Ok, I think that resistor is between the heatsink and the huge cap beside the rectifier bridge, it's covered with heat-shrink tubing so I can't see its resistance value. I'll peel it tomorrow and check it. Now to bed.
neutrino68
New Member
Last Activity: 09-23-2010, 12:53 PM
Joined: 09-20-2010
Location: Stockholm, Sweden
-
Re: AOC LM2028 - no voltage
Ok, I think that resistor is between the heatsink and the huge cap beside the rectifier bridge, it's covered with heat-shrink tubing so I can't see its resistance value. I'll peel it tomorrow and check it. Now to bed.
-
Re: AOC LM2028 - no voltage
This means 13.48V on VDD is too low for the controller to be enabled, then? Or is it 16V initially and drops to 13.4 after the startup process?...Leave a comment:
-
Re: AOC LM2028 - no voltage
Ok, here's my readings, all relative to pin 1:
Pin 2: 1.49V stable
Pin 3: 16.65V stable
Pin 4: 1.29V stable
Pin 5: 0V
Pin 6: 0.01V to -0.01V (constant and fast fluctuation around 0V)
Pin 7: 13.48V stable
Pin 8: looks like Pin 6Leave a comment:
-
Re: AOC LM2028 - no voltage
Didn't have time to get a new cap today because I worked too late, but I did some more probing now, and I think the fluctuations I saw yesterday may have been the fault of my digital multimeter. I turned the voltage selector back and forth a couple of times and then measured again:
Between pin 1 and 7 on the SG6841 controller, I read stable 13.4 volts.
Between + side of C922 and primary -, I read 14.1 volts, also seems stable.
I checked diodes D902 and D904 (right where C922 is, D904 is on solder side), they are...Leave a comment:
-
Re: AOC LM2028 - no voltage
It's 4.7uF 50V, "Elite". I'll replace it and see what happens....Leave a comment:
-
Re: AOC LM2028 - no voltage
First I have to correct myself a little; the 11.3 volts reading was without the video logics board connected. So I figured I should connect everything and measure.
Now, doing the same measurement as before, I get fluctuating values, between 8 volts up to 12.5 volts. Sometimes it stabilizes around 10-11 volts. Measuring between pin 1 and 7 directly on the controller gives the same fluctuating voltage.
edit: I'll redo the measuring tomorrow to make sure it wasn't me who was unstable, it's 2:53 AM here and my eyes are getting sore...Last edited by neutrino68; 09-21-2010, 06:55 PM.Leave a comment:
-
Re: AOC LM2028 - no voltage
I read 11.3 volts between the + side of C907 and negative on primary side. I'm checking out the Daytek F19AH thread, thanks for the pointer!...Leave a comment:
-
Re: AOC LM2028 - no voltage
@momaka: Thanks, this forum seems like a gold mine, I'm sure I'll spend hours and hours reading here. Regarding the cap you're talking about, I'm not quite sure which cap you are referring to, maybe the pics I've attached now can help you point it out to me using the board marking, so I can measure it.
@retiredcaps: Hi, and thanks for the hints re pics. I've taken some pics now, unfortunately I had to use the flash, light in here is not very optimal to say the least. Q901 is the main switching MOSFET, you can see it marked (text upside...Last edited by neutrino68; 09-21-2010, 04:17 PM.Leave a comment:
-
Re: AOC LM2028 - no voltage
dondrusco,
Sorry for bumping this old thread, but were you able to figure out what caused this problem, and fix it? I have a dead LM2028 here, which seems to show exactly the same symptoms on the power board as you described here, e.g. 0 volts on secondary side of the transformer, 320VDC on the primary side but Q901 seems dead.
This monitor has been showing signs of problems for a long time, sometimes it would lose power for some seconds, switch back on and off for a random number of times, and then resume normal operation. Now...Leave a comment:
No activity results to display
Leave a comment: