Yet Another Old Cyber-Coot

Tony Duell ard at p850ug1.demon.co.uk
Fri Oct 27 18:08:13 CDT 2006


> > 
> > I am not sure what you mean by 'in one package'. I personally think the 
> > Epson QX10 is one of the nicest CP/M machines ever, but that has a 
> > separate monitor and keyboard so it might not be 'one package'.
> 
> 
>     What I mean by "one package" is that the machine is a complete
> computer -- monitor and keyboard built in.  One plug, one diskette, and
> you're off...  My personal preference is for separates, in computers,

Well, the Epson QX10 meets the second of those criteria. It's 3 units 
(processor box, keyboard, monitor), but there's only one mains cable (the 
monitor, and obviously the keyboard [1] take power from the PSU in the 
processor box). 

[1] Although I do have a keyboard from a Ramtek graphics unit which does 
have it's own internal mains PSU.

> > I'm also partial to the RML380Z, but mainly becasue that was the first 
> > CP/M machine I used )at school).. And to be honest, CP/M was a let-down 
> > after the LDOS I used at home on my TRS-80 Model 1.
> 
> 
>     Perhaps...  But CP/M was a hobbyist O/S that sort of became the
> industry standard.  Cool, in a way.  The closest thing to THAT today is
> Linux, and that's a tad bit complicated (and too good) for hacking it to
> be much use.

I've always thought the analogy is between CP/M and MSDOS (and not 
because of the obvious technical similarities). Both are pretty minimal 
OSes, both became industry standards, and in both cases there were often 
better choices available. 

>     And, truth be told, it's clear that a lot of the people I've seen
> post in the last 24 hours obviously know a lot more than I do about
> quite a few things.  That is as it should be.  Normally, I'm the alpha
> geek wherever I am, so it's refreshing to think I'll be LEARNING things
> for a change.  So far, it reminds me of the Aloha Computer Club back in
> the 70s...  Everybody is knowledgeable, and some VERY much so, but all
> experienced in somewhat different areas.  Seems like a friendly group,
> too.  I'm a painfully honest person (I know, I know, liars say that,
> too) so I'll let people know when I don't know something.  But, I have

I think you are going to fit in here. I certainly consider that the day I 
stop learning is the day I die. And I think everyone here is basically 
very honset (certainly all the classic computer collectors I've met face 
to face are). 

> picked up quite a bit of knowledge since 1971, when I started out with
> computers by dialing in to an HP 2000B timeshare BASIC machine.  It's
> odd, spotty knowledge, but, one never knows WHAT issue is coming up
> next...
> 
> 
> 
> > > 6809 assembly language.  Am currently looking for a repair manual for
> > > the Monroe, as it has crapped out.  I have *** ALL  *** the software for
> > 
> > Produce your own repair manual. I've done it (but not for that machine). 
> > It's not that hard to trace out schematics of a classic computer [1], 
> > it's then not too hard to interpret what they mean and what should be 
> > happening...
> 
> 
>     Can I claim laziness as an excuse?  I know what you mean, a friend

Of course...

> of mine used to make repair manuals for obsolete, orphan, test
> equipment.  I do recall how he used to smoke a cigarette, drink his
> coffee, and stare at circuit boards for hours on end, and how,
> occasionally, he would set down the coffee, stub out the cigarette, walk
> calmly outside, close the door, and primal scream into the night.  He
> would then come back in, sigh, light another cigarette, take a sip of
> coffee, and go back to staring.  I have reached a point in my life where
> I value my time and blood pressure more than the $50 bucks or so for an
> old manual.

Oh, I buy manuals when they are available, but sometimes they aren't. For 
example, one of my intersts is HP desktop computers. AFAIK most of them 
never had real service manuals, only what I call 'boardswapper guides'. 
The same applies ot the PERQ AGW3300. Or the Torch XXX.

In all cases I have (or at least I've seen) the official service manual, 
but it doesn't contain schematics. So I've had to sit down for a few 
days/weeks/montsh and trace out schematics. And there's a lot more to 
producing a schematic than just noting down what connects where. A good 
shcematic is drawn in such a way that it's obvious what a circuit does 
(an obvious example of this would be a pair of cross-coupled NAND gats as 
an SR flip-flop. You don't want to draw it with one on one page and the 
other on a different page, even if you give the signals sensible names. 
Come back to that <n> months later and you won't spot it's a flip-flop!).


> 
> 
> 
> > In any case, you might not need a schematic. What does 'crapped out' 
> > mean? Have you checked the power supply outputs (at least the 5V line 
> > should be easy to find)? Is there a clock signal at the CPU? Are the 
> > buses doning anything? What about address lines on the DRAMs, 
> > RAS/CAS/etc?
> 
> 
>     Symptom is no video.  I don't have access to a 'scope any more,

So the fualt could be just about anywhere. PSU, video circuit, CPU (not 
intialising the video controller), monitor circuit, CRT, etc.

I know nothing about this machine, but you could at least (given a 
multimeter) check the 5V line. And maybe see if there are any voltages on 
the CRT electrodes (which would indicate the horizontal output stage is 
runniog). Given a logic probe or 'scope you could do a lot more.

> > This is one reason I stick to the older machines. I understand them. I 
> > know what every last chip a PERQ CPU does. I can see the connections, hang
> > my 'scope and logic analyser on them and sort it out.
> 
> 
>     I hear you, brother.  I know my IMSAI that way... but no other.  I
> didn't put the Monroe together, and that's a handicap to understanding.

Well, I didn't design or build the PERQ either. Or any of the other 
classics I've had to repair over the years...

While I like to have schematics, I have fixed many machines without them. 
The most recent was an HP9816 that I picked up on E-bay. For those who 
don't know this machine, it's a 9" monitor with a 68000-based computer 
hidden inside. 

Physcially the layout is :

Large PCB at the bottom containing the CPU, 256K RAM, boot ROM, HPIB 
interface, RS232 interface, keyboard interface, etc

This plugs into a small backplane which carries 2 DIO slots (standard 
HP9000/200 series expansion slots)

Also plugging into the backplane is a PCB above the expansion slots which 
carries the monitor analogue circuity, +/-12V regulators and the mains 
connector/switch/fuse (!). Also on this PCB are 2 more connectors for : 

Test (alpha) video PCB. A 6845 + RAM + a fair bit of TTL

and 

Graphics PCB (DRAM + TTL)

There's a SMPSU mounted inside the case which connects by cables to the 
monitor board.

Anyway, when I got it, it didn't work (this was declared in the E-bay 
listing, I am not moaning). It gave an error message 'Alpha video 
failure, RAM error, address = <nnn> W=<nnnnnn> R=<nnnnnn>'

Well, I had no documetnation at all, but the 9836 boardswapper guide 
(over on http://www.hpmuseum.net/) told me that address was in the text 
video RAM area. So it was likely all the errors refered to one problem. 
Assuming  'W' mandt the value that had been written and 'R' was the value 
read back, it appeared that bit 11 (IIRC) of the RAM had failed.

So I took the machine apart. It was obvious there were 2 2K RAM chips 
(6116-like) on the text PCB. I traced data bit 11 from the DIO slot 
(which I had a pinout of) across the monitor PCB to the text video PCB 
connecotr. Then on that board, I traced it through a buffer chip to a 
data pin on one of the RAMs. Decoldered that RAM and put in a new one 
from the junk box. 

And yes, the machine worked. I'd only had it for 12 hours...

> I'm an NIST certified calibration technician, so I'm not intimidated by

FWIW I have no qualifications at all in electronics or computing.

>     Oh, no, not at all.  When I whipped up a computer, though, when I
> got done I had something better than most people owned.  I can't do that
> now, unless you call buying a motherboard off the shelf, dropping a CPU
> into it, and plugging in the various cards "building a computer."  I

I call that 'assembling a computer' To me 'building' implies starting 
from simpler components and using a soldering iron or wire-wrap tool.

-tony




More information about the cctech mailing list