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Broan QS2 range hood fan control...


G. Paul Ziemba

Can anyone explain the electrical principles of the Broan \"Quiet Series\"
(also called \"Allure\") range hood fan?

This unit was made in 2005. There is an electronic control board
with three relays that appear to activate three blower speeds
(low, medium, high). The blower motor has four wires and there is
a 7.5 uF capacitor involved.

There are pushbuttons for the three speeds. Speeds 1 and 3 work correctly.
After 14 years of use, speed 2 (most frequently used speed) worked only
intermittently but did respond to impact adjustment. Now it doesn\'t even
do that.

I can hear a relay click for each of the three speeds. but the motor
does not turn at all for speed 2. I suspect either failed relay contacts
or a bad joint/broken trace, but I haven\'t gotten a look at the circuit
board yet (pending arrival of new membrane button cover which gets
destroyed when accessing control board).

Anyone know how the motor circuit works? Given that there are only
four wires it seems to be a bit more complex than common-cap-1-2-3.

Oh, and although it would be easy to throw parts at it, the control
board retails for $200. I\'d be happer to see if I can resolder or
throw a $5 relay at it.

G. Paul Ziemba
FreeBSD unix:
10:11AM up 50 days, 17:52, 41 users, load averages: 0.16, 0.18, 0.22


Three windings on the motor and a common. Most typically, such things are one/two/both, but in your case, it is one/two/three. So:

a) determine the motor voltage - likely the same as the line voltage.
b) If you can remove the motor from the circuit, do so.
c) Determine the common.
d) Apply voltage at each winding - additionally, not sequentially - and note if the motor speed increases as expected.
f) If so, the relay is likely bad. 15 years is not a bad service life.
g) If not, the motor likely bad - and it will be a close-run thing whether to replace the hood or just the motor.

Best of luck.

Peter Wieck
Melrose Park, PA

G. Paul Ziemba

\"pfjw@aol.com\" <peterwieck33@gmail.com> writes:

>Three windings on the motor and a common. Most typically, such things are one/two/both, but in your case, it is one/two/three.

It\'s been a while since my original post and Peter\'s reply, but I
finally got replacement faceplates and got a look at the control
board yesterday so I could trace the circuit.

Key discovery was that speed control is accomplished via tapped
autotransformer rather than tapped motor.

The faceplate is a flexible adhesive plastic that covers the pushbuttons
and LEDs. It is affixed to a plastic bezel on the front of the hood and
covers three screws holding the control board assembly.

By prying the faceplate carefully off the bezel, it can be saved and
reused. I was not confident that I could avoid destroying it during
removal, and some of the button areas had worn clear, thus I waited
for replacements before beginning.

The control board had some glue along the back and one side that I went
at carefully with a small flat-blade screwdriver to detach from the
control board housing (this step can be done on the bench).

There are three SPDT relays, but there is only one hot wire to the
fan motor. There is an external autotransformer, attached via plug J3,
which is tapped for medium and low fan speeds.

Relays are all the same kind, labeled 833H-1C-C-12VDC. They are
available from various sellers on ebay as well as at Mouser for
around a dollar. Data sheets with pinouts are available around the web.

The fan motor has a hot, neutral, capacitor tap, and ground. The hot
lead attaches to the control board at J1-8.

The rightmost relay applies line voltage to the top of the
autotransformer (black lead at J3-3). The bottom of the autotransformer
(white lead J3-1) probably goes to neutral but I did not trace it.

The middle and left relays switch the fan hot lead to either the AC
supply at the top of the autotransformer or to one of the two lower-
voltage taps (blue and red).

I measured the resistance across all combinations of the four leads
from the autotransformer to figure out the winding topology. Red seems
to be the lower voltage tap (low speed), and blue is the higher voltage
tap (medium speed).

The medium speed was the only flaky one, which corresponds to the
normally-open contact of the left relay.

I inspected all of the relay solder joints, traces, and related
connections on the board and did not see any cold solders or broken
traces. But I reflowed the solder in case there was a hidden flaw
(doing so did not correct the problem).

Since the relays were inexpensive, I ordered six and plan to replace
all three. I\'ll try to report results after swapping out.
G. Paul Ziemba
FreeBSD unix:
1:26PM up 7 days, 5:12, 32 users, load averages: 0.14, 0.20, 0.18
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