HP HDX9000 GPU Issue -
| posts: 3
Seeking assistance with an issue regarding a GPU upgrade on the HP HDX9000
I am experiencing an issue with screen brightness as explained below.
I am experienced engineer and have dug far deeper than anyone ever should into this problem and have listed my results below.
Looking for someone to help solve this last little issue.
Stock GPU MXM Card = Nvidia 8800m
Replacement GPU MCM Card = Nvidia Quadro FX2700 or FX3700
Pinout between cards is identical except for the LVDS channels being reversed. That is to say the ODD and EVEN LVDS channels are exactly a mirror of each other.
Pinout issue is resolved by flipping pin order on cable.
On this model Vbios is loaded from a module in the SBIOS. This is resolved via Vbios injection.
With these 2 changes made the card works nearly perfectly. Performance is great, fully recognized by Windows and Ubuntu.
The issue is the screen brightness. It is very low, and is not adjustable via keyboard keys or in OS.
Brightness issue is apparent from post and in all operating systems. This leads me to believe it is not driver or OS related.
Now here is where it gets strange.
If i inject one of several different VBIOS rather than the FX2700m or FX3700m i get correct brightness and working brightness control. This includes the stock 8880M vbios, as well as 8800m Vbios from IBM, and Dell.
Although the brightness works, just about everything else does not. In most cases it will crash within a few minutes.
This result is expected, but leads me to conclude the brightness issue is not a physical or electrical issue at all, but rather some element of the FX2700 or FX3700m VBIOS
This led me to believe it was a PWM signal issue. I fed an external PWM signal into the CCFL inverter and could control the brightness by varying the PWM signal. In this case with the FX2700m or FX3700m Vbios in use externally controlled maximum duty cycle resulted in the low brightness. It could be brought lower, but never higher. This is confirmed by measuring the frequency and duty cycle of the internal machine provided PWM signal. It is running at full brightness.
With the other Vbios (8800m) this exact same PWM signal results in an appropriately bright screen.
In addition, i took the CCFL inverter out of the equation, and used a fully external, and externally powered CCFL inverter. Results in a dim display with FX Vbios, and Bright Display with 8800m VBIOS.
This leads me to conclude it is not an issue related to the CCFL inverter, or CCFL inverter control (PWM).
I modified the EDID on the LCD screen itself to adjust GAMMA values, White Balance Values and a others. Although the image changed, nothing effected the brightness issue.