troubleshooting method for micro-controller board ?
 

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

troubleshooting method for micro-controller board ?
 

robb 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 :)

Well .... if the 5V supply went seriously high, the chances are it's all fried.
:-(

Have you tried powering the pcb from an external stabilised 5V power supply ?

The very first thing to look for is a clock oscillator (and valid reset signal).
Get the data sheets for those 40 pin chips, identify which one is the micro and
scope the relevant pin(s).

What are the 40 pin chip numbers btw ?

Graham

troubleshooting method for micro-controller board ?
 

"Eeyore" wrote in
message ...

robb wrote:

i have a micro-controller board ....
i believe the 32v shorted with 5V
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 ?


Well .... if the 5V supply went seriously high, the chances are
it's all fried.
:-(

there is a 630 mA Busman type fuses on all the lines i hope that
saved things ? but the fact that i am getting a short detected
between 0V and 5V line has me worried maybe thats good i do not
know hopeful someone can give me an method for finding problems ?


Have you tried powering the pcb from an external stabilised 5V
power supply ?

The very first thing to look for is a clock oscillator (and
valid reset signal).
Get the data sheets for those 40 pin chips, identify which one
is the micro and
scope the relevant pin(s).

What are the 40 pin chip numbers btw ?


one is the Phillips MAB 8051 micro,
then SRM 2017 Static RAM,
and NEC 8547E7 (D23256) ?? - can't find data sheet

then dual full bridge driver - L298
comparator - LM393 LM339 etc
some nor buffers and and and invertor pkgs

thanks again graham i really appreciate some help,
i can handle small problems but potential catastrophics like this
is a bit over

thanks
robb


Graham

troubleshooting method for micro-controller board ?
 

In article ,
"robb" 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

Clearly there is one or more shorts somewhere on the board. Your
mission therefore is to determine what is shorted, and where it is.

If the ICs are socketed, I'd probably pull them (making careful note of
what was where, if it's not clearly labeled on the PCB). This avoids
any (additional) damage to parts that may be quite hard to replace.
From there, checking components in the on-board power supply section
might be reasonable, as would checking the resistance between
permutations of the various power supply rails and ground for shorts
(preferably with something like an ESR meter that won't damage
semiconductors, especially if the ICs can't be removed.) Shorts between
rails could be caused by things like failed de-spiking capacitors. If
everything looks OK with ICs removed, maybe power up the board without
them and see what happens; if the power supply is stable and current
draw reasonable, the problem would seem to be with one of the removed
ICs, or with a circuit driven by one of them.

(It's not a bad idea to figure out what the output interface circuitry
looks like that's driven by the ICs before powering it up without them;
maybe you'd be wise to tie some of the outputs to a fixed level rather
than letting them float.)

What's the purpose of this board? What sort of board-level I/Os does it
have? Based on the atypical power supply voltages, I'm guessing it must
drive or interface with some external devices; maybe those output
circuits are damaged, or the things driven by them or the wiring to them.

Just some thoughts; hopefully they're helpful.

--
Andrew Erickson

"He is no fool who gives what he cannot keep to gain that which he cannot
lose." -- Jim Elliot

troubleshooting method for micro-controller board ?
 

robb wrote:

"Eeyore" wrote in
message ...

robb wrote:


i have a micro-controller board ....
i believe the 32v shorted with 5V
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 ?


Well .... if the 5V supply went seriously high, the chances are

it's all fried.

:-(


there is a 630 mA Busman type fuses on all the lines i hope that
saved things ? but the fact that i am getting a short detected
between 0V and 5V line has me worried maybe thats good i do not
know hopeful someone can give me an method for finding problems ?


Have you tried powering the pcb from an external stabilised 5V

power supply ?

The very first thing to look for is a clock oscillator (and

valid reset signal).

Get the data sheets for those 40 pin chips, identify which one

is the micro and

scope the relevant pin(s).

What are the 40 pin chip numbers btw ?



one is the Phillips MAB 8051 micro,
then SRM 2017 Static RAM,
and NEC 8547E7 (D23256) ?? - can't find data sheet

then dual full bridge driver - L298
comparator - LM393 LM339 etc
some nor buffers and and and invertor pkgs

thanks again graham i really appreciate some help,
i can handle small problems but potential catastrophics like this
is a bit over

thanks
robb


Graham


I use a low ohm meter (Kelvin), it's very good at
tracking down the nearest point of the short on the
board.
You may want to look at capacitors. Especially
tantalums, they short very nicely many times leaving
nothing but ash.





--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

troubleshooting method for micro-controller board ?
 

On Nov 6, 9:14 am, "robb" 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


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.

troubleshooting method for micro-controller board ?
 

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.

--
Linux Registered User # 302622
http://counter.li.org

troubleshooting method for micro-controller board ?
 

I use a low ohm meter (Kelvin), it's very good at
tracking down the nearest point of the short on the
board.
You may want to look at capacitors. Especially
tantalums, they short very nicely many times leaving
nothing but ash.





Sometimes it's possible to isolate sections of the circuit fairly easily, a
jumper link that can be removed, or in more drastic situations, a trace can
be cut. It doesn't take too many cycles of that to narrow things down.

Keep in mind that 5V TTL boards can pull quite a bit of juice, on larger
boards it can appear to be a nearly dead short when using an ohm meter
between Vcc and Gnd.

troubleshooting method for micro-controller board ?
 

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.

troubleshooting method for micro-controller board ?
 

robb wrote:

"Eeyore" wrote
robb wrote:

i have a micro-controller board ....
i believe the 32v shorted with 5V
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 ?


Well .... if the 5V supply went seriously high, the chances are
it's all fried. ::-(

there is a 630 mA Busman type fuses on all the lines i hope that
saved things ?

I'm afraid fuses are merely for preventing fires, not preventing damage (except
for the case of 'extreme' fuse types like the ultra-fast types).


but the fact that i am getting a short detected
between 0V and 5V line has me worried maybe thats good i do not
know hopeful someone can give me an method for finding problems ?

No, I'm afraid that's actually bad news. I assume therefore it literally 'wont
do anything' at present and any power supply connected to it goes into current
limit ?


Have you tried powering the pcb from an external stabilised 5V
power supply ?

The very first thing to look for is a clock oscillator (and
valid reset signal).
Get the data sheets for those 40 pin chips, identify which one
is the micro and scope the relevant pin(s).

What are the 40 pin chip numbers btw ?


one is the Phillips MAB 8051 micro,

OK. That's a real easy one to check AND replace (at least with a modern CMOS
version).
Data sheet here.
http://www.datasheets.org.uk/search....ub.x=0&sub.y=0

If it was working I'd check for activity (pulses/wvaeforms) on the Xtal1/2 pins,
ALE and PSEN first.


then SRM 2017 Static RAM,

OK. Not sure how easy that would be to replace.
Data here for the pinouts..
http://www.datasheets.org.uk/search....ub.x=0&sub.y=0


and NEC 8547E7 (D23256) ?? - can't find data sheet

I expect that's a 256k bit EPROM. Does it have a glass window ?

Important note. This is the most important part on the board. If it's fried so
are you. A dead EPROM will mean that the whole machine can't be repaired (unless
you can get the source file). Treat it with utmost respect.


then dual full bridge driver - L298
comparator - LM393 LM339 etc
some nor buffers and and and invertor pkgs

These are 'commodity' parts that are easily replaced. Not a problem here. First
you need to get the 'big' digital parts functioning.

General tip. Don't apply power to any high power I/O switching chips like the
L298 until the digital stuff is back to normal again.

Here are some ideas. You say you have a short across the 5V logic supply.
Firstly you need to clear that and find the cause. Are the chips socketed ? If
so it's easy to remove them and check for individually shorted chips. Check
across the power pins. Normally these are opposing corner pins like pin 20 and
40 on the 8051 for example ( or 7/14 8/16 and 10/20 on 74 series chips) but best
to get data sheets for anything unfamiliar. If you're lucky you may find one (or
two or threee) failed 'sacrificially' - saving the others but you need to find
the failed chips and get replacements for them.

If they aren't socketed now is the time to do this ! Removing ICs from PCBs
without damage is a skilled task so I would sacrifice anything that's easily
replaceable by cutting the pins at the IC body with fine cutters and removing
those pins one by one from the PCB. That way there's very little chance of doing
much damage. Be careful to fit sockets that firmly grip the leads especially if
this is some industrial controller used in areas where there's significant
vibration. That means DON'T use turned pin sockets, the pins will 'walk out' of
them.

How about you give is a complete list of the ICs on this pcb, plus make a scan
of it and post it where we can see it ? That'll help enormously.



Graham

troubleshooting method for micro-controller board ?
 

"Jamie" t wrote
in message ...
robb wrote:

"Eeyore" wrote in
message ...

I use a low ohm meter (Kelvin), it's very good at
tracking down the nearest point of the short on the
board.
You may want to look at capacitors. Especially
tantalums, they short very nicely many times leaving
nothing but ash.


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

troubleshooting method for micro-controller board ?
 

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.

That might be a lot funnier if we weren't talking about 32v on a 5v line,
but at this stage, a hammer certainly seems a viable tool.

Last time I had nearly 12v on a 5v line, (most of the board was 5v logic) I
didn't waste time diagnosing. It was faster to change all the silicon and
worry about shorted tantalums later.
Checking the semis afterwards, I found nearly half of them were stuffed, and
the other half I wouldn't have trusted anyway.

That was at nearly 12 volts. Not 32.

In your shoes, (depending on the scale of the baord and availability of
replacement boards) I'd either outright replace it, or, if this is the only
one left in existence I'd turf the silicon, and hope the EPROM or flash or
wherever the code is stored still works.

--
Linux Registered User # 302622
http://counter.li.org

troubleshooting method for micro-controller board ?
 

"Eeyore" wrote in
message ...


[trimmed lots of helpfull advice]

responses to helpfull questions in separate post


How about you give is a complete list of the ICs on this pcb,
plus make a scan
of it and post it where we can see it ? That'll help
enormously.


hi Graham thanks again for the help,

i posted pics of the board on
(alt.binaries.electronics.schematics)

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

troubleshooting method for micro-controller board ?
 

On Tue, 6 Nov 2007 07:34:53 -0500, "robb" 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.

Good luck, Robb.

Tom

troubleshooting method for micro-controller board ?
 

Tom2000 wrote:

Leave unsoldering any ICs as your very last resort.

Funny. That's where I'd START !

Graham

troubleshooting method for micro-controller board ?
 

Look for date codes. If its only a couple years old, some smart EE
might have actually put Transient Voltage Suppressors in some
important places to guard against incompetent operators. Can anyone
rattle off three TVS brand names from memory he can look for?

troubleshooting method for micro-controller board ?
 

"Eeyore" wrote in message
...


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.

troubleshooting method for micro-controller board ?
 

"John Tserkezis" wrote in
message u...
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.

i actually have quite array of hammers 5 oz. to 5 lb rubber,
brass, nylon etc

i just hope the time comes that i do not need to use them.... on
the man or the machine


That might be a lot funnier if we weren't talking about 32v
on a 5v line,
but at this stage, a hammer certainly seems a viable tool.

no it is still funny, in nervous and tearful kind of laugh


Last time I had nearly 12v on a 5v line, (most of the board
was 5v logic) I
didn't waste time diagnosing. It was faster to change all the
silicon and
worry about shorted tantalums later.

uhggg what a project my small project has become

Checking the semis afterwards, I found nearly half of them
were stuffed, and
the other half I wouldn't have trusted anyway.

That was at nearly 12 volts. Not 32.

In your shoes, (depending on the scale of the baord and
availability of
replacement boards) I'd either outright replace it, or, if this
is the only
one left in existence I'd turf the silicon, and hope the EPROM
or flash or
wherever the code is stored still works.


i really hope i actually make it to those problems considering
what i have read so far.

thanks for the help and ideas,
robb

troubleshooting method for micro-controller board ?
 

"Tom2000" wrote in message
...
On Tue, 6 Nov 2007 07:34:53 -0500, "robb"
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

troubleshooting method for micro-controller board ?
 

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

troubleshooting method for micro-controller board ?
 

"Eeyore" wrote in
message ...


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.

troubleshooting method for micro-controller board ?
 

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

troubleshooting method for micro-controller board ?
 

On Nov 5, 5:14 pm, "robb" 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.

troubleshooting method for micro-controller board ?
 

"robb" wrote in message
...

"Tom2000" wrote in message
...
On Tue, 6 Nov 2007 07:34:53 -0500, "robb"
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.

troubleshooting method for micro-controller board ?
 

On Tue, 6 Nov 2007 13:03:40 -0500, "Michael Kennedy"
wrote:


"Eeyore" wrote in message
...


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

troubleshooting method for micro-controller board ?
 

"robb" wrote in message
...

"Tom2000" wrote in message
...
On Tue, 6 Nov 2007 07:34:53 -0500, "robb"
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

troubleshooting method for micro-controller board ?
 

"James Sweet" 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

troubleshooting method for micro-controller board ?
 

"Arfa Daily" wrote in message
...

"robb" wrote in message
...

"Tom2000" wrote in message
...
On Tue, 6 Nov 2007 07:34:53 -0500, "robb"

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

troubleshooting method for micro-controller board ?
 

"Eeyore" wrote in
message ...


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

troubleshooting method for micro-controller board ?
 

On Nov 7, 7:46 am, "robb" 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

troubleshooting method for micro-controller board ?
 

wrote in message
ups.com...
On Nov 7, 7:46 am, "robb" 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

troubleshooting method for micro-controller board ?
 

On Nov 7, 12:57 pm, "robb" wrote:
wrote in message

ups.com... On Nov 7, 7:46 am, "robb" 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

troubleshooting method for micro-controller board ?
 

wrote in message
ups.com...
On Nov 7, 12:57 pm, "robb" wrote:
wrote in message

ups.com...
On Nov 7, 7:46 am, "robb" 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

troubleshooting method for micro-controller board ?
 

On 7 Nov, 20:40, "robb" 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

troubleshooting method for micro-controller board ?
 

"robb" wrote in news:13j1fghd5a5t9d7
@corp.supernews.com:

"John Tserkezis" wrote in
message u...
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.

remove ch100-5 to avoid spam trap

troubleshooting method for micro-controller board ?
 

wrote in message
ups.com...
On Nov 7, 12:57 pm, "robb" wrote:
wrote in message



What resistance do you get on the other rails?

TM


the 30V rail to 0V is 1.28 MegOhms

robb

troubleshooting method for micro-controller board ?
 

wrote in message
ps.com...
On 7 Nov, 20:40, "robb" 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

troubleshooting method for micro-controller board ?
 

wrote:

"robb" 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

troubleshooting method for micro-controller board ?
 

"Eeyore" wrote in
message ...
wrote:

"robb" 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

troubleshooting method for micro-controller board ?
 

robb wrote:

wrote in message
ups.com...

On Nov 7, 7:46 am, "robb" 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