reference ? i had presumed not good
>
As someone else pointed out, 73 ohms at 5V means a static draw of 5/73
= (about) 68 mA, which for a digital circuit sounds reasonable imho.
It is definitely not a short. What's the fuse rating on the 5V rail?
Regards
Francesco
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Author: bzDate: 15:22 07-11-07
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"robb" <some@where.on.net> wrote in news:13j1fghd5a5t9d7
@corp.supernews.com:
> "John Tserkezis" <jt@techniciansyndrome.org.invalid> wrote in
> message news:47305e43$0$30667$afc38c87@news.optusnet.com.au...
>> robb wrote:
>>
>> > Currently the only diagnostic tools at my immediate disposal
> are
>> >
>> > Fluke 177 DMM, a Tek 2236 oscope and a usb/PC based all
> purpose
>> > logic anal/spectrum anal/oscope
>> >
>> > i am hopeing these will be sufficient to solve / track this
>> > fault(s)
>> > if low ohm meter is not terribly expensive then i'll try to
> get
>> > one if it helps more than my current tools
>>
>> You're missing a hammer.
>>
>
> well i purposefully left the hammers out because i did not
> realize their usefull ness in this situation.
Since you have an "anal" scopes,
Google for RCA curve tracer. There are several different versions and plans
for building one.
There is a simple device that I have used for years for checking ICs,
transistors and diodes---
in circuit!
Basically, it consists of a transformer that gives some ac voltage (12 or
so will do fine), current limited with a resistor.
The voltages goes across the part to be tested and the scope monitors the
voltage across the resistor on the vertical axis
The scope uses the voltage across the leads that go to the part to drive
the horizontal trace.
You get a nice sharp knee for a good diode.
You get a slanted line for a resistor.
You get an oval for a capacitor.
You get multiple knees for some of the good ic gates.
After a while you will recognize a bad gate by the rounding of the knee.
A dead short is a vertical line
An open is a horizontal line.
You can often see reverse breakdown (zenering) for good ic junctions.
You want your series current limiting resistor large enough so that your
peak voltage from the transformer will not damage a good junction.
--
bz 73 de N5BZ k
please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.
bz+ser@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
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Author: robbDate: 15:42 07-11-07
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Author: robbDate: 15:47 07-11-07
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<francesco.messineo@gmail.com> wrote in message
news:1194465281.003352.4480@d55g2000hsg.googlegroups.com...
> On 7 Nov, 20:40, "robb" <s...@where.on.net> wrote:
> ...
>
> As someone else pointed out, 73 ohms at 5V means a static draw
of 5/73
> = (about) 68 mA, which for a digital circuit sounds reasonable
imho.
> It is definitely not a short. What's the fuse rating on the 5V
rail?
>
the fuse was a "T 630 mA 250v" so slow blow bussman type fuse
originally the 5v fuse blew i checked transformer out put then
replaced and powered and then all three fuses blew the 5v 12v 30v
maybe i need to take a closer look at the power regulators again
thanks for help,
robb
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Author: EeyoreDate: 18:02 07-11-07
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tonym924@gmail.com wrote:
> "robb" <s...@where.on.net> wrote:
> >
> > no shorts on any of the power regulator chips 5v L387 or the L298s
> >
> > and still get 76 ohm continuity between 5v an 0v ref.
>
> Ummm, what's wrong with that? I = E/R: 66mA. This
> (static) current isn't blowing the fuse.
Yes.
I thought it was a SHORT ! Not 76 ohms ! Looks like there may be hope yet.
Graham
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Author: robbDate: 18:44 07-11-07
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"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in
message news:473243FC.6DF1C352@hotmail.com...
> tonym924@gmail.com wrote:
>
> > "robb" <s...@where.on.net> wrote:
> > >
> > > no shorts on any of the power regulator chips 5v L387 or
the L298s
> > >
> > > and still get 76 ohm continuity between 5v an 0v ref.
> >
> > Ummm, what's wrong with that? I = E/R: 66mA. This
> > (static) current isn't blowing the fuse.
>
> Yes.
>
> I thought it was a SHORT ! Not 76 ohms ! Looks like there may
be hope yet.
>
> Graham
>
apologies graham and anyone else who thpught i knew what i was
saying :{
well i did say i was an amateur, i guess everyone forgot to ask
me if i plugged it in :}
ok, well i thought any thing less than couple of 100K Ohms was
bad news ( rather a short )
i said short because my meter (fluke 177) has continuity setting
that measures anything less than 250 Ohms as having continuity
(beep) and i thought this was a bad thing between high/low that
is 5v and 0v rails
so does this new light change my tactics any ?
maybe all are to upset with my mis-use of "short" ?
still in need of help,
robb
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Author: JamieDate: 19:08 07-11-07
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robb wrote:
> <tonym924@gmail.com> wrote in message
> news:1194453785.463668.239090@19g2000hsx.googlegroups.com...
>
>>On Nov 7, 7:46 am, "robb" <s...@where.on.net> wrote:
>>
>>>no shorts on any of the power regulator chips 5v L387 or the
>>>L298s
>>>
>>>and still get 76 ohm continuity between 5v an 0v ref.
>>
>>Ummm, what's wrong with that? I = E/R: 66mA. This
>>(static) current isn't blowing the fuse.
>>
>>TM
>>
>
> oh yes the fuses blow.
>
> ther were 3 bussman fuses on different lines and such and they
> are all blown
>
> right now i am trying to track down the short(S) so i ca do
> better static tests on various components without removing and
> then try and power the board back up and look for other problems
>
> at least according to the advice i have recieved etc.
> thanks for taking time to look and offer some help , i sorely
> need it,
> robb
>
>
I have an idea for you.
get your self a low voltage auto tail light lamp.
use it in place of the fuse that blows. start disconnecting
things until the lamp glows dim or not at all.
this will allow you to keep the circuit on, you can then
track down some heat traces which won't be much..
actually, you'll be able to do a volt tracking using that
method..
You might have some logic issues that is causing current
to exist only when the circuit is fired up.
--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5
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