test-drb April 2016

test-drb@ccmp.vtda.org

203 participants
299 discussions

Voltage regulator with alternate voltage source...

by jrr＠flippers.com

On 04/07/2016 2:18 PM, Bill Sudbrink wrote: > drlegendre wrote: >> Not saying it's going to smoke-out, but it does >> seem like a wonky thing to do. > I disagree about "wonky" let me try with more > diagram and less English: > > (+8) > | > VIN| ceramic cap > |-----][----- > ___|____ | > | 7805 |----------GROUND > -------- | > | | > VOUT|(+5) | > | | > ___|____ | > | LOAD |-------| > -------- > > +8 is not currently available (no pun intended). > I would like to test LOAD without removing 7805 > as it is soldered in place. Is damage to 7805 > likely if alternative regulated current is applied > at (+5) and (+8) is left open? > > Bill S. > > > Yes, you can damage the 7805 - READ the data sheets... Raising the Output Voltage above the Input Voltage: Since the output of the device does not sink current, forcing LM340/LM78MXX Series 3-Terminal Positive Regulators LM340/LM78MXX Series 3-Terminal Positive Regulators the output high can cause damage to internal low current paths in a manner similar to that just described in the ?Short- ing the Regulator Input? section. LM340/LM78MXX Series 3-Terminal Positive Regulato John :-#(# -- John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, VideoGames) www.flippers.com "Old pinballers never die, they just flip out"

8 years, 3 months

Why do good floppy disks go bad?

by kspt.tor＠gmail.com

The problem with lifetime warranties is that they're not about the lifetime of the owner, and they're not about the lifetime of the product. What it means is "as long as it's a product we're still selling" (except for those cases where it *really* is the lifetime of the product.. in which case it means "the warranty is valid until the product fails").

8 years, 3 months

Mac SE/30 analogue board and PS caps

by dave＠661.org

Does anyone have a list of the capacitors on the analogue board and power supply for a Mac SE/30? -- David Griffith dave at 661.org A: Because it fouls the order in which people normally read text. Q: Why is top-posting such a bad thing? A: Top-posting. Q: What is the most annoying thing in e-mail?

8 years, 3 months

Voltage regulator with alternate voltage source...

by geneb＠deltasoft.com

On Thu, 7 Apr 2016, Bill Sudbrink wrote: > Maybe I'm overthinking this. If I just put > regulated +5 on the 7805 VIN will it work? > Isn't the minimum input voltage for a 7805, 6vdc? g. -- Proud owner of F-15C 80-0007 http://www.f15sim.com - The only one of its kind. http://www.diy-cockpits.org/coll - Go Collimated or Go Home. Some people collect things for a hobby. Geeks collect hobbies. ScarletDME - The red hot Data Management Environment A Multi-Value database for the masses, not the classes. http://scarlet.deltasoft.com - Get it _today_!

8 years, 3 months

Voltage regulator with alternate voltage source...

by henk.gooijen＠hotmail.com

-----Oorspronkelijk bericht----- From: Bill Sudbrink Sent: Thursday, April 07, 2016 10:38 PM To: 'General Discussion: On-Topic and Off-Topic Posts' Subject: Voltage regulator with alternate voltage source... 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. --------- It is a special situation I have never seen, but I would try to disconnect the output of the 7805 before connecting a foreign +5V to the circuit. It is good practice to have a diode reverse connected from output to input to prevent damage to the 78xx in the case that the output voltage gets higher than the input voltage. Normally that would not happen, but if you have a high capacitance at the output and the load is minimal it could be possible when power is switched off that the input voltage dropped, but due to the big capacitor at the output the output voltage did not yet drop. And then that diode in reverse from output to input comes into play. Now the input is not connected, but GND and the output are ... I would have a look at a data sheet of the 78xx series to see what could happen if the input is not connected, but the output is. So, if possible, simply disconnect the 78xx output lead first. - Henk

8 years, 3 months

Voltage regulator with alternate voltage source...

by wh.sudbrink＠verizon.net

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.

8 years, 3 months

Front Panels Latest

by rodsmallwood52＠btinternet.com

Hi Guys PDP-8/e A panels now shipping PDP 8/e B panels ship on Friday PDP-8/ f and /m ship on 14th I have some extras of the above if you are quick. Rod (Panelman) Smallwood

8 years, 3 months

DEC fieldguide

by shadoooo＠gmail.com

Hello, I'm a modest collector of DEC and PDP11 stuff, I always thank who wrote the PDP11 field guide with the almost complete list of all the existing boards... Now comes the idea: could be useful having a website where the field guide assume a graphical aspect, including pictures of the parts, descriptions, and so on? Of course it would be almost impossible for one alone to do all the work, but I'm thinking of a sort of wiki, where subscripted users can upload pictures, informations and documentations. Maybe something similar already exists? Thanks Andrea

8 years, 3 months

Giving away 0.35 metric tons of books*

by alexey.toptygin＠gmail.com

*some restrictions apply :-) Evan Koblentz pointed me to a rescue here in the triangle, NC area back in August 2015. Some items were set aside for VCFed, but there were A LOT of books and other media that were up for grabs. Because I'm a sucker, I took and then carefully cleaned and catalogued them all. The master list is here: https://docs.google.com/spreadsheets/d/19UYeJlhiVYVExCAO2NSzcAkBww0kEeAYrEG… There really are 17 boxes, and they really do weigh 780lb or approximately 0.35 metric tons. They're mostly books (from the 80s and 90s), but there are some floppies, some boxed sets, and even a small box of VHS tapes. The previous owner stored all this stuff in abysmal conditions, so there was a lot of mold (and some dead insects and some live insects, and... you know how it goes). I cleaned every item as much as possible. Some items had to be disposed of for safety reasons. That which made it into the cataloging stage is at least scanable, but if it says 'mildewed' on it, and you have a mold allergy, you don't want it. I don't know if any floppies are readable, and unless the catalog says it comes with media, I haven't got the media. Luckily most items survived relatively intact. You can have anything in the spreadsheet free of charge provided: 1) You are willing to take WHOLE BOXES at VCF East XI, you let me know by Weds 4/13/16, and they fit in my car when I pack for VCF. OR 2) You want to come to Durham to pick them up at a prearranged time after VCF OR 3) You are willing to wait until the next VCF East, and let me know far enough in advance that I can set items aside for you. If you want single items, and you don't want to wait until VCF East 2017, I'll do my best to mail them to you after this VCF is over, but you'll need to pay for shipping. I would prefer not to ship whole boxes; they're sturdy moving boxes but they weigh 40-60lb each and I'm pretty sure if you drop them hard enough the contents won't like it. I'm in Durham, NC 27701. I don't want any of this to go to recycling, so I'll try to hold it for at least a year or the next VCF East after this one. After that, all bets are off. Let me know if you are interested in any of this stuff, or if you have questions; in case the mailing list(s) eat it, my email is alexey.toptygin at gmail dot com. Thanks!

8 years, 3 months

AT&T 4425 (Teletype 56D) repair

by lists＠loomcom.com

About a month ago I was given a very nice AT&T 4425 terminal, which was AT&T's OEM of the Teletype 56D. Alas, the terminal suddenly died on me last week and I'm going to have to dive in and figure out why. It appears to be something going wrong with the digital board, not the analog, since sometimes I can get strange characters to show up on the screen (but not always). I did my normal searches of BitSavers and Google, but I haven't found any schematics for the 4425. I don't suppose anybody has them? At least it looks easy to work on. Kudos to whoever designed the innards, it comes apart very easily and cleanly. -Seth -- Seth Morabito seth at loomcom.com

8 years, 3 months

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test-drb April 2016