Wow, thanks! So with a multi layered pcb like this one, you cannot access the ground plane because it is covered by another layer. So, in order to 'touch it, one can use for example the ground pins on the molex connector (which I did just now).
Here are the results from the test points (voltages) to gnd:
Bad card
- TP1: nothing
TP2: updated: 1.66-1.70v (3d same)
TP3: nothing
TP4: nothing
TP5: 0.01V (3D the same)
TP6: 1.66-1.70v (3D same)
TP7 through 11: nothing
Good card
- TP1:
TP2: 1.62v(3D same)
TP3: nothing
TP4:
TP5: 0.01 to 0.03 (3D same)
TP6: 1.62v(3D same)
TP7 through 11: nothing
Downclocking the card from 166mhz to 133mhz did not show a difference in voltage on those Tp's (my guess was that the 1.66v was linked to 166mhz, it isn't).
Update: also did TP's to 5v and 12v:
Bad card:
- TP2 to 5v: 3.20v
TP2 to 12v: 9.88v
TP5 to 5v: 5V
TP5 to 12v: 12.24V
TP6 to 5v: 3.22v
TP6 to 12V: 9.82
3d no big difference (when it crashes that is). Single chip or dual chip no difference
Good card
- TP2 to 5v: 3.4v
TP2 to 12v: 10.55v
TP5 to 5v: 5v
TP5 to 12v: 12.18v
TP6 to 5v: 3.4v
TP6 to 12v: 10.55v
Now the resistance on the Tp's
- TP1: nothing
TP2: 11.86 for good card, 11.90 for bad card
TP3: nothing
TP4: nothing
TP5: nothing
TP6: 12.42 for good card, 11.16 for bad card
TP7 through 11: nothing
Like you drawed on the picture '3.3V plane' reads 3.0V on the bad card. 2.8V on the good card.
To the left of C91 a small hole reads 5V for both cards. Near R115 reads 3.3V for both cards. Near R114 reads 6v for the good card, 6.4v for the bad one.
I couldn't find a 12v.
Bad card Q1-Q4 to gnd
Q1 0.5v 1 side 3.0v other side
Q2 1.75v to 3.0v
Q3 3.5v to 3.0v
Q4 12v to 3.0v
Good card Q1-Q4 to gnd
Q1 0.5v to 2.8v
Q2 1.9v to 2.8v
Q3 3.5 to 2.8v
Q4 12v to 2.8v
So it looks like the bad card has 3.0v on places and the good card 2.8v
Q6 reads 3.32V for both cards (metal plate)
All replaced caps have continuity with the ground pins on the molex connector.
Update: I believe I found what U4 (NJA) is: TPS3801J25DCK 2.25 V ULTRA-SMALL SUPPLY VOLTAGE SUPERVISORS (Texas Instruments)
http://www.hk-electronics.com/components/Lumi … 1J25DCKRG4.html