PDP-12 Restoration at the RICM

Mike Ross tmfdmike at gmail.com
Tue May 26 07:48:35 CDT 2015

"The M706 receiver failed in the board tester"

Do tell more about this mythical and very useful sounding board tester?

I'm looking at my racks and racks of logic, mostly M-series - 12, 16,
18, & 36 bit - and contemplating the debuggering with some dread...


On Tue, May 26, 2015 at 12:07 PM, Michael Thompson
<michael.99.thompson at gmail.com> wrote:
> Today we pulled all of the M113 flip-chips and tested them because SN7474
> and SN7400 ICs seem to be a problem in these early DEC systems. The ones in
> slots J33 and K30 were bad. Replacing them fixed the problem with the JMP
> instruction. We did some more testing with the toggle-in programs and found
> that ISZ cleared the AC. Replacing the M119 in slot H28 fixed that. All of
> the toggle-in tests pass, so the processor is substantially functional.
> Core memory in field 1 with addresses X5XX didn't work. We replaced the
> G221 in slot D10 to fix that.
> We tried the ASR33 Teletype that came with the system. The mechanics were
> sticky from not being used for 30 years, but we got most of it free and
> working. We could send characters to the Teletype, but could not receive
> anything. The M706 receiver failed in the board tester. The spare is also
> broken, so we need to fix both.


'No greater love hath a man than he lay down his life for his brother.
Not for millions, not for glory, not for fame.
For one person, in the dark, where no one will ever know or see.'

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