DEC Rainbow PC100-A

Paul Koning paulkoning at
Mon Jan 18 09:29:15 CST 2016

> On Jan 18, 2016, at 9:59 AM, emanuel stiebler <emu at> wrote:
> On 2016-01-17 18:11, Warner Losh wrote:
>> Would love to help, but I have the PC100-B. The PC100-A board is somewhat
>> different than the
>> PC100-B, but not super different.
>> Have you checked the diagnostics table in the technical reference to see
>> what all LEDs lit means?
>> I'd crack open my copy, but it is buried in boxes at the moment.
> All LEDs on, means, "replace the system board".
> I'm not sure, he wanted to hear that ;-)

The typical DEC design approach to diagnostic LEDs is that the logic turns them all on at powerup reset, then the boot / diagnostic ROM turns some of them off as it sequences through the startup.  Typically, the first LED change occurs quite early in that process.

So if all LEDs remain on, that most likely means the CPU is not able to execute instructions at all.  It might mean a busted CPU, busted ROM or CPU bus, or missing power or clock.


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