Challenging question on DDR4 identification needs expert to answer. Help?

[Weelcup]

Hi
I have 5 dell motherboards. All dell inspirons but with 3 models 5570 and 7373 and 7570. They all have a very strange issue. When the ram is not connected they indicated (by blinking) that there is no ram installed. While when I install the ram the blinking code code indicate that there is an issue with the ram. I tried many good working rams but no luck.
All power rails are working fine. No heating on any component.

My only question is " do anyone know which signals identify the ram modules?" Of in any DDR4 slot. Is it like a sensor like chip or it is identified in the CPU.

I would really appreciate any advise.

Sorry I do not have any schematics but I would assume the ddr4 identification sequence would be the same on any board. I might be mistaken.

[eccerr0r]

Re: Challenging question on DDR4 identification needs expert to answer. Help?

Ever since SDRAM memory has been identified per slot with a serial presence detect EEPROM. The firmware scans each slot for this EEPROM and then proceeds to test each module based on the data in the EEPROM, so it's more than just one signal. Quite possibly it reads the EEPROM and hence detects the memory, and then when it comes testing the module it fails...

[Weelcup]

Re: Challenging question on DDR4 identification needs expert to answer. Help?

Ever since SDRAM memory has been identified per slot with a serial presence detect EEPROM. The firmware scans each slot for this EEPROM and then proceeds to test each module based on the data in the EEPROM, so it's more than just one signal. Quite possibly it reads the EEPROM and hence detects the memory, and then when it comes testing the module it fails...

Thank you very much for the reply.
If I understand you correctly, you mean that the ram module eeprom which is soldered on the ram module talks with the bios to identify itself?

[mcplslg123]

Re: Challenging question on DDR4 identification needs expert to answer. Help?

You can refer to any schematic with a ddr4 module and check its pins for voltages.Probably, some missing voltage on ram slot pins.

[piernov]

Re: Challenging question on DDR4 identification needs expert to answer. Help?

RAM stick will receive 3 power rails (values are for DDR4 here): 3.3V (SMBUS), 1.2V (VDDQ) and 0.6V (VTT). Missing 3.3V will result in RAM not detected. Missing 1.2V will result in RAM test error, but usually it doesn't even get to that point (stops before in the power sequence). Missing 0.6V will result in RAM test error too.
It can also be a damaged RAM slot, a damaged CPU (which contains the RAM controller) or a damaged trace on the board.
Different platform may have different RAM compatibility, depending on size and frequency, but also internal organization of the RAM chips. Also for DDR3, it is common to make the mistake of using a DDR3 stick in a DDR3L only machine, it'll not work.

[SMDFlea]

Re: Challenging question on DDR4 identification needs expert to answer. Help?

You can buy slot testers quite cheap. https://www.ebay.com/itm/Laptop-Moth...D/323736213911

[Weelcup]

Re: Challenging question on DDR4 identification needs expert to answer. Help?

You can refer to any schematic with a ddr4 module and check its pins for voltages.Probably, some missing voltage on ram slot pins.

Thanks for the help.
I have already tested all the voltages and seems all present.

[Weelcup]

Re: Challenging question on DDR4 identification needs expert to answer. Help?

RAM stick will receive 3 power rails (values are for DDR4 here): 3.3V (SMBUS), 1.2V (VDDQ) and 0.6V (VTT). Missing 3.3V will result in RAM not detected. Missing 1.2V will result in RAM test error, but usually it doesn't even get to that point (stops before in the power sequence). Missing 0.6V will result in RAM test error too.
It can also be a damaged RAM slot, a damaged CPU (which contains the RAM controller) or a damaged trace on the board.
Different platform may have different RAM compatibility, depending on size and frequency, but also internal organization of the RAM chips. Also for DDR3, it is common to make the mistake of using a DDR3 stick in a DDR3L only machine, it'll not work.

Well that is a quite beneficial info. Thank you very much.
Yes I agree with regard to ddr3 and ddr3l. With this board I tried different ddr4 frequencies. These models are accepting pc4-2400T. But it does not work indicating same error.

I just wanted to some the odds and looks for any chances to repair in case it is not a CPU related issue.
I also dont have an oscilloscope tester to test. But I tried to replace the ram step down chip which provide the 1.2v and same issue.


I hope it is not related to a damaged cpu Although the cpu rails resistant to ground seems ok.

I will buy a ram tester and will share the result with you.

Thanks again

[Weelcup]

Re: Challenging question on DDR4 identification needs expert to answer. Help?

You can buy slot testers quite cheap. https://www.ebay.com/itm/Laptop-Moth...D/323736213911

Thanks for the reply.
That a lot for referring to the tester. I will definitely buy it to check. And will come back with the result.


Thanks again.

[Weelcup]

Re: Challenging question on DDR4 identification needs expert to answer. Help?

Finally, I got the ddr4 tester. There were couple of testing leds that were not turning on. But it they did not turn on on a similar fully working board. So I assumed the ram socket is working.
However, accidentally, I turned on the board while I was pressing the ram module toward the mother (soft press) and surprisingly it did post with no issues. I kept it pressed for a very long time and was using windows explorer for about 30mins. No restating and not a single abnormal behave. Every thing was normal. And when I released the press on the ram the laptop screen flicker and it did freeze. And when I turned it off then on again the same issue " ram not recognised appeared". Now when gently pressing the ram module everything works fine and when releasing it then ram issue. So I tried to keep pressing the ram by using some tape . The laptop worked fine for two hours then again same issue... may be the tape loosen but was not very clear.


Thanks