Both the mobo and the PSU were both purchased from very reputable sellers on Ebay and were described as tested and functioning. I tried moving the jumpers to reset the CMOS and replaced the battery with a new one. Still no success. I am convinced at this point that I have two bad mobos and two good power supplies.
The replacement mobo shows the symptoms of a bios that was probably permanently corrupted during a failed bios update attempt (1 beep then shutdown after 3 seconds).
Even though the seller said it was tested and functioning, it likely wasn't though (he agreed to a full refund including return shipping cost). I finally found another Dell PSU BIST self test for PSU's without a BIST test button and which I had missed the first time around. Both the replacement and the old PSU passed successfully (green light goes out after 3 seconds connected to power).
I am running on a backup machine now but since I new to get a new primary system up without and further delay, I just went ahead and found a new (not refurbished) Inspiron 3891 at a good price at the Dell outlet. This way they will ship it fast (tomorrow) and it will give me more memory capacity, a bigger cache, a faster, newer processor, and the ability to use an NVMe SSD.
I just decided not to spend any more time on this 3668. I may decide to try another mobo if I can find one inexpensively that works and just use this as a spare or backup machine. If that happens, I will update this thread so that people will know for sure that it was a bad mobo.
if you have a spare working 24/4 pin psu you can get a 24 to 6 pin adapter to test motherboard. the green light on Dell proprietary psu is not guarantee that it is working. unfortunately without a verified working psu it is hard to be sure whether it is psu or mobo that prevents POST.
if you plan to replace the motherboard w identical model, MS will likely activate Win 10 for you automatically if you use your Microsoft account to log in. MS remembers you.
Thanks for the prompt response. I do have 2 other working power supplies from some older Inspirons on hand but I have searched high and low for a 24/4 pin adapter. There are plenty of 24/6 and 24/8 adapters around for Dell motherboards but I have completely been out of luck in finding the 24/4 one.
I do have a replacement motherboard on the way which I found at a good price so I will be able to try that. The problem now is going to be that if it is the motherboard, my Windows 10 system will likely not be able to be re-activated after the MB is replaced. The Windows 10 system I have is an upgrade from the pre-installed Win 7 that came new on the system and I also don't think I have the CPU license linked to my MS Acct. That means I would have to purchase a new Windows license which I am not pleased about.
Thanks for the response. I see now that there are actually two power supply connectors on this board. What happens to connector #20 (4 pin connector) if you only attach the adapter to connector #9 (6 pin connector)? Isn't there some part of the board that isn't getting power?
#20 4 pin is for cpu and #9 6 pin is for motherboard. you always need both plugged in to start the board. plugging only one would not work.
conventional standard atx is 24 pin for mobo and 4 pin for cpu. Dell was using a proprietary prototype of ATX12VO standard where the 24 pin is trimmed to 6 pin.
PS the newest Dell is using full standard ATX12VO of 10 pin to replace conventional 24 pin for mobo.
When you say you got another psu and another 3668 mobo, were they tested to be working before, or you just got them untested?
Re: get an amber light lit up on the board and it would repeat the same cycle....the fans would run about 5-6 seconds, then a chirp and it would drop power.
that is usually sign of bios unable to finish POST. have seen it before w board that has bad CMOs. Try replace CMOs battery with a brand new CR2032 (You said you did this on the old board) and clear CMOs settings by jumper reset on motherboard.
Thanks for all of the helpful responses. I couldn't find a way to test the power supply. None of the commercial PSU testers I could find would work on a PSU which had only a 4 pin and 6 pin plugs. I managed to locate another one however and swapped it in. There was absolutely no change in my original symptoms in order words, the drives still powered up on their own but I couldn't power up the drives or the rest of the machine.
Since I figured it had to be the mobo, I got another one and swapped it in.I figured that would have to fix it since there was nothing left it could be. I got different results this time but it still didn't work. This time, as soon as I plugged it in the FANS were the ones that powered up on their own before I could hit the power button but the drives didn't.
Some other things were different this time also. After the fans ran about 5 second or so, I could hear a loud "chirp" from somewhere in the system and it immediately dropped power. Before I changed boards, the drives (which were the only ones that powered up) would stay running as long as it was plugged in.
Also, if I hit the power button this time I would get an amber light (nothing would light up on the old board) and it would repeat the same cycle....the fans would run about 5-6 seconds, then a chirp and it would drop power.
The one other thing different this time is that when it dropped power, the green light went out immediately whereas with the old board, the green light stayed on all the time as long as the machine was plugged in.
I love a good mystery as much as anyone else but this has me completely baffled. There is simply nothing left that could be causing the problem. I even tried disconnecting the power on button to see if that could be figuring in but it made no change. And, as I had done previously all the drives and ram were disconnected so none of them are the culprits.
The only thing I can conclude at this point is that either both mobos are bad or both psu's are bad (or both sets are bad). I'm more suspicious of the boards though. I wish I could find a way to test the voltages on the PSU pins with a multi-meter but I've only found ways to do that on PSU's with a 24 pin connector.
I wish I could tell for sure if it was the PSU or the board before I invest much more time and money in this machine.
Scott_SK
62 Posts
0
December 21st, 2021 10:00
Both the mobo and the PSU were both purchased from very reputable sellers on Ebay and were described as tested and functioning. I tried moving the jumpers to reset the CMOS and replaced the battery with a new one. Still no success. I am convinced at this point that I have two bad mobos and two good power supplies.
The replacement mobo shows the symptoms of a bios that was probably permanently corrupted during a failed bios update attempt (1 beep then shutdown after 3 seconds).
https://www.dell.com/support/kbdoc/en-us/000124349/understanding-beep-codes-on-a-dell-desktop-pc
https://www.dell.com/community/XPS/Laptop-turns-on-for-3-sec-then-shuts-off/td-p/7353693
Even though the seller said it was tested and functioning, it likely wasn't though (he agreed to a full refund including return shipping cost). I finally found another Dell PSU BIST self test for PSU's without a BIST test button and which I had missed the first time around. Both the replacement and the old PSU passed successfully (green light goes out after 3 seconds connected to power).
I am running on a backup machine now but since I new to get a new primary system up without and further delay, I just went ahead and found a new (not refurbished) Inspiron 3891 at a good price at the Dell outlet. This way they will ship it fast (tomorrow) and it will give me more memory capacity, a bigger cache, a faster, newer processor, and the ability to use an NVMe SSD.
I just decided not to spend any more time on this 3668. I may decide to try another mobo if I can find one inexpensively that works and just use this as a spare or backup machine. If that happens, I will update this thread so that people will know for sure that it was a bad mobo.
Thanks for all the help.
.
redxps630
9 Legend
•
15.4K Posts
0
December 10th, 2021 20:00
if you have a spare working 24/4 pin psu you can get a 24 to 6 pin adapter to test motherboard. the green light on Dell proprietary psu is not guarantee that it is working. unfortunately without a verified working psu it is hard to be sure whether it is psu or mobo that prevents POST.
redxps630
9 Legend
•
15.4K Posts
0
December 11th, 2021 11:00
you actually need a 24 to 6 pin adapter, not 24/4.
Amazon.com: COMeap Cable adaptador de alimentación ATX de 24 pines a 6 pines para placa base Dell con puerto de 6 pines de 13.4 in : Electrónica
if you plan to replace the motherboard w identical model, MS will likely activate Win 10 for you automatically if you use your Microsoft account to log in. MS remembers you.
Scott_SK
62 Posts
0
December 11th, 2021 11:00
Thanks for the prompt response. I do have 2 other working power supplies from some older Inspirons on hand but I have searched high and low for a 24/4 pin adapter. There are plenty of 24/6 and 24/8 adapters around for Dell motherboards but I have completely been out of luck in finding the 24/4 one.
I do have a replacement motherboard on the way which I found at a good price so I will be able to try that. The problem now is going to be that if it is the motherboard, my Windows 10 system will likely not be able to be re-activated after the MB is replaced. The Windows 10 system I have is an upgrade from the pre-installed Win 7 that came new on the system and I also don't think I have the CPU license linked to my MS Acct. That means I would have to purchase a new Windows license which I am not pleased about.
Scott_SK
62 Posts
0
December 12th, 2021 05:00
Thanks for the response. I see now that there are actually two power supply connectors on this board. What happens to connector #20 (4 pin connector) if you only attach the adapter to connector #9 (6 pin connector)? Isn't there some part of the board that isn't getting power?
redxps630
9 Legend
•
15.4K Posts
0
December 12th, 2021 06:00
#20 4 pin is for cpu and #9 6 pin is for motherboard. you always need both plugged in to start the board. plugging only one would not work.
conventional standard atx is 24 pin for mobo and 4 pin for cpu. Dell was using a proprietary prototype of ATX12VO standard where the 24 pin is trimmed to 6 pin.
PS the newest Dell is using full standard ATX12VO of 10 pin to replace conventional 24 pin for mobo.
redxps630
9 Legend
•
15.4K Posts
0
December 19th, 2021 05:00
When you say you got another psu and another 3668 mobo, were they tested to be working before, or you just got them untested?
Re: get an amber light lit up on the board and it would repeat the same cycle....the fans would run about 5-6 seconds, then a chirp and it would drop power.
that is usually sign of bios unable to finish POST. have seen it before w board that has bad CMOs. Try replace CMOs battery with a brand new CR2032 (You said you did this on the old board) and clear CMOs settings by jumper reset on motherboard.
PS orange light on board is from 5V the board generated itself after receiving 12V from psu. Drives such as dvd or fans work do not mean much.
Re: then tried replacing the CMOS battery and again
you need a brand new one, not removing or reseating old battery.
Scott_SK
62 Posts
0
December 19th, 2021 05:00
Thanks for all of the helpful responses. I couldn't find a way to test the power supply. None of the commercial PSU testers I could find would work on a PSU which had only a 4 pin and 6 pin plugs. I managed to locate another one however and swapped it in. There was absolutely no change in my original symptoms in order words, the drives still powered up on their own but I couldn't power up the drives or the rest of the machine.
Since I figured it had to be the mobo, I got another one and swapped it in.I figured that would have to fix it since there was nothing left it could be. I got different results this time but it still didn't work. This time, as soon as I plugged it in the FANS were the ones that powered up on their own before I could hit the power button but the drives didn't.
Some other things were different this time also. After the fans ran about 5 second or so, I could hear a loud "chirp" from somewhere in the system and it immediately dropped power. Before I changed boards, the drives (which were the only ones that powered up) would stay running as long as it was plugged in.
Also, if I hit the power button this time I would get an amber light (nothing would light up on the old board) and it would repeat the same cycle....the fans would run about 5-6 seconds, then a chirp and it would drop power.
The one other thing different this time is that when it dropped power, the green light went out immediately whereas with the old board, the green light stayed on all the time as long as the machine was plugged in.
I love a good mystery as much as anyone else but this has me completely baffled. There is simply nothing left that could be causing the problem. I even tried disconnecting the power on button to see if that could be figuring in but it made no change. And, as I had done previously all the drives and ram were disconnected so none of them are the culprits.
The only thing I can conclude at this point is that either both mobos are bad or both psu's are bad (or both sets are bad). I'm more suspicious of the boards though. I wish I could find a way to test the voltages on the PSU pins with a multi-meter but I've only found ways to do that on PSU's with a 24 pin connector.
I wish I could tell for sure if it was the PSU or the board before I invest much more time and money in this machine.