stacey@guug.de (05/26/91)
- Here are some PC532 construction tips, (that could be annexed to John Connin's
build list notes, section 3.0).
- Listed below, rather than mailed solely to John, to give you the chance to
add your ideas, or dispute suggestions you may disaprove of :-) before the
next group start buying parts & building, (the next PCB run being imminent).
- Most points are obvious in retrospect, but they were not obvious enough to
consistently avoid some mistakes on the boards I've seen (mine included).
- Hoping this saves future builder/owners some trouble.
Julian Stacey (stacey@guug.de)
ANNEX: - - - - - - - - -
- IC Sockets:
Hollow base/skeletal sockets allow you to follow tracks/traces under sockets,
useful for hardware debugging, or if you suspect damaged tracks/traces/pads,
whether from clumsy soldering, later desoldering, scratching, or whatever.
- CONN 1:
Use 90 degree offset IDC (not straight) pins. Some SCSI plugs are very stiff,
the PCB is unsupported nearby, heavy up/downward force could stress the PCB.
Mount D1 & F1 Under the PCB to avoid obstructing CONN 1.
- METAL CAN OSCILLATOR MODULES:
Caution, with a rim easily caught by cables, & just 4 pins loosely held in a
DIL socket, you may get problems now or later, consider soldering direct,
or using 14 pin black IC type modules, or at least cropping pins a bit shorter
on 4 pin cans, to mount flush to the socket.
- XTAL 1:
Solder flush to board with no surplus lead length (to minimise capacitance),
quickly (to avoid overheating crystal), & glue (clear) to PCB for stability.
- TANTALUMS & ELECTROLYTICS
If using a substitute, use a higher (or even a lower) value tantalum rather
than a same value electrolytic (which have much higher parasitic inductance).
- ADD EXTRA TANTALUMS:
I suggest around the RAM, (+ a few scattered elsewhere), better 4 * 10uF
around the RAM array, rather than 1 * 40 at 1 corner. (Some dram types used
to present switching transients (@ refresh?)-I guess such things don't change.
- TANTALUMS & CERAMICS:
Solder extra tantalums on top of some of the 0.1 uF ceramics, give ceramics
preference when deciding which get the shortest lead length (to minimise
parasitic inductance of capacitor). Glue tantalums flat to PCB for strength.
- SPARE IC LOCATIONS
In case you later use the spare PCB IC spaces (I already use one):
- Solder sockets in now to avoid having to solder a board full of expensive
static sensitive CMOS later.
- Equip the adjacent capacitor holes with ceramics, + mount the tantalums
shown on the schematic on top, rather than just using tantalums alone.
- SOLDERING:
Use a resistive earthed, temperature regulated iron, solder everything
possible before inserting any ICs; insert your expensive CPU & RAM last,
(avoids connecting CPU to unterminated static conducting long tracks).
- CHECK POWER BEFORE INSERTING ICs
Before inserting ICs, check there's no shorting power plane or capacitors,
(expect ~70 Ohm between +5V & 0V (see George's postings)).
- CHASSIS:
Avoid using cheap clone flip top (Baby AT type ?) boxes made just of thin
folded steel, as insufficient torsional stiffness stresses the PCB.
- WHEN FIRST TRYING HARDWARE:
- The monitor will talk to 9600bd 8bit no parity terminals.
- For those who buy their RAM last (seeking best/lowest prices):-
- The LEDS come on even with no RAM (& go out when reset is shorted).
- The EPROM monitor wont talk to you without ram present (I had wondered if/
hoped a first "hello" might have been announced without needing a stack).
- Some old 100nS Ram I had allowed me to talk to the monitor, & read disc,
but not run minix, (I got an impossible op. code report, I was lucky it
didn't silently crash, as I wasn't using parity). If you try slow ram you
already have, it might work for you too, but dont buy slow ram though!.
- If you are missing U[1-4] 74F280 parity generators, or have only 8bit
memory omit the parity pal (as posted previously).
End Of Annex - - - - - - - -rickr@virtech.UUCP (Rick Rodman) (06/05/91)
> > - Here are some PC532 construction tips, (that could be annexed to John Connin's > build list notes, section 3.0). > - Listed below, rather than mailed solely to John, to give you the chance to > add your ideas, or dispute suggestions you may disaprove of :-) before the > next group start buying parts & building, (the next PCB run being imminent). .. Next time, let's use some low-insertion force PGA sockets such as those avail- able from Preci-DIP. What's the point of using a socket if you can't ever get the chip out again? (Not soldering it, I suppose.) ZIFs would be even nicer but they're too big. Rick Rodman uunet!virtech!rickr "Yesterday's Tomorrow is Here Today"
stevel@eleazar.dartmouth.edu (Steve Ligett) (06/06/91)
In article <9106050317.AA19630@virtech.UUCP> rickr@virtech.UUCP (Rick Rodman) writes: >Next time, let's use some low-insertion force PGA sockets such as those avail- >able from Preci-DIP. I don't recall if you got your socket from me; the ones I have ARE low-insertion force sockets from MillMax/PreciDip. But low-insertion force is relative... -- steve.ligett@dartmouth.edu or ...!dartvax!steve.ligett