Lincoln radio turn-on adj (for pwr amp)?

[jm]

The Lincoln radio system (90 TownCar) has the power amp in the trunk with
four pair (balanced) audio signals coming from the tuner/casette player in front.
The tuner biases the audio signals to +12VDC when the tuner goes on and
the power amp senses this and turns on (or so I am told).

The 90-92 tuners suffer from bad design/bad electrolytics which die after 10 years
and I have a much improved design 94 model which is plug compatible except for
the turn-on bias which only goes to +5VDC, and is apparently driven directly from
the output pins of a driver IC (no apparent handy single resistor to change).

Does anyone have any experience in modifying the power amp in the trunk to
lower its turn-on threshhold to respond to +5 instead of +12, or is it better to
cut the cable and insert a cap (or zener?) with a resistor pull-up to +12, or something else?

Where can I get a schematic?
No one would give/sell/copy/etc a schematic of the old tuner part, including their official
FoMoCo sources or repair places.
Help please.

Thanks.

-JM

 

[mike appenzeller]

jm <sgm@venue1.com> wrote in message news:<bugp8k$9ii$1@pyrite.mv.net>...

The Lincoln radio system (90 TownCar) has the power amp in the trunk with
four pair (balanced) audio signals coming from the tuner/casette player in front.
The tuner biases the audio signals to +12VDC when the tuner goes on and
the power amp senses this and turns on (or so I am told).

The 90-92 tuners suffer from bad design/bad electrolytics which die after 10 years
and I have a much improved design 94 model which is plug compatible except for
the turn-on bias which only goes to +5VDC, and is apparently driven directly from
the output pins of a driver IC (no apparent handy single resistor to change).

Does anyone have any experience in modifying the power amp in the trunk to
lower its turn-on threshhold to respond to +5 instead of +12, or is it better to
cut the cable and insert a cap (or zener?) with a resistor pull-up to +12, or something else?

Where can I get a schematic?
No one would give/sell/copy/etc a schematic of the old tuner part, including their official
FoMoCo sources or repair places.
Help please.

Thanks.

-JM

JM,

Have you tried your 94 head unit with your amp?

3 years ago we bought a 90 Town Car, with the same amp-in-the-trunk
system, but the head unit had been replaced with one of the newer
mid 90's models(no knobs, all digital keypad, Fluorescent display -
recognized it from a Ford we rented on our last move, around '96).
I don't think any mods would have been done to the amp.

+5V sounds reasonable for an output bias, as an op-amp or
other push-pull amplifier will naturally have an output bias =
midpoint of the supply voltage. (I.E. If the driver uses a single
+10 volt supply referenced to ground, the output will be biased at
+5 volts), unless a blocking capacitor is used. Extra components
would be needed to change this to a different voltage.

I doubt if +5 volts would damage anything if the amp really is
expecting +12 - it just wouldn't turn on.

I'm surprised they use this type of system to turn on the amp. All
aftermarket systems use a separate switched +12 V line (originally
intended to activate a power antenna, but later used as amp turn-on).
Maybe that's where your source got the +12V voltage from.

Mike
WB2MEP

 

[jm]

Thank you. You were right - the turn-on signal came from another line -
the top (blu) wire in the power connector - which only goes to +6V on the 94 head.
Although I noticed that the adjacent connector wire does go to +12,
I still wanted to do it the 'right way' - make the top wire go to +12 or as close as possible.
After a bit of tracing thru a 220 ohm resistor and a diode, I found a 10K to ground and
a 4.7 K to a signal that goes to to about +11 from somewhere.
I removed the 10K and found that the amp would turn on, but only on ACC, not while runnning!
I then paralleled the 4.7K with a 270 ohm, and it seems to work OK with the engine on too!
Thanks for getting me started - the fact that you had a retrofit helped.
I bet your car probably just tied the blu wire to the adjacent wire.

Maybe you know something about the whine (around middle C, lotsa harmonics)
which starts when the rear tires turn - going about 5+ MPH but holds a constant pitch?
Anti-lock system? What to bypass/filter/ground/etc?
Also, any way to reduce the ignition noise too?

Thanks again
-JM

michael.w.appenzeller@lmco.com (mike appenzeller) wrote:

jm <sgm@venue1.com> wrote in message news:<bugp8k$9ii$1@pyrite.mv.net>...
The Lincoln radio system (90 TownCar) has the power amp in the trunk with
four pair (balanced) audio signals coming from the tuner/casette player in front.
The tuner biases the audio signals to +12VDC when the tuner goes on and
the power amp senses this and turns on (or so I am told).

The 90-92 tuners suffer from bad design/bad electrolytics which die after 10 years
and I have a much improved design 94 model which is plug compatible except for
the turn-on bias which only goes to +5VDC, and is apparently driven directly from
the output pins of a driver IC (no apparent handy single resistor to change).

Does anyone have any experience in modifying the power amp in the trunk to
lower its turn-on threshhold to respond to +5 instead of +12, or is it better to
cut the cable and insert a cap (or zener?) with a resistor pull-up to +12, or something else?

Where can I get a schematic?
No one would give/sell/copy/etc a schematic of the old tuner part, including their official
FoMoCo sources or repair places.
Help please.

Thanks.

-JM

JM,

Have you tried your 94 head unit with your amp?

3 years ago we bought a 90 Town Car, with the same amp-in-the-trunk
system, but the head unit had been replaced with one of the newer
mid 90's models(no knobs, all digital keypad, Fluorescent display -
recognized it from a Ford we rented on our last move, around '96).
I don't think any mods would have been done to the amp.

+5V sounds reasonable for an output bias, as an op-amp or
other push-pull amplifier will naturally have an output bias =
midpoint of the supply voltage. (I.E. If the driver uses a single
+10 volt supply referenced to ground, the output will be biased at
+5 volts), unless a blocking capacitor is used. Extra components
would be needed to change this to a different voltage.

I doubt if +5 volts would damage anything if the amp really is
expecting +12 - it just wouldn't turn on.

I'm surprised they use this type of system to turn on the amp. All
aftermarket systems use a separate switched +12 V line (originally
intended to activate a power antenna, but later used as amp turn-on).
Maybe that's where your source got the +12V voltage from.

Mike
WB2MEP

 

[jm]

jm <sgm@venue1.com> wrote:

Thank you. You were right - the turn-on signal came from another line -
the top (blu) wire in the power connector - which only goes to +6V on the 94 head.
Although I noticed that the adjacent connector wire does go to +12,
I still wanted to do it the 'right way' - make the top wire go to +12 or as close as possible.
After a bit of tracing thru a 220 ohm resistor and a diode, I found a 10K to ground and
a 4.7 K to a signal that goes to to about +11 from somewhere.
I removed the 10K and found that the amp would turn on, but only on ACC, not while runnning!
I then paralleled the 4.7K with a 270 ohm, and it seems to work OK with the engine on too!
Thanks for getting me started - the fact that you had a retrofit helped.
I bet your car probably just tied the blu wire to the adjacent wire.

Maybe you know something about the whine (around middle C, lotsa harmonics)
which starts when the rear tires turn - going about 5+ MPH but holds a constant pitch?
Anti-lock system? What to bypass/filter/ground/etc?
Also, any way to reduce the ignition noise too?

Thanks again
-JM

Just for the record, disturbing that voltage divider
caused the head audio output to drop significantly.
I put it back, then connected the turn-on line to the
+11V signal thru 220 ohm resistor and a diode, like it was done in the old unit.
It seems to work OK, but there is a significant turn-off thump, though.
Same with you?
Thanks
-JM

 

[mike appenzeller]

jm <sgm@venue1.com> wrote in message news:<bumcq3$idh$2@pyrite.mv.net>...

jm <sgm@venue1.com> wrote:

Thank you. You were right - the turn-on signal came from another line -
the top (blu) wire in the power connector - which only goes to +6V on the 94 head.
Although I noticed that the adjacent connector wire does go to +12,
I still wanted to do it the 'right way' - make the top wire go to +12 or as close as possible.
After a bit of tracing thru a 220 ohm resistor and a diode, I found a 10K to ground and
a 4.7 K to a signal that goes to to about +11 from somewhere.
I removed the 10K and found that the amp would turn on, but only on ACC, not while runnning!
I then paralleled the 4.7K with a 270 ohm, and it seems to work OK with the engine on too!
Thanks for getting me started - the fact that you had a retrofit helped.
I bet your car probably just tied the blu wire to the adjacent wire.

Maybe you know something about the whine (around middle C, lotsa harmonics)
which starts when the rear tires turn - going about 5+ MPH but holds a constant pitch?
Anti-lock system? What to bypass/filter/ground/etc?
Also, any way to reduce the ignition noise too?

Thanks again
-JM


Just for the record, disturbing that voltage divider
caused the head audio output to drop significantly.
I put it back, then connected the turn-on line to the
+11V signal thru 220 ohm resistor and a diode, like it was done in the old unit.
It seems to work OK, but there is a significant turn-off thump, though.
Same with you?
Thanks
-JM

JM,

I'm glad to hear of your success with the radio.

The late-model head unit was already installed in our car when we
bought it, but as the original owner was an elderly man, I'm sure
he had it installed at the Lincoln dealer. I'm sure the dealer wouldn't
make internal mods to the radio, it probably just came with retrofit
instructions to connect the amp turn-on lead to the wire that goes to +12.
(The +12 wire is probably for the power antenna control.)

There is a thump, or more like a crack and a thump, but I don't
remember if it's at turn-on or turn-off - it's my wife's car so I
don't drive it very often.

The whine could be the electric fuel pump in the gas tank. Is it coming
thru the speakers, or acoustically? Our fuel pump is acoustically
very noisy at times, you can sometimes hear it 20 feet away from
the car, but is not very audible inside the car. It runs at a steady
speed regardless of engine/car speed. If it's coming thru the audio
system, it could be filtering/bypassing problems, or a loose cable
ground somewhere. We get no whine thru the speakers, but a lot of
ignition noise on AM. My wife only plays cassettes, never the radio,
and I don't listen to AM talk radio when we're riding together, so
I never pursued the ignition noise problem. I do know that they
make resistive("radio suppression") spark plug wires, and resistor
spark plugs to minimize AM ignition noise but I don't think you can
use both the resistor wires and plugs at the same time - engine
performance issues - that's something you can ask your mechanic about.

Hope this helps,

Mike
WB2MEP

 

[jm]

JM,

I'm glad to hear of your success with the radio.

The late-model head unit was already installed in our car when we
bought it, but as the original owner was an elderly man, I'm sure
he had it installed at the Lincoln dealer. I'm sure the dealer wouldn't
make internal mods to the radio, it probably just came with retrofit
instructions to connect the amp turn-on lead to the wire that goes to +12.
(The +12 wire is probably for the power antenna control.)

There is a thump, or more like a crack and a thump, but I don't
remember if it's at turn-on or turn-off - it's my wife's car so I
don't drive it very often.

The whine could be the electric fuel pump in the gas tank. Is it coming
thru the speakers, or acoustically? Our fuel pump is acoustically
very noisy at times, you can sometimes hear it 20 feet away from
the car, but is not very audible inside the car. It runs at a steady
speed regardless of engine/car speed. If it's coming thru the audio
system, it could be filtering/bypassing problems, or a loose cable
ground somewhere. We get no whine thru the speakers, but a lot of
ignition noise on AM. My wife only plays cassettes, never the radio,
and I don't listen to AM talk radio when we're riding together, so
I never pursued the ignition noise problem. I do know that they
make resistive("radio suppression") spark plug wires, and resistor
spark plugs to minimize AM ignition noise but I don't think you can
use both the resistor wires and plugs at the same time - engine
performance issues - that's something you can ask your mechanic about.

Hope this helps,

Mike
WB2MEP

Mike-
The whine definitely comes thru only on weak AM stations (not acoustic), is NOT related
to RPM (revving the engine does not start it) but definitly related to the turning
of the rear wheels (Spin them on ice to more than 5 MPH) that starts the whine.
Unlike alternator whine, my whine is constant pitch (about middle C) and sounds
sharp (lotsa harmonics). Sometimes it changes in loudness when I go over a bump.
I wish I knew where to look. I tried puting a 0.1 uf across the motor on the anti-lock
with no help.

As for the engine noise, it changes in intensity when I go over a bump (Ground loose!)
and I discovered that there is a antenna connection at the lower edge of the dash
where it meets the passenger kick panel - they used a small antenna wire to that point -
and it apperntly goes on to the antenna in the back. That connnection was loose when
I got the car and noticed that when I hit the glove box lid, the AM noise would drop.
However, even in the best conditions, it still seems much too noisey compared to the
reception when the engine is off (and I get RF from the dash when I turn it IGN ON)
- much too much for a Lincoln. I tried putting big ferrites on the cables into the head unit -
no help.

A personal fixation for me is AM Stereo - I'm fastinated by the efforts to get stereo out of
AM, and wonder what IBOC will do.

Your suggestions are appreciated.

-JM