Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Default Help to identify SMD diode

Hi, I am repairing the power supply of my video projector and I need to
understand what type of diode is mounted here, in the green circle:

http://tinypic.com/r/2ltiwko/6

I see that it have three colored rings, but if I decode it with resistor
color code I obtain 652, that don't tell me nothing...
because the red ring is more width than others, I suppose that the
reading is 6522, but I don't find SMD diodes with this coding...
this diode is connected between gate and source of power mosfet, that
its source is connected to ground through 1.2ohm resistor.

this is a zener diode or schottky diode? :-(
thanks for your aid
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Default Help to identify SMD diode

Telespalla Bob wrote in message
. ..
Hi, I am repairing the power supply of my video projector and I need to
understand what type of diode is mounted here, in the green circle:

http://tinypic.com/r/2ltiwko/6

I see that it have three colored rings, but if I decode it with resistor
color code I obtain 652, that don't tell me nothing...
because the red ring is more width than others, I suppose that the
reading is 6522, but I don't find SMD diodes with this coding...
this diode is connected between gate and source of power mosfet, that
its source is connected to ground through 1.2ohm resistor.

this is a zener diode or schottky diode? :-(
thanks for your aid


Try looking up data on
1N*256
I've only seen that convention with 3 bands plus one wide though


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Telespalla Bob wrote in message
. ..
Hi, I am repairing the power supply of my video projector and I need to
understand what type of diode is mounted here, in the green circle:

http://tinypic.com/r/2ltiwko/6

I see that it have three colored rings, but if I decode it with resistor
color code I obtain 652, that don't tell me nothing...
because the red ring is more width than others, I suppose that the
reading is 6522, but I don't find SMD diodes with this coding...
this diode is connected between gate and source of power mosfet, that
its source is connected to ground through 1.2ohm resistor.

this is a zener diode or schottky diode? :-(
thanks for your aid


1N4256 ?
Can you identify the exploded 8pin driver?
Are the 4 pin devices ,over the isolation slot, opto couplers ?
Do you know the failure initiation/progression?


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Default Help to identify SMD diode

Telespalla Bob wrote in message
. ..
Hi, I am repairing the power supply of my video projector and I need to
understand what type of diode is mounted here, in the green circle:

http://tinypic.com/r/2ltiwko/6

I see that it have three colored rings, but if I decode it with resistor
color code I obtain 652, that don't tell me nothing...
because the red ring is more width than others, I suppose that the
reading is 6522, but I don't find SMD diodes with this coding...
this diode is connected between gate and source of power mosfet, that
its source is connected to ground through 1.2ohm resistor.

this is a zener diode or schottky diode? :-(
thanks for your aid



what is the make and model ?


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Default Help to identify SMD diode

Il 20/06/2012 12:20, N_Cook ha scritto:
Telespalla wrote in message
. ..
Hi, I am repairing the power supply of my video projector and I need to
understand what type of diode is mounted here, in the green circle:

http://tinypic.com/r/2ltiwko/6

I see that it have three colored rings, but if I decode it with resistor
color code I obtain 652, that don't tell me nothing...
because the red ring is more width than others, I suppose that the
reading is 6522, but I don't find SMD diodes with this coding...
this diode is connected between gate and source of power mosfet, that
its source is connected to ground through 1.2ohm resistor.

this is a zener diode or schottky diode? :-(
thanks for your aid



what is the make and model ?




Hi, thanks for your reply, here in Italy nobody is answering me...

the model is EzPro 715H from Optoma

Here some photos of burned power supply:


http://tinypic.com/r/2z8zt61/6

http://tinypic.com/r/6steag/6

http://tinypic.com/r/2urvzew/6

the exploded chip I think is an UC3844. With a magnifier lens I can read
over an not burnt portion of chip surface the signature "1844A", but I
see that the UC1844A is designed for military and aerospace standards,
then is probably that the correct device is UC3844A (with 1844A core
inside...)
the application schematic in the datasheet is very similar to this,
except for gate driving circuit
This is a schematic that I have drawn down from board:

http://tinypic.com/r/2h6drbp/6

The two units over insulation slot are optocouplers
In fact, all semiconductors in the primary side is burned or shorted...
I don't know if the transformer is good, I have measured impedance and
the primary winding is 2,2mH and the winding that supply the controller
is about 190uH...
The small toroidal transformer was burned, but I have counted windings
and I have already rewinded it.
I would want to try to repair the entire power supply. I think the fault
is born from short circuit in line rectificator diode. The main high
voltage supply for the lamp is now working again, and the logic boards
of projector is also working.
which is the anode in the diode with three rings?
is a zener diode or schottky?
Thanks again.


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Default Help to identify SMD diode

Il 20/06/2012 16:27, Telespalla Bob ha scritto:


the exploded chip I think is an UC3844. With a magnifier lens I can read
over an not burnt portion of chip surface the signature "1844A", but I
see that the UC1844A is designed for military and aerospace standards,
then is probably that the correct device is UC3844A (with 1844A core
inside...)
the application schematic in the datasheet is very similar to this,
except for gate driving circuit
This is a schematic that I have drawn down from board:

http://tinypic.com/r/2h6drbp/6


uhm... I'm sorry... perhaps the toroidal coils scheme is wrong, this
should be that correct

http://tinypic.com/r/30ag7ic/6
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Default Help to identify SMD diode


"Telespalla Bob" ha scritto nel messaggio
. ..
Hi, I am repairing the power supply of my video projector and I need to
understand what type of diode is mounted here, in the green circle:

http://tinypic.com/r/2ltiwko/6

I see that it have three colored rings, but if I decode it with resistor
color code I obtain 652, that don't tell me nothing...
because the red ring is more width than others, I suppose that the reading
is 6522, but I don't find SMD diodes with this coding...
this diode is connected between gate and source of power mosfet, that its
source is connected to ground through 1.2ohm resistor.

this is a zener diode or schottky diode? :-(
thanks for your aid


I just sent you a pdf to make you clear the trouble.
ciao Vale


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