Daytek F19AH

[UserName666]

Re: Daytek F19AH

Could you possibly explain you last post a bit more? Does that mean the secondary of the transformer in not providing the voltage to pin4 of IC101? IC101 being the SMPS controller? Confused here.

[UserName666]

Re: Daytek F19AH

It was this exact unit here. Just a cheap direct from Hong Kong thing but it does what its supposed to.

http://cgi.ebay.ca/ws/eBayISAPI.dll?...m=150501632382

[PlainBill]

Re: Daytek F19AH

I'm trying to figure out meaningful tests. The problem appears to be that the tertiary winding is not providing run voltage to the SMPS controller.

What brand and model of 0-30V power supply did you get? I'm interested in the specs.

PlainBill

[UserName666]

Re: Daytek F19AH

Alright something I tried today was removing the 10uf cap next to the big filter cap since that is the only one that wasn't replaced brand new and still no go. According to the analog meter when this cap fills up the transformer clicks at the same time it discharges back to 0.

When around the board again and took some voltage readings again after installing the new SG6841.

IC101:
1-2 = 0~1.3v
1-3 = 11~19v
1-4 = .000~.298v
1-5 = 1.1~1.9v
1-6 = .000~.030
1-7 = 10~16v
1-8 = .000~.457v

Filter Capacitor = 158~163v (Usually around 162.5v)
Opto-Isolator pins 1-2 = .812~2.3v
Transformer - 161v in 0v out

Rectifier by filter cap and coil:
Pins 2-3 116vac
Pins 1-4 162vdc

IC1: all readings = .000-.040

IC4:
1-2 = 0v
1-3 = 0v
1-4 = 0v
1-5 = .825v
1-6 = .820v
1-7 = .850 ~ .9v
1-8 = 0v

Also for this monitor I have gotten some new tools.
I have a 0-30v variable power supply in for if I need to "APPLY" voltage somewhere to this board as well a a multi-meter with more options that my current. I included a pic of the multi-meter in case any of the function may be handy for figuring this out.

[PlainBill]

Re: Daytek F19AH

Did not work Still no output voltage from the transformer though it remains clicking. IC101 now has it's 15~19v input voltage back and voltage has also returned to pins 1-2 of the opto-isolator but monitor still will not power up.

Give me a few hours to get my day started and I will review the thread. We WILL get this working.

PlainBill

[UserName666]

Re: Daytek F19AH

Did not work Still no output voltage from the transformer though it remains clicking. IC101 now has it's 15~19v input voltage back and voltage has also returned to pins 1-2 of the opto-isolator but monitor still will not power up.

[UserName666]

Re: Daytek F19AH

So my replacement SG6841's finally came in. Just finished installing it. Plainbill, your suspicions about that chip were correct. I know have the clicking back in the transformer. Gonna hook everything up now and see if it works.

[UserName666]

Re: Daytek F19AH

OK so I just ordered a 10 pack of SG6841SZ chips for IC101 and a kickass soldering/rework station for getting the little bugger off the board. This monitor WILL live again.

edit: Pretty bad that I know the numbers "SG6841SZ" off by memory now

[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.

[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..

[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**.

[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.

[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

[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

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

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

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

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.

[UserName666]

Re: Daytek F19AH

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

[UserName666]

Re: Daytek F19AH

This power board is seriously starting to piss me off now