A7V8X-MX-UAY 5 VOLTS ON SPEAKER?

[oostrich]

on page 1-22 in the motherboard manual it shows there is +5 volts on
the case speaker connector.

why does it need 5volts, case speakers dont need this voltage.

my internal speaker does not work when connected to this connector, my
case speaker has 2 wires like 600 million other case speakers out
there
, why the 5 volts?
thanks oostrich

 

[Paul]

on page 1-22 in the motherboard manual it shows there is +5 volts on
the case speaker connector.

why does it need 5volts, case speakers dont need this voltage.

my internal speaker does not work when connected to this connector, my
case speaker has 2 wires like 600 million other case speakers out
there
, why the 5 volts?
thanks oostrich

From a previous post:

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&[email protected]

There are probably many ways to drive a speaker - from the few
reference schematics I've got on disk here, the driver could be
an emitter follower design or an open collector design. The Asus
boards seem to use the open collector method, and the schematic
for that is shown in my previous Google post.

Basically, the speaker forms the load for the collector lead
of the transistor, and the current through the transistor is
modulated to make sound on the speaker.

The circuit is not intended for high fidelity, and is more
like a logic circuit than an audio circuit.

HTH,
Paul

 

[oostrich]

many thanks Dave for the reply, a bit strange the 5 volts, but anyway
do you have any idea why the speaker may not work?
i have tried 2 speakers, none work.

maybe this mb is different?, cheers oostrich

 

[Paul]

many thanks Dave for the reply, a bit strange the 5 volts, but anyway
do you have any idea why the speaker may not work?
i have tried 2 speakers, none work.

maybe this mb is different?, cheers oostrich

I downloaded another copy of the manual, and I see a piezoelectric
buzzer in between the area bounded by the CHA_FAN header and the
PANEL header. Maybe the buzzer is supposed to function instead
of a speaker ? Is that buzzer actually present on your motherboard,
or is the picture in the manual incorrect ?

Considering the drive circuit for the speaker (assuming it is
installed and present on the motherboard), it is pretty hard for
it to be damaged. The only failure mode I can think of, is if you
accidently shorted the +5V connection to an adjacent GND. That
might draw enough current to burn out the connection to +5V.
Apparently, motherboards don't have polyfuses on that pin.

To test that theory, I'd unplug the computer from the wall,
then get an ohmmeter and check the resistance between the +5V
pin on the PANEL connector, and a +5V pin on some other header or
connector. For example, one of the pins on a disk drive power plug
goes to +5V, and should read close to zero ohms between a power
plug and that +5V pin on the PANEL connector.

The drive transistor might have failed - it should be a three
legged plastic device in the vicinity - but it would be hard to
test. In the figure below, I'd touch a 1K ohm resistor from +5V
to the base (B) lead on the transistor, then listen for a click
in the speaker, as a way to test that the transistor works.


+5 /
| __/
|_____|
_____ SPKR
| |__
| \
/ \
\ 33 ohm
/ resistor
\
|
| C
B | /
_______|/ 2N3904
|\
| \
| E
|
-----
--- GND
-

The 33 ohm resistor shown in the circuit, is a current limiter, and
that thing should have a 1/4W to 1/2W power rating (depending on
whether the designer planned for a 32ohm speaker, or planned to make
the circuit bulletproof against the speaker being shorted). I don't
see any suspiciously large resistors in the area of the PANEL
connector, to help identify where the drive circuit is located.
As you can eyeball the board, you may be able to see the copper
track that connects to the corner pin labelled "speaker" in the
manual - if you follow that wire, it should take you to the current
limiting resistor and the driver transistor.

Paul