viewsonic part ID

[gstringe]

Viewsonic P220f still on it but flying in the dark with no
schematic.QH07 and QH08 are a complementary pair in the horiz ckt and
attached to each other but since removing them and marking them I am
having second thoughts of whether I put them back correctly. Anyone
have a schematic that they could look at for me. They are BD140 and
BD139 transistors.
Many thanks

 

[Franc Zabkar]

Viewsonic P220f still on it but flying in the dark with no
schematic.QH07 and QH08 are a complementary pair in the horiz ckt and
attached to each other but since removing them and marking them I am
having second thoughts of whether I put them back correctly. Anyone
have a schematic that they could look at for me. They are BD140 and
BD139 transistors.
Many thanks

I'm not familiar with your monitor, but are you sure this transistor
pair is part of the horizontal circuit? I normally see such
arrangements in the vertical output of old TV sets. Either way, I
expect the BD139 (NPN) to connect to the positive rail, and the BD140
(PNP) to connect to ground or negative rail. Are the two emitters and
bases tied together?

Follow the direction of current flow in the external circuit. Current
flows from E to C in a PNP transistor, and from C to E in an NPN
transistor. Transistor pinouts are BCE in both cases.


- Franc Zabkar

 

[gstringe]

Viewsonic P220f still on it but flying in the dark with no
schematic.QH07 and QH08 are a complementary pair in the horiz ckt and
attached to each other but since removing them and marking them I am
having second thoughts of whether I put them back correctly. Anyone
have a schematic that they could look at for me. They are BD140 and
BD139 transistors.
Many thanks

Thanks Frank, So far what I see on the pc board is that the parts have
a letter designating the circuit they are part of, hence the H for
horiz. This goes for all the parts, caps, resistors, coils etc.

I really haven't traced the circuit to look for the power connection
as I figured someone with a schematic would be easier but I guess I am
getting lazy in old age ;-)

 

[Franc Zabkar]

Thanks Frank, So far what I see on the pc board is that the parts have
a letter designating the circuit they are part of, hence the H for
horiz. This goes for all the parts, caps, resistors, coils etc.

Could the transistors be from some kind of horizontal centring
circuit?

I really haven't traced the circuit to look for the power connection
as I figured someone with a schematic would be easier but I guess I am
getting lazy in old age ;-)

Can you power up the monitor in the absence of the transistors? If so,
then measure the voltages at the pins. That should tell you which way
the current flows.


- Franc Zabkar