Hello, I have been experiencing an odd issue with a Gigabyte GA-7VT600 1394 motherboard where screen resolutions at 800x600 and above seem to have weird interference on the VGA display, which goes away during low CPU usage... The best way I can describe it is faint horizontal lines flickering like TV static visible on dark colors, and dark text seems to blur and jump, all in sync with CPU or Hard Drive activity, possibly gets less intense when machine warms up... Also, tons of noise on Soundcard/TV Tuner audio also in sync with CPU usage.
I have recapped all large capacitors with new Rubycon MBZ's (Older ones were MBZs and Sanyo WG series), I tried three different ATX supplies, a 450Watt, 300Watt and a brand new (overkill) EVGA NEX750B 750Watt, no difference, tried two CPUs Athlon XP 2600+ and Athlon XP 3200+, same situation.
Voltages are as follows:
VCore: 1.67 to 1.69
3.3: 3.31 to 3.36
5V: 4.75 to 4.83
12V: 12.49 to 12.610
+5Vsb: 5.05 to 5.16
CPU Vid: 1.850
I went to great lengths to diagnose this, even ran the board on my desk and connected the Oscilloscope to look at VRM's MOSFET Gates (All were being driven properly), I checked voltages, and ripple and found that the 5V and 3.3V rails had 60mV+ ripple, and oddly enough the 3.3V rail had disturbances (periods of drooping voltage) that aligned with the flickering, not sure if that is related to the issue or not.
This board has two phase VRMs, each phase has two identical MOSFETs on high and low side (70N03S), 180degrees out of phase, uses the FAN5091 to regulate them.
I'm at my wits end here and the only thing I can think might be causing this is failing VRM Mosfets, because when I swap out the XP 2600+ for the XP 3200+ the system becomes unstable and freezes or resets randomly, but works fine if I reduce system bus to 100Mhz (reducing CPU clock to 1100Mhz).
Edit: I should also mention I tried upping CPU voltage, AGP voltage, DDR voltage, reducing DDR speed, reducing AGP from 8x to 4x, swapped several different DDR sticks, no dice.
Should I replace the MOSFETs, and if so, should I use originals or MOSFETs with lower RDS(on)?
Any help is greatly appreciated, thanks in advance,
Richard.
I have recapped all large capacitors with new Rubycon MBZ's (Older ones were MBZs and Sanyo WG series), I tried three different ATX supplies, a 450Watt, 300Watt and a brand new (overkill) EVGA NEX750B 750Watt, no difference, tried two CPUs Athlon XP 2600+ and Athlon XP 3200+, same situation.
Voltages are as follows:
VCore: 1.67 to 1.69
3.3: 3.31 to 3.36
5V: 4.75 to 4.83
12V: 12.49 to 12.610
+5Vsb: 5.05 to 5.16
CPU Vid: 1.850
I went to great lengths to diagnose this, even ran the board on my desk and connected the Oscilloscope to look at VRM's MOSFET Gates (All were being driven properly), I checked voltages, and ripple and found that the 5V and 3.3V rails had 60mV+ ripple, and oddly enough the 3.3V rail had disturbances (periods of drooping voltage) that aligned with the flickering, not sure if that is related to the issue or not.
This board has two phase VRMs, each phase has two identical MOSFETs on high and low side (70N03S), 180degrees out of phase, uses the FAN5091 to regulate them.
I'm at my wits end here and the only thing I can think might be causing this is failing VRM Mosfets, because when I swap out the XP 2600+ for the XP 3200+ the system becomes unstable and freezes or resets randomly, but works fine if I reduce system bus to 100Mhz (reducing CPU clock to 1100Mhz).
Edit: I should also mention I tried upping CPU voltage, AGP voltage, DDR voltage, reducing DDR speed, reducing AGP from 8x to 4x, swapped several different DDR sticks, no dice.
Should I replace the MOSFETs, and if so, should I use originals or MOSFETs with lower RDS(on)?
Any help is greatly appreciated, thanks in advance,
Richard.
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