11/23 clock issue

[Holm Tiffe]

Noel Chiappa wrote:

> So I'm debugging a dead PDP-11/23 board (M8186). The first thing I check is
> the clock; specifically the output of the first stage buffer-inverter (pin 16
> of E4, a 74S240, upper right corner of page 2 of the prints), which is
> distributed to a number of places. Nada. Totally flat-lined. So I checked the
> input (pin 4), and it's sitting at about 2V. Also flat-lined. This does not
> seem good... :-)
> 
> So here's my question: what's the likely fault here? The only thing upstream
> of that gate is the 13MHz crystal itself. So the fault has to be either the
> crystal or the S240 (which seems to be some sort of octal 3-state inverting
> buffer). Any guesses as to which?
> 
> As usual, thanks in advance for any help!
> 
> 	Noel


Hmm.. it looks to me as if the Board is missing the jumper W1 and the clock
is disabled. Look at this website (mot mine)

http://www.avitech.com.au/pdp-11-03/ba11nc.html

The jumper next to the crystal can seems to connect the clock from the
crystal oscillator to the 74S240. check the clock on both posts of W1.

Regards,

Holm

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