Need help identifying smd

[caphair]

Re: Need help identifying smd

So the processor is the problem. Can't be corrected without replacing the processor?

[budm]

Re: Need help identifying smd

Or the processor detects fault or what ever the exact problem is so it shutdown that control line, I do not the details of how this unit is designed to function, that is why you did see the Voltage on the Collector of Q12 did the toggle LOW and HIGH due to activity of the processor output that feeds Q33 Base.

[fzabkar]

Re: Need help identifying smd

        VCC   5V = power on
        +  0.22V = standby
        |
      .---+--.
      |   |
      .-.  .-.
      | |  | |
      | |  | |
      '-'  '-'
  display |   |
    o----+ Q12 |
      |   |
  5V = OFF \|  |
  0V = ON  |----+
       <|  |      hi = OFF
      |    \|  ___  lo = ON
      |  Q33 |--|___|---o
      |    <|     from micro
      |   |
      '---+--'
        |
        ===
        GND

KTC3875-GR / BR3DG3875M, KEC / Blue Rocket Electronics, NPN transistor, 60V 150mA, hfe = 200-400, marking HALG or ALG:
https://cdn.badcaps-static.com/pdfs/...ef4b37225e.pdf
https://cdn.badcaps-static.com/pdfs/...2ec8d6d3bf.pdf

[caphair]

Re: Need help identifying smd

So just for reference, how does a processor turn an LCD display on?

Does it first send backlights signal then once that's on it turns LCD display on?

Doesn't make sense why if it's on it stays on but soon as it's turned off it won't come back on unless you keep trying

[fzabkar]

Re: Need help identifying smd

Can you give us the part numbers of the major ICs and the model number of the device?

[caphair]

Re: Need help identifying smd

I'll provide part numbers of major ICs when I'm home but it's an Absolute DD-3000ABT

[fzabkar]

Re: Need help identifying smd

Is there a PDF manual for this thing?

[caphair]

Re: Need help identifying smd

I don't know I couldn't find one

[fzabkar]

Re: Need help identifying smd

What about an FCC ID? Sometimes there are useful documents in the FCC database.

[caphair]

Re: Need help identifying smd

Don't see an FCC ID unfortunately

[caphair]

Re: Need help identifying smd

Where would the main processor most likely be located, the circuit board with DVD drive/psu or circuit behind the LCD assembly?

[caphair]

Re: Need help identifying smd

Ok here's the area where Q12, Q33 are. There's another transistor Q60 that feeds 1.5v to base of Q33 through R193. It's base isn't connected to anything though, how does that work?

It's emitter connects to R154 which goes out to a pin that I traced to a chip right under the DVD drive. I'll post a pic of that next as my phone only allows one pic per post. I'm not sure if this is power for the DVD drive or linked to power on for the LCD?

[caphair]

Re: Need help identifying smd

R154 connects to pin where I marked with a red line. There's no trace going to it on the board though?

[budm]

Re: Need help identifying smd

The Base of Q60 is connected to R324, another end of R324 goes to the VIA to connect to what ever, the board may be more than 2-layer board.

[caphair]

Re: Need help identifying smd

The end of R324 that connects to base of Q60 has 1.95v when the display doesn't turn on. The other end of R324 has 5v

When the display come on, base of Q60 drops to .70v 5v stays same on other end of R324. Is it normal to have that big a voltage drop across a resistor?

I wish I could figure out what's not switching every single time.

[budm]

Re: Need help identifying smd

You can esily find out if the Transistor are switching as it should or not by check the DCV between E and B, and E and C.
if E and B changes state then E and C will also change state.
You should look up on how Transistor operate.

[caphair]

Re: Need help identifying smd

Ok I have a question. When the display doesn't come up on Q60 there's 1.92v on the base and 1.25v on emitter and collector. When display comes on there's a difference of those voltages on the collector at .67v

Does this show something wrong with that transistor or something else?

[budm]

Re: Need help identifying smd

'Q60 there's 1.92v on the base and 1.25v on emitter and collector'
You need to check the Voltage between the E pin and B pin, and between E and C pin. What are they?

[caphair]

Re: Need help identifying smd

B and E .65v
C and E 0v

[budm]

Re: Need help identifying smd

B and E .65v
C and E 0v

As I explained before, as you can see, the E-B junction of the transistor is bias ON, so the Voltage between E and C will be close to 0V (Transistor is turned ON , saturated condition).
https://learn.sparkfun.com/tutorials/transistors

https://en.wikipedia.org/wiki/Bipola...sistor_biasing

http://www.electronics-tutorials.ws/...r-biasing.html