PDP-11/10 repair started

Noel Chiappa jnc at mercury.lcs.mit.edu
Sun Oct 4 21:16:11 CDT 2015

    > From: Tony Duell 

    > I am working from 2 Printsets, both from Bitsavers. One is the GT40 one
    > (yet another backplane of course, but the same CPU, core memory, etc).

Ah, thanks for that pointer; I'll see if it shows the same board versions as
my 'early' hardcopy set.

    > The other is the 11/05S schematic, which shows the later boards with
    > the crystal UART clock

Say what? The "11/05S schematic" from Bitsavers shows the RC clock; look on
page 61, bottom left corner, there's an RC circuit (and a couple of flops)
producing an output "DPH TTY CLK (I) H", which is fed into the baud rate
divider in the upper left corner.

(Ooooh, what an ugly circuit! You have to tweak the trim pot to change from
the 110/220/440/880/1760 speed set to the 150/300/600/1200/2400! Ugly!!)


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