Mulja tv repair portal
Equipment Repairs => DVD/VIDEO/Home Cinemas/Hi-Fi/Mp3/Camcorder => Topic started by: blackillusion on November 04, 2012,08:00:37
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I have an LG DVD and stereo system LG-Ht33S or HS33S.
It arrived making a terrible loud high pitch noise from the subwoofer, which house the power supply board.
The dvd gets power through a cable from the Sub, it originally had a red standby light. You press the on button to switch it all on the dvd would start up and then the loud high pitch noise would come.
So I entered the subwoofer and found a capacitor? page 44 l606 on the PWM circuit that had bad solder joints, literally dropped off. Check it for a short and it tested like the l605 with continuity. Resoldered it.
Now I get absolutely no power on the dvd no standby light.
No voltages out of the power supply board to the others.
I have the power supply board on its own, and trace 340vdc to the two ICs 901 and 902 and nothing comes out after.
I am really looking for any tips for this. What to test and what to do.
Service manual and schematic is attached.
http://elektrotanya.com/lg_hs33s-a2p_afn70208657.pdf/download.html
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Check L-932 on secundary PSU (14V)
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Thanks for your reply jordan.
Please excuse my stupidity it was late last nite and I have not tested with negative probe to chassis ground point and positive probe to test point.
I find at CN901
1.GND - 0v
2.P-CNT - 0v
3.P-Sens - 5.9v
4.5.6v - 5.7v
5.12v - 0v
6.5v - 0v
7.GND - 0v
8.GND - 0v
9.14v - 16v
10.14v - 16v
so L-932 is showing 16v also.
IC931
pin 1 = 14.7v
pin 2 = 0v
pin 3 = 0v
pin 4 = 0v
IC932
pin 1 = 5.7v
pin 2 = 0v
pin 3 = 0v
pin 4 = 0v
IC933
pin 1 = 8.5v
pin 2 = 0v
pin 3 = 0v
pin 4 = 0v
Thanks for your help
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Should 12v and 5v be present or do they have to be switched
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Capacitors appear to be fine ESR.
Anyone able to help here, I'm quite novice at this and don't understand why I have no output of those 3 IC's be they permanent? I only see capacitors to GND after each IC so tested ESR and seems ok?
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Im stuck for ideas, I desolder and tested optocouplers. Check resistors, check diodes, check IC's, check transistors. Everything I tested seems okay.
Im missing some voltages on secondary side. ICs not output voltage, big diode test ok. I'm trying to learn and won't give up, just keep coming back to it.
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Ok so I must apologize for wasting some time. I found that a ribbon was not connected properly on other unit. Now back to the high pitch sound
http://youtu.be/ryxeJLIIbaY
It comes from the PWM board.
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Right, you sound to be going round in circles here, at least you have the machine powering up again. First of all tell me if the high pitched noise varies with the volume being adjusted, and is the noise you mention actually coming from the sub woofer drive unit or from components within the sub enclosure, by the way we are LG!
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hi tony thanks for the reply. I have since located a voltage regulator on the power supply that is meant to be a 3.3v and someone had put a 5v reg in there. It supplies the PWM so i'm guessing thats why its making that noise. Just waiting for replacement parts.