Hi All,
I helped a friend to replace or upgrade some electrolytic capacitors on one of the circuit boards of his sony projector. Upon powering up, it tripped its power supply, burnt off 2 resistors.
All orginal caps were normal blue rubycon 85deg stuff. Value in the picture shows the orginal values.
I had replaced C508 and C509 to 47uF 250V, 105deg low ESR. And C527, C502 and C506 to 22uF 63V, again 105deg low ESR.
After powering up, resistors R568 & R570 which are parallelled burnt.
There are 6 of these circuits on the same board, only one have the resistors burnt.
I am clueless on pinpionting the problem. Can anyone please help me out?
Thank you very much
Yeo
I helped a friend to replace or upgrade some electrolytic capacitors on one of the circuit boards of his sony projector. Upon powering up, it tripped its power supply, burnt off 2 resistors.
All orginal caps were normal blue rubycon 85deg stuff. Value in the picture shows the orginal values.
I had replaced C508 and C509 to 47uF 250V, 105deg low ESR. And C527, C502 and C506 to 22uF 63V, again 105deg low ESR.
After powering up, resistors R568 & R570 which are parallelled burnt.
There are 6 of these circuits on the same board, only one have the resistors burnt.
I am clueless on pinpionting the problem. Can anyone please help me out?
Thank you very much
Yeo
If the resistors burned directly after power was applied, it means a big current was drawing.
If for some reason Q501 is short circuit between collector and emitter, the full current flows trough the burned R's.
Try this link to learn how to measure transistors:
http://www.eatel.net/~amptech/elecdisc/ampfail.htm
/Hugo
If for some reason Q501 is short circuit between collector and emitter, the full current flows trough the burned R's.
Try this link to learn how to measure transistors:
http://www.eatel.net/~amptech/elecdisc/ampfail.htm
/Hugo
Do not underestimate the transient that can flow when you power on a low esr capacitor.
Consumer electronics are designed to get the last cent out of it. So by doubling the capacity and going to low esr you may have quadrupled the transient. Maybe not in peak current, but in duration. Having done measurements on a similar problem, I measured currents up to 30-40 Amps, blowing even surge rated resistors.
Consumer electronics are designed to get the last cent out of it. So by doubling the capacity and going to low esr you may have quadrupled the transient. Maybe not in peak current, but in duration. Having done measurements on a similar problem, I measured currents up to 30-40 Amps, blowing even surge rated resistors.
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