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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Benq G2420HD power supply heat issue?
Hi all..
I have a BENQ G2420HD 24" LCD monitor. Display backlight seems good, etc. But unit shuts down completely after about 20-30 mins (no backlight, power LED goes out). Holding down power switch at this point will cause unit to come back up after about 30-40 seconds. Then it will die again within 5-10 mins, but can be restarted the same way. I've already replaced all the elect caps on the power supply board. Is the power board still the most likely problem here? Any suggestions as to how to pinpoint the cause would be most welcome. |
#2
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Benq G2420HD power supply heat issue?
On 07/02/2014 16:53, 2phar wrote:
Hi all.. I have a BENQ G2420HD 24" LCD monitor. Display backlight seems good, etc. But unit shuts down completely after about 20-30 mins (no backlight, power LED goes out). Holding down power switch at this point will cause unit to come back up after about 30-40 seconds. Then it will die again within 5-10 mins, but can be restarted the same way. I've already replaced all the elect caps on the power supply board. Is the power board still the most likely problem here? Any suggestions as to how to pinpoint the cause would be most welcome. IR thermometer, targetted narrow jet freezer spray or hot air through na silicone tube |
#3
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Benq G2420HD power supply heat issue?
"2phar" I have a BENQ G2420HD 24" LCD monitor. Display backlight seems good, etc. But unit shuts down completely after about 20-30 mins (no backlight, power LED goes out). Holding down power switch at this point will cause unit to come back up after about 30-40 seconds. Then it will die again within 5-10 mins, but can be restarted the same way. I've already replaced all the elect caps on the power supply board. Is the power board still the most likely problem here? Any suggestions as to how to pinpoint the cause would be most welcome. ** The fault condition is being brought on by rising temperature - right ? So you need to apply heat ( ie hot air) SELECTIVELY to various parts of the PSU until you find the area that is most sensitive. This could take quite a while. I have an amplifier module ( from an ART 322A) here that reacted to the application of hot air by going silent. The cause was a number of cracked vias ( plated through holes) in the PCB going open when the board became warm. The particular vias are about 0.25mm dia and not filled with solder. Unusual fault and a nightmare to find and fix. .... Phil |
#4
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Benq G2420HD power supply heat issue?
On 2/7/2014 8:57 PM, Phil Allison wrote:
"2phar" I have a BENQ G2420HD 24" LCD monitor. Display backlight seems good, etc. But unit shuts down completely after about 20-30 mins (no backlight, power LED goes out). Holding down power switch at this point will cause unit to come back up after about 30-40 seconds. Then it will die again within 5-10 mins, but can be restarted the same way. I've already replaced all the elect caps on the power supply board. Is the power board still the most likely problem here? Any suggestions as to how to pinpoint the cause would be most welcome. ** The fault condition is being brought on by rising temperature - right ? So you need to apply heat ( ie hot air) SELECTIVELY to various parts of the PSU until you find the area that is most sensitive. This could take quite a while. I have an amplifier module ( from an ART 322A) here that reacted to the application of hot air by going silent. The cause was a number of cracked vias ( plated through holes) in the PCB going open when the board became warm. The particular vias are about 0.25mm dia and not filled with solder. Unusual fault and a nightmare to find and fix. ... Phil Yes.. it sure seems like it's heat related. I redid the compound on the heatsinks and stuff, and nothign seems extraordinarily hot when it shuts down. I have gone and got an IR thermometer as N_Cook suggested, so I'm gonna see if I can track it down. I'm curious as to why its possible to get it to restart within 40 seconds and it keeps going for several minutes again, if it was due to some thermal expansion or thermal shutdown, that does seem kind too fast a recovery? I also wonder if it could be a fault elsewhere like in the inverter board that's able to cause the whole power supply to shut down? |
#5
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Benq G2420HD power supply heat issue?
On Fri, 7 Feb 2014, 2phar wrote:
On 2/7/2014 8:57 PM, Phil Allison wrote: "2phar" I have a BENQ G2420HD 24" LCD monitor. Display backlight seems good, etc. But unit shuts down completely after about 20-30 mins (no backlight, power LED goes out). Holding down power switch at this point will cause unit to come back up after about 30-40 seconds. Then it will die again within 5-10 mins, but can be restarted the same way. I've already replaced all the elect caps on the power supply board. Is the power board still the most likely problem here? Any suggestions as to how to pinpoint the cause would be most welcome. ** The fault condition is being brought on by rising temperature - right ? So you need to apply heat ( ie hot air) SELECTIVELY to various parts of the PSU until you find the area that is most sensitive. This could take quite a while. I have an amplifier module ( from an ART 322A) here that reacted to the application of hot air by going silent. The cause was a number of cracked vias ( plated through holes) in the PCB going open when the board became warm. The particular vias are about 0.25mm dia and not filled with solder. Unusual fault and a nightmare to find and fix. ... Phil Yes.. it sure seems like it's heat related. I redid the compound on the heatsinks and stuff, and nothign seems extraordinarily hot when it shuts down. I have gone and got an IR thermometer as N_Cook suggested, so I'm gonna see if I can track it down. I'm curious as to why its possible to get it to restart within 40 seconds and it keeps going for several minutes again, if it was due to some thermal expansion or thermal shutdown, that does seem kind too fast a recovery? I also wonder if it could be a fault elsewhere like in the inverter board that's able to cause the whole power supply to shut down? Only if it's causing a load on the actual power supply which cause the PS to shut down. Are you sure you got all the capacitors? I dragged a 19" Acer monitor home, and it worked fine, or so it seemed. But if I left it on, it would go into standby and then I couldn't get it activated again, the Acer logo would go on and nothing more. I changed the obvious capacitors and it's fine. So it was resetting because one of those bigger electrolytics in the power supply wasn't quite right. I nitially thought it was something else, but changed the capacitors because it was easy. Michael |
#6
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Benq G2420HD power supply heat issue?
"2phar" I'm curious as to why its possible to get it to restart within 40 seconds and it keeps going for several minutes again, if it was due to some thermal expansion or thermal shutdown, that does seem kind too fast a recovery? ** Nothing unusual in that. Temperature rises according to an exponential curve, fast at first and then slower and slower until it settles completely. It also falls the same way. ..... Phil |
#7
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Benq G2420HD power supply heat issue?
On 07/02/2014 18:08, N_Cook wrote:
On 07/02/2014 16:53, 2phar wrote: Hi all.. I have a BENQ G2420HD 24" LCD monitor. Display backlight seems good, etc. But unit shuts down completely after about 20-30 mins (no backlight, power LED goes out). Holding down power switch at this point will cause unit to come back up after about 30-40 seconds. Then it will die again within 5-10 mins, but can be restarted the same way. I've already replaced all the elect caps on the power supply board. Is the power board still the most likely problem here? Any suggestions as to how to pinpoint the cause would be most welcome. IR thermometer, targetted narrow jet freezer spray or hot air through na silicone tube If you use a standard hot air gun then low temperature of course. And you have to divert off some of the air, via a silicone rubber tube ,off a silicone rubber cover or something with plenty of other holes in it or you will block the air flow and damage the air gun probably and also too much heat while it still works |
#8
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Benq G2420HD power supply heat issue?
On 2/8/2014 1:16 AM, Michael Black wrote:
Are you sure you got all the capacitors? I dragged a 19" Acer monitor home, and it worked fine, or so it seemed. But if I left it on, it would go into standby and then I couldn't get it activated again, the Acer logo would go on and nothing more. I changed the obvious capacitors and it's fine. So it was resetting because one of those bigger electrolytics in the power supply wasn't quite right. I nitially thought it was something else, but changed the capacitors because it was easy. Michael I replaced them all except the big 450V one.. mainly cos its not even included in capacitor repair kits and everyone seems to say failure of it is extremely rare. |
#9
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Benq G2420HD power supply heat issue?
On Sat, 8 Feb 2014, 2phar wrote:
On 2/8/2014 1:16 AM, Michael Black wrote: Are you sure you got all the capacitors? I dragged a 19" Acer monitor home, and it worked fine, or so it seemed. But if I left it on, it would go into standby and then I couldn't get it activated again, the Acer logo would go on and nothing more. I changed the obvious capacitors and it's fine. So it was resetting because one of those bigger electrolytics in the power supply wasn't quite right. I nitially thought it was something else, but changed the capacitors because it was easy. Michael I replaced them all except the big 450V one.. mainly cos its not even included in capacitor repair kits and everyone seems to say failure of it is extremely rare. It wouldn't. That one is just running at 60Hz (50Hz in some countries), which requires less effort on the part of the capacitor. It can go bad, but not in the same way as the capacitors on the output of the supply. A switching supply is a feedback system, so if a capacitor goes bad, what the problem is may not immediately be obvious. So I was thinking if a small value electrolytic was overlooked, it might be more problem than would seem from the small value. Phil's comment about bad solder joints is good. You have to look carefully. Michael |
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