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CX750M - startup/graphics issues/rebooting/wayward fans...


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Hi,

 

I've been having trouble for a while now, and I think I'm about at the point of asking for an RMA, but I wanted to check in and see if anyone had any thoughts that I'd overlooked.

 

(Sorry for the length of this post; it's been a long troubleshooting process so far)

 

For Christmas I got an XFX 7870, and upgraded my old PSU to a CX750M at the same time. Things were working fine, until a few months ago.

 

Initially the problem manifested as some graphics problems at start up. They varied, but I'd typically get either large squares (white, or green and pink), and/or lines across the screen. These would sometimes be static, sometimes in motion. Sometimes the image on screen would be frozen at the same time, but at other times the display was working ok. The screen would also be blank on occassion. These problems only ever appeared at boot, and if I hit restart, they usually disappeared entirely. Once it was up and running, my pc seemed to work fine, but would occassionally reboot without warning. If I shut the PC down, and then restarted within about ten minutes, it would work fine. If I left it off overnight and switched it on, it would have all the issues I've described. If I left it and it went into any kind of powersaving, it would have issues when I came back to it (if it was longer than a few minutes, that is). Even when the screen was frozen, I think the pc itself was running ok.

 

The event log would often (but not always) have an error: Display driver amdkmdap stopped responding. Looking into this a bit more, I found that for a lot of people with 7870s this was a power issue, and sometimes resolved this error by increasing the GFXs power in its BIOS. But the XFX that I have has the BIOS locked, so that wasn't a solution for me. Anyway, I completely reinstalled the GFX drivers, several times, refreshed Windows, and then did a full clean install of windows. None of this helped the issues, though the error message seemed to stop. But in the process of troubleshooting, I changed the BIOS settings to disable quick boot, and found that the graphics issues were occurring before Windows was starting anyway. It was POSTing okay, though.

 

I forget the order that I did things, but I removed all non necessary components, and eventually breadboarded it. I ran various stress tests (CPU, memtest, and graphics), and they never showed any problem. I tried different monitors and different cables. I reset the BIOS. I used a multimeter to test the connections under load. I'm sure there were other things I tried that I can't even remember.

 

Now, at this point it seems very likely to be either the GFX card or the PSU, right? And the most sensible thing would be to test the card and supply separately to try to narrow it down. But I don't have access to the spare parts to do a conclusive test. I got the card because it was such a step up from my old one, and I got the PSU because my old supply wasn't close to being powerful enough. But I've done my best:

 

Using the integrated graphics, on the lowest resolution, the problems mostly seem to resolve. But the random restarts still occur (albeit possibly less often; I didn't spend much time with that setup, as it was so useless).

Using my older card (HD6670), the issues likewise seem a little better (little or no GFX issues, but still resbooting). But, again, it doesn't seem like a fair test of the PSU anyway, since that card is only using a fraction of the power compared to the 7870.

Testing the 7870 on its own: I eventually got an adapter that would allow me to at least connect my 7870 to my old, generic, underpowered PSU. Not expecting much, I powered it up... and it worked. BIOS and Windows started okay. I was using desktop applications. No problem. But doing anything graphically intensive (unsurprisingly) caused issues. Yes, artifacts onscreen, and reboots, but the artifacts were of a different type, and the reboots occured under conditions I could replicate. Which leads me to think it may be the PSU rather than the GFX card.

 

Finally, there's the fans. My case has four fans, of two different brands. The rear fan is powered via the mobo, the top two fans are connected together and powere directly by molex (but with a high/low switch on the case), and the front fan is powered by another molex, with no other control or connection at all. Anyway, on one occassion while the pc was running I was looking at the top of the case and noticed that the top two fans had stopped. The pc seemed to be running okay, and the other fans were on. I tried the high/low switch, but it made no difference. While I was wondering whether to switch the pc off and take a closer look, they both spontaneously started again.

 

On another occassion, again when I happened to be peering into the case while it was on, the front fan stopped working. It just wound down to a halt. It was only a few seconds, and I didn't have time to do anything about it before it started again.

These are the only two times that I'm aware of this happening, but since the fans are very quiet, I'm not in the habit of spending time looking into the case, and I only noticed because I happened to be looking directly at them at the time, I believe that it was happening when I wasn't paying attention, too. Now, it COULD be a problem with three different fans (of two different brands), but I think the PSU is again the more likely culprit?

 

It's a weird coincidence if not.

 

Anyway, I've been using my old 6670 with the old generic PSU for a few weeks, and haven't had any problems at all.

 

Is an RMA reasonable at this point? Any alternative suggestions? Anyone still reading? ;)

Thanks.

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  • Corsair Employees
The fans spinning down is hard to explain. Fans will typically run as long as there's at least 7V going to them and, quite honestly, if the PSU was only putting out 7V on the +12V rail, your PC wouldn't be running at all.
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Yeah, I've read the same thing elsewhere, and I'm not really sure what to make of it. It's not even as if all the fans stopped at the same time, and, as I say, they're different brands, too.

 

Is it remotely possible that the modular molex cables could be faulty? I can't remember for sure at this point whether they were all running off the same cable, or two different ones. But I guess even if that's the case, it's unlikely to explain the other issues. :s

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The front fan is just a molex connector (and connected directly to the PSU). The case is closed at the moment, but I believe the top fans are each three pin, connected to a single molex adapter. There's the high/low switch for the top fans, as well, but I can't visualise exactly how it's connected. I'll take a look tomorrow.
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Okay, so as I thought, the top fans are three pin, connected to some kind of y-adapter which is routed through the body of the case to the high-low switch, and a single molex comes out from the same place. There's no obvious loose connections, and the pins seem to be okay. But I can't rule out both molex connectors being the issue (at least with the fans). I have disconnected these in the past, though.

 

In any case, the fans have got to be either just a symptom of the main issue, or something unrelated, like faulty molex, right? I still had all the other issues when the fans weren't connected at all.

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  • Corsair Employees

Well... if we take the fans out of the equation, I could say bad video card. The reboots could be anything from faulty memory to faulty motherboard to faulty PSU.

 

Without having redundant parts around, it's hard to troubleshoot.

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Yeah, it is.

 

Well, I'd swapped out the memory a couple of times, and I've not had any issues since putting my old card and PSU in. I can't see it being the memory or mobo if changing the PSU clears up the problem (?).

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