test-drb February 2011

test-drb@ccmp.vtda.org

155 participants
210 discussions

by jfoust＠threedee.com

At 11:14 PM 2/3/2011, William Donzelli wrote: >There is currently a pretty big PDP-11/44 collection on Ebay (just >search for PDP-11/44). It is located in Milwaukee. Item 130481622084 ? Only $500 so far? Nine days to go. Cheese, it would be worth that even if you ground it up for gold scrap. :-) I'm in the area but I don't know what I'd do with it or where to put it. - John

13 years, 10 months

Odd resistor failure

by tshoppa＠wmata.com

>> But... electronic ballasts are switching devices and the current >> is not steady-state. If twice the current flows for half the time, >> then the power dissipation doubles (Remember, I-squared-R, you doubled >> I, so I squared goes up by a factor of four.) > Let's do the math. Suppose the current went from 0.5A to 4A. > Probably, the 2A fuse in series with this thing would blow. If that > didn't happen, the resistor would be called on to dissipate about 5W-- > on a transient basis, the resistor could handle this; on sustained > basis, the resistor would overhead and discolor and the PC board > would also be discolored. That didn't happen. > The resistor is a plain-Jane 2W light-brown painted body with orange- > orange-silver-gold markings. No letterings or other notations, no > discoloring--just two paint chips missing from the body. > I can post photos if you want. You might have heard the rule of thumb that "in the case of an overcurrent fault, the most expensive component in the circuit will burn out to protect the fuse". That rule is only slightly facetious. In reality almost any component (no matter what the $ value) will burn out to protect the fuse :-). You might think I'm being facetious but I'm not! I still suspect that, for example, bad bulbs or some other ballast failure had taken out the resistor. Fluorescent ballasts and CFL's are not known as places where manufacturers spend many dollars on high quality components to increase lifetime and decrease the possibility of failure. Resistor wattage ratings are not always mathematically related to the maximum voltage or current that you should put on/through the device. At the high ohm end (say a 22MOhm 1/2W resistor, which would imply 3300 volts) the calculated voltages are more than the bodies are rated for, and at the low ohm end (especially for lowest-bidder resistors) there can be weak spots in film resistors that become "hot spots" in transient overcurrents you might think the resistor should be able to survive. Good metal films can survive massive overload, and all they do is glow bright orange and burn off their outer coatings. But I strongly hint above, that such good components will not generally be found in ballasts or CFL's. Tim.

13 years, 10 months

I'm looking (been looking actually) for a Zenith Z-100/120

by chrism3667＠yahoo.com

Preferably *not* the low profile version (which means to me the models that don't have a built in monitor). But then again maybe I'd be better off, because those models had RGB video capability, IINM. I don't know, tell me what you got. Also *still* looking for Atari ST/Mega/TT/Falcon stuff, working or not. Does anyone know of the Atari ST related machine that had a built in monitor? Saw the thing on eBay ages ago, should have bid on it.

13 years, 10 months

anyone in Ft.Lauderdale that can do me a big flavor?

by chrism3667＠yahoo.com

It involves shipping an item. I can help the same person out if they need helps up here...

13 years, 10 months

[OT] Sunfire V880 Diagnostic Key

by austin＠ozpass.co.uk

I hope that you can forgive the off-topic post, but I find myself in desperate need of a "diagnostic" key for a Sun Fire V880. They're the same for all v880's but I can't get similar ones to fit. I live in the uk and will willingly send beer vouchers in exchange. -Austin. Sent from my iPhone

13 years, 10 months

IBM PC-Radio

by chrism3667＠yahoo.com

Hi Is me and Uncle Roger and the other dude in Italy the only ones w/these things? I have 2, but neither turn on. Anyone know what type of power it requires? I had thought these had color stn displays or something, but now I'm thinking they're just mono. Halp.

13 years, 10 months

SCSI -1 to IDE and SD project

by lynchaj＠yahoo.com

Hi! Several weeks ago there was a discussion on CCTALK about a free/open SCSI to IDE and SD project. I designed a PCB using the Z53C80 and a Z80 with RAM/ROM/UART/IDE and SD. There is a prototype available waiting for some interested builders to take on the project. As far as I know none of the builders have a completed unit although I think if we had at least one working unit the project would make some real progress. I have four remaining SCSI to IDE/SD prototype boards so if anyone would like to join the project as a software developer please let me know. I believe much of the software can be reused from previous N8VEM and/or other free/open software projects. http://n8vem-sbc.pbworks.com/w/page/35044530/PCB-Inventory Thanks and have a nice day! Andrew Lynch

13 years, 10 months

GSX porting project

by lynchaj＠yahoo.com

Hi! Recently on the N8VEM project we've developed an uPD7220 GDC display board. It can display 16 colors on a VGA compatible monitor in 640x480 or 800x600 resolution. The uPD7220 Graphic Display Controller is an intelligent controller peripheral for raster graphics. It was used in a variety of early microcomputers such as the NEC APC in the late 1970's and early 1980's. http://www.old-computers.com/museum/computer.asp?c=333 http://n8vem-sbc.pbworks.com/w/browse/#view=ViewFolder <http://n8vem-sbc.pbworks.com/w/browse/#view=ViewFolder&param=ECB%20uPD7220% 20V2%20Prototype> &param=ECB%20uPD7220%20V2%20Prototype Now that the hardware is maturing, I would like to use it for a port of GSX to the N8VEM SBC V2 (Z80 based) and/or SBC-188 (80C188 based). GSX is a predecessor to the more widely known GEM graphical user interface operating system. I have PCBs for the project. There are both 8 bit and 16 bit versions of GSX roughly corresponding to CP/M-80 and CP/M-86 operating systems. The N8VEM SBC V2 already has CP/M 2.2 and CP/M 3.0 and the SBC-188 runs CP/M-86, FreeDOS, etc. The project would be porting the existing GSX code to the N8VEM hardware. Here are some useful information links on GSX-80 and GSX-86 http://en.wikipedia.org/wiki/Graphical_Environment_Manager http://jba.freeshell.org/gsx-readme.html http://www.cpm.z80.de/download/gsxdrv-s.zip http://www.gaby.de/cpm/drilib.html http://www.z80.eu/gsx.html http://www.gaby.de/cpm/manuals/archive/index.htm http://www.gaby.de/cpm/roche/index.html http://www.gaby.de/cpm/roche/NCRGRAF.ASM (direct application to the uPD7220) http://www.gaby.de/cpm/binary.html If you are a software intensive builder you may enjoy working on this interesting project. The project would involve compiling and porting the legacy GSX sources to run the graphical primitive routines. http://en.wikipedia.org/wiki/Graphical_Kernel_System Thanks and have a nice day! Andrew Lynch

13 years, 10 months

Looking for Papertapes for PDP 11/05

by billdeg＠degnanco.com

I have a PDP 11/05 all dressed up and ready to go, stock config. Does anyone have or be willing to make copies PDP 11/05 or 11/10 papetape programs available? (diagnostics, assembler, editor, utilities). I have an ASR 33 and the computer has 8K core. Worst case I guess I could toggle in the code, then punch it for use next time! Bill Degnan

13 years, 10 months

Odd resistor failure

by tshoppa＠wmata.com

Chuck writes: > I've been going over a small stack of failed T8 bulb solid-state > fluorescent lamp ballasts from about the mid 90's. They all have the > same failure and it suprised me. > > There's a 2W 0.33 ohm carbon film resistor used as a current sensing > element. In all failure cases, the resistor has failed open, with no > signs of burning, but rather the outer paint flaking off. > > To me, this is a puzzle. At 120v, the current through an 0.33 ohm > resistance in series with a 64W load is about half an amp. I2R gives > less than a tenth of a watt power dissipation across the resistor. > (There's also a 2A fuse in series with the whole circuit). > > I replaced the failed resistors with 5W composition ones of the same > value, and they seem to work okay. > > But the original failure has left me scratching my head. Does anyone > have an insight on this type of failure? If the current is steady-state, your math works out correctly. But... electronic ballasts are switching devices and the current is not steady-state. If twice the current flows for half the time, then the power dissipation doubles (Remember, I-squared-R, you doubled I, so I squared goes up by a factor of four.) All that said, it has little to do with your electronic ballasts :-) I betcha the original resistor was a fusible resistor to begin with. SMPS 101: when you see a blown up or burnt out component, you can bet that some other component failed and took it out. Typically a fusible resistor will heat up to mildly-red-hot before it blows. Do the same with a non-fusible metal film and it'll be fine (if discolored!). Tim.

13 years, 10 months

← Newer
1
...
5
6
7
8
9
10
11
...
21
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 February 2011