PDP-8E diagnostic help needed

Rod Smallwood RodSmallwood at mail.ediconsulting.co.uk
Tue May 13 02:44:05 CDT 2008

Now that's interesting.. 

I have a PDP-8/e as well. I can't store in locations 000 000 000 000  to
000 000 011 000 (0 - 24 Dec)
Above is OK

If somebody has an answer to your problem. They might know something
about mune.

Rod Smallwood

-----Original Message-----
From: cctech-bounces at classiccmp.org
[mailto:cctech-bounces at classiccmp.org] On Behalf Of Mark G. Thomas
Sent: 09 May 2008 16:36
To: cctech at classiccmp.org
Subject: PDP-8E diagnostic help needed


I've got a PDP-8E which I've almost got working.

Can anyone here help me figure out this remaining problem?

As I examine memory, the address lights count up to 01111, then go back
to 00000, instead of 10000. I can manually enter an address higher than
1111, but the 10000 and 100000 bits don't stick -- they go low, as soon
as I hit the examine switch to step to  the next memory location.

I can manually load an address 1000000 or 10000000, and hit examine to
see 1000001, 1000010, 1000011, etc..., but once I reach 1001111, it's
back to 1000000.

It was recommended to me that it might be the carry between E52 and E37,
or the E38 input multiplexer for bit 7 (on M8300), so last night I
socketed and replaced all three of those ICs, but I still see the same

I have extender boards, so can access M8300 during operation. I measured
the carry line between E52 and E37 go low when I reach 1111, but the
light for line 10000 doesn't light on the front panel on the next
address, and I see the data from memory location 0000, 0001, etc.
repeated, displayed as I continue to step through memory locations, as
described above.

Of course, if someone has a spare M8300 they would be willing to sell
me, that's another option.


Mark G. Thomas (Mark at Misty.com)
voice: 215-591-3695

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