I got back my "fixed" PVR-500 today. I can now boot into Windows (most the time) when I have both the tuners installed. However, now I get a nice little error message box about every five seconds...
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MSVIDCtl System Broadcast Message Receiver: ehRecvr.exe - Application Error
The instruction at "0x51000000" referenced memory at "0x51000000". The memory could not be "read".
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I've already tortured my RAM and CPU with memtest and HotCPU... there is nothing wrong with either.
I checked the IRQs on a few devices... and for some strange reason, my Creative SB Audigy 2 ZS (WDM) uses IRQ 18, and my Hauppauge WinTV PVR PCI II (23xx)(Tuner 2) uses IRQ 18. When I only have one of the two tuners installed, I don't seem to get the error message. As soon as the second tuner is installed, I get the ehRecvr.exe spammage.
My BIOS on my MSI Neo 4 SLI Platinum offers no way to manually set the IRQ (it will let me set IRQ assigning to "manual" which lets me list some IRQ numbers as "reserved" or "PCI Device"... which seems to do jack.) I've not had to touch IRQs since Windows 98, so I've forgotten how to resolve that issue.
The two variables that I've not been able to 100% eliminate:
A) Getting my devices on seperate IRQs (could use help here)

Testing my video card in another system (waiting for OCZ to respond to my RMA request, so I can get a good stick of RAM for a test system... they've not responded after my 4 attempts and two weeks.)
Worth mentioning:
Windows Vista Prerelease Candidate 1 installs and runs fine on the same computer (other than a few obvious beta glitches).
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The recap:
Antec P108B case
Athlon x2 4400+ with Sythe Ninja passive heatsink
MSI K8N Neo 4 SLI Platinum (with latest BIOS update) with Zalman ZM-NBF47 passive northbridge heatsink
2 x 512 MB crucial ballistix PC3200
EVGA 6800 Ultra in x16 slot 1
Sound Blaster Audigy 2 ZS Platinum
Happauge 500 PVR dual tv tuner
OCZ Modstream 520 watt power supply
Maxtor Maxline III 300 GB SATA hard drive (primary)
Western Digital 120 GB special edition ATA HD (slave on cable 2)
Lite-On DVD-RAM/-RW/+RW (master on cable 1)
Lite-On DVD-ROM/CD-RW combo drive (master on cable 2)
Windows Media Center Edition 2005
Dell 2405FPW color monitor
Microtek ScanMaker 5800
Logitec MX-1000
Microsoft Natural Ergonomic Keyboard
I purchased a new dual core CPU for my single core computer that was happily chuggin along. Had the latest BIOS, drivers, windows patches, updates, etc... everything was grand... but I wanted more speed...
so, I lobbed in a dual core x2 4400+ and everything went to [content edited]. WEEEEEEE!!! Yup. All it took was one "upgrade" and my system committed hari kari.
Stuff I've already tried (without success):
1) roughly 20 reformats and clean installs of Windows XP Media Center Edition in which I did some of or all of the following:
2) Installing the latest drivers (including the AMD dual core drivers and patches) and Installing the drivers in different orders
3) Confirmed my BIOS was indeed the most recent
4) ran multiple extended memtests. All passed.
5) ran multiple HotCPU diagnostics. All passed.
6) rewired the computer 4+ times.
7) put the sound card and tv tuner card in a variety of different PCI slots.
8) Tried a windows hotfix suggested to me in the forums here.
9) whined a [content edited] of alot
10) Tried BETA drivers on my video card.
11) RMAd my PVR-500 to Hauppauge for a "fix" they could do so my system would be able to boot when I had the card installed on my system. (they replaced some chip on it).
12) confirmed, reconfirmed, and kept reconfirming that thermals were within tolerance for the CPU and system. CPU hit low 50 degrees celcius during HotCPU. Generally runs 42-48 celcius during standard usage or gaming.
13) spent about 100 hours over the last month doing these all over again in different combinations/posting on forums for anything I may be overlooking.
14) tried different assignments for the drives on my IDE cables.
15) RAM is running at default timings, also 2T. The motherboard uses and nforce 4 chipset.
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My System:
Antec P108B case
Athlon x2 4400+ with Sythe Ninja heatsink
MSI K8N Neo 4 SLI Platinum (with latest BIOS update) with Zalman ZM-NBF47 passive northbridge heatsink
4 x 512 MB crucial ballistix PC3200
EVGA 6800 Ultra in x16 slot 1
Sound Blaster Audigy 2 ZS Pla