29 Apr
2007
29 Apr
'07
1:10 a.m.
On Sat, 2007-04-28 at 22:21 +0100, Tony Duell wrote:
I'm away from the HP-150 for a couple days. I will certainly check
that, first thing, when I see it again. I certainly hope you've guessed
it right on this. What a lovely problem THAT would be to fix.00
Oh, sure, but, in any case, I've generally found that a functional
understanding of the boards involved usually gives one a good idea for a
couple "Easter Eggs" to try, often with cheap parts, to try for a
schematic-free solution. Obviously, some problems are resistant to this
kind of solution. Also, sometimes the most likely "Easter Eggs" involve
expensive parts, and I want to be sure before I lay down some real cash.
Still, I'd say most problems can be solved, rather quickly, without a
schematic.
On the other hand, if I'm able to contact you, and you have one,
that is almost as good as having one myself... assuming I don't cheese
you off somehow.
They don't. It is as if all characters were spaces.
On Fri,
2007-04-27 at 23:11 +0100, Tony Duell wrote:
One quick question. You replaced the real-time-clock battery, didn't you.
IIRC, that's physically on the video PCB. Is it possible the video PCB is
not correctly seated in the backplane (well 'frontplane' in the HP manual)
So, if you disable PAM and just get na MS-DOS
screen, what you're saying
is that the screen is mostly white, with black blocks where the prompt
would be ? THat's really strange...
You have it... Yeah, I thought it was strange, too. Dunno...
Is working on mostly the same type of equipment lucky? If
MAybe.
But then I've worked on many HP98x0 machines. All had the same fault --
no display. And yet it wasn't a common fault, or even always on the same
PCB. I've had defecty carry FFs, dead shift registers in the M (memroy
address) register, dead flip-flops on the I/O PCB, a cracked clock
crystal (!), and so on. That's when you need scheamtics//
so, I am. I just get familiar with the "top
ten" failures, and often
'Lucky Dip' sericing may work most of the time, and it may save time when
it does, but IMHO three is _no_ substitute for actually tracing the fault
and curing it. Particularly in your own classic computers (where there
isn't the pressure to get the thing runing again by yesterday) Slow down?
How about a burnt-out amp in the mixer that is not
passing the dot data?
Yes, but then why do spaces look different from all other characters? Sure. But it was my impression that if you got a
signal from a beam
standard, and if the circuitry was 'locked' (rather like a PLL locking),
then it was on-frequency. In other words, if it was working (and there
were ways to tall if it was locked), then it was accurate.
I was using my knowledge of Cs standards for this, which has been
corrected by Dave McGuire. (Thanks Dave!) Sorry. My bad. I assumed
they functioned similarly. Since it's a different process, and we
didn't use them, I don't know how they work, and should probably add a
period to this text, and quit typing.
I can beleive there are adjustments to get it to lock.
But I am suprised
there's one that controls the output frequency.
That's the WAY a Cs standard works... The electronic oscillator's
frequency is minutely adjusted to keep the Cs beam on target. The
adjustments are tiny, and keeping them in range means that the
oscillator's drift is being canceled by the adjustments by the PLL
obtained through aiming the Cs beam correctly. Within a small range,
the circuitry keeps adjusting the frequency to aim the beam, thus
ensuring that any normal drift is compensated. On the HP models, the Cs
Beam Frequency Reference has a meter that shows where the "range" sits.
Occasionally, the "coarse" adjustments are changed, in order to keep the
current level of adjustment at about the center of the range over which
the electronics can lock. And, yes, as long as the PLL is maintained,
the accuracy is maintained.
Peace,
Warren E. Wolfe
wizard at voyager.net