Fixed a ViewSonic N3260w

[budm]

Re: Fixed a ViewSonic N3260w

OK, the diagram that I found does not match, as you can see it does not have Q7, ZENER, ETC.

[budm]

Re: Fixed a ViewSonic N3260w

Check and see if Q11 Collector is connected to PFC IC VCC pin.

[12rounds]

Re: Fixed a ViewSonic N3260w

it is...
should be 5v on emitter and something on the base?

[budm]

Re: Fixed a ViewSonic N3260w

OK, then Emitter should have the same DC Voltage as the Emitter of Q7.

[12rounds]

Re: Fixed a ViewSonic N3260w

i will check it and post back...

[12rounds]

Re: Fixed a ViewSonic N3260w

13.9vdc on emitters of q9 and q11; nothing on collector of q11, base has around 13vdc. need to replace q11... is this the same part as q11?

[budm]

Re: Fixed a ViewSonic N3260w

Lets measure the Base-Emitter junction DC voltage first to see if it is being bias on or not, make sure the PS_ON is still present.

[12rounds]

Re: Fixed a ViewSonic N3260w

not sure what you mean... you want me to probe the base and emitter on q11 to see if there is a difference in potential?

if that is what you mean, there is about 1vdc drop across base-emitter.

[budm]

Re: Fixed a ViewSonic N3260w

It should be around 0.6~0.7V for it to bias on and will let the current to flow through to the Collector to supply the VCC to the PFC IC.
So do the diode test on that transistor, it is PNP from the way it has Emitter connected to the + Voltage source.

[12rounds]

Re: Fixed a ViewSonic N3260w

Is it necessary to do that since there is no voltage on q11 collector? I'll check it tomorrow, but it seems like no voltage on output is a good failure indicator. What are your thoughts?

[budm]

Re: Fixed a ViewSonic N3260w

You can pop in another PNP will be the easiest.

[12rounds]

Re: Fixed a ViewSonic N3260w

looked at q11 under the scope today and it has a marking "2T" on the top. i think that this would make it a fairchild mmbt4403. which has different on characteristics than most of the other PNP transistors that i have laying around. going to have to order this part....

[budm]

Re: Fixed a ViewSonic N3260w

That is correct, it is 2N4403 PNP transistor.

[12rounds]

Re: Fixed a ViewSonic N3260w

so, based on my random sampling of parts, the 4403 is an oddball pnp with positive vbias characteristics? all my pnp parts seem to be negative. am i missing something here?

[budm]

Re: Fixed a ViewSonic N3260w

Just a plain PNP, nothing special. Vceo 40V rating, 600mA Ic, beta 100.
"the 4403 is an oddball pnp with positive vbias characteristics? all my pnp parts seem to be negative. am i missing something here?" I do not understand.

[12rounds]

Re: Fixed a ViewSonic N3260w

pretty much all of the pnp transistors that i have found laying around are similar to this.

[budm]

Re: Fixed a ViewSonic N3260w

It can only handle 200mA, You can use it for testing for now.

[12rounds]

Re: Fixed a ViewSonic N3260w

yes, but why does it say -200ma where the 4403 says +600ma? and why is Vce -40v where the 4403 says +40v? that's what confuses me.

[budm]

Re: Fixed a ViewSonic N3260w

It shows-40V, -600mA in the spec sheet page 2, see post 75.

[12rounds]

Re: Fixed a ViewSonic N3260w

ok. weird. i have the same datasheet with different signs!