Testing a voltage regulator in-circuit

[Uriah]

I really appreciate everyone's help in understanding some of the
problems I encounter.

I am working on one of those emergency lights that are in most
businesses. The ones with the battery that come on when the power
fails. There is a 6 volt battery wired to a transformer and a little
circuit. The light doesn't come on. The battery is good. The bulbs
are good. It has two transistors and a voltage regulator, a bunch of
resistor and diodes. I tested everything with my DVM and Huntron and
I see no faults. When I test the transistors with the battery hooked
up I get a 6VDC drop from Emitter to Collector. Does this mean that
the transistor is acting like a open switch? There is no voltage
between the base and emitor or collector. Can you generalize about
transistors like this? I am thinking that there is no drive to the
base and that is why the transistor is not conducting. This sound
right? Also, along the same line, there are some diodes that are also
getting this 6VDC drop when you measure them in either direction. Does
that show a problem with that diode? And... how would I go about
confirming that the voltage regulator is working? It is a LM340T5.
Thanks for all of the help.
Russ

 

[Eeyore]

Uriah wrote:

I tested everything with my DVM and Huntron and I see no faults.

Since you clearly don't understand how the circuit functions, how can you
say that ?

What's a 'Huntron' btw ?

Graham

 

[Bill Bowden]

On Jan 2, 9:03 pm, Uriah <uriah...@hotmail.com> wrote:

I really appreciate everyone's help in understanding some of the
problems I encounter.

I am working on one of those emergency lights that are in most
businesses. The ones with the battery that come on when the power
fails. There is a 6 volt battery wired to a transformer and a little
circuit. The light doesn't come on. The battery is good. The bulbs
are good. It has two transistors and a voltage regulator, a bunch of
resistor and diodes. I tested everything with my DVM and Huntron and
I see no faults. When I test the transistors with the battery hooked
up I get a 6VDC drop from Emitter to Collector. Does this mean that
the transistor is acting like a open switch? There is no voltage
between the base and emitor or collector. Can you generalize about
transistors like this? I am thinking that there is no drive to the
base and that is why the transistor is not conducting. This sound
right? Also, along the same line, there are some diodes that are also
getting this 6VDC drop when you measure them in either direction. Does
that show a problem with that diode? And... how would I go about
confirming that the voltage regulator is working? It is a LM340T5.
Thanks for all of the help.
Russ

The diodes will have about a 0.7 volt drop if the anode is more
positive than the cathode. Otherwise the drop will be whatever the
existing voltage is since the diode will be reverse biased and not
conducting. You need to pay attention to the polarity of the
measurments you make. Same goes for transistors. If the transistors
are bipolar NPN types, they will conduct when the base is more
positive than the emitter by about 0.7 volts. If they are PNP types,
the base must be more negative than the emitter for the transistor to
conduct. Look more closely at the polarity of the measurments to
figure out what is happening.

-Bill

 

[Michael A. Terrell]

Eeyore wrote:

Uriah wrote:

I tested everything with my DVM and Huntron and I see no faults.

Since you clearly don't understand how the circuit functions, how can you
say that ?

What's a 'Huntron' btw ?

What is a dumbass donkey? Use a search engine, dumbass. All will be
revealed, even to your minuscule 154 IQ.


--
http://improve-usenet.org/index.html

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm


There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.

 

[John Fields]

On Fri, 2 Jan 2009 21:03:09 -0800 (PST), Uriah <uriahsky@hotmail.com>
wrote:

I really appreciate everyone's help in understanding some of the
problems I encounter.

I am working on one of those emergency lights that are in most
businesses. The ones with the battery that come on when the power
fails. There is a 6 volt battery wired to a transformer and a little
circuit. The light doesn't come on. The battery is good. The bulbs
are good. It has two transistors and a voltage regulator, a bunch of
resistor and diodes. I tested everything with my DVM and Huntron and
I see no faults. When I test the transistors with the battery hooked
up I get a 6VDC drop from Emitter to Collector. Does this mean that
the transistor is acting like a open switch? There is no voltage
between the base and emitor or collector. Can you generalize about
transistors like this? I am thinking that there is no drive to the
base and that is why the transistor is not conducting. This sound
right? Also, along the same line, there are some diodes that are also
getting this 6VDC drop when you measure them in either direction. Does
that show a problem with that diode? And... how would I go about
confirming that the voltage regulator is working? It is a LM340T5.

---
Can you post a schematic of the device?

JF

 

[Uriah]

On Jan 3, 4:27 am, John Fields <jfie...@austininstruments.com> wrote:

On Fri, 2 Jan 2009 21:03:09 -0800 (PST), Uriah <uriah...@hotmail.com
wrote:



I really appreciate everyone's help in understanding some of the
problems I encounter.

I am working on one of those emergency lights that are in most
businesses. The ones with the battery that come on when the power
fails.  There is a 6 volt battery wired to a transformer and a little
circuit.  The light doesn't come on.  The battery is good. The bulbs
are good.  It has two  transistors and a voltage regulator, a bunch of
resistor and diodes.  I tested everything with my DVM and Huntron and
I see no faults.  When I test the transistors with the battery hooked
up I get a 6VDC drop from Emitter to Collector.  Does this mean that
the transistor is acting like a open switch?  There is no voltage
between the base and emitor or collector.  Can you generalize about
transistors like this?  I am thinking that there is no drive to the
base and that is why the transistor is not conducting. This sound
right?  Also, along the same line, there are some diodes that are also
getting this 6VDC drop when you measure them in either direction. Does
that show a problem with that diode? And... how would I go about
confirming that the voltage regulator is working?   It is a LM340T5.

---
Can you post a schematic of the device?

JF  

If I can't figure it out I will try and trace out a schematic. There
is about forty parts on a little 2" square board. You think with
something this small I would be able to check each component and find
a problem but nothing so far.

 

[Uriah]

On Jan 2, 10:12 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:

Uriah wrote:
I tested everything with my DVM and Huntron and I see no faults.

Since you clearly don't understand how the circuit functions, how can you
say that ?

What's a 'Huntron' btw ?

Graham

Well using my DVM I look for things like diode drops and opens on the
resistors. If I suspect anything I remove one end and test. The
Huntron I think is a great tool. You have used something similar I am
sure. Just a V/I tester or Signature Analysis. Where you inject a
low current/voltage sine wave into a component and view the results on
screen. I have found many problems with it. But, it works best when
using it to compare one signature to another taken from a known
working board, of which I don't have in this case. By the way, has
anyone ever seen a pocket size Huntron style tester. One that is
about the size of a standard DVM? I would like to have one that I can
take a long with me.
Russ

 

[Uriah]

On Jan 2, 11:46 pm, Bill Bowden <wrongaddr...@att.net> wrote:

On Jan 2, 9:03 pm, Uriah <uriah...@hotmail.com> wrote:



I really appreciate everyone's help in understanding some of the
problems I encounter.

I am working on one of those emergency lights that are in most
businesses. The ones with the battery that come on when the power
fails.  There is a 6 volt battery wired to a transformer and a little
circuit.  The light doesn't come on.  The battery is good. The bulbs
are good.  It has two  transistors and a voltage regulator, a bunch of
resistor and diodes.  I tested everything with my DVM and Huntron and
I see no faults.  When I test the transistors with the battery hooked
up I get a 6VDC drop from Emitter to Collector.  Does this mean that
the transistor is acting like a open switch?  There is no voltage
between the base and emitor or collector.  Can you generalize about
transistors like this?  I am thinking that there is no drive to the
base and that is why the transistor is not conducting. This sound
right?  Also, along the same line, there are some diodes that are also
getting this 6VDC drop when you measure them in either direction. Does
that show a problem with that diode? And... how would I go about
confirming that the voltage regulator is working?   It is a LM340T5.
Thanks for all of the help.
Russ

The diodes will have about a 0.7 volt drop if the anode is more
positive than the cathode. Otherwise the drop will be whatever the
existing voltage is since the diode will be reverse biased and not
conducting. You need to pay attention to the polarity of the
measurments you make. Same goes for transistors. If the transistors
are bipolar NPN types, they will conduct when the base is more
positive than the emitter by about 0.7 volts. If they are PNP types,
the base must be more negative than the emitter for the transistor to
conduct. Look more closely at the polarity of the measurments to
figure out what is happening.

-Bill

So what does it mean when testing a diode in circuit with power
applied, 6VDC and you test 6VDC across the diode in either direction.
With the meter set to read DVM. Does that show a problem?

 

[Jamie]

Uriah wrote:

On Jan 2, 11:46 pm, Bill Bowden <wrongaddr...@att.net> wrote:

On Jan 2, 9:03 pm, Uriah <uriah...@hotmail.com> wrote:




I really appreciate everyone's help in understanding some of the
problems I encounter.

I am working on one of those emergency lights that are in most
businesses. The ones with the battery that come on when the power
fails. There is a 6 volt battery wired to a transformer and a little
circuit. The light doesn't come on. The battery is good. The bulbs
are good. It has two transistors and a voltage regulator, a bunch of
resistor and diodes. I tested everything with my DVM and Huntron and
I see no faults. When I test the transistors with the battery hooked
up I get a 6VDC drop from Emitter to Collector. Does this mean that
the transistor is acting like a open switch? There is no voltage
between the base and emitor or collector. Can you generalize about
transistors like this? I am thinking that there is no drive to the
base and that is why the transistor is not conducting. This sound
right? Also, along the same line, there are some diodes that are also
getting this 6VDC drop when you measure them in either direction. Does
that show a problem with that diode? And... how would I go about
confirming that the voltage regulator is working? It is a LM340T5.
Thanks for all of the help.
Russ

The diodes will have about a 0.7 volt drop if the anode is more
positive than the cathode. Otherwise the drop will be whatever the
existing voltage is since the diode will be reverse biased and not
conducting. You need to pay attention to the polarity of the
measurments you make. Same goes for transistors. If the transistors
are bipolar NPN types, they will conduct when the base is more
positive than the emitter by about 0.7 volts. If they are PNP types,
the base must be more negative than the emitter for the transistor to
conduct. Look more closely at the polarity of the measurments to
figure out what is happening.

-Bill


So what does it mean when testing a diode in circuit with power
applied, 6VDC and you test 6VDC across the diode in either direction.
With the meter set to read DVM. Does that show a problem?

As was posted before, you must pay attention to the polarity of that
voltage you're measuring.

It could be a zener diode you're looking at, or simply, the voltage
on the cathode side of a diode that is (+), which means no forward flow
through the diode..

P.S.
The cathode end is that of the band.

You may want to do a dead circuit test first.

http://webpages.charter.net/jamie_5"

 

[John Fields]

On Sat, 3 Jan 2009 13:24:41 -0800 (PST), Uriah <uriahsky@hotmail.com>
wrote:

So what does it mean when testing a diode in circuit with power
applied, 6VDC and you test 6VDC across the diode in either direction.
With the meter set to read DVM. Does that show a problem?

---
It depends on what you mean my measuring the voltage "across" the diode.

If you mean that the voltage reads the same polarity of 6V whether the
meter is hooked up like this: (View in Courier)


|<-------+
| |
|A |+
[DIODE] [METER]
| |
| |
|<-------+


or like this:


|<-------+
| |
|A |
[DIODE] [METER]
| |+
| |
|<-------+

Then I'd get the meter exorcised.


However, if you meant that the voltage measured like this:


|<---[+METER-]--+
| |
|A |
[DIODE] |
| GND
|


was the same as the voltage measured like this:


|
|
|A
[DIODE]
|
|
|<---[+METER-]--+
|
GND

Then I'd suspect a diode which failed shorted or something failed
somewhere which allowed 6V to live on both sides of the diode.

JF

 

[ehsjr]

Uriah wrote:

I really appreciate everyone's help in understanding some of the
problems I encounter.

I am working on one of those emergency lights that are in most
businesses. The ones with the battery that come on when the power
fails. There is a 6 volt battery wired to a transformer and a little
circuit. The light doesn't come on. The battery is good. The bulbs
are good. It has two transistors and a voltage regulator, a bunch of
resistor and diodes. I tested everything with my DVM and Huntron and
I see no faults. When I test the transistors with the battery hooked
up I get a 6VDC drop from Emitter to Collector. Does this mean that
the transistor is acting like a open switch? There is no voltage
between the base and emitor or collector. Can you generalize about
transistors like this? I am thinking that there is no drive to the
base and that is why the transistor is not conducting. This sound
right? Also, along the same line, there are some diodes that are also
getting this 6VDC drop when you measure them in either direction. Does
that show a problem with that diode? And... how would I go about
confirming that the voltage regulator is working? It is a LM340T5.
Thanks for all of the help.
Russ

Here's a general description which may help:
Emergency lites such as you describe contain three basic
functional circuits: power supply, charge controller
and "light controller".

The power supply is the transformer, diode(s) and an electrolytic
capacitor. It provides the input voltage to the charge controller,
and 1 input to the light controller.

The charge controller is usually a simple float charge circuit.
For a 6 volt light, it should provide something between 6.5 to 6.9
volts. That is likely what the LM340T5 is used for - with a
couple of resistors added it can be set to provide the charge
voltage.

The light controller senses the voltage from the power supply.
If it does not detect any voltage, it turns the light on.
It may have a second function - to turn off the lights if
the battery voltage drops too low. Some emergency lights
have that, some don't.

Some things you can do: 1) Test the battery and bulbs by
connecting the bulbs to the battery. If you tested it
with the DMM but without the bulbs glowing while testing,
you cannot rely on the DMM reading. The battery can
look good when using the DMM, but fail when the bulbs
are conected. The *most common* failure of these emergency
lights is the battery, and simply checking the battery
with a voltmeter is useless. They _must_ be tested under
load.

2) Post the part numbers for the transistors.
3) Look for a relay - often these lights use one in
the light control circuit.
4) With the unit connected to the mains, measure the
voltage across the battery It should rise above 6
volts. If it does not, the charge control circuit is
not working. Let it run for a couple of hours if
you don't see it rise right away and the check again.
5) Pull the circuit board and try to determine what
completes the path from the battery to the bulbs.

The hardest thing is to draw a schematic based on
the board, but that could ultimately be necessary.
If you do it, check it over and over and over and over
again. If you draw it wrong, it will impede your
troubleshooting efforts. If you draw it right, you
can then analyse what the circuit does, right down to
what each component does - a good learning experience.

Ed

 

[Uriah]

I am not sure the examples appear correct on my browser. But I think
I understand what you mean. Just to clarify what I meant. If I
measure the voltage drop directly across the diode, putting my meter
black lead on the cathode of the diode in-circuit with the power on
and putting my red lead on the anode I get 6VDC on the DVM. If I
reverse the red and black leads I still get 6VDC. If I put the black
lead on ground and the red lead on the cathode I get 6VDC. If I put
the black lead on ground and put the red lead on the anode I get
0VDC. This can't mean a meter problem?

If I take a jumper and short the diode the light turns on! Somehow I
should be learning something in all of this but it is not sinking in.

 

[Jamie]

Uriah wrote:

I am not sure the examples appear correct on my browser. But I think
I understand what you mean. Just to clarify what I meant. If I
measure the voltage drop directly across the diode, putting my meter
black lead on the cathode of the diode in-circuit with the power on
and putting my red lead on the anode I get 6VDC on the DVM. If I
reverse the red and black leads I still get 6VDC. If I put the black
lead on ground and the red lead on the cathode I get 6VDC. If I put
the black lead on ground and put the red lead on the anode I get
0VDC. This can't mean a meter problem?

If I take a jumper and short the diode the light turns on! Somehow I
should be learning something in all of this but it is not sinking in.
It won't matter which way you have your probes on it.

the meter will just read the same value + or - etc...

YOu need to perform some in circuit non powered test.
if something looks strange, pull it to test it.

Use a diode test for the basic primitive procedures on
transistors and diodes.


http://webpages.charter.net/jamie_5"

 

[Eeyore]

Uriah wrote:

On Jan 2, 10:12 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com
wrote:
Uriah wrote:
I tested everything with my DVM and Huntron and I see no faults.

Since you clearly don't understand how the circuit functions, how can you
say that ?

What's a 'Huntron' btw ?

Well using my DVM I look for things like diode drops and opens on the
resistors. If I suspect anything I remove one end and test. The
Huntron I think is a great tool. You have used something similar I am
sure. Just a V/I tester or Signature Analysis. Where you inject a
low current/voltage sine wave into a component and view the results on
screen. I have found many problems with it. But, it works best when
using it to compare one signature to another taken from a known
working board, of which I don't have in this case. By the way, has
anyone ever seen a pocket size Huntron style tester. One that is
about the size of a standard DVM? I would like to have one that I can
take a long with me.

Sounds intruiging but should be totally unnecessary to fix a simple circuit.

Do you have the schematic and can you post it somewhere ? There will be key
places in the circuit that should form good 'test points'.

Graham

 

[Eeyore]

Uriah wrote:

So what does it mean when testing a diode in circuit with power
applied, 6VDC and you test 6VDC across the diode in either direction.
With the meter set to read DVM. Does that show a problem?

It means the diode is DEAD !

Graham

 

[Eeyore]

Uriah wrote:

I am not sure the examples appear correct on my browser. But I think
I understand what you mean. Just to clarify what I meant. If I
measure the voltage drop directly across the diode, putting my meter
black lead on the cathode of the diode in-circuit with the power on
and putting my red lead on the anode I get 6VDC on the DVM. If I
reverse the red and black leads I still get 6VDC.

Not -6V ?

Graham

 

[Phil Allison]

"Eeysore"

Uriah wrote:

So what does it mean when testing a diode in circuit with power
applied, 6VDC and you test 6VDC across the diode in either direction.
With the meter set to read DVM. Does that show a problem?

It means the diode is DEAD !

** ROTFL !!!!

DC voltages always read the same " in either direction " with a DVM.

Just the sign changes .....



....... Phil

 

[Uriah]

Ed,

Everything you say matches what I am learning about this thing. Only
that there is no relay on it. Everything is OK, except the little
circuit board controller. I checked the battery, bulbs, transformer
and they all seem OK,, I mentioned above that I shorted a diode that
is connected to the base of a transistor that connects the positive
battery terminal to the light bulb lead. This completes the light
bulb path and it lights up. So something is not getting through to
the fire the base. This is connected to the battery or bench PS. I
will sketch the circuit out, but boy this is a lot of work for such a
small circuit with maybe 30 components on it. I hope I learn
something that will save time. I did find a resistor that was
supposed to be 11 ohms but measured 44 ohms, and a cap that measured
bad on my Sencore LC102 but after changing them it still didn't
work.

The parts are
120AC to 12AC transformer.
Q1 D44h8
Q2 2n4403
LM340t5
A bunch of diodes, a few resistors, five caps, a zener diode and that
is it.
Thanks so much
Russ

 

[Phil Allison]

"Uriah"

I am not sure the examples appear correct on my browser. But I think
I understand what you mean. Just to clarify what I meant. If I
measure the voltage drop directly across the diode, putting my meter
black lead on the cathode of the diode in-circuit with the power on
and putting my red lead on the anode I get 6VDC on the DVM. If I
reverse the red and black leads I still get 6VDC. If I put the black
lead on ground and the red lead on the cathode I get 6VDC.

** Is the " - " segment in the display of your DVM not functioning ??

Or are you stubbornly choosing to ignore it?

BTW:

How are you sure the device is meant to run on 6 volts ??

Could it not be a 12 volt unit?



...... Phil

 

[Eeyore]

Phil Allison wrote:

"Eeysore"
Uriah wrote:

So what does it mean when testing a diode in circuit with power
applied, 6VDC and you test 6VDC across the diode in either direction.
With the meter set to read DVM. Does that show a problem?

It means the diode is DEAD !

** ROTFL !!!!

DC voltages always read the same " in either direction " with a DVM.

Just the sign changes .....

Which isn't what he said. If the sign didn't change it would be a dead
diode.

Graham