Re: Motorcycle flasher problem.

On Sun, 30 Dec 2007 05:59:06 -0800 (PST), steve
<stevesemple@xxxxxxxxx> wrote:


Well I changed the zener to a 3.3 zener. The slight differnece now is
that the light now is on. Still no flash.

I tried to concentrate on the base to raise it up. But cant seem to do
it.
First out of frustration I tried to swap the 220k for a 10k. No real
change.

Then I tried to "divide" the current as you suggested. But still no
luck. I didnt have a 1.5k but I did have a 1.2k Resister. So used it
instead. No Luck.

I tried replacing the two 3.3 Zeners with two 4v Zeners Still no luck.

I have now tried to Remove Emitter and test the voltages as suggested
in previous post. I do not now get the >12 volts I had in past I only
get .86 at base. Its like the lower 3.3 zener has reduced this
voltage. Please see the schematic below. It has new tested voltages
with the 3.3 Zener. This schematic is with the EMITTER DISCONNECTED.




+o----------------------,
| + |
(2.9) | |
.------------.-|<-.----o--------------o------------------. |
Lamp
| 1N4148 | | | .-.
| . - . | | Mosfet | ( X )
| .------. | | IRFZ34 | '-'
o | T R | | | 60v 30A | |
| |2n3906| o | 0.050 Ohm | |
|(2.93v) '------' | | | |
.-. | | | .-. | Front | |
| | 100k | | | | | 220k | .--o---. | |
| | E B C | | | | | | |
'-' '-' | | | | |
|(1.97v) | | '------' | |
o-----. o | | | | | |
| | TR 2N3906 | | | | | | |
| | | | | | | |
| [Emitter Removed] | | G D S |
'--.
| | E | | |
|
| (Q1)>| (.86v) | (Q2) |(2.93 v) |3.3
|
| |-----B--------o o---o |
1N4728|
| + /| | Mosfet | | |Zener
|
--- | C | VF5408 | D | |
|
--- |(1.97v) | ||-+ - /--/
|
10uf |(0v) | 10k (1.79v)| G||<- ^ ^
|
/16v | '----|___|-------|----o------||-+ | |0v
|
Elec | | | | | |
|
trol | | .-. o---o |
|
ytic | 3.3Vz | | |100k | S |
|
| 1N4728 /--/ | | | |
o--'
| Zener ^ '-' |(0v) | +
| |(0v)|(0v) | |
o----------------------o----o---------o------------------'
| - -
'------------------------o




Then I tried to remove the Mosfet from the equation completely. See
the Schematic below. It has no mosfet and the EMITTER DISCONNECTED and
the COLLECTOR DISCONNECTED. So the only thing actually connect to the
Transistor is the base. See the voltages.



+o-------,
| + o
Diode1N4148 (2.93) | | /
.------------.-|<-.----o--------o---. |Lamp
| Anode | | .-. /
| . - . | | ( X )- ---
| .------. | | '-' \
o | T R | | | | \
| |2n3906| o | o
|(2.72v) '------' | | |
.-. | | | .-. | |
| | 100k | | | | | 220k | |
| | E B C | | | |
'-' '-' | |
|(2.69v) | | |
o-----. o | |
| | TR 2N3906 | | |
| | | |
| [Emitter Removed] | | '--.
| | E |(.86) | |
| (Q1)>| (.86v) | |3.3 |
| |-----B--------o |1N4728|
| + /| | |Zener |
--- | C | | |
--- | | /--/ |
10uf |(0v) | 10k | Collector ^ |
/16v | '----|___|-------|----Removed |0v |
Elec | | (open) | |
trol | | | |
ytic | 3.3Vz | | |
| 1N4728 /--/ | o--'
| Zener ^ | +
| |(0v |
o----------------------o----o---o---'
Anode | - -
'---------o


Perhaps makeing the circuit simpler (initially) can diagnose the
problem.
I wonder if the light has some effect or as you mentioned the power
supply.

If I put a cap across the + and - where it comes out of the adapter.
Should I use an electroliytic cap. and do I put + on + and - on -.

Regards

And Happy New year.
I suppose you could say this darn thing is spanned the years.

Hi Steve

Taking the mosfet out was a good move - no way for the light to turn
on (in theory).

I must have led you astray. When I looked at the original schematic I
thought the 15 V zener was in the 3 volt circuit. There are two
zeners; one actually affects the operation (3 V), the other is there
solely as a protection for the mosfet (16 - 25 V).

The one protecting the mosfet has to have a higher Vz than the power
supply - it will never be doing anything if all goes according to
plan. In a vehicle there are transient voltages that can eat
semiconductors and it is only there to protect against a voltage
spike.

A diode of the correct Vz voltage in there, but with the polarity
reversed will also cause the lamp to come on.

IF (that is what it appears) you have a 3.3 Vz Zener diode in the
"transient protection" slot (across the mosfet) it will begin
conducting when you put 14 volts on it via the lamps and the lamps
will come on with 11 volts across them (and depending on the current -
the zener may get hot and short out - effectively turning the diode
into a piece of wire - conducts in both directions at all voltages).

The only way for the lamp to come on with no mosfet is for the zener
to supply the path for current - nothing else. Use a small
incandescent lamp too until we get it working - a single led might
just come on due to leakage in the rest of the circuit and that would
only add to the troubleshooting problems. One thing at a time . . .

You had a clear, and presumably correctable, problem in that biasing
circuit and we should be dealing with that. Now, with the lamp on all
the time you have two distinct problems.

You want to get back to square one - it is a simple circuit but
multiple problems in one circuit tend to make troubleshooting
exponentially harder to deal with.

If it is lighting dimly (while troubleshooting - mosfet in the
circuit) tie the gate of the mosfet to the source (ground) that should
keep the mosfet in an "off" condition (while the gate is NOT connected
to the PNP transistor) and then we can deal with the collector of the
PNP without any outside influences. OR - as you've done,leave the
mosfet out until we get the PNP transistor doing what it is supposed
to do.

Mosfet gates are incredibly sensitive. A smidgen of dirt or solder
flux that's acidic or a de fluxing solvent that is mildly conductive
or just high humidity and a hygroscopic substance on the terminals or
circuit boards and they can turn on when they should be off. Floating
terminals with long enough wires on them pick up noise from the
surroundings and will cause the mosfet to amplify the noise. This is
normally just a problem while the gate is not connected to anything -
but it can affect the ability to troubleshoot.

THEN:
Concentrate on getting four volts or more at the collector of the PNP
transistor - without that nothing can work. That voltage exceeds the
mosfet's threshold voltage and should be turning it on fully - when
the gate is back in the circuit.

In my circuit breadboarding I haven't encountered a mosfet turning on
with its gate disconnected - it can happen though. If it is turning
on enough - it lowers the voltage at the input to the PNP circuit and
can be masking the problems there.

To make the communications clearer, is there an email address you can
use? It is relatively easy for me to draw schematics and put them in
a gif or jpg format and that can eliminate some misunderstandings.

If you can also make drawings that would be great. My spam stop email
address is ganeth <at> movemail <dot> com. It will handle
attachments.

I have some trouble making out the ascii schematics. That may be some
of the communication problem. In my reply window I can't see the
schematic at all, and have to go back and forth to the message window.

Regards
bob
--
.

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