15 May
2008
15 May
'08
9:22 a.m.
On Thursday 15 May 2008 04:13, Ade Vickers wrote:
(Snip)
I did that for the case where the plug was missing altogether. Though it
seems to me to be possible to solder the wire on one side of each of those
contacts and still allow the plug to be used...
I wonder if anybody ever sold anything that plugged in there?
As I say, it only goes away if you can put up with the computer being
completely crashed (a soft-reset won't do the business, it has to be mains
off/mains on to get it restarted; and then the video's loopy again.
In other words:
1) Power up. Video shaky
2) Pull ext. vid block, video goes off
3) Replace block, video returns, stable, computer totally crashed.
4) Power off. Goto 1.
Hmm. Might be the load on the power supply then, if it's marginal.
Might be aging caps in there then.
Not fun, for sure...
A scope is a nice thing to have when trying to troubleshoot this sort of
thing, definitely.
The odd characters I noticed in some of the pictorial info you linked to
earlier suggests memory corruption, which would also be power-supply
related.
I'm not sure, but I believe that these monitors might have been made by
Zenith. Or at least I'd heard that to be the case with the one in the Exec.
If you see blobs of hot glue here and there holding down larger components
that's a pretty good giveaway.
I'd worry about both the monitor and the computer getting good clean power
first. Until you get sure about that I wouldn't mess with any adjustments.
That's why I suspect the power supply first. :-)
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
If you still
have some erratic operation, you can take little bits of
wire-wrap wire and solder them to both sides, which I had to do in at
least one case.
I'd like to avoid that if I can, but if that's what it takes, that's what
I'll do. unfortunately, it's crashed the computer... From
this, I deduce that it
must be something in the mainboard electronics that's failed (a cap,
maybe?), rather than something in the monitor unit.
Monitor not getting sync would be a problem all right and if
your display problem went away that easily then maybe just
cleaning those contacts up will fix it right up.
Ok, so you're getting solid video or shaky video? I thought
you had said that wiggling the connector fixed that...? And does this
unit have a screen-pac upgrade? If so, it'll
have an RCA jack in one corner of the front panel, you can
feed that to a composite-input monitor. If not we'll have to
work on what's there.
No, it's standard unmodified. Although the Ext Vid block shows some signs
of damage, like someone's tried to pry it open. I've no idea if that's
causing the problem, although I should point out that this machine worked
3-4 years ago, and has "gone off" in storage. I'd have a
look at the outputs of the power supply, start
out with the unit off and the power disconnected and _don't_
touch that big power transistor or it _will_ bite!
Fear not! I have a healthy regard for self preservation whilst working
around mains-level circuitry... hv had 3 mains jolts in my life, the last
one made my chest hurt in alarming fashion. That was when I was 13 years
old... Stay on the
output side and measure what's there. The +5, and + and
-12 should be within 5% of where they're supposed to be, particularly the
+5. Better yet would be to scope them and see how much trash is there.
You might have power supply issues. Or you might have monitor issues,
too. I can recall reading about some monitor problems in those machines
or maybe Execs that turned out to be bad capacitors but I can't recall
which ones and I don't have those issues of Foghorn handy any more.
OK, will check that today (the levels), and if I find the 'scope probes,
then I'll see if that still works (been 2-3 years since I used the 'scope,
so that may have died also!) Tony Duell wrote:
They are.
Now, I don;t know this machine at all, but I am
assuming the mainboad
contains the video and sync generation circuitry, while the 'monitor'
contains the deflection circuits that lock to said sync signals, the video
amplifier, HV generator, etc.
I believe that to be the case. I could take some close-ups of the monitor
circuit if you like. There are a number of trimpots covering vertical
hold/lin/synch, one for the horizontal centering, one each for
bright/contrast. There is only one IC on the monitor circuit board.
Are the signals between the monitor and mainboard
separate
syncs and video or a composite video signal?
I'll have to do some tracing, but I think they are separate V & H. There are 10 wires going from the mainboard to the
monitor, but not sure
what signals they carry.
Horizontal and vertical sync, video, and power, as far as I can recall.
sync circuit.
It's unlikely to be a digial problem. And this
is a horizontal problem (picture breaks up into sloping
likes)not a vertical problem (picture rolls), right?
Hmm; I don't think it is wholly an analogue problem: I would expect the
screen to break into horizontal slopes, as you say - and I've seen that on
badly adjusted monitors in the past (I used to have an old Philips monitor
which could be provoked into this with the front panel adjusters).
What's happening is a corruption of the display, rather than an adjustment
fault. For example, I just booted the machine again, and (ever so briefly)
got an entire screenful of the letter "U". Then it went away, and the
Osborne logo came back (and that *did* show some signs of an analogue issue
- the horizontal slopes; but lots of them, not just a few). There's no way
a horizontal hold failure could cause the screen to be filled with "U"s...
If you do have
seaprate signals to the monitor, start by 'scoping the
horizontal sync signal while the monitor is malfunctioning. Is it the
right frequency and stable?
I'll look for it... the monitor circuit board is quite well labeled; but
I'm not sure if the connectors themselves have individually labelled
connections. Then, if
there's a horizotnal frequency control on the monitor PCB (it
might be an inductor!), try carefully tweaking it. The idea is to (a) see
if the thing will jump into lock, or if not, at least if you can get it to
slope both ways (that is, can the horizotnal oscillator run above
and elow the right frequency, if so, it's a good bet it'll work _at_ the
right frequency, and that the problem is in the sync circuit).
I couldn't find a h-freq trimpot; but will pull it all out again later
today for a looksee. Question: How long should I leave the tube to
"cool down" (unplugged)
before I can rummage around it without fear of major electrocution?
The HV wire in there is going to be pretty obviously going to one side of the
tube, as opposed to the rest of the connections which will go to the tube's
base (small end of the "funnel") or the deflection yoke. Just staying away
from that should be good enough.
Rik wrote:
A strong light helps with that but I haven't found too much in the way of bad
soldering in this equipment.
First step, is checking the boards visual for
corosion and
bad solder joints (crystaline with a round marking in the
solder) good joints are shiny and curved, if you don't trust
one remove the old solder and resolder.
I had a quick glance over the board, and didn't see anything really
obvious; will check again properly. When old
electronics is stowed away in storages for a long
time, elcos are going to degrade and eventualy won't work at all.
The picture your showing indicates a fault in the horizontal
sync circuit of the video, pausible cause degraded elco's.
That kind of figures - except for the fact it will go rock steady when the
external video plug is pulled & replaced - but as mentioned, that freezes
the whole machine solid (soft reset doesn't work, I have to cycle the power
to restart it). I therefore think it must be something interfering with the
h-sync generation while the machine is running which is causing the
problem.