Original Audio System - FM Reception

[my8950]

Hello Noah,

I hope that wasn't a dig at Sony. I worked for Sony Canada for many years in the late '90s. They made some very fine products at that time, can't comment on the current situation. I moved to Sony after more than a dozen years at Panasonic Canada and was shocked at the loyal and quality driven customer base that Sony had.

It's from a movie...

https://youtu.be/nb_R1VZqLcE

[brokencase]

The FM signal booster arrived today so I should have an update within the next few days.

I am curious to know how you intend to install the booster.

Here's the deal... The first amplifier in the chain is the most important with regard to signal to noise ratio.

In the case of the Scorpio the first RF amp in the chain is inside the defrost grid interface module.

So I don't know if you will see much improvement by putting the booster after the interface module. If the rf amp inside the interface module is not working then you might see an improvement.

Furthermore...you can't just connect the booster directly to the defrost grid. There is special voltage isolation and impedance matching that occurs in the interface module.

It sure would be nice to have a schematic of the interface board.

[Ed Lijewski]

What also can make a (subjective) difference is to remove and reinsert the antenna cable to the radio.

I had thought about doing that to my '89s radio over past months to see if it could improve reception at least somewhat. A few days ago I saw that the station light bulb had burned out so on replacing it I also removed the antenna end from the radio and reinserted it. While I was at the rear of the tuner I likewise removed and reinserted the two black plastic female harness connectors.

Again, subjective, but I sensed an improvement in FM reception (I mention FM because until just now I forgot to check AM reception).

The same manuever--remove/reinsert--at the hatch end of the antenna cable could be worthwhile.

YMMV

So AM reception is now static free across the tuner. Before only the stronger signals were. FM to my ears is clearer; both voice and music.

To clarify, I also removed and reinserted the speakers plug along with the antenna cable and the power connectors.

I didn't expect such a significant change. Or really any change at all.

Your results may differ.

[brokencase]

I got curious about the antenna module so I took a look at the EVTM.

First let me state that I have an aftermarket radio installed and my reception presently is good, but I am in a metropolitan area with many strong stations. Also I don't often listen to the radio - I am typically listening to digital audio from the USB drive.

However I do notice that reception is slightly degraded when I turn on the rear defroster. This never really bothered me as I seldom turn the rear defrost on. Anyone else notice this?

Looking at the diagram below there is Red/White wire that goes from the radio (39) to the module. According to the description in the EVTM this is power to the module that is enabled when the radio is turned on. I don't recall addressing this wire when converting to my aftermarket radio. It may be addressed - I used a harness adapter from Crutchfield. But I though that only managed the speakers and power to the radio.

Fresh Air Inspector - You should check that power is getting to your antenna module through this wire when you have the radio turned on by measuring with a meter back at the module.

Looks like I need to pull my radio from the dash and take a look at my connections as well.

radiosch.jpg (135.96 KiB) Viewed 2638 times

[brokencase]

My Kenwwod manual shows that my radio has a Power Control Wire that is used to turn on external amplifier when the radio is turned on.

It is a standard connection that most aftermarket radios have. So this could be used to turn on the Antenna module in the Scorpio.

Questions are: How much current can this wire source? How much current does the antenna module need?

[john keefe]

Interesting... I guess rather than two separate switches, it was simpler to route both antenna and defroster through one module. My AM/FM reception is good anywhere, but I think the antenna wire that enters the hatch from under headliner is kaput. I've fried a couple rear defrost switches. Since they're not lighted switches, its hard to tell if they're on/off, but I had both buttons "extended" out (off?) and they lasted less than a week before frying. Maybe an issue with that antenna module in the diagram, or the disconnect in the antenna wiring to the defrost grid?

[Ed Lijewski]

The rear window defrost switches have a yellow light in the center when powered. Your replacements must have had burned out bulbs.

YMMV

[john keefe]

Yeah, never saw the button light come on in any of them. Probably whatever short occurred, the bulbs must have blown immediately, leaving me guessing if the button was in or out on/off. Last time, we had big fires around here and a lot of smoke. I had left the windows down a little, and the car smelled like it. So, I thought it must be residual aromatics getting blown through the vents, until it got worse and it changed to a real electrical smell, and a hot button.

Guessing that whatever kink/break there is in the antennae wiring at the hatch may be causing the defrost issue.

[andyofcolumbusmerkur]

However I do notice that reception is slightly degraded when I turn on the rear defroster. This never really bothered me as I seldom turn the rear defrost on. Anyone else notice this?

It is an issue on the later XR's. Turn on the rear defrost and the radio is staticy.

[andyofcolumbusmerkur]

My Kenwwod manual shows that my radio has a Power Control Wire that is used to turn on external amplifier when the radio is turned on.

It is a standard connection that most aftermarket radios have. So this could be used to turn on the Antenna module in the Scorpio.

Questions are: How much current can this wire source? How much current does the antenna module need?

One of those universal ford adapters they give you may already be wired for that module. Since the blue wire marked "amp/ant" turns on those power antennas. You know the kind that go up and down. I guess you could put a clamp meter on the wire going to that module and see what kind of current there is.

[Fresh Air Inspector]

Hello Brokencase,

I checked the power to the antenna interface module and all is well. Your EVTM diagram is interesting, yours is on page 94 and my 1988 version (March '87 edition), has it on page 107.

Hello All,

I tested my FM antenna amplifier today but before I did I ran some basic tests using a distant / static compromised FM station;

1. Unplug / reconnect antenna cable plug at stereo housing - no difference.

2. Unplug / reconnect DIN amplifier connector and electrical connector below it - no difference.

3. Connected FM signal amplifier - no difference. *

* This was a long shot as ideally you want to amplify the signal as it leaves the antenna. Unfortunately this isn't possible with the Scorpio antenna interface unless someone out there has a schematic AND it is possible to modify the circuit. But at ~$10 for the FM signal amplifier it was worth it as a 'test tool'.

So .... the only conclusion I can draw from my repairs and tests is that replacing the two capacitors in the antenna interface module is the only change that improved radio reception. NOTE; I did not test AM reception as we never use that band, nor did I test with the rear window defogger on.

Hope it helps.

[brokencase]

Fresh Air Inspector - Perhaps your reception is an issue with your original Scorpio radio and not so much the antenna module?

If you have an alternative and known good car radio just clip lead power and connect antenna wire to test the theory?

As I recall the original radio is easy to remove with two wire hanger "u shaped" pieces installed into the two holes on either side of the unit and pull out.

[brokencase]

Interesting... I guess rather than two separate switches, it was simpler to route both antenna and defroster through one module. My AM/FM reception is good anywhere, but I think the antenna wire that enters the hatch from under headliner is kaput. I've fried a couple rear defrost switches. Since they're not lighted switches, its hard to tell if they're on/off, but I had both buttons "extended" out (off?) and they lasted less than a week before frying. Maybe an issue with that antenna module in the diagram, or the disconnect in the antenna wiring to the defrost grid?

Problem is the stock defrost switch can't handle the current in the circuit. I can't believe Ford Europe made such a mistake.
Just about all Scorpio defrost switches go bad because of this.

Solution (which I have done) is to wire in a 30 amp automotive relay. Switch now only turns on relay and relay carries the current to the defrost grid.
Relay is stuffed behind dash. Try to find a small auto relay.

Here is the mod..

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[brokencase]

However I do notice that reception is slightly degraded when I turn on the rear defroster. This never really bothered me as I seldom turn the rear defrost on. Anyone else notice this?

It is an issue on the later XR's. Turn on the rear defrost and the radio is staticy.

This has to be alternator and ignition noise coming in on the +12v side going into the antenna module when the grid is turned on.
As I have indicated previously it is very likely that there is a JFET RF amplifier inside the antenna module. Any noise on the defrost grid gets amplified.
I'll bet you could put an RFI choke on that power wire and it would minimize the problem.

Problem is that it has to be a high current capable RFI choke. I think I'll consult the "EECIV chief" on this matter....as it is right up his alley.

[brokencase]

"EECIV chief" proclaims...

Run the power line to the antenna module several loops through a big ferrite like this:
https://www.ebay.com/itm/174334571946

Then tap off a ceramic capacitor of a .0047 uf value to ground.

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