Note: Prior to considering the procedure outlined below please try resetting the CMOS RAM (i.e. BIOS’ settings) via the ‘jumper’ provided for that purpose – I am aware of three instances (two involving HP Vectras and a third involving a Nanosys system) wherein the ‘CMOS’ had somehow become corrupt such that startup via the ‘power button’ cycled the system on then immediately off after which it had no effect pending reset of the PSU (via disconnection from the mains) – In each case hardware reset of the CMOS RAM proved remedial.
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Ok! I know it’s become ‘vogue’ to view the system board as a ‘black box’ – A stance I tend to concur with where the failed unit is a soldered on, near microscopic, and/or proprietary SMD --- However power conditioning (and other ‘manageable’ discrete generic components) are quite another matter!
Shorted or ‘electrically leaky’ electrolytic and tantalum capacitors are a common cause of the following symptoms: No power-up or very brief power-up (On time < 2 Sec with the necessity of resetting the PSU prior to subsequent attempts)
Shorted caps may be readily located using a multimeter (low
resistance scale) and, in the case of electrolytics, as noted by Tedster, often by mere visual inspection.
Quality electrolytic and tantalum caps are both inexpensive (typically less than $10 USD -- often much less) and readily available (one of many
retailers being Jameco Electronics
www.jameco.com) inasmuch as said caps are relatively large thru-hole devices replacement requires only modest soldering skills. And is a H___ of a lot less expensive than a new system board!!! -- But please observe the following caveats.
-Prior to commencing work please remove the CPU and all bus cards (That the range of Murphy’ s Law might be constrained
)
-The replacement capacitor’s working and surge voltage ratings must meet or exceed the replaced unit.
-
Observation of correct polarity is critical!!!
-The replacement's capacitance must at least equal that of the replaced cap (but may exceed same by no more than 10%)
-The replacement’s tolerance & temp coefficient should be equal to or ‘narrower’ than that of the replaced component.
-When handling the system board great care is required to avoid mechanical damage to the copious, minute SMDs figuratively peppering the board.
-Desoldering the failed cap requires both care and patience as said component is often attached to the board with RTV or similar elastic adhesive – Care must be exercised to avoid thermal delamination of the board.
Good luck!!!
Very best regards
Dan S.
