Help Needed!
I need you to use a multimeter and measure continuity between the 12V ATX pin and AGP pin A1.
Measure between the yellow square in the AGP port, and either of the other yellow squares in the picture below.
The attachment or840_12V.jpg is no longer available
Background
My OR840 has developed a nasty problem with its AGP slot: I'm unable to use most AGP cards.
At first I thought it was related to AGP signaling and proper voltage generation—AGP 1.0 cards run at 2x and use 3.3V, while AGP 2.0 cards can run at 4x while using 1.5V.
However, taking measurements right at the MOSFET (signaled in blue in the picture), I saw proper voltages when using a Voodoo3 (3.3V card), when using a GeForce2 (1.5V card), and when using a Radeon8500 (1.5V card)
So the voltage switching and generation seems to be working properly. I measured VREF for each card as well, and its within the expected ranges for each of them.
The plot thickens:
- The Voodoo3 gives me video and the system POSTs properly.
- The GeForce2 doesn't give video and I don't hear any POST beeps, so the system doesn't POST. Also, the fan on the card doesn't spin.
- The Radeon8500 doesn't give video but I hear POST beeps, the fan on the card spins just fine.
The fans gave me my next clue: the Radeon powers it from 5V, while the GeForce powers it from 12V.
When I checked continuity between the ATX 12V pin and the A1 AGP pin, there was none! In every other motherboard I have, there is a direct connection.
With the system running, I measured the voltage in the A1 AGP pin with the different cards. Here are the results I got
- Voodoo3 --> 0.01V
- GeForce2 --> 1.26V
- Radeon8500 --> 3.75V
So right now I have the following question before I can take action:
In the OR840, should there be a direct path from ATX 12V pin to A1 AGP pin, or are there elements in between?
Tracing proved impossible, so I need someone to help me!
- If there is a direct path, then I'll solder a patch cable, with a fuse just in case.
--> In this case, the voltages measured with each card are just the result of the circuit in the card doing funny things without the 12V supply.
- If there isn't a direct path, then I'll need further help finding the faulty element.
--> In this case, there is a faulty element in the path between ATX 12V and AGP A1, and the measured voltages are due to different load from each of the cards
Thanks in advance, everyone!
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