Help wanted: Factory radio aux/bluetooth mod retrofit 89-92

[RobbieD]

Finally; these two pages list the voltages at IC pins, for testing.

Hopefully this gives you some more info, in making the modifications to the radio.

I think that your idea is real interesting, and I'd like to see you pull it off.

If there's anything else that might help, just let me know.

Good luck!

 

[Luis5.oh]

Finally; these two pages list the voltages at IC pins, for testing.
View attachment 127770
View attachment 127771

Hopefully this gives you some more info, in making the modifications to the radio.

I think that your idea is real interesting, and I'd like to see you pull it off.

If there's anything else that might help, just let me know.

Good luck!

Wow! I can't express how grateful I'am, nowdays people refuse to help this much :'), That's enough to entretain me for a while...
Did some wiring and failed.

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1 - The first photo shows a cheap USB adapter for the 12v outlet (cigarette) that I'm going to use instead of a 5v regulator, this should be more sofisticated and small enough, I connected the 12v feed into the main radio input ACC pin 3 and the ground into pin 6 and this is what I think my mistake (I'll tell you why next)
2 - The second photo shows how I connected the BT board.
3 - The last picture shows that I removed the AUX output on the board that did let me mount the board flush with the LCD light and added 4.7uf capacitors on the audio outputs.
So, what went wrong? I plugged the radio on the truck and as soon as I turn the acc on, the BT module blew literally, the IC fried inmediattly, and noticed the red LED didnt turn on, BUT if I turn the lights on the led would turn on, strange enough I think I choosed the incorrect ground for the voltage regulator, I'll try again tomorrow with other spare BT board I have.

Also I'll take a look at every picture you attached, thanks again buddy!

 

[MaicoDoug]

Sorry for the fail, I was looking at the 0.7Vdc at IC 401/2. pins 2 & 4 power amp, that is where I was going to recommend to sniff around. Looked about right, but I have not dug into the print yet, just not able to see anything. 1 volt in, many watts out. I was going to recommend something silly, but could work. Putting a large 8 ohm resistor on a pair of wires powered with music or test tone, and float around the active circuitry listening with headphones not actually touching anything electrical. Sort of reverse probing to see where the "deck/radio" would pick it up from. The mod your attempting is an extremely popular one.

Some early cell phones did have a small FM transmitter which interfaced into the FM radio wirelessly allowing you to stream anything that your phone was playing.

External FM transmitters are also available that have USB.

I actually have a AM/FM tuner built into a cassette. New in the box, it's yours if you pay the shipping. I still believe you came to the right place here at TRS. The dream is still alive, you'll get there.

 

[pentode]

I have a couple questions to make sure I'm fully up to speed.
What points did you get your 12V from? You said the BT module blew up - did the regulator module blow too? I would test to make sure you have a good 5V supply before connecting anything else because it sounds like you ended up with more than 5V potential somewhere.
Did you connect the audio outputs, and if so, where did you decide to connect those? There are 2 pins on the muting IC for AM stereo and a note that says "jumper for AM mono" - I would make sure those aren't jumpered and use those pins as my inputs. I'm curious why you connected caps to the audio outputs. If it's just for DC blocking I would think the BT module has those already, but either way 4.7uf seems a bit on the big side to me. That wouldn't be your problem but it would affect your audio quality.
I'm just trying to get an accurate sense of how things are hooked up to see why it failed.

EDIT: 99% sure I know why it failed. I spent some time looking at the schematics but I hadn't blown up your pics. You'll want to check your datasheet on thar BT module but I'm willing to bet that where you connected your 5V is actually a point for charging a 3.7V lithium cell. If there's no datasheet for your module look up the chip and see if it has built in lithium charging capability. If so, I think that was your problem. Easy mistake to make. It might survive/work if you gave it 3.7 volts there, but safer to either get 5V to the micro USB pins or do it the hacky way and cut up a micro USB cable and wire that to your 5v source and plug it in the USB socket.

 

[Luis5.oh]

I have a couple questions to make sure I'm fully up to speed.
What points did you get your 12V from? You said the BT module blew up - did the regulator module blow too? I would test to make sure you have a good 5V supply before connecting anything else because it sounds like you ended up with more than 5V potential somewhere.
Did you connect the audio outputs, and if so, where did you decide to connect those? There are 2 pins on the muting IC for AM stereo and a note that says "jumper for AM mono" - I would make sure those aren't jumpered and use those pins as my inputs. I'm curious why you connected caps to the audio outputs. If it's just for DC blocking I would think the BT module has those already, but either way 4.7uf seems a bit on the big side to me. That wouldn't be your problem but it would affect your audio quality.
I'm just trying to get an accurate sense of how things are hooked up to see why it failed.

EDIT: 99% sure I know why it failed. I spent some time looking at the schematics but I hadn't blown up your pics. You'll want to check your datasheet on thar BT module but I'm willing to bet that where you connected your 5V is actually a point for charging a 3.7V lithium cell. If there's no datasheet for your module look up the chip and see if it has built in lithium charging capability. If so, I think that was your problem. Easy mistake to make. It might survive/work if you gave it 3.7 volts there, but safer to either get 5V to the micro USB pins or do it the hacky way and cut up a micro USB cable and wire that to your 5v source and plug it in the USB socket.

Yes the BT module blew as soon as I turned car ACC on, I saw the spark and smoke.
The regulator I think it survived, acts weird, when I turn on the lights, its LED lights up too.

I used pin 3 for the +12v on the main radio connector so it only turns on with car ACC, for the ground I used pin 6 which I believe it's my mistake, that ground most likely feeds the actual AMPs on the radio, Idk how but that's what I think, I'll just switch to pin 2 which is the ground for the other components (I believe).

I didn't test the voltage before because I was pretty confident with it, so I'll do that and test the voltage before soldering my last BT module because if I blow it too then my project will be delayed for a couple days
I used the caps as per recommendation, but I'll take your advice I have more values in my inventory.
There is no schematic for this BT module at least that I know it's just a china 5$ board, all I know is it takes 3.7v to 5.5v.
I noticed some other mistakes I made seeing the info @RobbieD schematics. I'll make a lot of testing today and I'll look into getting a 12v charger or something to make a test bench, putting it on the truck over and over is boring.

 

[pentode]

For what you're trying to do, I'd suggest skipping the caps on the audio output - there really shouldn't be any DC voltage there and you can test for that before you connect that to the radio.

I don't think your choice of ground was a problem. Here's what I do when looking for (power) grounds on projects like this. Measure from grounds you like the look of to the actual metal chassis of the radio. A good ground point is going to read 0 ohms unless it's a funky circuit where the chassis is isolated from the actual board. I'd prefer to just use the chassis as ground because it's easy and it's safe.

Now, the part of the equation that released the smoke... I'm sure that board will run in that 3.7 - 5.5 volt range when it comes through the microUSB... but that BAT connector, like I said, is most likely meant for connecting a lithium battery to, which maxes out at 4.2 volts. Assuming it's actually a charger circuit, I'm guessing it would react very badly to having 5V or more connected there. I think that's where things went wrong for you. Hopefully you bought 2 of those modules.

I'd break things down into stages. Connect your 12v-5v regulator, make sure you have 5v coming out, then figure out how to get that 5v into the USB connector, not the BAT pads on the board and I think you'll be fine.

 

[Luis5.oh]

This is the section of the HUGE schematic sheet that covers circuitry between IC201 and IC551. I have added some highlight to trace the AM audio circuit between them. Unfortunately, it turned out lo-res.
View attachment 127767

I could PM you a higher-res of this image, if you'd like it.
Interestingly, AM audio input is on two jumpered pins on IC551, because there's an option for AM stereo. If you could get a bluetooth signal in at this IC, it might be possible to have 2 channels for stereo, I'm thinking.

These two pages show the PCB layout, top and bottom, in case it's helpful.
View attachment 127768
View attachment 127769

One more post to follow . . .

I noticed my motherboard does not have the IC551, I tried to send you a message but I'm a new user and I can't, if you still have the high res images, please PM them if you don't mind.

 

[RobbieD]

I noticed my motherboard does not have the IC551, I tried to send you a message but I'm a new user and I can't, if you still have the high res images, please PM them if you don't mind.

On the way.

 

[RobbieD]

I noticed my motherboard does not have the IC551

What is the Ford part number of your radio? Does it start with "E", or "F"?

 

[BlackBII]

@RobbieD that's some awesome documentation you have!

 

[Luis5.oh]

Quick update: Im not absent, Im still up to the project, just finishing my Lean Six Sigma green belt certification. So im not wasting the time of those who have helped me.

I bought another cheap 12v to 5v usb adapter for the cigarette lighter socket, disassembled it and replaced the burnt one, replaced the burnt BT module too, I discovered my mistake, it a was a pretty noob one, I didn't pay attention that the connector on the radio was 7pin instead of 8 shown in the schematic, so I was off by one pin in the ground side, I tapped it into the lights system and even tho it gave me continuity to chassis ground maybe it was floating or something. Works well now, so im still analyzing the schematics @RobbieD PM'd me.
I also ordered few more spare BT modules for later testing and a "lab" power supply to make a test bench. Thanks everyone!

 

[901wd#2]

Awesome project thank you for taking it on.

I had a big console stereo when I was 14. It sounded great, but I didn’t have many 8 track cassettes, so I snipped the wires off the magnetic head spliced in RCA connectors and plugged it into my CD player I kept that thing around until I was 22.

I’ve taken a few tape decks apart, trying to do the same thing but way too small for me to mess with.

 

[Luis5.oh]

Update:
Removed the metal shield on the back with the hope to find the IC551 but no, it was IC101 and 102 (both FM related), so I can conclude:
-This kind of radio DOES NOT have the IC551 or MUTE IC
The easy thing would be to use the tape circuit but thats not what I want so I'll do some more testing but so far I have made no good progress

 

[RobbieD]

Thank you for the update.

Please keep us posted.