Mark VII stereo question

[arj]

My '91 Mark VII came with an aftermarket stereo that works properly, but I have a hard time with the looks of it. So I bought a Ford radio/cd deck from a Contour. Today I installed it and it doesn't work right. The display lights up, and all of the buttons appear to function correctly, but... no sound. Not even any crackling, popping or white noise.

The Mark VII harness plugs directly into the Contour radio. Both have the 7-pin connection for the power/ground/dimmer/etc, and the square 8-pin connection for the output to the factory amp. When I checked the voltage at the radio's output to the amp, all 8 pins have 4.8 volts. I can't figure out if that's how it's supposed to be, or if the pins should have closer to 12 volts.

The amp and speakers all worked before, and the amp still has power and ground and doesn't appear to have a separate fuse. I also checked the voltage at the amp's input and it's the same 4.8 volts as the deck's output, so the amp doesn't seem to be the problem. Any ideas??

[Zephyr 351C]

I had this problem with my explorer, IIRC, I bypassed the factory amp and all was well.

[DustDevil]

Was the deck working before you pulled it out of the contour? Did you hear it playing? I've had this happen before, bought what was supposed to be a good head unit and when I plugged it in, nothing.

[arj]

I bought it through Ebay, so I haven't heard it work. It was advertised as NOS, which it probably is not, but the face does look like new. No scratches on the display and no wear on the buttons. So it could be bad, but it seems unlikely.

I guess it depends on whether the output to the amp is supposed to have the 4.8 volts that it does, or if it's supposed to have closer to 12. The shop manual doesn't show how much voltage there should be.

[arj]

Even though the Mark VII amp worked properly with the aftermarket deck that I removed, I tried bypassing it, to see if there's an incompatibility between it and the newer Ford deck.

Rather that no sound at all, I now hear a very subtle 'thump' noise as I change the volume level... And with the volume turned all the way up, I can hear the radio, but it's very faint.

Is the Contour deck no good? Or is there anything else that I should test/check?

[Greywolf]

I'm guessing you're hearing the quiet noise of the line-level (pre-amp) outputs.
So the question is probably why isn't the amplifier amplifying?

There is power at the amp; but is it actually turning on? Make sure the Contour radio is outputting the 12V signal to turn the amp on. If you know which pin it is (should be on the old radio, I think it's one of the 7 pins on the power harness?) you could jumper it to a 12V power source to force the amp to come on and test that way.

If the radio amp power-on signal is bad, you could tie it to the ignition power or a toggle switch.

[arj]

Besides the speaker wires, there's only one wire that runs between the deck and the amp. The shop manual calls it 'logic mute' and it's related to the factory integrated phone option. When the radio is on, the logic mute wire has 6 volts. I tried hooking it up to a different wire, so that the amp would get 12 volts instead of 6, but there was still no sound besides a popping noise.

[Greywolf]

Did you remove power from the mute? Perhaps voltage on the mute forces the amp to stop amplifying?
I'd start looking for another radio or another amplifier. :/

[arj]

Nothing changed when I disconnected the logic mute wire.

I tried reinstalling the aftermarket deck that came with the car, and it still works properly. But the factory amp appears to have given up. The aftermarket deck and factory amp worked together before I installed the Ford deck, but now the aftermarket deck only works when I bypass the amp. So who knows if the amp coincidentally died, or if something about the newer Ford deck killed it off.

If the Ford deck has no internal amplifier, then it likely works properly, since it produces very faint sound when the amp is bypassed. I guess I'll know if it's good or not, after I replace the amp. Until then, the aftermarket deck sounds better without the factory amp than it did with it. So I'll live with the teenager-style display until I replace the amp and see if the Ford deck works like it's supposed to.

[Greywolf]

You could adapt the Ford wiring to RCA plugs and use an aftermarket amp.

[arj]

That's what will likely happen, but first I'll check the Mark VII's in the junkyards. The Mark VII's came with two different amps. My car has the cheaper one, which Ford calls 'Premium'. It's just a sheetmetal box which apparently is less powerful than the aftermaket deck's internal amp. But Mark VII's also came with a much larger JBL amp, which I've seen in junkyards before. Since the JBL amps were a factory option they use the same connectors as the Premium amp, and are likely to be far more powerful. I'll try to find one before buying aftermarket.

[GopherBaroque]

I found this page researching the proper voltage to supply to the "premium" JBL amp and would like to contribute that:

Apparently, twelve volts does not harm the amp but makes the speakers pop when switching on and off.

You can easily and cheaply supply the preferred five volts with a Radio Shack 276-1770 regulator. http://crutchfield.custhelp.com/cgi-...ZwX3BhZ2U9MQ!!

[arj]

That's good to know, and it reminds me that I was at the junkyard last week and forgot to look for a JBL amp. I'll try to find one next time.