test-drb April 2016

test-drb@ccmp.vtda.org

203 participants
299 discussions

by sales＠elecplus.com

When I was at the recycler last week, I saw a lot of really OLD test equipment. I started looking through it to see if there were things I could recognize, but the closest thing I could figure out was a 1940s telephone equipment tester. All of these were portable, with lids that closed with latches. Probably weighed abt 20-30 pounds each. Any cables that might have been needed to run the equipment was gone. If things like this are of interest in the $25 range, then I can pick some up next time I see them. Unfortunately I have no cell phone numbers for anyone in the DFW area to tell them to come and see the goodies while I am there, and they will not let strangers come in and poke around. I am (or was) an electronics tech, but most of the functions on these old test machines eluded me. --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus

8 years, 11 months

Shipping big things across the atlantic.

by pontus＠Update.UU.SE

Hi. I'm considering to ship an empty full height rack from the USA to Sweden. It is definitely something I wont find here so it might be worth the cost and effort. What are my options to get it here safely? If you have any experience I would greatly appreciate if you could share them. Thanks in advance, Pontus.

8 years, 11 months

Voltage regulator with alternate voltage source...

by wulfman＠wulfman.com

You should be just fine. On 4/7/2016 1:38 PM, Bill Sudbrink wrote: > If you have a circuit which is normally designed to > operate with an unregulated supply, through a regulator... > say unregulated +8 through a 7805 to a regulated +5 and > you want to test it independent of the +8 supply, if > you leave the unregulated rail unattached and put +5 > switcher straight onto the regulated +5 rail, will you > damage the 7805? Clearly the VIN is open, but the ground > pin will still be attached. Would this push voltage > back through and screw things up? > > Thanks, > Bill S. > > > -- The contents of this e-mail and any attachments are intended solely for the use of the named addressee(s) and may contain confidential and/or privileged information. Any unauthorized use, copying, disclosure, or distribution of the contents of this e-mail is strictly prohibited by the sender and may be unlawful. If you are not the intended recipient, please notify the sender immediately and delete this e-mail.

8 years, 11 months

Why do good floppy disks go bad?

by jplist2008＠kiwigeek.com

I had one of those Japanese Koan moments recently when someone asked me "Why do floppy disks stop working?" and I realised I... didn't actually know. I thought I'd throw it to the group and get some theories/proofs. Let's work on the assumption we're talking about 5.25" and 3.5" disks. Several guesses: - Repeated use slowly wears away the magnetic media layer on the mylar. - When left in an unprotected state, or a poor environment, damp, mold and dust can damage the surface, either degrading the magnetic layer or causing the gap to shrink enough that the drive head physically damages the disk? - Quantum fluctuations in the state of the universe, caused by millions of mostly non-interacting particles passing through a disk in any given minute, alter the magnetic spin of the ferric atoms causing gradual data loss over time (mostly tongue-in-cheek) - Given the lack of use of most floppy drives they themselves pick up 'gunk' and on first reading a diskette after a long time of disuse damage it. It _seems_ like when you put a 3.5" disk down for ten years and pick it back up, a disk that used to work fine no longer does. Of course, after ten years, it could be your own memory that's failed. Dare I ask, what's the consensus? - JP

8 years, 11 months

Voltage regulator with alternate voltage source...

by ard＠p850ug1.demon.co.uk

> > > 1) I have a 12 volt DC supply. 12 volts seems to be > > > within the VIN range for the 7805s whose data > > > sheets I've now read. Can I simply apply 12 volts? > > > > Yes, but that regulator might get mighty hot! I would > > not do this for fear of cooking the poor thing. > > That's what I figured to start with, before reading the > datasheets. If as your photos (in another message) suggest it will run OK from 8V with no heatsink on the 7805, then I would be pretty sure it will be OK at 12V if you bolt a reasonable heatsink to the regulator. Give it a smear of silicone grease, of course. -tony

8 years, 11 months

Voltage regulator with alternate voltage source...

by ard＠p850ug1.demon.co.uk

> > First, a few quick "whys": > > 1) The 7805 is actually a Motorola MC7805CP, date > code 7308 with gold leads. Very hard to exactly > replace. Any reason why it would have to be an exact replacement? In any case, the behaviour of the 7805 if you apply a voltage to the output with the input floating may well depend on the manufacturer and even the date (some devices were improved over the years). Unless you have a 1973-or-so data sheet from Motorola, I don't think you know whether it will be damaged or not. [...] > 1) I have a 12 volt DC supply. 12 volts seems to be > within the VIN range for the 7805s whose data > sheets I've now read. Can I simply apply 12 volts? Yes, but... The power disipated in the 7805 will increase, in fact it will be more than doubled. To put it crudely, a linear regulator acts like an automatic variable resistor. I have no idea what current the load takes, let's call it I. If you supply 8V, then the power disipated in the 7805 is 3*I watts, if you supply 12V it's 7*I. This may or may not be a problem. > 2) Could I place a resistor in series between the 12V > supply and the 7805 to drop the voltage at the 7805 > to somewhere around 8? Yes. You need to know the maximum current the load will draw, which will be much the same as the current drawn >from the PSU. Then just calculate the resistor to drop 4V at that current. If you can find one, you could probably use a 7808 to supply 8V to the unit from a 12V supply. Or a 7805 'jacked up' with a 3.3V zener diode (in series with the common lead to the extra 7805 only). My guess is that giving it 12V will be fine though. What is the device, and do you have any idea how much current it is going to draw? -tony

8 years, 11 months

Voltage regulator with alternate voltage source...

by wdonzelli＠gmail.com

> 1) The 7805 is actually a Motorola MC7805CP, date > code 7308 with gold leads. Very hard to exactly > replace. Is that the big flat plastic package with the wide flat leads? I might have a few of those around, but I agree, not an easy variant to find. > 1) I have a 12 volt DC supply. 12 volts seems to be > within the VIN range for the 7805s whose data > sheets I've now read. Can I simply apply 12 volts? Yes, but that regulator might get mighty hot! I would not do this for fear of cooking the poor thing. > 2) Could I place a resistor in series between the 12V > supply and the 7805 to drop the voltage at the 7805 > to somewhere around 8? Yes, you could do this. Pick an appropriate power resistor, or use a big wirewound rheostat. > 3) If I was to "tack on" a jumper between VIN and VOUT, > would that protect the 7805 and allow me to power the > circuit with 5 volts? I would not do this at all. -- Will

8 years, 11 months

Dumb terminals for daily use today; failure scenarios

by echristopherson＠gmail.com

If one were to use a dumb CRT terminal from the early '70s regularly in this day and age, would it be more prone to hardware failure than if it were kept in storage or just kept to look at but powered off? -- Eric Christopherson

8 years, 11 months

VCF Europe, April 30th - May 1st, Munich + registration for VCF Berlin

by stueberahoo＠yahoo.de

Hi list, the 17th edition of VCF Europe[0] is coming soon! It will take place on April 30th and May 1st in Munich, Germany. Please be aware that the information on the English version of the website might be outdated or less detailed than on the German page, but Google Translate will help. Also the registration for VCF Berlin[1] in October is open now. We are looking for speakers, workshop instructors and exhibitors, both for the regular exhibition and this year's special exhibition on computers and languages. It will be open for visitors on Sunday, 2nd and Monday, 3rd of October, as the 3rd October is a public holiday in Germany, but we are thinking about inviting people to build up on Friday already and using Saturday, 1st of October as a day just for the participants and the community. This way there would be more time to talk and see the other exhibitions. Maybe we could even offer advanced workshops on Saturday. Come and visit us! Ping me if you need a place to stay. Regards, Anke [0] http://vcfe.org/E/index.html [1] http://vcfb.de/2016/index.html.en

8 years, 11 months

Pinging Joe Rigdon

by connork＠connorsdomain.com

Anyone know if Joe Rigdon is still around? Thanks, -Connor K

8 years, 11 months

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test-drb April 2016