I have a dead battery/ac powered radio that I'd like to use to learn how to repair things. But I'm already stumped. There's a component near where the power comes in that I can't identify. I'd like to test it because there was some rust and dirt near it so I suspect water damage. There are no markings on the component. Is there anything I can do to identify it then test it? It's the black thing in the middle of the picture. (And if this isn't the right place to ask, please suggest where would be better.) EDIT: I forgot to say it has 3 pins. I'll try some of the advice below.

 

1) Identify the case. Looks like a TO-220. Dimensions help. (https://en.wikipedia.org/wiki/TO-220 )
2) How many pins?
3) Are any pins connected to ground or VCC (i.e., negative or positive supply)?

 

Nice picture. Now back off a bit and show us a wider view from a different angle, e.g. frontal view.
It looks like a power transistor.

Also show us the entire circuit board from above.

 

There are no markings on the component.

there might be fainted out markings you can see in relatively high luminous flux at "just about the right" incidence and eye angles (with zooming lens of the right magnitude) . . . might be complicated if the device is attached on the PCB . . . try making some photos of the front plate (fix you camera on a steady mount or lean your hands onto a ??? pile of books on the table to get a sharp shot ... press the camera button at the time you are exhaling just after your heart-beat)

 

It's the black thing in the middle of the picture.

+1 for transistor.

It's a single sided board, so it should be easy for you to trace components around the transistor and make a schematic so we can determine polarity and important specs.

 

What is the make and model of the radio? Also, scrape off the hot glue near that component and post the circuit designation for it. I suspect it will be Qxx where xx is a number.

Dan

 

AC/DC radio... Could be a bridge rectifier or even single rectifier. Maybe a voltage regulator. Need to know the number of pins.

 

I scraped off the glue and took some more photos. There's something printed on the circuit board but I can't make it out. The radio says "Jeep" on it. It has a CD/Tape cassette player, AM/FM. The data plate says Model WPSS-1A, AC 110v, 60Hz, DC: 12v. The brand is Telemania. Here are some more photos:

 

Seeing the etch side of the board I would guess that it is a 78 series voltage regulator. The center pin is the negative supply rail. The pin near the end og the board is the output which is decoupled to ground with an electrolytic capacitor. the other pin is the unregulated input. There is now way to know it's voltage rating if you can't read the part number. If the device is NOT faulty then you should be able to work out it's voltage by doing some testing.

Les.

 

Agree. Three pins suggest either a transistor or voltage regulator for that circuit. Center to ground and a silkscreen label IC?00 is consistent with that.

Where do the red and brown wires go?

 

I got fed up and just desoldered it so I could get a better look at it. It does have (nearly invisible) markings. It's a L7808CV, Linear Voltage Regulator 8.0v. I tested it by putting about 12v into the input pin and measured about 1.4v on the output. So I guess that means it's bad?

 

So I guess that means it's bad?

Or it has a load that's high enough to cause it to go into its safe mode.

 

Did you have the ground (Common.) pin connected and did you have capacitors decoupling the input and output to ground that met the requirements on the datasheet ?

Les.

 

https://www.st.com/resource/en/datasheet/l78.pdf
re-check the pinout and chk again . . . those things tend to fail , however ... but not as easily as LM317 & LM337
(if you messed the I/O pins -- then Q16/17 might be causing the apx. 1V drop)

 

It's a 5V regulator, LM7805 .

 

Thanks for all the tips. I replaced the voltage regulator and that did the trick. It works!