test-drb April 2005

test-drb@ccmp.vtda.org

269 participants
730 discussions

by jdaviscl2＠soupwizard.com

Hi, I just picked up a Sun 3/80 chassis from the local university surplus. It looked lonely sitting there. It's dusty inside but appears to work (checked console via serial port). Has a floppy, 8MB memory, no hard drive, and a dead NVRAM. I'll consult the various faq's on the web about the NVRAM, and maybe drill some mounting holes for a hard drive (didn't come with a hd carrier, and I can't find any). I'll run it headless with netbsd, since I don't have room for another monitor. I don't know much about the Sun 3 series though - most of what I see from a google search is about the 3/50 and 3/60's. Is the 3/80 an ignored bastard child from sun? A 68030 in a pizzabox, not a classic Sun 3, but not a Sparc either? Are the hd carriers hard to come by? Thanks, Jeff

19 years, 5 months

Switch Handle Pictures

by dwight.elvey＠amd.com

>From: "Jay West" <jwest at classiccmp.org> ---snip--- > >Ok, total neophyte input here on my part. But most of the techniques I've >seen involve doing the casting inside a small dixie cup. If the problem is >air bubbles, what about using a common (at least back in the 70's) device >that many people still have in their kitchens... a "seal-a-meal". Mine has a >vacuum attachment, to suck the air out of the container. So what about >putting the cast inside a mason jar, to which you've hooked up the Hi Just be careful using glass containers with a vacuum. Usually these jars have some nice gooey stuff inside them when they fail from a vacuum. Without that stuff inside, the glass can go flying everywhere. Use safety glasses. Even metal containers can be dangerous when they collapse. Still, glass works well because you can watch for the stuff outgassing and making too much foam. It is much easier to regulate how fast the vacuum it done. Dwight >seal-a-meal (or maybe the backend of an aquarium pump) to suck out all the >air and let the cast set in a vacuum? > >Maybe a nutball idea, as I haven't a clue about this stuff. Just a thought. > >Jay > > >

19 years, 5 months

Funny ebay auction

by williams.dan＠gmail.com

It made me laugh and it's on topic. http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&category=96944&item=5181057…

19 years, 5 months

Switch Handle Pictures

by dwight.elvey＠amd.com

>From: "vrs" <vrs at msn.com> ---snip--- > >I'll have a look, thanks! One of my goals is to stick with technology we >can (theoretically at least) do at home with a minimal investment. If I >spend a ton of time buying or building equipment, I start to feel like I >need a business plan :-/. > > Vince > > Hi Vince Like I said, the pump can be made from an old bicycle hand pump. If you need a chamber, watch garage sales for an old preasure cooker. Most of these are strong enough to hold a vacuum. They should be big enough to hold a small mold. Dwight

19 years, 5 months

Oscilloscope question

by png＠ideaphile.com

Just a quick comment on this one-- You want an scope with several times as much "bandwidth" as the frequency of the fastest digital signal you will examine-- 4X minimum. The analog frequency content of a digital signal is much faster than its clock rate. Without a substantial margin, the signal will be badly distorted. Analog scopes are cheap and widely available, but they have limited value for troubleshooting digital electronics. They can only show you repetitive signals, or the envelope of a randomly changing signal. They can't show you something that happens only once, or very rarely, but that's the nature of most digital problems. Expensive analog "storage" scopes can hold a signal on the screen, but only if you can figure out how to capture it in the first place. You might as well spend the money on a digital scope. If you're getting a digital scope, you need a "sampling rate" that is also much faster than the frequency of your fastest signal. The Nyquist theory says you need 2X the sampling rate to reconstruct a signal, but that theory applies ONLY to reconstructing a known waveform given a large number of samples. Again, in practice, you want a sampling rate at least 4X your digital clock rate, and preferably more like 10X. This ratio determines how accurately you can measure the position of your signal edges. You will find old digital scopes that quote two sampling rates. The higher figure will be a "repetitive sampling rate" specification that applies ONLY to reconstructing periodic signals such as radio carrier waves or computer clock signals. For non-periodic sources such as logic signals, only the lower "raw" or "real-time" or "one-shot" or "instantaneous" sampling rate matters. Today, even for under $1,000, you can get a digital scope with a true sampling rate much faster than you'll probably ever need. These are usually priced according to analog bandwidth. For troubleshooting old computers, even 100MHz is probably more than sufficient. A good probe reduces the load on the signal being observed, as David Holland said. An o-scope input has a 50-ohm impedance; that kind of load will stop many circuits from working. So-called "active" probes present an almost undetectable load, but you will rarely need anything that sophisticated. If you're going to use a scope for ANYTHING, get this book: Troubleshooting Analog Circuits, Bob Pease, ISBN 0750694998 http://www.amazon.com/exec/obidos/tg/detail/-/0750694998/ Or buy an autographed copy from the author by emailing rap at galaxy.nsc.com. Though written about analog circuits, all of these electrical principles and troubleshooting techniques apply to digital circuits. Let's face it, the circuits themselves are analog anyway. . png

19 years, 5 months

Switch Handle Pictures

by James＠jdfogg.com

> Ok, total neophyte input here on my part. But most of the > techniques I've seen involve doing the casting inside a small > dixie cup. If the problem is air bubbles, what about using a > common (at least back in the 70's) device that many people > still have in their kitchens... a "seal-a-meal". Mine has a I think the usual approach is a vibrating table shake the bubbles to the surface.

19 years, 5 months

Oscilloscope question

by ajp166＠bellatlantic.net

>Subject: Re: Oscilloscope question > From: "John Allain" <allain at panix.com> >Subquestion Number one for me would be the reasoning why >those probes are so important. How bad are readings taken >with just direct wired connections? The probe is the "interface" between teh scope and the circuit. The wrong type of connection will either pick up undesired signals, load the signal resistively or capacitively. The latter is signigicant as digital signals are time based and the capacitive load of raw coax cable and alter that timing or worse introduce ringing into the circuit. >Should a scope rating 2X the computer clock speed keep the >readings useful? Scopes are like telescopes, even the cheapest can see Mars, slightly better can see the bands on Mars. Relating the bandwidth to CPU clock is mostly meaningless. The parameters your are mesuring is timing of the waveform and possibly the waveshape. If the bandwidth (and corosponding rise time of the scope amplifiers) is not adaquate you will distort the waveshape and if the timebase(X or horizontal scan time) is either porrly calibrates or cannout go fast enough it may be impossible to determine if a event occurs 450nanoseconds (10^-9) later. Risetime is a measure of how fast the amplifer in a scope can go from 10% to 90%. Usually you want that to be faster than the waveshape you wish to view by more an two and as much as 10 times. Note most TTL have rise times well under 20ns and even some of the older logic families can be very fast rise and fall times. So this is why a 50mhz (465b) scope of better is used. The key here is risetime is the measure used to understand the faithfulness of the reproduction for a given wave shape. An example may be a very fast rise time square wave can end up looking more like a saws teeth when reproduced using a scope with inadaquate risetime in the most extreme case. For the math types 1/risetime+falltime give an approximate repetition rate or frequency 1/40ns=25,000,000 Reptitions/Second. So 2x that is only 50mhz! Also bandwidth and rise time are only related as a scope can have good rise time but limited bandwidth or the reverse. >I suspect the approact to an oscilloscope for the typical person >on this list wouldn't be the same as for a "rank dummy". Yes. In both cases there is a requirement to understand electronic basics and what waveforms result from basic circuits. Complex circuits are just many simple ones combined in many ways. Allison

19 years, 5 months

Tapes (9track & DC600A) new - anyone interested? UK

by listmailgoeshere＠gmail.com

Hi list, A contact has the following up for grabs: Euromagnetics "Calculus Mk III" 9track tapes, 6250BPI, 7 off Unknown brand (but ex-UK MOD so will be *extremely* high quality) DC600A tapes, 60MB, 10 off All are brand new and still sealed in their packaging. If you would like to buy any, email an offer (he doesn't know what they're worth, neither do I ;) to chrissi(at)ntlworld(dot)com. The tapes are located in Cleethorpes, UK, but he will ship anywhere. Regards, Ed.

19 years, 5 months

Oscilloscope question

by ajp166＠bellatlantic.net

>Subject: Re: Oscilloscope question > The whole thing of O'scopes is manifold. Having a scope adaquate for tha task. Generally an operational Tektronix 465B, 475 or the newer equiventls are an excellent bet. However.. The other is having the right probes, knowing where and how to hook up. With all that accomplished you fire it all up and are faced with a display that doesnt match what you wish(hope) to see. So you twiddle the knobs and its still different. The problem is now interpreting the display and taking the required action IE: adjust scope or adjust equipment at hand or maybe even fix broken equipment. The latter part is far harder as most people have no point of referece to what it all means. That the part of learning to use a O'scope many of the books and site may not even touch. Sometimes if your tweeking a disk the manuals will provide a procedure down to the nth detail and if followed and the drive is otherwise working it's easier. The usual problems is "I made xxx adjustment and I'm to the end and it's still a bit off. What do I do?". There knowledge and experience really helps. If your tweeking a RK05, one suggestion. Find a mentor (EXfield service guy maybe) that has done it before. Even if it's dim memory it maybe very helpful. Allison

19 years, 5 months

PDP 11/45 Display register.

by jim＠g1jbg.co.uk

Hi, A quick question raised by my ongoing work.... Is it possible to write directly to the "display register" - the one accessed by one position of the data switch. I think it should be at memory location 777570, but I can't get data into it, either using deposit from the console, or moving data under program control. Have I got a fault, or am I doing something wrong? Thanks Jim. Please see our website the " Vintage Communication Pages" at WWW.G1JBG.CO.UK

19 years, 5 months

← Newer
1
...
50
51
52
53
54
55
56
...
73
Older →

Jump to page:

2024

2023

2022

2021

2020

2019

2018

2017

2016

2015

2014

2013

2012

2011

2010

2009

2008

2007

2006

2005

2004

2003

2002

2001

2000

1999

1998

1997

test-drb April 2005