First IPL of used P550 in Home Lab displayed this on Control Panel: Line-1(01 M F), Line-2(HMC=0 T). Issue #1: Changed "01" to "02" and "M" to "N" on line-1, but IPL failed; no change on display panel. Set "M" back to "N" and exit function "2", but function "3" for IPL restart would not display. Issue #2: Set up Hyperterminal and cable as defined, but IVM screen stayed blank. Each letter I typed repeated itself. Issue #3: Same result as #2 for Serial Cable, ASMI screen stayed blank. Please help the Z/OS Guy...!!!
IPL = boot ? 
Terminals in half duplex echo keys even if disconnected
DGPickett:
Thanks for your prompt response. I un-select <echo typed characters locally> on the "ASCII Setup" tab of the HyperTerminal configuration to resolve character repeat/echo problem...see "(File => Properties => Settings => ASCII Setup)".
The IPL issues remain unresolved. Pressing the <Power On> button on the Control Panel, the Data Display area showed <11002613>. The documentation indicates this a "power or back plane" issue. My power supply is correct, it is "100-127" for the
"1-2 core" model I have in my Home Lab. Please help the z/OS guy
HMC=0 means this system has been connected to an HMC. You will need to use the web-based ASMI to perform a reset to factory settings.
The hard part might be figuring out what the IP addresses are:
the defaults for the HMC ports are: 192.168.2.147 and 192.168.3.147 (if you power on with nothing connected). If an IP address had been configured, you will need to do that.
Most of this I hope I covered in one of the first films I ever tried to make (no audio) at Demo: ASMI: Ways to react to an emergency!
Can you get a serial cable in to it? It's a specific wiring, but the same for most serial consoles (not network switches though)
You will need to set your communications to use BAUD 19200 rather than 9600, and that is a common problem.
From the powered off state (wait a few minutes for the service processor to restart), you should be able to press ENTER and get a text login to the service processor where you can then set the IP addresses of the ports labelled HMC, and probably go through and reset any other settings you need to.
I hope that this helps,
Robin
Liverpool/Blackburn
UK
If I recall correctly - as long as the display says "HMC=0" the serial port is disabled once the service processor is powered on. This might have been changed, and if so, rbatte1 advice is very useful (19200 baud, null modem wiring).