Testing a voltage regulator in-circuit

[Phil Allison]

"Eeysore the FUCKING IDIOT "
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.

** WRONG.

The OP only said the voltage reading was the same.

If the sign didn't change it would be a dead diode.

** Wot UTTERLY INSANE CRAP !!!

ROTFLMAO !!!!!

If the sign does not change when reversing the probes on a DC voltage, then
the DVM display has no " - " showing.


YOU UNBELIEVABLY STUPID SAD ASS !!!!




...... Phil

 

[Jamie]

Eeyore wrote:

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

Do you have a comprehension problem? It's clear to me what he is doing.

He's rotating the leads on the DVM. He'll get 6V DC either way.

Did you notice he stated "In Circuit"? That should have rang a bell.

Lets try this.

How about if the 6VDC(+) volts on the cathode side of the diode..


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

 

[ehsjr]

Uriah wrote:

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

Ok, that helps a bit.
The D44H8 is used to switch the lights on/off. It's an NPN,
meaning the base must be about .6v more positive than the
emitter for the transistor to turn the lights on. The
2N4403 is a PNP, meaning the base needs to be about .6v
more negative than the emitter to turn that transistor on.
You can look at the base circuit for the D44H8 to see
where the + comes from that is needed to turn the transistor
on.

They are probably using the 2N4403 to control the D44H8, with
some sort of input for checking whether the power supply is
providing DC for the unit. The idea would be to drive the
D44H8 hard so that it saturates, when mains power drops.
Likely, the zener would also be in the circuit to cause the
D44H8 to turn off when battery voltage drops to roughly
5.7 volts.

Is the zener the diode that you are shorting out? Can you
read the part number on the zener? (From that you can find
its voltage rating.) It is probably something like 1N4733

Also, these lights usually (always?) have a test button or
switch. If it has one, the switch circuit can provide
helpful clues about the circuit. Tracing it will lead you
to the circuit that turns the D44H8 on. Also you can use
your ohmmeter to find out if the switch is normally open or
normally closed. Do that test only with the battery removed
and the AC power off.

Ed

 

[Clint Sharp]

In message <49601B5C.14F319C2@hotmail.com>, Eeyore
<rabbitsfriendsandrelations@hotmail.com> writes

Sounds intruiging but should be totally unnecessary to fix a simple circuit.
Totally unnecessary as you say but if you have one it can become like a

third hand if you do a lot of analogue repair work.

Extremely useful device, similar to the component test on Hameg scopes
if it's what I think it is. With a little experience you can spot faulty
components very easily in circuit, leaky caps and analogue ICs included.

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

--
Clint Sharp