Understanding System Power supply IC: Help Needed

[Salvaging]

Understanding System Power supply IC: Help Needed
IC is BA4900 12 pins System power supply for car stereos:

I've pulled apart an old car stereo to troubleshoot why it is not powering on at all.
It doesn't power on in the car or when I connect to a 12v bench power supply.

Goal:I will use it to attempt to convert the cassette connection to an AUX-in for an old Toyota used as a beach car - which will be other threads I start I'm sure.

I'm finding it hard to follow the traces, but I'm currently testing at the IC BA4900 which when googled I get System power supply for car stereos.

Data Sheet:
Link

Using Pin 12 GND for a test point of my black COM cable on my multimeter
I only get readings from pin5(VDD)=5.9v and pin7(VCC)=12.1v
The others show 0.0v
I'm worried that the issue may not be here though and VDD needs to reach a controller which would send a voltage back to the correct pin then other pins would light up if instructed.

Is anyone that is knowledgeable in this able to see anything in the datasheet that would tell you if any of the other pins should be alive even without the a voltage getting to the controller

Pin Votages from the datasheet
1 - VAR output 10v
2 - MODE2 SW 5v
3 - MODE1 SW 5v
4 - Stand by 5v or 0v
5 - VDD output 5.8v
6 - AMP output 1v
7 - VCC - 12v
8 - ANT ouput 1v
9 - COM output 8v
10 - Radio output 8V
11 - FM Output 8V
12 - GND

Thanks in advance.

 

[Salvaging]

Recommended Use

 

[ximikas]

Hi, you are saying this ic currently has only 5.9v output for cpu,and no other voltages. Try to look at table, it says pins 2 3 4 are control pins.They have 5volts from cpu.So these three pins should have 5 volts when radio is operating, check if the cpu is getting 5v supply .Maybe some buttons are dead,of flat cable broken,or some voltage must present at cpu pins,telling it that radio has both 12v supplies and can be turned on. Mostly one supply is for cpu to keep stations memory and should be constant, and another one is from ignition or acc key positions.In one old radios i found shorted zener, on cpu supply pins,and that was reason why radio was unable to turn on.

 

[Salvaging]

Thanks. This is my problem I can't find a data sheet for the CPU and struggling to find\follow the traces from the IC.
My theory was if I could prove that there should be another voltage present at one of the pins in the state it is in it would prove that the IC is the problem. I've ordered one and it will take a few weeks in China Mail but want to keep grinding at this.

 

[Salvaging]

Slowly identifying things

 

[Salvaging]

I'd better answer all your questions. pin5 and pin7 showing voltage.
Pin5 would be the pin for the constant power supply to keep memory would it?

#Your question prompted a thought.
I removed VCC power but left ignition power. pin5 goes to zero as I was expecting. But pin7 dropped to 1.2 mV.

Removed Ignition and left VCC only and get the original results.
i.e. pin5(VDD)=5.9v and pin7(VCC)=12.1v

 

[Salvaging]

Finally been able to trace the ACC 12v a bit after getting a bit of light in the right direction and getting a photo to zoom in.
It went through the board a couple of times via holes but managed to get to this resistor.

Now I need to find out if this is correct output of the resistor for that IC next to it to be requiring.

 

[Salvaging]

I'm hoping someone will step in here and say that your resistor shouldn't drop the voltage by this much and this is an issue.

I doubt that a resistor can do this???

I have tracked a datasheet on this latest IC that I have moved too i.e. the one under this resistor. The data sheet has the same number. You can't see it in the photo due to the flash glared it out.
It says the Voltage ranges from 5v to 24v so really looking like this resistor is an issue.

Some readings on that IC:

 

[ximikas]

This ic ad8056 is a opamp, if it is getting power at pin7 only when acc or ignition has 12volts,looks logical. Check if its pin7 doesnt route to ba4900 pins or D power transistors. It can get power not directly,but through a resistor less than 1k. Does power connector has all 3 power 12v pin? + Bu +acc amp

 

[Salvaging]

This ic ad8056 is a opamp, if it is getting power at pin7 only when acc or ignition has 12volts,looks logical.

With Just ACC pin 7 gets 0.594v
With just VCC pin 7 get 5.36v

Pin2 I'm concerned about as the ACC 12v traces to the resistor above the IC then drops to 1.2v on the other side.
...and at pin 2 it is 1.2v.
I've been tempted a few times to put 12v jumper directly to pin2 but stop myself. I may have to try and remove the resistor to test resistance.

Check if its pin7 doesnt route to ba4900 pins or D power transistors. It can get power not directly,but through a resistor less than 1k.

Pin 7 just seems to soldered to the board and I cannot see any traces from/to it. It doesn't seem to go through the board like other connections that transfer to each side, they use a small copper hole.
On the opposite side of the board there is a big ground plane.

Does power connector has all 3 power 12v pin? + Bu +acc amp

BU (which I'm calling VCC) and ACC when both connected there is no life in the device. They both read 12v in the car (ACC only reading when ignition turned on)
And I have connected both pins to a bench power-supply. (Bench Power supply 12v 25amps)
AMP pin does not have a wire to the connector in the car.

If I connect AMP on the bench all the Pins on ic 8056 show no voltage.

I am now searching for a better Datasheet for ic 8056 as it is probably completely different as the chip is actually ic 8056S

 

[Salvaging]

Pin2 I'm concerned about as the ACC 12v traces to the resistor above the IC then drops to 1.2v on the other side.
...and at pin 2 it is 1.2v.
I've been tempted a few times to put 12v jumper directly to pin2 but stop myself. I may have to try and remove the resistor to test resistance.

Damn. Because ximikas is not even bothered by the low voltage here, I thought more deeply.
The other resistors next to the IC could be setup as a Voltage divider.
And there are other IC's I'm stumbling on in my search for a datasheet that are expecting low voltages into some pins.


Update:
Using an online divider Calc and the resistor value that is connected to pin2
12v
27k ohms
4.7k ohms
Vout= 1.779
...so close enough in my books.

So I think I have debunked my theory and now have to re-read your comments ximikas, to see if I can pick up some other clues

 

[Salvaging]

Bah. when testing AMP I was on the wrong pin
But still with the new test it does not change any values with AMP connected or not.
But with both VCC and ACC connected.
I'm guessing this is correct and I can move on now.
We have to ignore the datasheet I have I think i.e. the black text in the image.

 

[Salvaging]

Back to your other advice ximikas about tracing from the IC.
I see there are a number of traces coming from under the IC.
I will see which light-up when ACC is turned on and trace them.

 

[ximikas]

This car radio does have a some known manufacturer / model ? Or it is orginal car radio ? Have you tried find a schematic for it ? That would help a lot . Looking at pcb photo ,i didn't get which type panel ,with LCD or removable panel ,it does have . Connectors to car looks specific ,not ISO standard . I'm suspecting some of these original car radios will not work ,until they have connection to car computer (CAN bus).Recently i repaired bad solderings on Toyota's car radio with cd ,cant remember a model ,but the interesting thing was that looking at connectors ,i found 4 positive voltage contacts ,+12v .Of course i supplied them all from power supply ,bus was unable to turn on that radio at home ,so we put it back in original car ,and it worked fine . So at first ,what model this car radio is ?

 

[Salvaging]

Thanks for persevering ximikas.
It is from an old Toyota RAUM. I've done a few searches for schematics but I may need to try harder.

You maybe wondering why bother and just replace it, but it has been interesting learning and I really want to get it going now that I've come this far.
I also want to attempt changing the tape drive input into and AUX-in cable.

Model: 08600-00770 Ref: CQ-JS0751C
Matsushita Electric Industrial Co ltd Japan.
Also now that I have added the faceplate pic I see there is another model number on the front that I have not noticed on mine due to smudges and glare.

KCN-5170

This is a googled Faceplate with it working.

 

[ximikas]

I just tried to find a schematic,but no luck too .
One of the connectors has tx rx pins ,i don't know exact their purpose,maybe to external display in car ,or to car computer ,so there is a some possibility ,this radio may not work without car .

Changing tape to aux input should be much easier than repairing this unit ,just need to trace tape preamplifier ic , its outputs going to audio processor TAPE inputs .Cut both (L R) channels traces and make voltage divider ,ac coupled with capacitors from audio processor side ,and also need to remove connection to motor and short the switch,which switches when tape is inside ,or leave a old tape inside Any progress with repair ?

 

[Salvaging]

No progress.
Started to wonder about the IC ba4900 Stand By connector, pin4. It sits a 0v. When this pin4 is 5v COM and AMP pins are turned on.
Traced that back to the big square CPU looking chip. Then got know where further.

I think this also related to the Amplifier/CD-Stacker connector on the back of the stereo. It is the same connector as where the tx pins are - from a pinout I found searching for the model number. My guess is tx is data and possibly relating to COM and to amplifiers/CD-stackers.
In the car there is no connector sitting loose for that whole third connector

I'm stumped for now. Will stare at if for a few days.

 

[Pano]

Moved to Car Audio

 

[Salvaging]

No progress.
Started to wonder about the IC ba4900 Stand By connector, pin4. It sits a 0v. When this pin4 is 5v COM and AMP pins are turned on.
Traced that back to the big square CPU looking chip. Then got know where further.

I think this also related to the Amplifier/CD-Stacker connector on the back of the stereo. It is the same connector as where the tx pins are - from a pinout I found searching for the model number. My guess is tx is data and possibly relating to COM and to amplifiers/CD-stackers.
In the car there is no connector sitting loose for that whole third connector

I'm stumped for now. Will stare at if for a few days.

I got this COM definition incorrect.
Looking at my own pin diagram from the second post Com is for system Common power supply.
So is it an IC, a component, the on/off button to light up the stand by pin???


The search continues...

 

[ximikas]

You can desolder the BA4900 and test it ,supply it from 12 volts ,and supply 5 volts to control pins ,and measure voltages it outputs . Have you tested volume control encoder with power button ? Does it gets 5 volts from cpu or ba ic ?