Hi Guys,
Just to share & hope to get opinions from the experts here. and sorry for the big wall of text.
Do bad things come in Twos or in Threes?.. I have 2 sets of the same monitors hoping to have a quick fix (because I have done a few of them before having bad caps and poor solderjoints), but these two sets were giving me more headaches and not to mention the money involved (total damage so far is US$100 for the sets & parts).
LCD monitor : 2493HM
Power board model : BN44-00195A
Mainboard : BN41-00962A
Symptom/Fault :
Set #1 – Initially the set was having Blank screen with steady power LED, I guess this is the common failure which I have read a few threads here. Replaced the capacitors with Panasonic FM, FC, FR series and assembled it but still no joy. Resoldered all the joints again but I forgot to place the plastic protector below the Power board and to screw it tightly, the second time while assembling it. It got shorted to the panel when plugged. DAMN!
The two main fuses, MOSFETs (QM802 & QM803), sense circuitry resistor (RM801) were the goners in my initial check. Buy the parts & replaced them and two main fuses, MOSFETs (QM802 & QM803) went kaput again. Further probing confirmed that the two pins on the bottom right of the Transformer (TM801) (facing down) were fused (no longer shorted) comparing with the identical pair on the other side. Removed it from the board and found out that it was burnt. I use wires and a 5A fuse to jump between the two burnt Transformer pins and replaced the MOSFETs again. This time I used the ‘bulb (current limiter) test’ on the power board alone. Bulb flash momentarily and went off.
When I hooked up the Mainboard and test it again, this time the bulb brightly light up and stays and then a few seconds later it blinks brightly & quickly. I managed to do some measurements on the Power board and got PSON= 3V and S_B =5.2V while the rest of the output voltages are giving 0V. Using Page 4 of the schematic downloaded from Elektrotanya, managed to trace the points of the VDDC & VDDP of the Main IC300. As compared to VDDP, resistance measured from VDDC (+1.8V_live) to Gnd (screw ring of the mainboard) is 30ohms one way & 100ohms when reversed. Removing the tiny capacitors of the VDDC rails (C332, C334, C335, C336, C337, and C338) also yield the same resistance reading. Dead end.
Set #2 – Hoping that by getting this dead (No power LED) monitor of the same model I could revive Set #1 or at least any one of them. But once upon disassembly, checked that it is having the same symptoms on the power board (Fuses blown, MOSFETs shorted, sense circuitry resistor blown and the SAME two pins on the Transformer TM801 not shorting anymore). What a bummer! I replaced the MOSFETs and sense circuitry resistor plus wired the two blown Transformer pins with a fuse and performed the current limiter test again. I couldn’t believe my LUCK! The result was same as SET #1 when the mainboard was connected to the power board. sigh!.
So is it correct to say that both sets Mainboard is the culprit for the high current drawn, blowing the components on the Power boards? Or am I missing something? If yes, and if I was to purchase the main board, can both the Power board be usable again? What I am worried is the transformer TM801 with the two pins blown. I have googled for a replacement but could not find one. Is jumping a pico fuse (not sure which Amperes to use) between the pins a good idea and can it hold-up for long? As for purchasing the mainboard, I have checked through ebay but could not find any. However, I found this. Any opinions on the reliability of this online store? I do not want to spend another US$50 and adding more piles of junk at my home. At the rate of all the fail repairs, I think I will be sleeping on them instead of on my bed. Geez….
Thanks in advance for all your feedback. I have uploaded the pictures of my Power and Mainboards (Set #2), the blown transformer and the schematic of the main board. Let me know if more measurements or pictures are required.
Just to share & hope to get opinions from the experts here. and sorry for the big wall of text.
Do bad things come in Twos or in Threes?.. I have 2 sets of the same monitors hoping to have a quick fix (because I have done a few of them before having bad caps and poor solderjoints), but these two sets were giving me more headaches and not to mention the money involved (total damage so far is US$100 for the sets & parts).
LCD monitor : 2493HM
Power board model : BN44-00195A
Mainboard : BN41-00962A
Symptom/Fault :
Set #1 – Initially the set was having Blank screen with steady power LED, I guess this is the common failure which I have read a few threads here. Replaced the capacitors with Panasonic FM, FC, FR series and assembled it but still no joy. Resoldered all the joints again but I forgot to place the plastic protector below the Power board and to screw it tightly, the second time while assembling it. It got shorted to the panel when plugged. DAMN!
The two main fuses, MOSFETs (QM802 & QM803), sense circuitry resistor (RM801) were the goners in my initial check. Buy the parts & replaced them and two main fuses, MOSFETs (QM802 & QM803) went kaput again. Further probing confirmed that the two pins on the bottom right of the Transformer (TM801) (facing down) were fused (no longer shorted) comparing with the identical pair on the other side. Removed it from the board and found out that it was burnt. I use wires and a 5A fuse to jump between the two burnt Transformer pins and replaced the MOSFETs again. This time I used the ‘bulb (current limiter) test’ on the power board alone. Bulb flash momentarily and went off.
When I hooked up the Mainboard and test it again, this time the bulb brightly light up and stays and then a few seconds later it blinks brightly & quickly. I managed to do some measurements on the Power board and got PSON= 3V and S_B =5.2V while the rest of the output voltages are giving 0V. Using Page 4 of the schematic downloaded from Elektrotanya, managed to trace the points of the VDDC & VDDP of the Main IC300. As compared to VDDP, resistance measured from VDDC (+1.8V_live) to Gnd (screw ring of the mainboard) is 30ohms one way & 100ohms when reversed. Removing the tiny capacitors of the VDDC rails (C332, C334, C335, C336, C337, and C338) also yield the same resistance reading. Dead end.
Set #2 – Hoping that by getting this dead (No power LED) monitor of the same model I could revive Set #1 or at least any one of them. But once upon disassembly, checked that it is having the same symptoms on the power board (Fuses blown, MOSFETs shorted, sense circuitry resistor blown and the SAME two pins on the Transformer TM801 not shorting anymore). What a bummer! I replaced the MOSFETs and sense circuitry resistor plus wired the two blown Transformer pins with a fuse and performed the current limiter test again. I couldn’t believe my LUCK! The result was same as SET #1 when the mainboard was connected to the power board. sigh!.
So is it correct to say that both sets Mainboard is the culprit for the high current drawn, blowing the components on the Power boards? Or am I missing something? If yes, and if I was to purchase the main board, can both the Power board be usable again? What I am worried is the transformer TM801 with the two pins blown. I have googled for a replacement but could not find one. Is jumping a pico fuse (not sure which Amperes to use) between the pins a good idea and can it hold-up for long? As for purchasing the mainboard, I have checked through ebay but could not find any. However, I found this. Any opinions on the reliability of this online store? I do not want to spend another US$50 and adding more piles of junk at my home. At the rate of all the fail repairs, I think I will be sleeping on them instead of on my bed. Geez….
Thanks in advance for all your feedback. I have uploaded the pictures of my Power and Mainboards (Set #2), the blown transformer and the schematic of the main board. Let me know if more measurements or pictures are required.
Attached Files
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