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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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CRT computer monitor dies with loud crack
Last time I powered it, my Iiyama HA202-DT made a cracking
sound, similar to the sounds CRTs make when powered on, but longer, louder and ominous. The screen is completely black and, when fed a video signal, the monitor keeps "resetting" itself every few seconds (the same "click" it makes when changing video modes). I suspect something in the high voltage circuit is blown but see no obvious sign of damage. Any ideas ? Thanks in advance. -- André Majorel URL:http://www.teaser.fr/~amajorel/ It's a good life, bowing to a tyrant. |
#2
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CRT computer monitor dies with loud crack
It sounds like the switching power supply is detecting an over-current
situation and is shutting down, then trying to restart itself again. I would check the diodes in the secondary of the power supply and all large transistors and diodes in the horizontal/high-voltage section. John |
#3
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CRT computer monitor dies with loud crack
Possibly flyback arcing, & shorted the output. Don't see
that unit around here. Sky. "Andre Majorel" wrote in message ... Last time I powered it, my Iiyama HA202-DT made a cracking sound, similar to the sounds CRTs make when powered on, but longer, louder and ominous. The screen is completely black and, when fed a video signal, the monitor keeps "resetting" itself every few seconds (the same "click" it makes when changing video modes). I suspect something in the high voltage circuit is blown but see no obvious sign of damage. Any ideas ? Thanks in advance. -- André Majorel URL:http://www.teaser.fr/~amajorel/ It's a good life, bowing to a tyrant. |
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CRT computer monitor dies with loud crack
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#6
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CRT computer monitor dies with loud crack
B-E short may be OK if it's driven by a transformer. It's C-E short that's guaranteed dead. Be sure to understand that Sam is talking about in-circuit ohmmeter testing. Out of circuit, B-E short is fatal. |
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CRT computer monitor dies with loud crack
On 2005-11-13, Charles Schuler wrote:
B-E short may be OK if it's driven by a transformer. It's C-E short that's guaranteed dead. Be sure to understand that Sam is talking about in-circuit ohmmeter testing. Out of circuit, B-E short is fatal. I'm not an EE, but I had figured that much. :-) Thanks. If I can't get the schematics, I guess I'll have to desolder the transistor to make sure. The 2SC5570 is spec'd for voltages in the kV range ; that makes it a good candidate for arcing. There were long "whiskers" of dust on the leads. Could an arc have developed that way ? Perhaps the replacement could use some heat shrink tubing on its leads... -- André Majorel URL:http://www.teaser.fr/~amajorel/ It's a good life, bowing to a tyrant. |
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CRT computer monitor dies with loud crack
Andre Majorel writes:
On 2005-11-13, Charles Schuler wrote: B-E short may be OK if it's driven by a transformer. It's C-E short that's guaranteed dead. Be sure to understand that Sam is talking about in-circuit ohmmeter testing. Out of circuit, B-E short is fatal. I'm not an EE, but I had figured that much. :-) Thanks. If I can't get the schematics, I guess I'll have to desolder the transistor to make sure. The 2SC5570 is spec'd for voltages in the kV range ; that makes it a good candidate for arcing. There were long "whiskers" of dust on the leads. Could an arc have developed that way ? Perhaps the replacement could use some heat shrink tubing on its leads... It may be the horizontal output transistor. If it is shorted, the next question is whether it deid on its own or due to some external cause. Sure, dust can result in a short circuit but could be elsewhere. If it really made a loud noise as it died, there may be visible evidence somewhere. --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html Important: Anything sent to the email address in the message header above is ignored unless my full name is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
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CRT computer monitor dies with loud crack
"Charles Schuler" bravely wrote to "All" (13 Nov 05 16:56:59)
--- on the heady topic of " CRT computer monitor dies with loud crack" CS From: "Charles Schuler" CS Xref: core-easynews sci.electronics.repair:348456 B-E short may be OK if it's driven by a transformer. It's C-E short that's guaranteed dead. CS Be sure to understand that Sam is talking about in-circuit ohmmeter CS testing. Out of circuit, B-E short is fatal. Most modern H-output transistors virtually have a near B-E short because of an internal damping resistor between 10 and 100 ohms. At least it will seem like a short on the 20K & 2K dmm range. A*s*i*m*o*v .... You may be a tech if you're entertained by a 6-pack and sparking HV. |
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CRT computer monitor dies with loud crack
On 2005-11-14, Asimov wrote:
"Charles Schuler" bravely wrote to "All" (13 Nov 05 16:56:59) --- on the heady topic of " CRT computer monitor dies with loud crack" CS From: "Charles Schuler" CS Xref: core-easynews sci.electronics.repair:348456 B-E short may be OK if it's driven by a transformer. It's C-E short that's guaranteed dead. CS Be sure to understand that Sam is talking about in-circuit ohmmeter CS testing. Out of circuit, B-E short is fatal. Most modern H-output transistors virtually have a near B-E short because of an internal damping resistor between 10 and 100 ohms. At least it will seem like a short on the 20K & 2K dmm range. The DMM shows 1.1 ohm. Sounds high for a short, but it's the same figure if I put both probes on the same lead. :- -- André Majorel URL:http://www.teaser.fr/~amajorel/ It's a good life, bowing to a tyrant. |
#11
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CRT computer monitor dies with loud crack
The DMM shows 1.1 ohm. Sounds high for a short, but it's the same figure if I put both probes on the same lead. :- It's probably the secondary of the drive transformer causing that, remove the transistor and check it out of circuit. |
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