16 Jan
2017
16 Jan
'17
6:14 p.m.
On 01/16/2017 08:37 PM, Adrian Graham wrote:
Likely history but if the parts move and the head is ok then clean it
really well
replace the caps and try.
I had bought the Netronics explorer 8085 just before that bolt. That
gave me
a S100 chassis that would run even bad cards (think SDK85 with S100 bus
interface).
That made it possible to go a card at a time for function and level of
function.
Figure maybe 250 more more hours to get it running again and almost a year
chasing random failures that were overstress induced. I still use that
machine
after dumping the 8kx8 cards for a larger 64K static it has performed well.
Around 1980 it went through a series of mods and adds to upgrade it to
multiporcessor.
The turned pin are heavy and will stand that.... the copper under them
or leading to them may be gone
FYI vinegar or lemon juice will neutralize it, the battery (likely nicd)
is alkaline.
Rinse with water and dry.
Ok, blown.... that make
what I said earlier of a ESD incident likely.
Check the DRAM too. They all LOOK ok in that I get active traces at DIN/DOUT and
none of them
get hot so they're hopefully OK. I know from working on a few PET 80xx that
a single bad 4116 can stop the machine booting but I don't want to start
desoldering those unless it's obvious one or more have died. You can always
inject a really slow processor clock, isn't rated for it
but it does
run down to less than 1khz. You can then watch signal with a bunch of leds.
It's all excellent help!
Keep plugging.
That's why I like them. I can actually get it all in my head where
30million
transistors and 4 cores causes major brain tilt.
Allison
On 15/01/2017 16:59, "allison" <ajp166 at
verizon.net> wrote:
only
1K.
Yep, done that fortunately. My MQP programmer can read it and also the PAL
that does the ROM selection so I know they're both OK.
I don't remember seeing that when I was monitoring all the control
lines and
I've just noticed on my drawings I've left out INTA, must rectify that.
http://bitsavers.informatik.uni-stuttgart.de/pdf/intel/MCS80/MCS80_85_Users…
That's the later 1983 version but its the book you want.
I've
thought of that which is why I'm chasing down details on the Viewdata
chip and the D8741A which I assume is being used as a keyboard controller.
There are also 3 modules on the phone side which I can't find anything
about, marked "NKT NMC1515", NMC1516 and NMC1517.
8741A is likely
keyboard controller. FYI its the eprom version of 8041A
(the a is important). That part is easy to dump the EPROM and analyse as its
You can use a 8048 disasembler on that, nearly the same part save for
the slave IO structure and a few instructions.
Glen Slick has already done that
for me, much better results than what I
could get out of the d48 disassembler.
So its possible to use those pins (4 of them) as
inputs without interrupts
on all or none as you can read their state. RST7.4 is also special as
its edge
triggered (and transition activates it and it sets a latch) so unlike
the other
the state of the pin can be a pulse rather than a LEVEL.
OK, that might explain
why there's only two entry points for those interrupt
pins in the code.
So it seems there is a keyboard interrupt and
video (scan line) interrupt
plus the RTC (time keeping and ?). You also have phone line events in
there.
Tonight I discovered the D8741A is a controller for the little
microcassette
unit that's seriously not well with rust and damaged/rotted/exploded caps :/
FYI the software structure is familiar and likely
straight out of the
book for the 8085.
You are preserving cpu status (AC-PSW), BC, DE, HL pairs, then working
on the interrupt event.
OK.
Ok, it
never gets interrupted then.
You would also see /INTA (interrupt acknowledge)
trigger. Do find a copy (its definitely on line) of the
8085 users manual,
september 1978
I'll have a look for that at work tomorrow, there's every
chance we've got
it in the library. It really
sounds like the unit suffered a high voltage transient
(lighting, ESD, power supply
over voltage).
Yeah, the previous owner did power it up and got smoke but I
thought that
was just the RIFA mains filter popping. Currently I'm up to 6 replaced chips
that all had dead inputs and the startup opamp (ICL7611). Fortunately the
non-replaceable ones are OK.
On the tape drive controller board are a pair of very messy 25V caps that I
thought had rotted because of damp - the tape transport itself is probably
beyond saving through rust - but could they have exploded I wonder.
of TTL across
12 boards to bring it back to life. The only MOS device
(had a hole in it)
was a 8251A USART to the H19 terminal (also toasted). Z80 was still
good and still
in that system working to this day (along with a 8085A subprocessor).
Strewth,
that's some troubleshooting effort! Sockets on the
other hand have caused me no small amount of bedevilment.
If its not machined pin and old its likely trouble.
I do wonder about the sockets
though they're all turned pin. The RAM refresh
and first ROM socket were badly verdigris'd with the battery leaking all
over that part of the board but they test OK with a DMM.
Hummm... 4116
dram, that means you have external refresh logic or they are
going cheap and doing refersh on a interrupt (or maybe) timed loop.
There's an
MC2342A doing the refresh and that's looking OK now that I've
swapped it. The original chip had no working outputs. If you guys weren't around to put up with my
amateurish questions I'd have
never started work on it and it would've remained just another unloved bit
of kit on a table in a museum like the other 5 that are known to exist.
We try.
I enjoy
working with 8048(family), 8085 and z80 have built with them for
decades
and do both HW and SW. Its fun to apply modern software techniques to
old hardware as often they do it well even if not lighting fast.
I still find it
difficult to get my brain to acknowledge that despite their
speed I really am looking at things happening on individual clock ticks,
I'll get there :)
Cheers