Intel IXP425 power supply

[ealex]

Hello

I've got a switch based on an Intex IPX425 cpu that is acting up.
I could identify 3 different power supplies: a 3.3 switch mode one that is working properly and 2 linear ones based on LX8384-00 - 5A adjustable LDO.

Both of the LDO's are powered from the 3.3V rail.
One of them gives out 1.95V with 0.61V on the adjust pin and the other one gives out 1.3V with just 0.060V on the ADJ pin.

The 1.95 one goes to the ethernet isolation transformers and to some RTL8309 switch controllers ( seems appropriate according to the RTL manual) .
The 1.3V one seems to go directly to the CPU.
From what i can read on the LDO's datasheet they try to achieve 1.25V on the ADJ pin ( Reference Voltage is 1.25V ).

I'll try to remove the voltage set resistors from the circuit to measure them - in circuit they have some very strange values.

Is the 1.3V rail correct for the intel CPU ?

After a while it gets warm but i can't see no activity on the RAM of FLASH bus.

I'll start by replacing the capacitors after the LDO's

[cyr]

I'm almost positive 1.3V is the correct core voltage, that's what we had on an IXP425 design I worked on.

[ealex]

Thanks.
So the LDO's might be ok.
I'll try replacing caps,etc as soon as I get at my work bench.

[ealex]

Update:
I've replaced the caps but no changes - when i plug it in all LAN led's turn on and no reaction whatsoever.
I've probed around the CPU - no activity on the memory bus or on the FLASH, just several 33Mhz clocks and a lot of pins that are sitting at ~ 280mV.
There is a CF card that has a file system with some configuration data that seems ok ( no change when this card is unpluged )
No activity on the serial console, etc.
I'll try to see if i can connect to the boot flash (intel 28F320)- there is a 2x8 connector next to it.

The CPU is in a BGA package - maybe there is a loose connection ?

[garak]

I don't know this CPU from Adam, but have you checked the other obvious things? CPU reset lines etc? Often in embedded designs these are connected to a supervisory chip. Pulling up the D/S for this would tell you what it's looking for which might help you in finding electrical issues.

[ealex]

I had to return that switch - i could not find info. regarding it's pinout.
There were no supervisor chips on board - just several clock drivers that were working and a lot of realtek / network dedicated ic's that i could not test.

Thanks for your hints