23 Aug
2014
23 Aug
'14
5:20 p.m.
Ok good call gents, thanks for pointing this out.. yes, the LM309 only
provides power for the termination network (marked VT+). Here's what I see
in the network:
- Some lines have no connection to the network at all
- Most lines have a 330R pull-up connected to the VT+
- A number of lines are biased at +roughly+ 1/2 VT+ by being placed at the
junction of a 330R and 470R -> Gnd resistor.
And for some reason, all of the data lines - with the exception of D2 - are
in the latter category. They're biased at the 330 / 470 junctions. So my
current questions are..
Why did they skip D2 of all things?
Will any of this have any effect on the operation of the machine, once I
plug in an original CPU board & static RAM board?
And lastly...
Does anyone have a 1K or 4K static RAM board for this, that I can beg, buy,
barter or steal off them? Howzabout an original mainboard, so I don't have
to whack this one to pieces.. which seems to throw up huge red flags in my
mind, as I'm loath to modify or damage any kind of vintage parts!
On Sat, Aug 23, 2014 at 6:51 PM, drlegendre . <drlegendre at gmail.com> wrote:
I'll take another look (pulled the boards out of
the case) but I'm pretty
sure the LM309 is serving the entire +8 / +5 supply. Good point, though.
I began asking this, as when I powered-up the boards for first smoke test,
I noticed that all of the Data LEDs are on.. +except+ for D2. Investigation
found that all data lines (except D2) are sitting at 1/2 Vcc causing the
connected 7404 inverter outputs to go low, which turns on the LEDs (as the
other leg of the LEDs is tied to Vcc). So when the inverter output remains
high, both sides of the LED see Vcc and hence no current - inverters go
low, and they sink current and turn-on the LEDs.
It was that D2 being off that drew my attention. And upon further reading,
I don't think +any+ of those data LEDs should be on, when no other boards
are installed.
Will report back in just a few mins.
On Sat, Aug 23, 2014 at 3:55 PM, Eric Smith <spacewar at gmail.com> wrote:
On Sat, Aug 23, 2014 at 12:56 PM, drlegendre .
<drlegendre at gmail.com>
wrote:
This machine has a Processor Tech. MB-1 mainboard
in it. Full-width, 16
slots, and some mods I don't understand.
First, there's an LM309 (TO-3 case) mounted to the board, apparently
providing reg'd 5VCD to the normally 8V (un-reg'd) line. Why would that
be
there? Every plug-in board I've seen - which
isn't all that many,
admittedly - has its own regulator for 5V on-board.
Secondly, on the far left side of the board, there are several columns
of
resistors that seem to be doing a couple
different things - some are
pulling-up various groups of lines to what seems like 1/2 of VCC, others
are either there for termination or some other unknown function.
Are you sure the LM309 doesn't have its input tied to the 8V supply,
and its output to those termination resistors?