head unit disc loading problem

[scampo77]

i have a dvd drive inside the head unit and it doesnt seem to recognize when a disc is coming or going. there is 4 IR led 2 above and 2 below the disc. the 2 on top have 2.9v and the 2 on the bottom have 1.1v. is there a way to align these? they are flat square leds can i replace them with round ones? if i press down on the top 2 leds i can get the disc to jitter around.

are these ir leds? how can i "see" infered light to see if they are working?

the model is a t-view dvd70ts. i asked them for a wiring schematic but so far no response from them.

[Perry Babin]

Measure the DC voltage across the receiver of the IR pair. Does the voltage change significantly when you insert a disc? What is the voltage with/without the disc?

[scampo77]

i figured out that the top ones are the sensors i can get them to react to my desk lamp quite consistently. i can also watch both of them change in voltage when light is taken away or introduced.

the bottom 2 however i cannot seem to get going. i pulled the LEDs to get a better picture of the board. if i try to install a normal led i get a faint light but i do get light. with the LEDs installed i get around 1vdc. with them out like now i can only get voltage at pads B+D and i am getting 5vdc.

[Perry Babin]

If there isn't sufficient current through the emitters, you will need to follow the circuit back to find the current limiting resistor. Check it to confirm that it's within tolerance and there are no bad solder connections on it.

[scampo77]

am i chasing the 5v source back? i chased it out of the dvd drive to a ribbon cable that is marked
lcd5v. does this mean this part is ok because it is measuring 5v? or do i keep going back or forward?

am i even doing this correctly? am i chasing things in the correct direction? (see picture)

[Perry Babin]

If the 5v line is directly connected to the 5v regulator, the current limiting resistor may be in the ground side, possibly on the other side of the board.

[scampo77]

your right there is a 221 on the other side and it is measuring up at 215. is that enough to be concerned?

[Perry Babin]

That's not a problem. Can you measure the DC voltage across the resistor when the LEDs are in place?

[scampo77]

sorry for the late response i had to reassemble all the plastic parts in the dvd drive

in reference to my last posted picture the voltage is...

B-5v
A-4v
C-4v
D-3v

and on the 221 resistor on one side the volatge is 3v and the other side of the resistor the volatge is 0v

[Perry Babin]

1v per emitter seems low. I would have expected something closer to 1.6v. The current flow through the resistor and emitters (~14ma) would probably be enough if the forward drop of 1v was normal so either way, I'd suspect that they're defective.