This is another of my hacks for the AOR AR3000 scanner. A really quick
and dirty one ("un taglio e via"), but I liked it. What I'm describing
here refers properly to the old AR3000. That section of the circuitry
has been revised for the 3000A, and the hack may be unnecessary, though
the 3000A has basically the same motherboard.
What annoyed me in this case was the fact that the audio output is muted
by the cpu whenever the tuning is changed. Apparently, this is done in
order to mask digital glitches which may occur during the adjustment. I
found this muting time unnecessary long, and I didn't like the "tremolo"
effect which results when the tuning knob is spun faster. I prefer
little glitches but no trembling than the other way round.
To evaluate if you will like or not the mod, you can take advantage of
the fact that the audio output on the rear panel DIN8 connector is
unmuted and unsquelched (and also a little richer in basses). You can
connect that to an audio amplifier, and hear the difference.
This is a sketch of the muting path:
+---|<|--
| D26 other muting signals (squelch,...)
+---|<|--
J9 1/2 D34 R161 10Kohm |
(7) o---+---|>|---+---/\/\/\-----+--------- base of Q32 (muting control)
| |
| --- C170
to --- 0.1 uF
"PLL UNLOCK" |
=
The cpu sends muting pulses on pin 7 of J9. It sends ~1 msec pulses when
the tuning is changed, and a little longer ones during scanning (the
audio is also muted by the squelch, in that case). In the AR3000A
revision, the capacitor C170 has been eliminated, and some of the
surrounding muting circuitry has been simplified.
The dirty hack just consists in cutting the track between D34 and C176.
This way the muting is drastically eliminated. An alternative would be
to eliminate just C170, so to cut the decay of the pulse (as was done in
the 3000A), but I'm happy ths way.
This unmuting reveals the glitches of the AR3000 - notably of two sorts:
-a short click which is heard also whenever a key is pressed, in the 0.1
- 29.9995 Mhz band. This is due to diaphony between the digital command
signals and the front end, and is masked by stronger signals. I hope to
tack it with another mod someday...
-a "plop" which can be heard when 10Khz boundaries are crossed. This is
due to the IF design of the AR3000, in which the IF has a huge bandwidth
(and can suffer of blocking), and the fine tuning is achieved by
adjusting the 2nd local oscillator on 10Khz spans. The plop is more
marked in the vicinity of strong signals, due to IF saturation.
The mod is trivial - needs just a screwdriver and scraping off a single
thin track - anyway, as usual, it's your business to know what you are
doing, and I TAKE NO RESPONSIBILITY for how you may screw your scanner
up.
Operation:
----------
-disconnect the power cord! Turn the scanner uspide down. Unscrew the
bottom cover (2 screws on the bottom and 2 on the backside) and remove
it. Disconnect the loudspeaker connector.
-unscrew the lowermost board, which is the IF/audio/power-supply board
(6 screws). Locate J_7_, which is an 8 pin connector. Labels are printed
on the board. Disconnect gently the thin coax wire socketed to J1. Turn
gently the board upside down to see the SMD components side.
-locate these components by the pins of J7, on the SMD side of the pcb -
D34 is recognizable for its rectangular 3-pinned case, R161 and C170
should have the value printed on them:
IC5 (4066)
^^^^^^^^^^^^
[]
R10K
[] [] []
D34 /
[]-x-[]C.1uF[]
|_
J7 O O O O O O O O |
8 1
vvvvvvvvvvv
fuse (on the opposite side)
(in the sketch O represents a pin, [] the soldered terminal of an SMD
component)
-scrap away the track between C170 (O.1 uF) and D34, in the point x.
(it should be clear what to do if instead you want to remove C170)
-remount the board, rescrew, reconnect connectors, close the unit and
enjoy.
A final note: I'm indebted to Henry Laviers , who
sent me a copy of the service manual two years ago, and to Marc Gauw
who forwarded me the schematics of the 3000A
(which should be available and orderable from aor-uk, just to prevent
requests to us).
I'd like to very much hear comments or to know if anyone has tried other
hacks on the same box. Please email me.
Enrico Segre, segre@polito.it
ps: check out also my hacks for improving the audio bass fidelity and
narrowing AM to 6kHz...