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Fused Motherboard 4 pin power connector?
I have a motherboard I acquired cheaply, but which does not even post on poower
on. This was in a case, and had the 4 pin power connector plugged in 90 degrees wrong so that the pairs of 12V and GND connections would each receive one 12V and one GND supplied from the power supply. I suspect, that the internal board connections to this connector could have fused. What I'm wondering, is if there would be any possibility of determining if this is so, and if it can be repaired. If I turn on the board with the large power supply connector installed, and the 4 pin connector disconnected, I see no significant voltage on either 12V lead of the motherboard 4 pin connector, so voltage is not getting through to the 4 pin connections from the main power connector. The board is an Asus M4A87TD EVO Any ideas about how to test my hypothesis, or perform repairs? |
#2
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Fused Motherboard 4 pin power connector?
Bob F wrote:
I have a motherboard I acquired cheaply, but which does not even post on poower on. This was in a case, and had the 4 pin power connector plugged in 90 degrees wrong so that the pairs of 12V and GND connections would each receive one 12V and one GND supplied from the power supply. I suspect, that the internal board connections to this connector could have fused. What I'm wondering, is if there would be any possibility of determining if this is so, and if it can be repaired. If I turn on the board with the large power supply connector installed, and the 4 pin connector disconnected, I see no significant voltage on either 12V lead of the motherboard 4 pin connector, so voltage is not getting through to the 4 pin connections from the main power connector. The board is an Asus M4A87TD EVO Any ideas about how to test my hypothesis, or perform repairs? ATX12V 12V 12A max 1V ~100A Yellow ---+------------------------ Vcore ------------ CPU_Core Yellow ---+ | Black ------+ | Black ------+------------------------+--------------- GND 12V 12A max 12V yellow ---+------------+---+------+----------------+ 12V yellow ---+ | | | | (24 pin main) fan fan PCI Express PCI Express -- ~2A load, video, high end | | Slot Power Slot Power -- 4.2A load (6600 card) | | | | -- (non-video card, much less) GNDS (multi) ---------------+---+------+----------------+ (The connector current rating varies with wire gauge a little bit. The ATX12V could handle a bit more current than shown in the diagram, as the pins have "fewer neighbors", which helps with heat. The above rating on ATX12V is intended to be conservative. I'm not going to argue if someone digs up the Mini-Fit Jr datasheet and corrects the above numbers.) In that diagram, as far as ohmmeter readings on the motherboard itself are concerned, there should be no DC path from the yellow pair on ATX12V, versus the yellow pair on the main connector. If you leave the ATX supply connected to the motherboard, on the ATX side the rails could be shared. But with the ATX supply completely disconnected from the motherboard, there should be no path from ATX12V to 12V1 pair on the main 24 pin connector. Exception to the rule, is on Biostar-branded motherboards. For some obscure reason, users have been finding the two 12V distributions connected together by Biostar. Users have reported connecting just the main ATX connector, and the processor runs and system comes up. This is not particularly good for the main connector, depending on total electrical load. Biostar was also doing this in the AGP era. It's hard to tell whether they're still doing it, unless a poster volunteers the information. Biostar doesn't admit to the practice, in the user manual. The Mini-Fit Jr connector family is keyed by the shape of the connector plastic. And that's intended to warn the user about the orientation. The ATX12V also has matching latch elements on both connector bodies, as a "hint" as to orientation of the two bits. While a person can override the orientation with enough pounding, usually a person would notice something was wrong, before forcing it into place. The connector might not even want to stay there, as the latch cannot engage if the connector is installed in any (non-preferred) orientation. So is something blown ? Yeah, could be. Especially if the rotation is 180 degrees, and the 12V is applied reversed. If 12V was shorted to GND, maybe that triggered the OC protection on the ATX supply. If a monster supply was used (like 12V 60A single output), maybe something nasty could happen. But I would have expected the ATX wire harness plastic to start to melt if that happened. While individual outputs are supposed to have current limiter implementations (20 amp limit on some wire sets), we can't always be sure what is there, because the manufacturer usually does not provide proper detail about what they've done. The product labeling, if believed, tells you the whole 60A could be burning that connector. And I don't think we want to believe that. That isn't safe. If you want to bypass the ATX12V connection point, you'd want to find the input point on the VCore circuit. You can see a typical VCore implementation here on page 11 (this is the chip used on my P4C800-E Deluxe). You would want to connect the ATX12V to the left leg of inductor L1 in the upper left hand corner. Where it says "Vin 12V". http://web.archive.org/web/200403310...5ADP3180_0.pdf But I'd do some serious ohmmeter work first, before doing any more "live fire" tests :-) For example, use the ohmmeter to ohm from ATX12V motherboard connector yellow, to the equivalent of the left leg of inductor L1. You can usually spot the inductor, because it's slightly different than the matched inductors on the phases. You would also want to do a check for a short from 12V to GND, using low power ohms, on the motherboard. To see if there is a DC short already present in the circuit. If you look up the VCore regulator used on the motherboard, you can see what protections it has on output. Usually it has overcurrent protection. And that's to prevent the copper planes of the motherboard from becoming so hot, the PCB FR4 starts to become charred. That's when the processor is shorted out for some reason. Paul |
#3
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Fused Motherboard 4 pin power connector?
On Monday, November 17, 2014 10:44:23 PM UTC-7, Paul wrote:
Bob F wrote: The board is an Asus M4A87TD EVO In that diagram, as far as ohmmeter readings on the motherboard itself are concerned, there should be no DC path from the yellow pair on ATX12V, versus the yellow pair on the main connector. If you leave the ATX supply connected to the motherboard, on the ATX side the rails could be shared. But with the ATX supply completely disconnected from the motherboard, there should be no path from ATX12V to 12V1 pair on the main 24 pin connector. Exception to the rule, is on Biostar-branded motherboards. For some obscure reason, users have been finding the two 12V distributions connected together by Biostar. Users have reported connecting just the main ATX connector, and the processor runs and system comes up. This is not particularly good for the main connector, depending on total electrical load. Biostar was also doing this in the AGP era. It's hard to tell whether they're still doing it, unless a poster volunteers the information. Biostar doesn't admit to the practice, in the user manual. The Mini-Fit Jr connector family is keyed by the shape of the connector plastic. And that's intended to warn the user about the orientation. The ATX12V also has matching latch elements on both connector bodies, as a "hint" as to orientation of the two bits. While a person can override the orientation with enough pounding, usually a person would notice something was wrong, before forcing it into place. I had a BioStar M7VIZ designed with no ATX12V connector. Normally motherboards like that power the CPU from the four +5V wires on the 20-pin connector, but this one powered it from the single +12V wire. This motherboard also had a BIOS bug: if no boot device could be found, you couldn't simply hit the reset button or power down but instead had to remove the CMOS battery. Even moving the CMOS jumper wasn't enough to make the thing boot. I have an Ultra V-Series power supply (by Wintech) that can easily be plugged in backwards with certain really cheap motherboards (Otto 586TX?). Ironically, the user manual tells people to do that with motherboards and floppy disk drives. |
#4
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Fused Motherboard 4 pin power connector?
Paul wrote:
Bob F wrote: I have a motherboard I acquired cheaply, but which does not even post on poower on. This was in a case, and had the 4 pin power connector plugged in 90 degrees wrong so that the pairs of 12V and GND connections would each receive one 12V and one GND supplied from the power supply. I suspect, that the internal board connections to this connector could have fused. What I'm wondering, is if there would be any possibility of determining if this is so, and if it can be repaired. If I turn on the board with the large power supply connector installed, and the 4 pin connector disconnected, I see no significant voltage on either 12V lead of the motherboard 4 pin connector, so voltage is not getting through to the 4 pin connections from the main power connector. The board is an Asus M4A87TD EVO Any ideas about how to test my hypothesis, or perform repairs? ATX12V 12V 12A max 1V ~100A Yellow ---+------------------------ Vcore ------------ CPU_Core Yellow ---+ | Black ------+ | Black ------+------------------------+--------------- GND 12V 12A max 12V yellow ---+------------+---+------+----------------+ 12V yellow ---+ | | | | (24 pin main) fan fan PCI Express PCI Express -- ~2A load, video, high end | | Slot Power Slot Power -- 4.2A load (6600 card) | | | | -- (non-video card, much less) GNDS (multi) ---------------+---+------+----------------+ (The connector current rating varies with wire gauge a little bit. The ATX12V could handle a bit more current than shown in the diagram, as the pins have "fewer neighbors", which helps with heat. The above rating on ATX12V is intended to be conservative. I'm not going to argue if someone digs up the Mini-Fit Jr datasheet and corrects the above numbers.) In that diagram, as far as ohmmeter readings on the motherboard itself are concerned, there should be no DC path from the yellow pair on ATX12V, versus the yellow pair on the main connector. If you leave the ATX supply connected to the motherboard, on the ATX side the rails could be shared. But with the ATX supply completely disconnected from the motherboard, there should be no path from ATX12V to 12V1 pair on the main 24 pin connector. Exception to the rule, is on Biostar-branded motherboards. For some obscure reason, users have been finding the two 12V distributions connected together by Biostar. Users have reported connecting just the main ATX connector, and the processor runs and system comes up. This is not particularly good for the main connector, depending on total electrical load. Biostar was also doing this in the AGP era. It's hard to tell whether they're still doing it, unless a poster volunteers the information. Biostar doesn't admit to the practice, in the user manual. The Mini-Fit Jr connector family is keyed by the shape of the connector plastic. And that's intended to warn the user about the orientation. The ATX12V also has matching latch elements on both connector bodies, as a "hint" as to orientation of the two bits. While a person can override the orientation with enough pounding, usually a person would notice something was wrong, before forcing it into place. The connector might not even want to stay there, as the latch cannot engage if the connector is installed in any (non-preferred) orientation. So is something blown ? Yeah, could be. Especially if the rotation is 180 degrees, and the 12V is applied reversed. If 12V was shorted to GND, maybe that triggered the OC protection on the ATX supply. If a monster supply was used (like 12V 60A single output), maybe something nasty could happen. But I would have expected the ATX wire harness plastic to start to melt if that happened. While individual outputs are supposed to have current limiter implementations (20 amp limit on some wire sets), we can't always be sure what is there, because the manufacturer usually does not provide proper detail about what they've done. The product labeling, if believed, tells you the whole 60A could be burning that connector. And I don't think we want to believe that. That isn't safe. If you want to bypass the ATX12V connection point, you'd want to find the input point on the VCore circuit. You can see a typical VCore implementation here on page 11 (this is the chip used on my P4C800-E Deluxe). You would want to connect the ATX12V to the left leg of inductor L1 in the upper left hand corner. Where it says "Vin 12V". http://web.archive.org/web/200403310...5ADP3180_0.pdf But I'd do some serious ohmmeter work first, before doing any more "live fire" tests :-) For example, use the ohmmeter to ohm from ATX12V motherboard connector yellow, to the equivalent of the left leg of inductor L1. You can usually spot the inductor, because it's slightly different than the matched inductors on the phases. You would also want to do a check for a short from 12V to GND, using low power ohms, on the motherboard. To see if there is a DC short already present in the circuit. If you look up the VCore regulator used on the motherboard, you can see what protections it has on output. Usually it has overcurrent protection. And that's to prevent the copper planes of the motherboard from becoming so hot, the PCB FR4 starts to become charred. That's when the processor is shorted out for some reason. I checked what I could. The +12V and Gnd connections on the 4 pin connector both have continuity between the same signal pin pairs, + Gnd goes to Gnd, and the 12V pins have solid connections to a bunch of what are probably regulators of some sort. So the problem must be elsewhere on the board or the processor. When powered up, the fans turn on, and stay on. But other than the 3 keyboard leds going on when the power button is hit, it does nothing including beeping. Pressing the "MemOK" button cause the DRAM LED to flash regularly, but that's all it does. No other results are seen. Clearing the CMOS changes nothing. I tried restarting it with a USB floppy drive containing a bootable floppy with the latest BIOS on it, and nothing happened. So much for the CrashFree BIOS3 feature. Unfortunately, I have no other compatable processors or motherboards to test these ones. I did test the DDR3 ram on another board, and it works fine. So until I find a way to test the motherboard and processor, I guess I am at a dead end. |
#5
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Fused Motherboard 4 pin power connector?
Bob F wrote:
I checked what I could. The +12V and Gnd connections on the 4 pin connector both have continuity between the same signal pin pairs, + Gnd goes to Gnd, and the 12V pins have solid connections to a bunch of what are probably regulators of some sort. So the problem must be elsewhere on the board or the processor. When powered up, the fans turn on, and stay on. But other than the 3 keyboard leds going on when the power button is hit, it does nothing including beeping. Pressing the "MemOK" button cause the DRAM LED to flash regularly, but that's all it does. No other results are seen. Clearing the CMOS changes nothing. I tried restarting it with a USB floppy drive containing a bootable floppy with the latest BIOS on it, and nothing happened. So much for the CrashFree BIOS3 feature. Unfortunately, I have no other compatable processors or motherboards to test these ones. I did test the DDR3 ram on another board, and it works fine. So until I find a way to test the motherboard and processor, I guess I am at a dead end. The single beep on a "good POST", is normally generated by means of BIOS executed code. Hearing no beep at all, means either the CPU isn't running, or the BIOS code is wiped out (bad flash) and the CPU simply crashes when reading in whatever garbage (all 1's) is in there. Asus used to have a good feature, called "Vocal POST", which was based on a Winbond voice recorder chip (playback voice sampes), plus a serial EEPROM with the messages recorded in it. That product would deliver messages such as "Failed memory test", if a tiny part of the initial POST completed, but the RAM test crashed half way through. That was a pretty good feature, and cost them a buck or two to implement. A less useful scheme, present on most motherboards, is Port 80 code. These are progress codes, written to PCI (or PCI Express) space. A "display card" can display the two digit value. Since they're progress codes, they tell you a certain subroutine has just started to run. But because they're not error codes, you don't get something informative like "the RAM is bad", or "your processor sucks". The people who own the display cards (available anywhere from $10 to $100 for the same hardware), they use the display mainly as an "activity indicator". For example, one PC tech used the additional LEDs on the card, that measured supply voltages, as a quick test for his PCs. The two-digit values are mostly worthless. If the card stays stuck with "0x00" of "0xFF" on the display (equals 0 or 255 decimal respectively), those are general indications the processor crashed early on, and no values are getting written to the POST display card. Some motherboards come with the two digit hex display, permanently affixed to the motherboard surface. That's an enthusiast level feature, only available on a few boards. At least that saves you buying a $10 display card from Hong Kong. This is an example of a PCI or ISA card. This would not work in my latest motherboard, with no PCI slot. Only my first Windows PC, from 1999 time frame, might have ISA. ISA is the "bigger contacts" one. The LEDs on this one are not diagnostic (the four individual red LEDs). The person with the other POST card, the LEDs were connected to window comparators, that would check the +12V was within +/-5%, making the LED more useful. One of these with the three square chips, are just the basic PORT 80 write function. http://www.amazon.com/Analyzer-Digit.../dp/B007Q92QWS They make them for PCI Express. I've seen a proper PCI Express card with a circuit on it. The ones I can find now, seem to be laptop ones of some sort. I couldn't find one with a PCI Express faceplate on it, for a desktop. http://www.amazon.com/Bheema-PCI-E-A.../dp/B00PC9MAK2 As for what slot you plug those into, I'd start with slot #1 closest to the processor if possible. The product is not likely to come with documentation, so you're largely on your own if it doesn't work. The reason I selected that last one, is the Altera chip isn't hidden on it. I was wondering what kind of chip could do it with all-in-one, and that chip is programmable array logic of some sort. Amazingly cheap, if so. That allows them to implement two bus standards, drive a LED display, and run it all off the 3.3V bus power. Pretty neat job. If you buy one of those Port 80 debug cards at a local computer store, they'll charge $100 for them. Even though they're buying them from China for $10 or so. ******* One other debug type. And I liked this one... Some enthusiast RAM products, were fitted with "flashing LEDs" on the DIMM. The LEDs would flash when the RAM was accessed. Using one of those DIMMs, a PC with a working CPU, could be seen to flash the LEDs regularly. Whereas a machine with a completely dead CPU (no BIOS code to run, cannot bootstrap itself to even begin programming the DRAM controller), the LEDs on the DIMM would not flash at all. So as well as a display card, stocking a few flavors of those would be additional (relatively cheap) test gear. Paul |
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