Fixed a ViewSonic N3260w

[12rounds]

Re: Fixed a ViewSonic N3260w

i am not getting 12 or 24v. i am getting about 65v in both of these places. there is also something wrong with q1 and q2 - possible with ic1. i get 346v on q1 drain, a pulsing low on the gate and what looks like nothing on the source. i have pretty much nothing on q2 anywhere.

i have 13.2v on p12 of ic1 so it is getting voltage. i have nothing on the EN1 line (ic1p8). i think that i have an issue with optocoupler 1c4 - i see that there is 5v on p1 and 4v on pin2, so the diode should be coming on. on the primary side of the coupler i have 14v on p4 (collector) and -8v on the emitter (p3).

i don't really know where to go from here. is t2's only output 5v? and t1 12 and 24v?

[budm]

Re: Fixed a ViewSonic N3260w

"i am not getting 12 or 24v. i am getting about 65v in both of these places." I do not understand on 65V reading.
"t1 12 and 24v?" That is correct, IC1 L6598 is the SMPS for the 12V/24V power supply.
Page 15:
PIN 8:
Comparators
Two CMOS comparators are available to perform protection schemes.
Short pulses (≥ 200 ns) on comparators input are recognized. The EN1 input (active high),
has a threshold of 0.6 V (typical value) forces the device in a latched shut down state (e.g.
LVG low, HVG low, oscillator stopped), as in the under voltage conditions. Normal operating
conditions are resumed after a power-off power-on sequence. The EN2 input (active high),
with a threshold of 1.2 V (typical value) restarts a Soft Start sequence (see timing
diagrams). In addition the EN2 comparator, when activated, removes a latched shutdown
caused by EN1.
So if pin 8 sees 0.6V 200 nano second pulse, it will then trip the shutdown.
You should check C15 (0.022uF 1KV cap) which is connected to one end of T1 Primary winding to ground, if the capacitance goes down, it will produce enough pulse to trip the IC.

[12rounds]

Re: Fixed a ViewSonic N3260w

i am reading 65v on cns1 where i should have 12 and 24v. i don't know why....

[budm]

Re: Fixed a ViewSonic N3260w

That has to be error in measurement, the 12V/24V are in the secondary side so you will use the chassis as the ground ref.

[12rounds]

Re: Fixed a ViewSonic N3260w

i switched my reference. still getting the weird 65v. it doesn't make any sense.

i'm confused because in order to get anything on cns1/2 i need to see voltage on the source side of q1 or nothing is going to propagate to across to the secondary side of t1. i don't see anything on q1 source, but somehow there is still 65v.

what i really don't get is where the different voltages are coming from. i thought that t2 was only 5v. the only thing that makes me wonder is the way that the schematic is drawn to show crs1 as a part of the t2 5v supply. then there is the cut-away showing crs1 and crs2 which doesn't make any sense - why aren't they labeled as being on the t1 secondary?

[budm]

Re: Fixed a ViewSonic N3260w

"i switched my reference. still getting the weird 65v. it doesn't make any sense" OK, in the primary side of the circuit, you have to use negative leg of the filter cap as the ground ref.
The CNS1 and CNS2 are in the secondary side so the ground ref is the chassis, so CNS2 PIN 1~5 (24vdc OUTPUT) you are getting 65V? are you sure you have the meter set to VDC? How about CNS1 pin 9~11, are you getting 5VDC?
Bottom line, what are you getting at 5V PINS, 12V PINS, 24V PINS?
Do not try to measure the voltage at the Source of Q1,if it is running you can have very high voltage that can damage your meter, it will be high frequency AC that meter cannot measure.
How about C15 capacitance?

[12rounds]

Re: Fixed a ViewSonic N3260w

Will check and double check tomorrow and post results.

[12rounds]

Re: Fixed a ViewSonic N3260w

OK. so, i don't know where my head was at before, but even knowing that i had 2 different ground references, i must have been on the wrong one measuring CNS1 and 2.

here are the results, with respect to chassis GND:
CNS2
pin 1-4 = 0
pin 5-8 = 0
p9 = 4.8
p10 = 4.8

CNS1
pin 1-4 = 0
p 5-6 = 2.5
p 7-9 = 5
p 10 = 3.4
p 11-12 = 4.8

i have a diagram that says p12 on cns1 is over current protect and should be 0v. i did not check capacitance of c15 - mains side is 346v, d12 side is 465v.

[12rounds]

Re: Fixed a ViewSonic N3260w

Went back and re-read to re-think...

Question (may be stupid and obvious) - active high means that the voltage on a pin will always be above the threshold in normal operation, correct?

If so, my pin8 is at pretty much 0. reading the description you posted of how the comparator and EN1/2 work, i expect that something is wrong in this portion of the circuit. I went through to verify the schematic diagram and there are some differences here. I think that i have an issue with optocoupler ic4 - i see that there is 5v on p1 and 4v on pin2, so the diode should be coming on. on the primary side of the coupler i have 14v on p4 (collector) and -8v on the emitter (p3).

2 questions - 1. if t1 is not on, where am i getting 14v from (measured on the secondary side of the optocoupler)? 2. what could cause the primary side of the optocoupler on the emitter to drop below reference and read as -8v?

i will lift a leg on c15 and try and measure its capacitance with my pos cap meter....

[12rounds]

Re: Fixed a ViewSonic N3260w

tried to measure cap c15... i think i have an issue, but i don't know if it is equipment or the part. i have a fluke12 to measure capacitance. 0.022u is out of range so i figured i could connect in series with a cap of known value and read the sum and calculate. i think that the meter has the resolution to do this in the 1u range. i get a reading of 0.001u when i do this. is this a equipment problem or a bad part?

[budm]

Re: Fixed a ViewSonic N3260w

You hook up a know value cap (something close to the same range) in parallel with C15, if the C15 is good then the reading should not be the same as the known good value, it should be = known value + 0.022uF. You will do the test with cap off the board.

[12rounds]

Re: Fixed a ViewSonic N3260w

so, i have a cap measuring 1.94u. In parallel with c15 my reading is still 1.94. i will try and find a cap tomorrow at work with a value closer to 0.022u, but is this looking like like i should replace the ceramic discs on the board? i am ready to spend the dollar!

question- the marking on the side of c15 is:
rr
102k
1kv64

doesn't that make this a 0.001uF cap?

[12rounds]

Re: Fixed a ViewSonic N3260w

measured c15 in parallel with another ceramic disc which measured 0.117u. I get 0.118u, which is right on, I believe. I don't have a way to measure esr.

[budm]

Re: Fixed a ViewSonic N3260w

So the know ceramic cap is measured at 0.117uF, then you connect the C15 0.022uf in parallel, then the total capacitance should be = 0.117 +0.022 = 0.139uF.
Am I reading your post correctly?

[12rounds]

Re: Fixed a ViewSonic N3260w

C15 is marked as 102k making it a 0.001uf cap. Unless i am misunderstanding the code.

[budm]

Re: Fixed a ViewSonic N3260w

.001 will be way too small, I think the SCH we are using does not have the matching designators to the board we are working on.

[12rounds]

Re: Fixed a ViewSonic N3260w

hang on... on a different page again. talking about c15 i referred to the schematic. after looking at your picture i realized that you are talking about something different! Let me pull that cap and check it

[12rounds]

Re: Fixed a ViewSonic N3260w

meter reads this one (c16) as 0.021uf

any thoughts on the ic4 question from post #109? there are some circuit changes compared to the schematic.

[12rounds]

Re: Fixed a ViewSonic N3260w

i replaced the optocoupler ic4. i still have weird measurements between NTC3 and EN1 of IC1. i don't understand how a i can have so many unpredicted changes in polarity across ic4 and along the feedback net???

NTC1 has to be bad. it is dropping nearly 14v. i think zd3 may be bad also. i don't have much of a clue what the values of these should be - any ideas?

[Pableros]

Re: Fixed a ViewSonic N3260w

Necesito ayuda urgente
VALORES DE ZD-1 Y ZD-3 DE VIEWSONIC FSP228-3F01
ESTAN EN CORTO Y EN EL DIAGRAMA NO VIENE
Por favor si alguien lo sabe los valores
Gracias amigos