Electrical help wanted!

spleenharvester · 17 Mar 2013 at 01:26

From a HP 6735s motherboard.

+VADP reads in at 19v like it should.

ADP_EN# should be reading in at a low voltage but is reading at 19v instead. Problem is almost definitely confined to this circuit. Any idea what could be causing?

D1010 - leg (2 on schematic) reads 8v, leg (1 on schematic) reads a full 19v.
I may have taken a bad measurement but I think ADP_EN (not ADP_EN#) reads in at 0v.

Would really appreciate some input!

Cheers

doofer · 17 Mar 2013 at 01:30

Have you tried switching it off and then back on again?

Makhaira · 17 Mar 2013 at 08:25

8v at D1010 leg 2 is probably about right since you've got a more or less 50% pot. divider set up there, so that feels right (although the value of the top resistor is unknown).

It's been a few years since I did my degree, but 19v would seem entirely reasonable at ADP_EN# if the op amp (as it's configured as a comparator) is making that judgement based on the LIMITsignal input. I'd take some measurements from that input and see if it's behaving as it should.

Hope that helps!

Fuzz · 17 Mar 2013 at 10:04

WOOOOOOOOOOOOOOOSH!

wannabedamned · 17 Mar 2013 at 10:17

orbspeed1 · 17 Mar 2013 at 10:21

Yep wooosh over my head.

neodude · 17 Mar 2013 at 10:36

Makhaira said:
It's been a few years since I did my degree, but 19v would seem entirely reasonable at ADP_EN# if the op amp (as it's configured as a comparator) is making that judgement based on the LIMITsignal input. I'd take some measurements from that input and see if it's behaving as it should.

This.

From how it looks the input at the non-inverting input of the op-amp (U1024-B) is fed from a voltage divider of roughly 3/4 - 1/4. Meaning roughly an input of 15V. If the voltage into the inverting input (from LimitSignal) is lower than this then the op-amp will output 19V, if it is higher then it will output 0V.

spleenharvester · 17 Mar 2013 at 11:08

Thankyou all, will take some more readings later :-)

EDIT: Limitsignal is reading from the DC jack at 0 volts

could it be because the adapter is a non-OEM? I swear if that's all it is I will go mental!

neodude · 17 Mar 2013 at 11:54

So it looks like a circuit that makes sure that the Limit Signal is above a certain level (15V) before allowing things to work.