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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 60 to 80.

Date: 15:15 08-11-07

On Nov 8, 11:24 am, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:
> tonym...@gmail.com wrote:
> > On Nov 8, 4:49 am, "Arfa Daily" <arfa.da...@ntlworld.com>
wrote:
> > > Well, I would have to say that it certainly indicates that you are not
> > > chasing down any kind of permanent 'short' on your 5v rail. So now that
you
> > > know where the 5v rail comes off the end of the LM317 (was it ?), can you
> > > disconnect it from that point, leave the fuses out of the 12 and 30v
feeds,
> > > and hook the unit back to line power, with a 5v fuse in place ? Measure
the
> > > IN, SET and OUT pins of the '317 to see what you get, and if you get a
> > > correct 5v on the OUT pin[...]
>
> > If the voltage isn't correct (e.g. 4.8-5.2V) at that point (but the
> > fuse isn't blown) tack a 470 ohm resistor from the OUT pin to GND. The LM317
> > has a load regulation spec of 10 mA, and a minimum operating current of
> > ~1mA (for low Vi-Vo); the adjust resistors may not be small enough to draw
> > this much. And don't isolate the regulator by lifting the OUT pin, or
> > you'll lose the adjust resistors.
>
> It's not an LM317 though, it's some funny STM part, an L387.

Oh. 5mA then, at least if it's the same as the L387A:
http://www.st.com/stonline/products/literature/od/1337/l387a.pdf
It's a fixed 5V regulator, so no Vset resistors.

TM

Author: robb
Date: 15:16 08-11-07

<tonym924@gmail.com> wrote in message
news:1194538067.753943.90950@e9g2000prf.googlegroups.com...
> On Nov 8, 4:49 am, "Arfa Daily" <arfa.da...@ntlworld.com>
wrote:
> If the voltage isn't correct (e.g. 4.8-5.2V) at that point (but
the
> fuse isn't
> blown) tack a 470 ohm resistor from the OUT pin to GND. The
LM317
> has
> a load regulation spec of 10 mA, and a minimum operating
current of
> ~1mA
> (for low Vi-Vo); the adjust resistors may not be small enough
to draw
> this
> much. And don't isolate the regulator by lifting the OUT pin,
or
> you'll lose
> the adjust resistors.

umm.. i think you lost me,.... yes yes this place is familiar it
is "lost land"

as in i am lost i hope there is another way to do this as it
sounds like i can cause more problems trying to find the problems
?

if there is no other ways then i will just have to learn but the
experience level of this diagnostic is really stretching my
noodle(s)

thanks for the help i am sure it is very useful advice and i just
need to understand it.
robb

Author: robb
Date: 15:22 08-11-07

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:c%HYi.19728$6v.14487@newsfe2-gui.ntli.net...
>
> Yes, good advice. Looking again, it seems it is an L387
regulator. I'll have
> to look that one up. It's so hard to cover all bases with
someone who's at
> the 'practice' level. Things like making sure that the V-set
resistors are
> still connected, is second nature when you do this sort of
stuff all the
> time ...
>
> Arfa
>
well i am glad to have this advanced second nature diagnostics
helping

but it is Zero nature foreign to me though i am trying to
understand it before i blow more components.

i am very happy to have the help from everyone that know so much
as i surely would have fried it worst if possible than it already
is.

i suppose i should read back through the data sheet on L387 again
before powering up

thanks again for help,
robb

Author: robb
Date: 15:25 08-11-07

<tonym924@gmail.com> wrote in message
news:1194544682.967423.159120@y27g2000pre.googlegroups.com...
> On Nov 8, 11:24 am, Eeyore
<rabbitsfriendsandrelati...@hotmail.com>
> wrote:
> > tonym...@gmail.com wrote:
> > > On Nov 8, 4:49 am, "Arfa Daily" <arfa.da...@ntlworld.com>
wrote:
> > > > Well, I would have to say that it certainly indicates
that you are not
> > > > chasing down any kind of permanent 'short' on your 5v
rail. So now that you
> > > > know where the 5v rail comes off the end of the LM317
(was it ?), can you
> > > > disconnect it from that point, leave the fuses out of the
12 and 30v feeds,
> > > > and hook the unit back to line power, with a 5v fuse in
place ? Measure the
> > > > IN, SET and OUT pins of the '317 to see what you get, and
if you get a
> > > > correct 5v on the OUT pin[...]
> >
> > > If the voltage isn't correct (e.g. 4.8-5.2V) at that point
(but the
> > > fuse isn't blown) tack a 470 ohm resistor from the OUT pin
to GND. The LM317
> > > has a load regulation spec of 10 mA, and a minimum
operating current of
> > > ~1mA (for low Vi-Vo); the adjust resistors may not be small
enough to draw
> > > this much. And don't isolate the regulator by lifting the
OUT pin, or
> > > you'll lose the adjust resistors.
> >
> > It's not an LM317 though, it's some funny STM part, an L387.
>
> Oh. 5mA then, at least if it's the same as the L387A:
>
http://www.st.com/stonline/products/literature/od/1337/l387a.pdf
> It's a fixed 5V regulator, so no Vset resistors.
>

whew , less complications is a welcome occurance to me
more good news please
thanks,
rob

Date: 16:26 08-11-07

On Nov 8, 3:16 pm, "robb" <s...@where.on.net> wrote:
> <tonym...@gmail.com> wrote in message
>
> news:1194538067.753943.90950@e9g2000prf.googlegroups.com...
>
>
>
> > On Nov 8, 4:49 am, "Arfa Daily" <arfa.da...@ntlworld.com>
> wrote:
> > If the voltage isn't correct (e.g. 4.8-5.2V) at that point (but
> the
> > fuse isn't
> > blown) tack a 470 ohm resistor from the OUT pin to GND. The
> LM317
> > has
> > a load regulation spec of 10 mA, and a minimum operating
> current of
> > ~1mA
> > (for low Vi-Vo); the adjust resistors may not be small enough
> to draw
> > this
> > much. And don't isolate the regulator by lifting the OUT pin,
> or
> > you'll lose
> > the adjust resistors.
>
> umm.. i think you lost me,.... yes yes this place is familiar it
> is "lost land"

Ignore all that.

1. As Arfa suggested, isolate the L387 output from the 5V rail.
(Probably doesn't matter if you lift Pin 5 or disconnect some
other way.)
2. Replace the 5V fuse (and only that fuse? or do you also need
the 30V fuse to feed the L387?).
3. Power up.
4. If the fuse didn't blow, measure the voltage from Pin 5 to Pin 3
of the L387 (5V OUT to GND).
5. If you got ~5V, reconnect the 5V rail and test again. If not,
connect a 470-1k ohm resistor from Pin 5 to Pin 3 and test again.
6. If still no 5V, measure the voltage from Pin 1 to Pin 3 (Vin to
GND)
- it should be ~30V.
7. If ~30V was present on Pin 1, the L387 is bad. If not, the 30V
bridge is probably bad.
8. If the fuse(s) blew, test the resistance of the bridges.

TM

Author: robb
Date: 17:19 08-11-07

Author: Jamie
Date: 19:00 08-11-07

robb wrote:

> "Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote
> in message news:KqsYi.131$5R7.3@newsfe02.lga...
>
>>robb wrote:
>>
>>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.
>>
>
>
> ok Jamie i tried this idea with a few compromises and tangents
>
> I only had 110 v bulbs and lattern light bulbs (~ 6V) so i used
> my lattern lightbulb and the lattern battery (showing 5.2 Volts)
> as my power source
>
> no components or tracks were wam enough to discern a change
> after several applications of power with increasing time ....
>
> so i inserted the milliAmp meter (the DMM) and that showed ~160
> mA with the 6V bulb in series and note the bulb was not shinning
> as bright as it could.
>
> so i removed the bulb and i get ~428 mA without the bulb and the
> only thing that gets noticeably warm (*but* no more than prior to
> the ZAP) is the 8051 procesor
>
> this same result occurs no matter where along the 5V rail i
> apply/inject the 5V ....
>
> so i am not sure what this means, maybe good news ??
>
> thanks for any help,
> robb
>
>
Have you looked at the bridge rectifier and filer cap before your regulator?

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

Author: robb
Date: 19:48 08-11-07

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote
in message news:kpNYi.101$RO1.76@newsfe05.lga...
> robb wrote:
>
> > "Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net>
wrote
> > in message news:KqsYi.131$5R7.3@newsfe02.lga...
> >
> Have you looked at the bridge rectifier and filer cap before
your regulator?
>

yes, that was the first thing i considered just because it was
there next to the fuses

i desoldered the bridge and then

i tested the bridge by using diode tester on the DMM so i chose
the combination of pin checks that tests each of the diodes AC1
to (+) .,AC2 to (+), (-) to AC1, (-) to AC2
and each gets ~.596 (+- .007) volts till turn on

and there is no "continuity" between aany combo of bridge pins

thanks for help and reply,
rob

Author: Arfa Daily
Date: 20:22 08-11-07

<tonym924@gmail.com> wrote in message
news:1194557184.656788.121020@k35g2000prh.googlegroups.com...
> On Nov 8, 3:16 pm, "robb" <s...@where.on.net> wrote:
>> <tonym...@gmail.com> wrote in message
>>
>> news:1194538067.753943.90950@e9g2000prf.googlegroups.com...
>>
>>
>>
>> > On Nov 8, 4:49 am, "Arfa Daily" <arfa.da...@ntlworld.com>
>> wrote:
>> > If the voltage isn't correct (e.g. 4.8-5.2V) at that point (but
>> the
>> > fuse isn't
>> > blown) tack a 470 ohm resistor from the OUT pin to GND. The
>> LM317
>> > has
>> > a load regulation spec of 10 mA, and a minimum operating
>> current of
>> > ~1mA
>> > (for low Vi-Vo); the adjust resistors may not be small enough
>> to draw
>> > this
>> > much. And don't isolate the regulator by lifting the OUT pin,
>> or
>> > you'll lose
>> > the adjust resistors.
>>
>> umm.. i think you lost me,.... yes yes this place is familiar it
>> is "lost land"
>
> Ignore all that.
>
> 1. As Arfa suggested, isolate the L387 output from the 5V rail.
> (Probably doesn't matter if you lift Pin 5 or disconnect some
> other way.)
> 2. Replace the 5V fuse (and only that fuse? or do you also need
> the 30V fuse to feed the L387?).
> 3. Power up.
> 4. If the fuse didn't blow, measure the voltage from Pin 5 to Pin 3
> of the L387 (5V OUT to GND).
> 5. If you got ~5V, reconnect the 5V rail and test again. If not,
> connect a 470-1k ohm resistor from Pin 5 to Pin 3 and test again.
> 6. If still no 5V, measure the voltage from Pin 1 to Pin 3 (Vin to
> GND)
> - it should be ~30V.
> 7. If ~30V was present on Pin 1, the L387 is bad. If not, the 30V
> bridge is probably bad.
> 8. If the fuse(s) blew, test the resistance of the bridges.
>
> TM
>

Yes. All agreed. This is basically the first set of tests that I was
suggesting, which Tony has usefully now converted to specific measurement
points for you.

Just to try to help you understand the points about the regulators that we
were making. Without being too 'blanket', there are two types of linear
regulator chips in common use. These are fixed, and variable. The fixed ones
are typically three pin, IN - GND -OUT, and come in many different voltages
eg 5v 8v 9v 10v 12v 15v and so on. They come in both positive and negative
flavours. In general, they don't care too much whether their output pin is
loaded or not, but they do have a minimum load figure specified to
*guarantee* regulation. Also, disconnecting the output pin from the board,
will likely isolate it from a small decoupling cap which will usually be
present, and this might, under some circumstances, lead to the regulator
oscillating.

The variable ones also often have just three pins, such as the LM317, but
sometimes have more. The main pins that are generally of any concern, are
IN - SET - OUT. The output voltage is determined by a potential divider
comprising two resistors, one strung between OUT and SET and the other
between SET and the circuit common ground. By altering the ratio of the two
resistors, any voltage to within a couple of volts of the input, can be set
as the output. Clearly, for this setup to work, the 'top' resistor of the
voltage-set divider, *must* remain connected to the output pin. What Tony
was saying, is that if you just disconnect the output pin from the board,
you will also be disconnecting it from the v-set resistors, which could lead
to all manner of nasties ...

The good thing about these regulators is that they are pretty bomb-proof.
They are safe area protected, short circuit protected and thermally
protected, and will go into a voltage foldback condition if any anomalies in
their operating conditions are detected. That is not to say that they don't
fail themselves. They do. But often, the measured conditions, particularly
the parameters measured by the Mk 1 finger-thermometer, are a big clue to
what's going on. Example. 5v fixed regulator - say a 7805 1 amp version.
Measured output voltage 1.8v. Measured device temperature, using Mk 1 finger
= Ouch. Conclusion ? More than an amp is being drawn, the device has
overheated, and gone into thermal voltage foldback, to keep within its SOA.
Example 2. Same regulator, same set up, same measured ouput voltage.
Measured device temperature = cool. Conclusion ? The regulator device itself
is faulty. Before there are lots of cries of anguish, a bit simplistic, I
know, and yes, there could be other reasons for the measured conditions, but
those two examples cover probably 90% of problems around those regulator
types.

Arfa

Author: Ken Fowler
Date: 01:02 09-11-07

On 7-Nov-2007, francesco.messineo@gmail.com wrote:

> Path:
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> From: francesco.messineo@gmail.com
> Newsgroups: sci.electronics.basics,sci.electronics.repair
> Subject: Re: troubleshooting method for micro-controller board ?
> Date: Wed, 07 Nov 2007 11:54:41 -0800
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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

Careful. He didn't say 73 ohms at 5V. If the 73 ohms is a DVM
measurement, it was probably made with a low voltage applied. When the
circuit is powered up with 5 V, other parts of the ICs are turned on and
the current may be much more than 68 mA. The best use of the ohmeter
measurement is to compare it to a good board. And yes, 73 ohms sounds low
to me.
Ken Fowler

Author: robb
Date: 03:56 09-11-07

<tonym924@gmail.com> wrote in message
news:1194557184.656788.121020@k35g2000prh.googlegroups.com...
> Ignore all that.
>
> 1. As Arfa suggested, isolate the L387 output from the 5V rail.
> (Probably doesn't matter if you lift Pin 5 or disconnect some
> other way.)
> 2. Replace the 5V fuse (and only that fuse? or do you also need
> the 30V fuse to feed the L387?).
> 3. Power up.
> 4. If the fuse didn't blow, measure the voltage from Pin 5 to
Pin 3
> of the L387 (5V OUT to GND).
> 5. If you got ~5V, reconnect the 5V rail and test again. If
not,
> connect a 470-1k ohm resistor from Pin 5 to Pin 3 and test
again.
> 6. If still no 5V, measure the voltage from Pin 1 to Pin 3 (Vin
to
> GND)
> - it should be ~30V.
> 7. If ~30V was present on Pin 1, the L387 is bad. If not, the
30V
> bridge is probably bad.
> 8. If the fuse(s) blew, test the resistance of the bridges.
>
> TM
>

hi TM,
I tested the L387 and i think it must be bad as i get more than
5v from the Vout ?

i had already desoldered it from some previous suggestions about
isolating the different supply rails

so i tested by connecting 5V/1A DC source between Vin and
GND-Pin3 and i checked the voltage with DVM between Vout and
GND-Pin3 and i was getting 3.47 V

i changed to a 18 v/3.5A DC source and i was measuring 8.67 V
between Vout and GND-Pin3

L387 is cool
and when i connected an LED load to Vout the L387 got very hot
very quickly
so i suppose i at least need to get an L387 ?

thanks again for help,
robb

Author: Arfa Daily
Date: 04:17 09-11-07

"robb" <some@where.on.net> wrote in message
news:13j8847j32g0i86@corp.supernews.com...
>
> <tonym924@gmail.com> wrote in message
> news:1194557184.656788.121020@k35g2000prh.googlegroups.com...
>> Ignore all that.
>>
>> 1. As Arfa suggested, isolate the L387 output from the 5V rail.
>> (Probably doesn't matter if you lift Pin 5 or disconnect some
>> other way.)
>> 2. Replace the 5V fuse (and only that fuse? or do you also need
>> the 30V fuse to feed the L387?).
>> 3. Power up.
>> 4. If the fuse didn't blow, measure the voltage from Pin 5 to
> Pin 3
>> of the L387 (5V OUT to GND).
>> 5. If you got ~5V, reconnect the 5V rail and test again. If
> not,
>> connect a 470-1k ohm resistor from Pin 5 to Pin 3 and test
> again.
>> 6. If still no 5V, measure the voltage from Pin 1 to Pin 3 (Vin
> to
>> GND)
>> - it should be ~30V.
>> 7. If ~30V was present on Pin 1, the L387 is bad. If not, the
> 30V
>> bridge is probably bad.
>> 8. If the fuse(s) blew, test the resistance of the bridges.
>>
>> TM
>>
>
> hi TM,
> I tested the L387 and i think it must be bad as i get more than
> 5v from the Vout ?
>
> i had already desoldered it from some previous suggestions about
> isolating the different supply rails
>
> so i tested by connecting 5V/1A DC source between Vin and
> GND-Pin3 and i checked the voltage with DVM between Vout and
> GND-Pin3 and i was getting 3.47 V
>
> i changed to a 18 v/3.5A DC source and i was measuring 8.67 V
> between Vout and GND-Pin3
>
> L387 is cool
> and when i connected an LED load to Vout the L387 got very hot
> very quickly
> so i suppose i at least need to get an L387 ?
>
> thanks again for help,
> robb
>

From that, it sounds as though the '387 is not doing its job correctly, so
replacing it would probably be a good move.

Arfa

Author: robb
Date: 04:17 09-11-07

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:wDOYi.19791$6v.10079@newsfe2-gui.ntli.net...
>
> <tonym924@gmail.com> wrote in message
> news:1194557184.656788.121020@k35g2000prh.googlegroups.com...
> > On Nov 8, 3:16 pm, "robb" <s...@where.on.net> wrote:
> >> <tonym...@gmail.com> wrote in message
> >>
> >> news:1194538067.753943.90950@e9g2000prf.googlegroups.com...
> >>
>
> Yes. All agreed. This is basically the first set of tests that
I was
> suggesting, which Tony has usefully now converted to specific
measurement
> points for you.
>
> Just to try to help you understand the points about the
regulators that we
> were making. Without being too 'blanket', there are two types
of linear
> regulator chips in common use. These are fixed, and variable.
The fixed ones
> are typically three pin, IN - GND -OUT, and come in many
different voltages
> eg 5v 8v 9v 10v 12v 15v and so on. They come in both positive
and negative
> flavours. In general, they don't care too much whether their
output pin is
> loaded or not, but they do have a minimum load figure specified
to
> *guarantee* regulation. Also, disconnecting the output pin from
the board,
> will likely isolate it from a small decoupling cap which will
usually be
> present, and this might, under some circumstances, lead to the
regulator
> oscillating.
>
> The variable ones also often have just three pins, such as the
LM317, but
> sometimes have more. The main pins that are generally of any
concern, are
> IN - SET - OUT. The output voltage is determined by a potential
divider
> comprising two resistors, one strung between OUT and SET and
the other
> between SET and the circuit common ground. By altering the
ratio of the two
> resistors, any voltage to within a couple of volts of the
input, can be set
> as the output. Clearly, for this setup to work, the 'top'
resistor of the
> voltage-set divider, *must* remain connected to the output pin.
What Tony
> was saying, is that if you just disconnect the output pin from
the board,
> you will also be disconnecting it from the v-set resistors,
which could lead
> to all manner of nasties ...
>
> The good thing about these regulators is that they are pretty
bomb-proof.
> They are safe area protected, short circuit protected and
thermally
> protected, and will go into a voltage foldback condition if any
anomalies in
> their operating conditions are detected. That is not to say
that they don't
> fail themselves. They do. But often, the measured conditions,
particularly
> the parameters measured by the Mk 1 finger-thermometer, are a
big clue to
> what's going on. Example. 5v fixed regulator - say a 7805 1 amp
version.
> Measured output voltage 1.8v. Measured device temperature,
using Mk 1 finger
> = Ouch. Conclusion ? More than an amp is being drawn, the
device has
> overheated, and gone into thermal voltage foldback, to keep
within its SOA.
> Example 2. Same regulator, same set up, same measured ouput
voltage.
> Measured device temperature = cool. Conclusion ? The regulator
device itself
> is faulty. Before there are lots of cries of anguish, a bit
simplistic, I
> know, and yes, there could be other reasons for the measured
conditions, but
> those two examples cover probably 90% of problems around those
regulator
> types.
>
> Arfa
>

Hi Arfa,
thanks for all the useful help and iinformatin i really do
appreciate your's and everyones helpful advice and information. I
started this project as a learning exercise guess its more a
workout.

Regarding the L387, since i had already removed it hat was asy
to test.

I am pretty sure it is bad from what you explained. that is 5V
regulators only output 5V .

when i applied a 5V/1A DC source to Vin/GND i measured 3.47V
between Vout/GND.
when i applied a 18 V / 3.5A DC source to the Vin/GND i measured
8.37V between Vout/GND

an LED load between Vout/GND caused the L387 to get very hot
quickly.

so a new L387 is in order so that i can complete the other tests
that you TM and others have suggested

thanks again for help,
robb

Author: Eeyore
Date: 04:36 09-11-07

Arfa Daily wrote:

> "robb" <some@where.on.net> wrote in message
>
> > I tested the L387 and i think it must be bad as i get more than
> > 5v from the Vout ?

How much more ? A couple of hundred millivolts, says 5.25 V is OK.

> > i had already desoldered it from some previous suggestions about
> > isolating the different supply rails
> >
> > so i tested by connecting 5V/1A DC source between Vin and
> > GND-Pin3 and i checked the voltage with DVM between Vout and
> > GND-Pin3 and i was getting 3.47 V

Pointless. It won't operate correctly with only 5V in. 3.47V is sort of what I'd
expect under those conditions. A linear voltage regulator has to have several
volts more on the input than the output to function correctly.

> > i changed to a 18 v/3.5A DC source and i was measuring 8.67 V
> > between Vout and GND-Pin3
> >
> > L387 is cool and when i connected an LED load to Vout the L387 got very hot
> > very quickly so i suppose i at least need to get an L387 ?

What value resistor did you have in series with the LED ?

> From that, it sounds as though the '387 is not doing its job correctly, so
> replacing it would probably be a good move.

He didn't say if he had a resistor in series with the LED ! Could explain a lot.

Graham

Author: Eeyore
Date: 04:41 09-11-07

robb wrote:

> Regarding the L387, since i had already removed it hat was asy
> to test.
>
> I am pretty sure it is bad from what you explained. that is 5V
> regulators only output 5V .
>
> when i applied a 5V/1A DC source to Vin/GND i measured 3.47V
> between Vout/GND.
> when i applied a 18 V / 3.5A DC source to the Vin/GND i measured
> 8.37V between Vout/GND

With a load or no load ? If there was no load on the regulator output then
that's quite possible even for a good L387. You must have a load resistor of
around 470 ohms on the 5V output for testing for the chip to regulate properly.

> an LED load between Vout/GND caused the L387 to get very hot
> quickly.

An LED with no series current limiting resistor might well do that ! You should
have a resistor of ~ 150 ohms in series with the LED.

> so a new L387 is in order so that i can complete the other tests
> that you TM and others have suggested

It may not be necessary. Your testing used flawed methods.

Graham

Author: robb
Date: 05:03 09-11-07

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in
message news:47342A10.A36320FE@hotmail.com...
>
>
> Arfa Daily wrote:
>
> > "robb" <some@where.on.net> wrote in message
> >
> > > so i tested by connecting 5V/1A DC source between Vin and
> > > GND-Pin3 and i checked the voltage with DVM between Vout
and
> > > GND-Pin3 and i was getting 3.47 V
>
> Pointless. It won't operate correctly with only 5V in. 3.47V is
sort of what I'd
> expect under those conditions. A linear voltage regulator has
to have several
> volts more on the input than the output to function correctly.
>
hi graham,
just being cautious and i do not have much in the way of handy
power sources, various wall warts.

>
> > > i changed to a 18 v/3.5A DC source and i was measuring
8.67 V
> > > between Vout and GND-Pin3
> > >
> > > L387 is cool and when i connected an LED load to Vout the
L387 got very hot
> > > very quickly so i suppose i at least need to get an L387 ?
>
> What value resistor did you have in series with the LED ?
>

you need to use a resistor ???

just joking it was 100 Ohm 1/2 watt (Brwn Blk Brwn Gold)

would you expect 8.67 Vout with 18V DC Vinput ?

thanks for help,
robb

Author: robb
Date: 07:19 09-11-07

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in
message news:47342B42.39DC9406@hotmail.com...
>
>
> robb wrote:
>
> > Regarding the L387, since i had already removed it hat was
asy
> > to test.
> >
> > I am pretty sure it is bad from what you explained. that is
5V
> > regulators only output 5V .
> >
> > when i applied a 5V/1A DC source to Vin/GND i measured 3.47V
> > between Vout/GND.
> > when i applied a 18 V / 3.5A DC source to the Vin/GND i
measured
> > 8.37V between Vout/GND
>
> With a load or no load ? If there was no load on the regulator
output then
> that's quite possible even for a good L387. You must have a
load resistor of
> around 470 ohms on the 5V output for testing for the chip to
regulate properly.
>

ok, i set it up as you suggest a 470 Ohms between Vout and GND
(Pin3) with 16v/3A DC source connected to Vin and GRD. The
measurement between Vout and GND was 8.03 V when i put a LED in
series with 470Ohms i get 7.92 V measured accross Vout and GND.

>
> It may not be necessary. Your testing used flawed methods.
>

that is why i am seeking help from "the group", "the fountain"
of electronic knowledge :(

thanks for help graham,
robb

Author: Eeyore
Date: 08:46 09-11-07

robb wrote:

> "Eeyore" wrote
> >
> > What value resistor did you have in series with the LED ?
>
> you need to use a resistor ???
>
> just joking it was 100 Ohm 1/2 watt (Brwn Blk Brwn Gold)
>
> would you expect 8.67 Vout with 18V DC Vinput ?

Not under those conditions.

You do need a new L387.

Graham

Date: 12:40 09-11-07

On Nov 9, 4:17 am, "Arfa Daily" <arfa.da...@ntlworld.com> wrote:
> "robb" <s...@where.on.net> wrote in message
>
> news:13j8847j32g0i86@corp.supernews.com...
>
>
>
>
>
> > <tonym...@gmail.com> wrote in message
> >news:1194557184.656788.121020@k35g2000prh.googlegroups.com...
> >> Ignore all that.
>
> >> 1. As Arfa suggested, isolate the L387 output from the 5V rail.
> >> (Probably doesn't matter if you lift Pin 5 or disconnect some
> >> other way.)
> >> 2. Replace the 5V fuse (and only that fuse? or do you also need
> >> the 30V fuse to feed the L387?).
> >> 3. Power up.
> >> 4. If the fuse didn't blow, measure the voltage from Pin 5 to
> > Pin 3
> >> of the L387 (5V OUT to GND).
> >> 5. If you got ~5V, reconnect the 5V rail and test again. If
> > not,
> >> connect a 470-1k ohm resistor from Pin 5 to Pin 3 and test
> > again.
> >> 6. If still no 5V, measure the voltage from Pin 1 to Pin 3 (Vin
> > to
> >> GND)
> >> - it should be ~30V.
> >> 7. If ~30V was present on Pin 1, the L387 is bad. If not, the
> > 30V
> >> bridge is probably bad.
> >> 8. If the fuse(s) blew, test the resistance of the bridges.
>
> >> TM
>
> > hi TM,
> > I tested the L387 and i think it must be bad as i get more than
> > 5v from the Vout ?
>
> > i had already desoldered it from some previous suggestions about
> > isolating the different supply rails
>
> > so i tested by connecting 5V/1A DC source between Vin and
> > GND-Pin3 and i checked the voltage with DVM between Vout and
> > GND-Pin3 and i was getting 3.47 V
>
> > i changed to a 18 v/3.5A DC source and i was measuring 8.67 V
> > between Vout and GND-Pin3
>
> > L387 is cool
> > and when i connected an LED load to Vout the L387 got very hot
> > very quickly
> > so i suppose i at least need to get an L387 ?
>
> > thanks again for help,
> > robb
>
> From that, it sounds as though the '387 is not doing its job correctly, so
> replacing it would probably be a good move.

So while you're waiting for the new L387 (or better yet, before you
even
order it), replace the 30V and 12V fuses, connect your (5.2V) lantern
battery to the 5V rail, and power up. Does the board work? Fuses
blow?
30V and 12V rails measure OK?

TM

Date: 13:04 09-11-07

On Nov 9, 4:36 am, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:
> > "robb" <s...@where.on.net> wrote in message
> > > so i tested by connecting 5V/1A DC source between Vin and
> > > GND-Pin3 and i checked the voltage with DVM between Vout and
> > > GND-Pin3 and i was getting 3.47 V
>
> Pointless. It won't operate correctly with only 5V in.

Agreed.

> A linear voltage regulator has to have several volts more on the
> input than the output to function correctly.

Some need 1-2V more, others around 1/2V (I think I've seen
LDOs down to 0.2V dropout [i.e. Vout-Vin]). I didn't find a spec
sheet for the L387, but the L387A has a max dropout of 0.8V
(and that's from 4.9V, so Vin[min] is 5.7V). Don't know whether
dropout is one of the improvements in the A version.

In most cases it's safe to test with Vin=Vout+2V, but with an
adjustable LDO operating near the top of the Vout range, that
may result in Vin exceeding spec. Checking the data sheet
first is always a good idea.

(LDO = Low DropOut, a category of linear regulator)

TM

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