Daytek F19AH

[PlainBill]

Re: Daytek F19AH

To narrow things down a little more I tested a few more things.

-The 10uf 63v cap by the filter cap that was previously fluctuating between 11 and 17 volts is now sitting steady at 1.584 volts

-IC101 Between pins 1-3 the input voltage is 4.27 volts where it used to fluctuate from 15-19v

-No voltage coming to opto isolator anymore

I will say that when I put D108 back in it did take quite a while. If it was good out of board and I somehow heat damaged that part does that give cause for the previous symptoms? If now damage it would have been the same result as not soldering it in???

That would indicate a problem with the SG6841 or you managed to create a solder short. Probably the former.

PlainBill

[retiredcaps]

Re: Daytek F19AH

That would indicate a problem with the SG6841 or you managed to create a solder short. Probably the former.

findchips.com finds no SG6841 anywhere. They are available on ebay for about $6 total (part + s/h).

For those that haven't used findchips.com (I just discovered it), it searches all the popular sites like digikey, mouser, and displays stock and price.

[UserName666]

Re: Daytek F19AH

Any chance the power supply has started? Remember, the clicking indicated the power supply was trying to start. Checked for 12V at the output? Power LED on? Have the voltages at pins 2,7 and 8 on IC101 changed?

Yes they have:
Pin 1 - 2 = .000 ~ 001v
-it was-
Originally Posted by UserName666 View Post
-The voltage on U1, pin 2.
***This one is giving really jumpy readings between .035v and 1.4v
Neg - Pin 1
Pos - Pin 2

Pin 1 -7 = 1.582v
Cant find a previous test for 1-7

Pin 1 - 8 = 1.573v steady
-it was-
Originally Posted by UserName666 View Post
-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

Ahh, crud. Here it is.

PlainBill

All caps as you marked

[UserName666]

Re: Daytek F19AH

That would indicate a problem with the SG6841 or you managed to create a solder short. Probably the former.

PlainBill

Possibly by forgetting to solder in D108 before plugging it in??
Heat damage to D108 while soldering it in??

Soldering iron never went near IC101. All solder joints clear.
If I fried IC101 I'm gonna have to stop because thats way too small to solder.

[retiredcaps]

Re: Daytek F19AH

Heat damage to D108 while soldering it in??

If I fried IC101 I'm gonna have to stop because thats way too small to solder.

I would say no to the heat damage. D108 is attached to a heat sink. When you soldered it back in, the heat sink sucks up some of the heat so D108 should have NOT gotten hot.

For soldering something that small, check out this video by CuriousInventor. After watching it, I think you should try it on some junk parts and attempt on the real thing.

http://www.youtube.com/watch?v=3NN7UGWYmBY

If you still are not confident, ask around who has good soldering skills and offer a 6 pack in exchange for their soldering services?

[UserName666]

Re: Daytek F19AH

OK that could be of some use if I do decide to try it but for now is there anything to check that might explain why all my readings went strange after putting D108 back in? I can trace 115 up to the rectifier which is putting out 161 to the filter cap but lose it from there. Something caused everything to go off after putting D108 back in.

[alexanna]

Re: Daytek F19AH

Visually inspect all your solder joints on the capacitors you replaced, And then wiggle the caps to check for movement on the solder pads. There is a possibility you moved something breaking the circuit.All this should be done power off.
Al.

[UserName666]

Re: Daytek F19AH

All the caps are fine. This started after reinstalling D108.

[UserName666]

Re: Daytek F19AH

This power board is seriously starting to piss me off now

[UserName666]

Re: Daytek F19AH

Is there anything to try next? I don't know what to do here.

[UserName666]

Re: Daytek F19AH

I think is has be something before the IC101 because it had 15~19 volts before coming into it and now it only has 4.27v at pin 3. In order for IC101 to work properly would it not need the proper voltage coming into pin 3? There is something holing back the full 15-19 volts coming into IC101's input.

[PlainBill]

Re: Daytek F19AH

I think is has be something before the IC101 because it had 15~19 volts before coming into it and now it only has 4.27v at pin 3. In order for IC101 to work properly would it not need the proper voltage coming into pin 3? There is something holing back the full 15-19 volts coming into IC101's input.

Refer to the schematic on the datasheet. R5 and R7 (750K ohm each) provide voltage to pin pin 3 of IC101. The voltage at pin 3 will vary depending on the load presented by IC 101, C9 (pdf), and D4 (pdf).

Hmm, you have a point. Double check the orientation of the diode you circled in orange. If you have it in backwards it will limit the voltage at pin 7.

One other point which you should take into consideration. I'm used to seeing dark spots on the PC board in the inverter area. These are usually due to heat generated by the transformer drivers. And indeed, I see some darkening between J31 and the two 22 ohm (red, red, black) resistors. However, there is a much darker spot nearer to the transformer. The only component that could be responsible for that is the inverter transformer.

PlainBill

[UserName666]

Re: Daytek F19AH

Refer to the schematic on the datasheet. R5 and R7 (750K ohm each) provide voltage to pin pin 3 of IC101. The voltage at pin 3 will vary depending on the load presented by IC 101, C9 (pdf), and D4 (pdf).
**I'm still having a real difficult time converting that schematic to my board.
Been looking for about 3 days now for a schematic/service guide for this thing an 0 luck.

Hmm, you have a point. Double check the orientation of the diode you circled in orange. If you have it in backwards it will limit the voltage at pin 7.
**Diodes are all in correct ways

One other point which you should take into consideration. I'm used to seeing dark spots on the PC board in the inverter area. These are usually due to heat generated by the transformer drivers. And indeed, I see some darkening between J31 and the two 22 ohm (red, red, black) resistors. However, there is a much darker spot nearer to the transformer. The only component that could be responsible for that is the inverter transformer.
**Would we not have to figure why the transformer stopped clicking before voltage will reach the inverter??

I also went over every solder joint I previously did and still cannot get the transformer to resume that clicking noise like it had before. For some reason I keep thinking I screwed something up by forgetting to solder in D108 before plugging it in.

[PlainBill]

Re: Daytek F19AH

Refer to the schematic on the datasheet. R5 and R7 (750K ohm each) provide voltage to pin pin 3 of IC101. The voltage at pin 3 will vary depending on the load presented by IC 101, C9 (pdf), and D4 (pdf).
**I'm still having a real difficult time converting that schematic to my board.
Been looking for about 3 days now for a schematic/service guide for this thing an 0 luck.

Hmm, you have a point. Double check the orientation of the diode you circled in orange. If you have it in backwards it will limit the voltage at pin 7.
**Diodes are all in correct ways

One other point which you should take into consideration. I'm used to seeing dark spots on the PC board in the inverter area. These are usually due to heat generated by the transformer drivers. And indeed, I see some darkening between J31 and the two 22 ohm (red, red, black) resistors. However, there is a much darker spot nearer to the transformer. The only component that could be responsible for that is the inverter transformer.
**Would we not have to figure why the transformer stopped clicking before voltage will reach the inverter??

I also went over every solder joint I previously did and still cannot get the transformer to resume that clicking noise like it had before. For some reason I keep thinking I screwed something up by forgetting to solder in D108 before plugging it in.

I suspect you did. I'm of the opinion that what was damaged was IC101. Others are entitled to disagree. I don't have any proof that is the cause.

My other point was that if the darker spot was caused by the inverter transformer we have an explanation of why the monitor smelled burnt.

PlainBill

[UserName666]

Re: Daytek F19AH

If the inverter transformer did fry out would that just make the light tubes go out or would that give cause for the power LED and everything to go out??

[PlainBill]

Re: Daytek F19AH

If the inverter transformer did fry out would that just make the light tubes go out or would that give cause for the power LED and everything to go out??

Well, that's the problem. In theory, it could; but it's unlikely. Let's describe a possible scenario. The insulation in a winding in the inverter breaks down. A small arc develops, the board overheats, the load increases, eventually the drive transistors short. This causes the output current of teh power supply to go over the limit and it shuts down. And of course, the power LED goes off.

Now we'll punch some holes in that scenario. The arc should reduce the output of the inverter transformer. The inverter controller should detect that and shut down; it's a safety feature. As an alternate scenario, the solder joint on one of the drive pins breaks down and an arc forms. Again, the inverter controller should shut down before the transistors fail. Now IF the transistors fail, this would overload the power supply. However, that would have to be be a low resistance - certainly less than 10 ohms, probably less than an ohm. And you have established that isn't the case.

PlainBill

[jetadm123]

Re: Daytek F19AH

Bravo to you for wanting to continue on! I'll put in my two cents worth. Going back to D108, if you look at the third photo on post #51, you notice that the screw holding it to the heatsink is going through a nylon insert and there's a square grey silicon pad (used for heat transfer and insolation) between D108 and the heatsink. It looks like the manufacturer is trying to electrically isolate it from the heatsink. The back of D108 has a metal tab, which some manufacturers internally connect to the middle leg (cathode) of the diodes.

The question is that when you re-inserted D108 did you remember to use the grey pad and nylon insulator? Now, if the heatsink is connected to ground and the metal tab is somehow in contact with it, then the output of D108 could be shorted to ground.

Things to check/verify with power off (you can perform checks in circuit):

1) Is the heatsink connected to ground?

2) Is D108 isolated from the heatsink? One probe on the the heatsink and the other probe on the tab of D108 will tell you.

3) Is the middle leg on D108 internally connected to it's backside metal tab? Again, a resistance check will tell you.

[UserName666]

Re: Daytek F19AH

I will verify the last post in the morniong as Ive drank a few wobbly pops tonight lol. WHat I can say though is when I put D108 back in they board and put the screw in **THE RUBBER PAD -WAS- INSERTED BETWEEN THE DIODE AN THE HEAT SINK**.

[UserName666]

Re: Daytek F19AH

Re: Post 97

1) Is the heatsink connected to ground?
**Not sure where to check that. Tried continuity setting from heatsink to the screwholes on each corner of the board and nothing. I put a pic with the 2 heatsink legs in red.

2) Is D108 isolated from the heatsink? One probe on the the heatsink and the other probe on the tab of D108 will tell you.
**27.6 ohms

3) Is the middle leg on D108 internally connected to it's backside metal tab? Again, a resistance check will tell you.
**00.3 ohms

Re: Heatsink <-> Ground..

[jetadm123]

Re: Daytek F19AH

1) Is the heatsink connected to ground?
**Not sure where to check that. Tried continuity setting from heatsink to the screwholes on each corner of the board and nothing. I put a pic with the 2 heatsink legs in red.

If you look at your photo, you can see that the legs of the heatsink are sharing real estate with other components, like the negative lead of one of the caps you replaced (next to R143)? Yes, it's probably grounded.

2) Is D108 isolated from the heatsink? One probe on the the heatsink and the other probe on the tab of D108 will tell you.
**27.6 ohms

This number could be influenced by other components on the board.

3) Is the middle leg on D108 internally connected to it's backside metal tab? Again, a resistance check will tell you.
**00.3 ohms

Looks to be internally connected.



Since the power supply is not working, a further test would be to isolate D108 by taking off the screw and gently prying it away from the heatsink and placing a thin piece of cardboard between the heatsink and D108 to ensure total isolation. Turn on the power supply.

If you still get nothing, you can try testing D108 off the board again. If you get the same results, then PlainBill's comments about IC101 maybe true.