Question RAM slots A1 B1 on motherboard not working

[ARTURIUS94]

I have a problem, I have 4 RAM sticks that do not work together

I have RAM: 2x16 GB + 2x16 GB,
they are working and work separately and in pairs, but only in slots A2 B2.

When I insert one or two sticks, for example, into slot A1 or B1 and connect the PC to the power supply,
even without pressing the PC power button - the orange LED is already on.

If you insert 4 RAM sticks at once, the orange LED will not light until you turn on the PC

That is, if you turn on the PC with 4 manually made sticks at the same time, then
on my board the orange LED is on, the fans are spinning and nothing happens.

I disabled: EXPO (memory works by default)

I removed the undervolt that I had

I found out that the BIOS has a function: MRC:

I inserted 4 RAM strips and waited 20-25 minutes: "enable" and "auto"
and also started disabling this mode
Memory context recovery (MRC): enabled/auto/disabled
Memory Power Down: enabled/auto/disabled

but nothing helped either, the orange LED is on, the fans are spinning and nothing else...

I also tried resetting the BIOS, but it didn't help me

my PC:

mat. board: ASUS TUF GAMING B850-PLUS WIFI
My board firmware version:
Version 1028 2025/04/30
RAM: Kingston FURY 2x16GB DDR5 6000 MHz Beast EXPO kf560c36bbe2k2-32 - 2 identical kits

Power supply: SeaSonic FOCUS Plus 750 GOLD (SSR-750FX)
Processor AMD Ryzen 7 9700x

 

[ARTURIUS94]

If the RAM isn't binned altogether 4 sticks, there is no guarantee 2 kits even though they are the same specs are compatible.

i can't start pc (enter bios) using slots A1 B1

 

[JeffreyP55]

I have a problem, I have 4 RAM sticks that do not work together

I have RAM: 2x16 GB + 2x16 GB,
they are working and work separately and in pairs, but only in slots A2 B2.

When I insert one or two sticks, for example, into slot A1 or B1 and connect the PC to the power supply,
even without pressing the PC power button - the orange LED is already on.

If you insert 4 RAM sticks at once, the orange LED will not light until you turn on the PC

That is, if you turn on the PC with 4 manually made sticks at the same time, then
on my board the orange LED is on, the fans are spinning and nothing happens.

I disabled: EXPO (memory works by default)

I removed the undervolt that I had

I found out that the BIOS has a function: MRC:

I inserted 4 RAM strips and waited 20-25 minutes: "enable" and "auto"
and also started disabling this mode
Memory context recovery (MRC): enabled/auto/disabled
Memory Power Down: enabled/auto/disabled

but nothing helped either, the orange LED is on, the fans are spinning and nothing else...

I also tried resetting the BIOS, but it didn't help me

my PC:

mat. board: ASUS TUF GAMING B850-PLUS WIFI
My board firmware version:
Version 1028 2025/04/30
RAM: Kingston FURY 2x16GB DDR5 6000 MHz Beast EXPO kf560c36bbe2k2-32 - 2 identical kits

Power supply: SeaSonic FOCUS Plus 750 GOLD (SSR-750FX)
Processor AMD Ryzen 7 9700x

The two working slots must be your default setup for 2 sticks.
You may have the same exact specs for your 2 kits. Kits are binned for a reason. Buy all four in a binned kit. Two of the same and 2 that are not binned together may not be compatible and not guaranteed to work together.

 

[geofelt]

Two non working slots suggests either a motherboard defect, or a bent/broken processor pin that controls that function.

And.. the comment above is correct.
To operate at specs all the ram must be from a matched single kit.
One might be able to up the ram voltage in the bios to make it work.

 

[Misgar]

I suspect @geofelt is correct. It looks like one of the CPU's two IMCs (Integrated Memory Controllers) is not working, namely Channel 1.

Quite often, as @geofelt says, it's due to one or more bent pins in the CPU socket associated with the IMC that isn't working.

Carefully remove the CPU and check for bent pins inside the socket. They're horribly fragile and easily bent if you inadventently drop one edge or corner of the CPU into the socket. Straightening bent pins can be difficult or a nightmare when they snap off. It's usually new motherboard time.

As for fitting two dissimilar pairs of DIMMs, it's not an ideal situation, but very few people I know buy a single kit of 4 matched DIMMs at the outset.

The problem is that even if the two kits are from the same manufacturer and have exactly the same part number, the individual memory chips on the DIMMs are probably from different "bins" and hence the timings may differ between the pairs.

So saying, my old 3800X is running quite happily with two different 2 x 16GB kits of Corsair Vengeance (not always good with Ryzen) at 3000MT/s. I upgraded from 32GB to 64GB and the 4 DIMMs run multiple MemTest86 passes with zero errors.

In your case, I believe failure of DIMM slots A1 and B1 points to a CPU/mobo problem, not mixing two unmatched pairs of RAM.

Regardless of what RAM you install, fitting 4 DIMMs places more load on the two IMCs and you may have to reduce any XMP overclocks to retain stability. 2 DIMMs often overclock faster than 4 DIMMs, even when fitting a single kit of 4 matched DIMMs.

 

[ARTURIUS94]

I want to draw your attention to this point, and I want to get a detailed answer specifically to this point:
2) is it normal when I insert 1 or 2 bars of RAM into slots A1 B1 and before turning on the PC already orange LED is on?
- so it should be like this? A1 B1 slots should work only when 4 strips are inserted together?!?!
and the A1 B1 channels themselves do not work and this is normal?!?!

let me remind you, the A2 B2 slots work normally as they should
(works even if you insert one strip into B2)
as I understand it, the A2 B2 slots are "primary"?
👌🙂👍

 

[geofelt]

I think the way the diagnostics lights work is that they are all turned on initially.
As each component is initialized correctly, the light is turned off.
The usual sequence might be ram, graphics, cpu.

 

[SkyNetRising]

is it normal when I insert 1 or 2 bars of RAM into slots A1 B1 and before turning on the PC already orange LED is on?
and the A1 B1 channels themselves do not work and this is normal?!?!

Not normal. Suspect hardware issue.

Check cpu socket for bent/broken pins.
Make several high resolution photos of cpu socket from different angles and show here.
(upload to imgur.com and post link)

And I don't know, what is orange led.
The board has 4 diagnostic leds (CPU,DRAM,VGA,BOOT) and CPU_12V_LED.
Manual doesn't list any led colors.

You have to find, what led exactly is being lit.
Or make a photo of your board with orange led visible and show here.

 

[ARTURIUS94]

In your case, I believe failure of DIMM slots A1 and B1 points to a CPU/mobo problem, not mixing two unmatched pairs of RAM.

I tried to insert different modules from different kits into A2 B2 slots and they work

"Quite often, as @geofelt says, it's due to one or more bent pins in the CPU socket associated with the IMC that isn't working."
I checked it today - everything is ok

"and you may have to reduce any XMP overclocks to retain stability."
I tried running 4 strips with EXPO disabled, it didn’t help

 

[ARTURIUS94]

Today I took out the CPU, looked at everything, and everything was fine,
the pins in the motherboard socket are not bent - everything is fine!

the orange LED is: "DRAM"

 

[ARTURIUS94]

Here's what gpt chat answered me about the A1 B1 slots not working:

"Yes, you're right: your Daisy Chain board does have two channels (A and B), each with two slots: primary (A2, B2) and secondary (A1, B1). And here's how they should work:

🔧 Why A1 and B1 don't work separately (for 1-2 modules)
In Daisy Chain, the first slot of each channel is the "end" of the chain (A2, B2). It is supplied with a signal directly, and it usually works even with one module.

A1 and B1 are connected "further" in the chain - they expect the "end" to be filled, otherwise the signal is reflected and creates interference.

Conclusion:

When you install 1 module - only A2 works.

With 2 modules - A2 + B2.

A1 and B1 start working only if all four are installed module.

📍 Orange LED Conclusion
Question: Is it correct that when you insert one or two strips into A1 or B1, the orange DRAM LED lights up immediately?

Yes, this is normal. Paving A1/B1 without base modules results in a signal error and the indicator shows that no memory was detected

Answer to your questions
1) Is it normal that when inserting into A1/B1, the orange light lights up, even with 1–2 boards?
Yes. Without primary slots, the signal does not reach there — and it is great that you see this immediately. No need to worry — this is how it should be.

2) Do A1/B1 work on their own?
No, they are designed to work only with all four modules. This is an important feature of the Daisy Chain topology"

 

[USAFRet]

Here's what gpt chat answered me about the A1 B1 slots not working:

Consult the manufacturers User Manual.
Not the AI bot.

 

[ARTURIUS94]

User Manual.
Not the AI bot.

i don't rely on gpt chat as 100% truth (i understand that)
that's why i came to this forum,
(but with gpt chat i sometimes find better answer and faster)

 

[SkyNetRising]

Today I took out the CPU, looked at everything, and everything was fine,
the pins in the motherboard socket are not bent - everything is fine!

Bent pins might not be easy visible. Without making a photo, you may not be able to spot it.
Even slightest cpu socket pin misalignment can cause issues.

 

[ARTURIUS94]

Bent pins might not be easy visible. Without making a photo, you may not be able to spot it.
Even slightest cpu socket pin misalignment can cause issues.

if I had read your post before I pulled out the processor, I would have taken this photo, but I don't want to pull the processor back out to take photos.

those pins in the socket are very difficult to bend (if they were on the processor, then yes, it would be more likely to do so)

and this was only the second time I installed the processor
and if the pins were bent, then in addition to the RAM slots, I think that not everything would work stably

 

[Misgar]

those pins in the socket are very difficult to bend

Many people have discovered to their cost how easy it is to bend pins in a CPU socket. Just search for "how to straighten bent CPU socket pins".

All it takes is for one important pin to be bent out of shape and something stops working. If you don't believe me, start poking around inside the socket with a pencil or Biro (only kidding).

View: https://www.youtube.com/watch?v=1fkioojsxX8



https://forums.tomshardware.com/threads/1-cpu-socket-pin-bent.2984290/

if the pins were bent, then in addition to the RAM slots, I think that not everything would work stably

If you bend a pin associated with an Integrated Memory Controller channel, I'd expect the fault to remain isolated to the relevant DIMM socket(s) and nothing else. The rest of the system might continue working fine. You've only disconnected a RAM data line.

The more pins you mess up, the greater the chance of multiple failures. If you bend a Vcc or GND pin, it's no big deal; there are "dozens" of spare pins performing the same function. But if the bent pin has a unique function, that function will stop working.

and this was only the second time I installed the processor

Lots of people have messed up the socket on the first occasion. If the CPU slips out of your fingers and an edge or corner hits some pins, it can cause damage.

if they were on the processor, then yes, it would be more likely to do so

I prefer bent pins on old AMD CPUs. They're easier to straighten with a credit card or the tip of a propelling pencil. You can even unsolder broken pins on a CPU and solder new pins back, removed from a donor chip.

Not so easy with broken pins in a CPU socket as this video shows. It helps if you have a powerful binocular microscope and an ESD workstation.

View: https://www.youtube.com/watch?v=pEhXwfPScxU


If you try returning a mobo with bent pins, the dealer may refuse RMA if they think you caused the damage yourself. The warranty covers manufacturing faults and they may keep photos of the CPU socket after factory testing, as evidence the pins were intact prior to sale.

 

[ARTURIUS94]

I just don't want to take the processor out for a photo a second time, can't I do without a photo?
You can't take my word for it?
I looked at everything and all the pins are perfectly straight, the problem is not in the pins!!! Why does everything depend on the photo?

 

[SkyNetRising]

I just don't want to take the processor out for a photo a second time, can't I do without a photo?

That's perfectly fine too.
You'll just have to live with your non-operational ram slots.

 

[Misgar]

the problem is not in the pins!!!

To confirm every single CPU pin is connected properly, we'd have to run the manufacturer's test software (as used in the factory) but we don't have that luxury.

Other possible culprits include flexing of thin motherboards by screwing down the cooler too hard. This can result in bad connections between the CPU and the socket, or even broken tracks on the motherboard. Try loosening off the cooler screws by half a turn, or maybe a complete turn.

https://forums.tomshardware.com/threads/flexing-of-my-motherboard-and-ram-slots.2916145/

Have you checked inside the DIMM sockets for dust or fluff? A malformed plastic socket might prevent the DIMM from seating properly. Are the DIMM socket latches fully engaged?

If the CPU socket is fine, there's a vague chance you've got a duff processer.

On one of my rigs, I'd simply swap the CPU over to another (similar) system and try a different CPU in the suspect board. If the fault follows the CPU, I'd know what to replace.

I bought a very cheap mATX mobo second hand on eBay and one of the two DIMM sockets didn't work. A few weeks later, it started working, as did the faulty Ethernet port.

You can't always think your way out of a problem. Sometimes after forming a hypothesis, you have to perform practical tests.