test-drb

test-drb@ccmp.vtda.org

101090 discussions

by jnc＠mercury.lcs.mit.edu

> From: Torfinn Ingolfsen > Most likely a bad solder joint. That was my first thought, and so I carefully inspected all the pins, but they all looked good to me. But I suppose it might have been something that wasn't visually obvious. Noel

10 years, 1 month

A tale of a chip and a socket

by jnc＠mercury.lcs.mit.edu

So I just had the incredibly amusing experience of managing to repair an -11/04 CPU by un-soldering a chip, putting in a socket, and putting _the same chip_ back in that socket! Before you go 'WTF?!?!', let me explain what happened. The CPU wouldn't run, and in poking around, I stumbled on the cause: all the registers would not 'take' 1's in the 0360 bits. Hmm, 4 contiguous bits - sounds like it might be a bad register file chip. But before I pulled it, I wanted to make sure it wasn't some other part of the data path - Mux, ALU, etc. So I put a DIP clip on the chip, whipped up a 3-instruction 'scope loop that would exercise it, and... while I was looking at it, the problem went away! WTF? So I pull the clip - and the problem comes back. Repeat. Clearly there's a bad connection in the chip, and the pressure of the clip is 'fixing' it. So I pull the chip, put in a socket (I always use sockets on repairs, I'm paranoid I'll overheat the parts - I don't mind living with an potential eventual bad contact from corrosion), and figure what the heck, let me see if fiddling with it fixed the bad connection - and sure enough, it now seems to work! And if it eventually fails, no problem - it's in a socket, I know where to go if the machine stops working, those P3101A's are rare and expensive, etc! :-) Noel

10 years, 1 month

Stuff searching for new home around Duesseldorf, germany

by cctalk.pkoch＠dfgh.net

Hi all, we have been using two Sun 6800 (each fully equipped with 96GB of RAM and 24 Sparc III processors 1.2GHz) for many years. Now they are retired and must leave our machine room to make place for newer machines. Anybody out there willing to give them a new home? They are very good in transforming electric energy into heat. And by activating only some of the processor boards you can regulate the heat flow. Your wife will love to stand behind it and use it as a whole-body blow-dryer. Take one for free and you will get another one for no additional costs. While rearranging our machine room, we found lots of other stuff that must go away too. Here's the current list: - Sun E250 - Sun A5200, 2xA5100, D1000 with lots of disks - Sun E450, 2x, one is still needed for a couple of months - Sun L1000, 3x, one is still needed for a couple of months - Sun 6800, 2 fully equipped and a third one for spare parts - Sun 880 with 12 disks - Sun 480 2x, with spare processor boards - Sun L11000 tape library (aka ATL P3000) with 6 drives and lots of tapes Be warned: You need a truck with lift to transport a Sun 6800. It's 191x130x61cm and weights approx 500kg. Same thing with the tape library: 192x72x145cm, approx. 600kg. On the other hand rumours are that kids do place stuff like this into their parents basement :-) I took some pictures and uploaded then to http://flic.kr/s/aHskuakSMT Peter

10 years, 1 month

really old test equip

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

10 years, 1 month

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.

10 years, 1 month

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.

10 years, 1 month

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

10 years, 1 month

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

10 years, 1 month

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

10 years, 1 month

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

10 years, 1 month

Jump to page:

2026

2025

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