[jklab]

I have a 5 years old system , equipped with an AGP slot. My PSU is a "THERMALTAKE W0061 TR2 POWER 420W" .
I have an "nVidia 5200 128MB AGP" , but a friend of mine gave me an "Sapphire HD 3850 512MB AGP"
I noticed that wants a 450W PSU (or 30A on 12V with 2*4 power connector) . I would like to take a new tower
and use the old for movies (3850 can playback Blu-ray) . If card wants more power than the PSU , may I underclock the graphic controller or lower the voltage?

[Advertisements]

It is not good idea.

Every time computer is reset or powered on, PSU will be stressed with high current consumption and there is increased probability the current limiter protection in PSU die (if not already dead). If that happens, fuse in PSU will be burnt if exists. Otherwise MOSFETs in PSU will be forced over their limits and probably burn which could cause a lot of damage to your hardware.

In your case even if such small difference in power requirement exists better do not do that. Your PSU is 5 years old meaning capacitors in it (electrolyte in capacitors) are leaked enough so it can not provide even declared 420W.

[dji]

It is not good idea.

Every time computer is reset or powered on, PSU will be stressed with high current consumption and there is increased probability the current limiter protection in PSU die (if not already dead). If that happens, fuse in PSU will be burnt if exists. Otherwise MOSFETs in PSU will be forced over their limits and probably burn which could cause a lot of damage to your hardware.

In your case even if such small difference in power requirement exists better do not do that. Your PSU is 5 years old meaning capacitors in it (electrolyte in capacitors) are leaked enough so it can not provide even declared 420W.

[jklab]

Hi again!
No the PSU is new and silent....(that's the reason I would like to keep it) . I am electrical engineer and I know the problem , but the difference is small.... (1A * 12v = 12W peak) . In articles I have read that a graphic controller rarely reaches the peak point. In my case CPU is far slower p4 2,8ghz ... can't stress cart...(I am wrong?)

[dji]

If your PSU is new then you can give it a try.

If you can monitor current consumption on 12V line by an ampermeter that would be great (it requires opening PSU and connecting ampmeter instead of fuse for 12V line) but that will cancel your PSU warranty. If you do not want to do taht then

1. try to temporary disconnect all unnecessary devices which require 12V line (floppy, DVD, all non-system hard drives etc) but keep fans connected
2. connect your graphics to SLI power lines (if PSU has it if not then you must use adapters but each adapter should be connected to different wires from PSU to avoid enormous voltage drop)
3. power on the system
4. if system doesn't power up then your PSU is not powerful enough
5. if system powers up then go to in BIOS and do monitoring of voltage on 12V line (more current is used the bigger voltage drop is)
6. if it is in 5% tolerance range then boot OS (because OS turn on some things that are turned off while you are in BIOS like high resolution and that will start consuming more energy because all GPU cores will start running)
7. Use some OS software for voltage monitoring
8. Try to force GPU to maximum by starting some game
9. if everything is ok with 12V line then shut down comp and add each disconnected device ONE BY ONE and repeating from step 5 all the time

If PSU can not handle it at some point it will failed (12V becomes 10.5V or current limiter is triggered) and system will not boot.
Before that you'll probably got unpredictable system resets.
If everything is ok, you'll never get system hangs or resets.

[jklab]

Thanks, I will try... 3850V and PSU