DEC H7260 PSU fault

[Glen Slick]

On Sat, Jan 27, 2018 at 1:02 PM, Jules Richardson via cctalk
<cctalk at classiccmp.org> wrote:
>
> OK, looking at the 630QB tech manual now, which seems to be where these were
> lifted from... and of course it points out that the LEDs on the M7606
> correspond to the hex codes on the panel (i.e. my four red LEDs with the
> middle pair flashing on and off equate to the alternating F-9 I'm seeing on
> the hex LED)
>
> The green LED on the CPU board is 'DC OK' and I'm also getting a green 'DC
> OK' on the front of the machine, and it seems odd those would be lit if
> there were a DC fault... but who knows. No explanation of the flashing
> codes, either; the manual seems to imply that it steps through in sequence
> down from 'F' and will stop when there's a fault.

Do you have a scope that you can use to monitor the BDCOK line? If it
is periodically dropping low that would cause a loop of the processor
halting and resetting. That could be happening fast enough that the DC
OK LED appears to stay on continuously.

That would be the same as periodically pressing the Restart button on
the front panel, which works by pulling down the BDCOK line. (See the
BA123-A Front Panel sheet, page 115 of the maintenance print sheet PDF
MP02071_630QB_Mar85.pdf)