8 Jul
2008
8 Jul
'08
1:13 p.m.
On Jul 7, 2008, at 10:27 PM, John Holden wrote:
That makes sense but it's a trace to the F connector (FK2 I think) and
the 8266 is at position E10? above the A connector...
I found the alleged location of W1 on the M7261 - it's not obvious
what's a jumper and
what's necessary copper. back to the print set before wielding and
Xacto.
On 08/07/2008, at 7:35 AM, Milo Velimirovic wrote:
I noticed that oddity while staring at the printset. One thought (and
a really ugly one at that) was to build a two chip replacement. Of
course the pinouts of an inverter and a "normal" quad mux not being
anything at all like the 8266 would really complicate matters. A last
resort.... Also would the two chip sol'n change the timing through the
AMUX - is it in a critical path?
hi all,
The recent flurry of activity in early pre-C UNIX for an 11 with a
small memory got me back to working on my 11/05. So far I've
identified two nasty problems with the data paths board, the M7260.
One of the 8266 MUX chips looks like the plastic boiled and bubbled
and circuit board is discolored underneath it. I'd welcome both
sources for replacement chips and techniques for replacing it.
Tricky. The 8266 is rather odd in that it inverts one of the inputs
and I know of no direct replacement. I'll check if I have a spare
M7260 card.
As for replacing chips, particularly on old cards. The only safe way
is to:-
1) with a fine pair of cutters, cut every leg of the chip and remove
the body
2) with needle nose pliers, grab each leg in turn, heat on the other
side
with a soldering iron and pull out the leg (use a light force and
make sure
the solder is molten on the top side, particularly if it has a track)
3) with a solder sucker (or desoldering station), remove the solder
from the holes
No surprises here. It's just painstaking, delicate work that I have
little experience with.
Additionally there's a lifted and broken
trace on the non-component
side of the module near the F edge connector. Any sugestions for
repairing a damaged trace would be welcome.
If the chip was toasted, then this track probably took all the
current. You can
either glue it down and bridge the break with solder, or cut the
track where it's
good, scrape off the PCB lacquer, then carefully solder in some
wire. If it is
a short run, use some stiff tinned copper, then hot glue in place.
Again no surprises. The broken trace is in an area densely packed with
runs as all the signals from the component side feed through the
module and are interleaved with the lines from the solder side, all
feeding into an area filled with resistors and diodes.
Lastly, I'd just as soon use a DL11W in the
11/05 rather than go to
the trouble of setting up an external clock to feed the on board
UART.
I can get both 9600 baud and RS232 from the DL11W instead of 2400
baud
current loop from the built-in interface. I haven't yet found the
jumpers to remove/install that would disable the built-in console
interface. There's also the LTC.
You can disable the serial interface by removing W1 from the control
logic /
microcode board M7261. It is not possible to disable the LTC, simply
don't
enable it on the DL11W.
Easy enough to disable the LTC on a DL11W.
I have, in the distant past, modified a M7260 for
9600 baud RS232, but it involves removing removing several
components and
modifying the 9602 oscillator timing. Using a DL11 is a better choice.
I'd much prefer the DL11 choice to more board mods.
- Milo
--
Milo Velimirović, Unix Computer Network Administrator
University of Wisconsin - La Crosse
La Crosse, Wisconsin 54601 USA 43 48 48 N 91 13 53 W