Power drops too much over TP1 and TP2 - Raspberry Pi Forums

from 2 pi's bought, 1 instable , destroys sd card time time.
serial fn120836992 fn120836993 256mb

made measurements , wonder if should return broken pi.
had unpowered 2 days after having connected usb power hub gave more 5.25v (in search of power supply).

compared between them using same short, fat usb cable (50cm), power supply hnp06 , sd card (sandisk 8gb type 4).

raspberry #1 (the one)
measure 4.94v on tp1 , tp2
measure 4.94v , 5.08v on both sides of fuse f3 black lead on earth shielding of micro-usb input connector.
measure across of fuse f3 0.13v
after 1 minute no power, measure f3 00.8 ohm

raspberry #2 (the broken one)
measure 4.63v on tp1 , tp2
measure 5.08v , 4.65v on both sides of fuse f3 black lead on earth shielding of micro-usb input connector.
measure across of fuse f3 0.42v
after 1 minute no power, measure f3 01.6 ohm (down 02.5 ohm 2 days ago)

guess low voltage in #2 cause instability (it below 4.75v minimum).
have waited several days see if fuse f3 perhaps recovering, no avail.

should do? did break pi connecting "wrong" power supply (although labeled 5v) or can count on warranty?

ps
share of measuring experience spend time on getting speed this.

memory card
wiki not explain if 1 should measure tp1 , tp2 sd card inside or not , hard see on picture. assume measurements need sd card inside may have dramatic effect on power measured in case of defect in fuse/board, believe.
http://elinux.org/r-pi_troubleshooting# ... r_problems

usb cable
voltage drops little more when cable longer or when adapter (micro mini) being used, worst case difference in case 0.04v (between tp1 , tp2).

power supply
after having tried many , having discussed technical support of manufacturer settled on hnp06-micro usb or usb version. can confirm 1 delivering stable 5v 1200ma when under load. unfortunately, not have usb version more amps. way, found higher amps on label, higher chance voltage low/instable. can coincidence of having selected low quality psu hi amps. appreciate suggestions stable, hi amp 2+a psu. should not custom made, perhaps neat, battery backed psu ideal solution here. can not provide stability power backup.

hnp-usbac-duo 2.1a 4.73v
hnp-usbac-duo 2.1a 4.77v
nokia ac-10e 1200ma 4.84v
sony ep850 1500ma 4.86v
htc tcp300 1000ma 4.97v
blackberry psm04a 700ma 4.97v
hnp06-usb 4.96v
hnp06-usb 4.97v
unknown 1000ma 5.23v
usb hub icidu ai-707926 2a >>5.25v

remarks: big thing seems if power supply stable under load.
hnp-usbac-duo not quality psu, bears name of hn admit not meant powering electronic boards , not have regulated power. hnp06 seems perfect power solution meant although wish amps higher in case want start overclocking.

(i had these instability problems, did not start going overclocking, appreciate information may have power supply needs in case of overclocking: 1200ma enough when connect hdmi , usb keyboard?).

note on multimeters
credits : http://www.petervis.com/raspberry_pi/ra ... _fuse.html)
used cheap power supply. e.g. single chip digital multimeter solution - can typically expect resolution of 0.1 ohm when set 200 range. accuracy typically around +/- (0.8% of rdg + 3 digits).

if measuring 2.5 ohms 0.8% of 2.5 ohm 0.02 ohm, hence 2.5 ohm drop measured [2.5 +/- 0.02] considered accurate , within error parameters can see.

did 4.63v on tp1 , tp2 no attached usb devices??

guess other thing try out check current drain power supply cable both pis comparison.
if both draw same amount of current tp1/tp2 vastly different may indicate faulty f3 polyfuse.

richard s.

raspberrypi