DEC H7260 PSU fault

Jules Richardson jules.richardson99 at
Sat Jan 27 14:43:32 CST 2018

On 01/27/2018 11:44 AM, Glen Slick via cctalk wrote:
> On Sat, Jan 27, 2018 at 9:04 AM, Jules Richardson via cctalk
> <cctalk at> wrote:
>> Time to add CPU/memory in, wire up a console cable and see what happens, I
>> guess.
> With the PSU working everything else should be easier to get going after that.
> Did you figure out what the hard drive is? A working RD54 would be
> nice and probably worth more than any of the boards.

Well, there's someone's hand-written sticker on the top saying it's a lowly 
RD51 - however the actual p/n sticker says it's an RD53-A and the defect 
table lists it as ST506, 85MB.

Of course it probably doesn't work anyway ;-)

> If you start with just the M7606 - CPU and the M7608 - 4MB ram once
> you get a console cable built it shouldn't be too hard to get some
> basic signs of life.

Yes, that's where I'm at right now...

Console default is 8 data bits, 1 stop bit and no parity (at whatever speed 
the switch is set to), correct?

I'm getting an alternating F and 9 on the hex LED diag display on the 
console panel, no output at all on my terminal, and the M7606 starts with 4 
solid red LEDs, then a solid green, then the middle pair of the red LEDs 
start a simultaneous slow flash on/off (while the outer two plus the green 
remain steady)

This is just with the M7606 CPU and M7808 memory plugged in, nothing else 
(apart from the half-height board at the end of the backplane which 
distributes signals to the RD53) - oh and the LEDs were observed with the 
card cage cover switch held down, so 'under normal operating conditions'.

For console cable wiring I'm using the following ref:

There's a ref here for the status codes:

.. however, I'm not sure what the alternating codes mean; 'F' seems to be 
power-related, but I don't know why the CPU would proceed if it thought 
there was a power fault, and '9' is related to terminal ID, but it seems to 
suggest it should automatically continue after 6 seconds.



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