Daytek F19AH

[UserName666]

Re: Daytek F19AH

Done. These are the highest megagpixel setting my camera can do.

[jetadm123]

Re: Daytek F19AH

One thing I should have mentioned right of the top is this monitor was used in a poorly ventilated cabinet and all of the sudden just went out and you could faintly smell burnt electronics. The poorly ventilated cabinet makes me think this was an overheat issue.

Since you mentioned that you got a whiff of the "magic smoke", can you please post two of your cool pictures of the entire board, both top and bottom.

[PlainBill]

Re: Daytek F19AH

I have been doing the tests with the power board out from the rest of the monitor. Got tired of installing it/removing it. I was gonna wait for the transformer click to stop before hooking it all back up.
Resistance across C122 in circuit with no voltage with power board removed from monitor is 25.9ohms one way and 27.1ohms reversing the leads.

OK, scratch that idea. I was thinking in terms of a short (or low resistance) across the output.

PlainBill

[UserName666]

Re: Daytek F19AH

Q102 reads as follows according to the pic I added (In circuit - No live power)
1-2 = 11.80 Mohms
1-3 = 9.97 Kohms
2-3 = 11.77 Mohms

[retiredcaps]

Re: Daytek F19AH

Can these resistance checks be made while it is still in the board??

Yes, you can do the tests in circuit. If the readings look suspicious, then you will have to desolder to be 100% sure.

PS. I'm planning to update the guide in a few weeks with some of the feedback I have gotten.

[UserName666]

Re: Daytek F19AH

To test for shorts on a transistor, test the following with ohms.

pin 1 to pin 2
pin 1 to pin 3
pin 2 to pin 3

If anything reads less than 50 ohms, it suggest a possible short.

lol I had a feeling it was gonna come to something like this. Can these resistance checks be made while it is still in the board?? I have a good feeling I won't be able to solder that small.

Okay, it looks like Q102 is a general purpose NPN transistor, PMBS3904. Spec sheet below. Pin 5 of IC101 is basically used to shut down the power supply in case of over temperature. Since a thermistor is not being used here like it is in the pdf schematic, the temperature function is not being used. From the IC101 specs, it looks like pin 5 has to be held at above .65 Volts to prevent power supply shutdown. Once it drops below .62 volts the supply will shutdown. With the monitor on can you measure the voltage of pin 5. If it's going below and above .62V, shut off the monitor and perform a short circuit check on Q102 using the numbering config on the spec sheet and retiredcaps instructions at this link:

https://www.badcaps.net/forum/showth...ng+transistors

I'm off to bed.

Re: Testing with monitor on for the 5 volts can't happen as it won't power up at all.

I've got a wild idea. With the boards hooked up the same way they were for the other voltage tests but with power off, measure the resistance across C122. It's on the back side of the board, close to the output connector.

PlainBill

I have been doing the tests with the power board out from the rest of the monitor. Got tired of installing it/removing it. I was gonna wait for the transformer click to stop before hooking it all back up.
Resistance across C122 in circuit with no voltage with power board removed from monitor is 25.9ohms one way and 27.1ohms reversing the leads.

[PlainBill]

Re: Daytek F19AH

I've got a wild idea. With the boards hooked up the same way they were for the other voltage tests but with power off, measure the resistance across C122. It's on the back side of the board, close to the output connector.

PlainBill

[jetadm123]

Re: Daytek F19AH

Okay, it looks like Q102 is a general purpose NPN transistor, PMBS3904. Spec sheet below. Pin 5 of IC101 is basically used to shut down the power supply in case of over temperature. Since a thermistor is not being used here like it is in the pdf schematic, the temperature function is not being used. From the IC101 specs, it looks like pin 5 has to be held at above .65 Volts to prevent power supply shutdown. Once it drops below .62 volts the supply will shutdown. With the monitor on can you measure the voltage of pin 5. If it's going below and above .62V, shut off the monitor and perform a short circuit check on Q102 using the numbering config on the spec sheet and retiredcaps instructions at this link:

https://www.badcaps.net/forum/showth...ng+transistors

I'm off to bed.

[retiredcaps]

Re: Daytek F19AH

The marking on Q102 is "W04" then to a right angle of the it says "57". The middle leg of Q102 appears to be connected to Pin 5 or the "RT" pin of IC101. I wouldn't know how to test that for shorts.

To test for shorts on a transistor, test the following with ohms.

pin 1 to pin 2
pin 1 to pin 3
pin 2 to pin 3

If anything reads less than 50 ohms, it suggest a possible short.

[UserName666]

Re: Daytek F19AH

Assuming pin 1 of the "opto-isolator" is the little circular indent and pin 2 is directly to the right on the same side under the X then yes its between 1.1v and 2.5v.

[PlainBill]

Re: Daytek F19AH

That is reasonable for 'R8'. The app note says .3 ohms for their example. Your DMM probably has .2 to .4 ohms resistance in the leads.

I'm getting confused here. You ARE getting voltage spikes at pins 1 and 2 of the opto-isolator so you ARE getting output of the SMPS transformer. Why didn't anything show up at the output?

OK, I'm going to be looking some more tomorrow. This is FUN!!! Maybe Jetadm123 will come up with something overnight.

PlainBill

[UserName666]

Re: Daytek F19AH

The marking on Q102 is "W04" then to a right angle of the it says "57". The middle leg of Q102 appears to be connected to Pin 5 or the "RT" pin of IC101. I wouldn't know how to test that for shorts.

The marks are from resoldering in the 10uf 63v cap. All I have is a crappy cold heat iron right now. I have a proper 30 watt iron and proper solder sucker on order.

R112 *APPEARS* to be (from top to bottom looking at the pic):
Black - Gold - Silver - Orange - Yellow.

[jetadm123]

Re: Daytek F19AH

Can you also read off the color bands on R112? Is it grey gold white orange yellow? If yes, I believe the 5th band makes it a precision resistor of 43.9 ohms

[jetadm123]

Re: Daytek F19AH

Great photo and fantastic job on the troubleshooting with PlainBill. Out of curiosity, just below IC101 is a a small transistor Q102. What is the marking on it? W04 something? Is it connected to IC101? If yes, can you check it for a short. Also, to the right of IC101 is C107. What happened above it? Looks as if something burned up.

[UserName666]

Re: Daytek F19AH

Further to my previous post (too late to edit) it looks like your right. It also looks like it connecting to the right leg of D103 too. I upped the megapixel rate on my camera and uploaded a better pic. This one is much clearer. Sorry about the blur before. Will keep my camera on this setting lol.

[UserName666]

Re: Daytek F19AH

One thing I should have mentioned right of the top is this monitor was used in a poorly ventilated cabinet and all of the sudden just went out and you could faintly smell burnt electronics. The poorly ventilated cabinet makes me think this was an overheat issue.

Alright...
R118 (In circuit - no live power) = 7.0 ohms

Across IC102 pins 1/2 (In circuit using live power) = Fluctuations between 1.1v and 2.5v

R8 (Big green resistor R112 on board - out of circuit - no live power) 00.7 ohms

**00.7ohms????? Ive never done an LCD monitor but even to me that seem not right lol

[PlainBill]

Re: Daytek F19AH

OK that schematic is throwing me on a real loop here. From what I can understand/find...

It's rough. This would be a lot easier if we had the schematic of the monitor.

Things to check:

-R8. If it's too high a resistance, Q2 shuts off early.
***Don't know where to look for R8

PDF R8 would be the green resistor standing on end on the top side of the board. It's between the blue ceramic cap at the lead end of the large cap and the heat sink for the power FET and the diode bridge.

-U1, pin 8. Do you see pulses there at about the same rate you saw them across the 10uF cap?
***Sort of. Fluctuates between .3?? - 0 - .4?? then it will fall to 0 for a few seconds then do that over again on a constant cycle.
Pos - pin 8
Neg - pin 1

Excellent. The IC is trying to drive the FET, then shutting down when Vdd drops too low. Once the 10uF cap charges up to 16 volts it tries again.

-D4 and R12. If either are open, U1 won't get run power.
***The 2 diodes on my board test as:
Out of circuit, no live power, DMM on diode setting:
Near transformer = 0 reverse leads .498v
Near filter cap = 0 reverse leads .493v

PDF D4 is on top of the board next to the 10uF cap. Yes, you circled it in yellow.

Not sure where to look for R12(PDF). I saw it going to pin 7 on the pdf so I traced back pin 7 on my board. Since the schematic shows the diode, cap and resistor near each other, is resistor R12(PDF) what I circled in Blue??
10uf 63v cap circled in orange
Diode circled in Yellow
Pin 7 is pink.

PDF R12 is board R118. 6.8 ohms, I think.

-T1 pins 4-5. If there is no continuity, U1 won't get run power.
***There is continuity between both places with the red lines.

Good.

-The voltage on U1, pin 2.
***This one is giving really jumpy readings between .035v and 1.4v

This one is a potential 'smoking gun', subject to other readings. Internally there is a pull-up resistor to 6V (generated internally). That should be at 6 volts until the opto-isolator pulls it low. It looks like the trace from pin 2 runs under IC101, C109, R120, Z101, across the board, under J101 then to pin 4 of IC102 (the opto-isolator). What is the voltage across pins 1 and 2 of IC102?

I also checked the voltage coming into the chip (per page 1 diagram of PDF) and its fluctuating between 15 ~ 19 volts at pin 3.
Neg - pin 1
Pos - pin 3

That makes sense.

The 2nd picture is to view the board without my circle marks.

That is much appreciated. You've done a heck of a job. Things I've mentioned above:

Check R118 on the board- should be 6.8 ohms.
Check the voltage across pins 1 and 2 of IC102
Check the resistance of R8 (pdf)

And for something new, I'm trying to establish the link between IC101 pin 8 and the power FET (Q2 pdf). On your picture it appears the upper pin is connected to a jumper which runs across the board to a point between R109 and the orange circle. The trace then runs down to R113, and from the other side of R113 under D103. Please verify this, and identify any other connections.

PlainBill

[UserName666]

Re: Daytek F19AH

OK that schematic is throwing me on a real loop here. From what I can understand/find...

Things to check:

-R8. If it's too high a resistance, Q2 shuts off early.
***Don't know where to look for R8

-U1, pin 8. Do you see pulses there at about the same rate you saw them across the 10uF cap?
***Sort of. Fluctuates between .3?? - 0 - .4?? then it will fall to 0 for a few seconds then do that over again on a constant cycle.
Pos - pin 8
Neg - pin 1

-D4 and R12. If either are open, U1 won't get run power.
***The 2 diodes on my board test as:
Out of circuit, no live power, DMM on diode setting:
Near transformer = 0 reverse leads .498v
Near filter cap = 0 reverse leads .493v

Not sure where to look for R12(PDF). I saw it going to pin 7 on the pdf so I traced back pin 7 on my board. Since the schematic shows the diode, cap and resistor near each other, is resistor R12(PDF) what I circled in Blue??
10uf 63v cap circled in orange
Diode circled in Yellow
Pin 7 is pink.

-T1 pins 4-5. If there is no continuity, U1 won't get run power.
***There is continuity between both places with the red lines.

-The voltage on U1, pin 2.
***This one is giving really jumpy readings between .035v and 1.4v

I also checked the voltage coming into the chip (per page 1 diagram of PDF) and its fluctuating between 15 ~ 19 volts at pin 3.
Neg - pin 1
Pos - pin 3

The 2nd picture is to view the board without my circle marks.

[PlainBill]

Re: Daytek F19AH

OK I have been looking at that IC101 data sheet pdf for about a half hour now and am unsure where to go with it. Am I supposed to test for input voltage at the VIN pin #3 with the other lead on the ground pin #1?

I've been looking it over and it gives some good information. Startup voltage is 15-17V, shutdown voltage is 9-11V. That handily explains the pulsing voltage on the 10 uF cap.

I'm going to give you the 'Cliff's Notes' version of what is happening, and speculate on what isn't happening. Refer to page 11 of the SG6841 datasheet. The part numbers I am using refer to that schematic. AC power comes in through CN1. F1 is the fuse, VZ1 is a surge suppressor, THER1 has about 30 ohms resistance at room temperature. That will drop as it warms up. The purpose is to reduce the surge as power is applied. L2 and L2, C1 and C2 are there to absorb noise transients. R1 and R2 discharge C1 and C2 so you don't get a jolt if you touch them with power off.

BD1 rectifies the 115 VAC in to 165 VDC. C4 is the large capacitor laying on it's side. R5 and R7 feed the start-up current to the IC. It charges C10. When the voltage across C10 reaches about 16 volts U1 pin 8 goes high and turns on Q2. This sends a burst of current through the primary of T1 (pins1,2 to pin 3). That causes corresponding pulses to appear at the secondary of T1 (pins8,9 to pins 6,7) and the tertiary winding (pin 4 to pin5). D4 feeds that pulse through R12, where it charges C9. The first thing we know is that pulse is not getting to C9 (the 10 uF capacitor we were discussing earlier). The secondary pulse goes through Q1 (a Schottky diode) and is filtered by C7, C8 and L3.

Regulation is handled by U2 and U3. R14 and R15 form a voltage divider. As Vo (the output voltage) rises the voltage at pin 1 of U3 also rises. When pin 1 reaches 2.5 volts U3 starts to draw current through pin 3, U2, pins 1 and 2, and R11. This turns the LED in U2 on. That causes pin 4 of U2 to pull pin 2 of U1 down, which reduces the width of the next pulse from U1, pin 8.

R8 is a safety feature. When Q2 turns on the voltage across R8 increases. This goes to U1, pin 6. If pin 6 goes too high, it shuts off Q2.

Things we know. U1 is probably good; at least it's trying to work. If you see voltage spikes on pin 8 that would more or less confirm it.
Q2 is not shorted. If it were, F1 would have blown. I believe you also checked the output diodes. (The transformer in your monitor probably has two secondaries, and two output diodes).

Things to check:

R8. If it's too high a resistance, Q2 shuts off early.

U1, pin 8. Do you see pulses there at about the same rate you saw them across the 10uF cap?

D4 and R12. If either are open, U1 won't get run power.

T1 pins 4-5. If there is no continuity, U1 won't get run power.

The voltage on U1, pin 2.

REMINDER: The component numbers are from the SG6841 schematic. You will have to translate them to your power supply.

PlainBill

[UserName666]

Re: Daytek F19AH

OK I have been looking at that IC101 data sheet pdf for about a half hour now and am unsure where to go with it. Am I supposed to test for input voltage at the VIN pin #3 with the other lead on the ground pin #1?