Pontus Pihlgren wrote: The 11/44 uses the H7140 power supply which was also used in the 11/24 and VAX-11/730. It is quite different than the H765 power supply used in the 11/34, 11/35, and 10.5-inch-tall 11/05 and 11/10.

On May 14, 2012, at 3:51 PM, Rob Jarratt wrote: Well, I'll gladly tell you to spend some money on a decent scope. You will come to wonder how you ever got along without one, even if it's a 2-channel analog scope with relatively low bandwidth. They're so useful for so many things; I promise you won't regret it (as long as you don't go bargain- hunting and find one that you also have to fix). My scope is a 100 MHz analog scope with 4 channels that I got on eBay for about $200. Everything worked great in it except for a fan, which was easy enough to replace. You should be able to find plenty of good ones in OK condition for around that price, assuming the UK second-hand market is in any way similar to ours. If you only need 5v or 12v, AT power supplies (or jury-rigged ATX ones) make reasonable ones. I'm willing to bet you have at least one of those lying about. :-) My 11/23, for example, runs off an AT supply (though its rather thin wires tend to get warm, so one of these days, I'll make the upgrade to a decent enclosure). Most AT supplies also offer -5v and -12v, should you need them. - Dave

Sounds ike you've got ripple on one of the supply lines for the Y amplifier. Do you have the schematics (Hameg used to be good about puttign those i nthe manual). If so, find out what supplies are used for the Y amplidier nad check/replace the large electrolytics associated with them (this is s linear supply with a nice big transformer, so it's not too ahrd to fix). [AT PSUs} An adjustable bench supply is also a very useful thing to have. One important feature that a lot of neew ones can't to is the ability to go right down to 0V on the output. The modern SMPUS-based ones start at 1V or so. Which is a right pain if you want to ramp the votlage up from nothing. Fiarly obviosuly the thing I use the most often is a multimeter. I think the bench PSU comes next (if you can't power sonmething, you can't test it :-)), then eitehr a 'scope or a logic analyser depending on what it is I am working on. -tony

On Mon, 14 May 2012, John Robertson wrote: Ah, yes. This is why one can easily find replacement switching power supplies for the Commodore 64 and friends. I've had a stock brick blow out on me, but fortunately it didn't kill the computer. Others in my cohort were not so lucky. -- David Griffith dgriffi at cs.csubak.edu 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?

Be very careful... Most SMPUs can produce around twice the requried output voltage if the regualtion loop fails. An open-circuit reference device can cause this in some cases. As can other problems i nthe regulation circuitry. There are non-issolated swtiching regulators used in amny classic ocmputers, run off the output of a normal mains transformer. The DEC power bricks are examples. HP did simular things. I am not sure if you call thsoe SMPUS or not, but if the chopper transistor in one of those fails, the output will leap sky-high. And there is a well-known 2-stage SMPSU which consists of a non-isolated swtichign regualtor to produce about 150V fro mthe 350V rectified mains follwed by a free-running oscilaltor drivign the main trasformer. Regulation is applied to the first stage. If the chopper in that stage shors, the PSU outs wil lelap to over twice their normal coltages, and quite often the seconnd stage will keep on running so the outptus stay at said voltages. A crowbar circuit is a good idea for any PSU, linear or switcher (amd I am still wondering why HP didn't fit them to the 9815 anmd 9825 machines, having fitted them to the 9800 series). -tony

full of evidnce of rodents, is it? Good test gear is an investment, but I do agree it gets very expensive to have everything that would be useful, particularly if you are not sure you're goign to need it again. Diehard hardware people probably can justify a room of vey obscure instrument, people who just want ot fix the machie so they can get one with using it probably can't... It's often psosible to manage without a particular insturment, but the people who are most likely to be able to do this are those who already have a lot of experience (and thus (a) understand what they need to measure and (b) know how to do that with what they have). And by Murphy's law, those are precisely the people who are likely to have accumulated all sorts of test gear over the years. It remidns me a bit of the books that tell you how to make an accurate metalwork lathe from scrap. I don't doubt it's possible, but the authors of suche books (a) often have access to machine tools through work, friends, clubs, etc) and (b), more importantly have been using lathes all their lives and know how to handle metal. To sum up, I think f you put an experienced hardware repairman on a desert island withjust a multimeter he could do a lot. But although that's what a beginenr might be limited to as well, he doesn't have the experience to use it in unconventioal ways. -tony

That is precisely my point. The 'brain' is the most importat piece of test gear. And it's one that gets better with experience. An experienced hardware guy will know how to make measuremtns with the instrumetns he has, even if those wouldbn't be his first choice, to find the fault. A beginner will not know how to do that. And the problem is that very often the beginner is the one lacking i nthe right instruments. -tony

On 05/14/2012 01:02 PM, Tony Duell wrote: Some 11/730 systems use the BA11-AS or -AT box, which has only minor differences from the other BA11-Ax boxes used for the 11/24 and 11/44, and uses the same H7140 power supply. The backplane is in the bottom of the box, so the modules go in from the top, and the power supply is in the rear. Some 11/730 systems (11730-Z) use the BA11-ZA box, which has the H7202 power supply. The power supply is on the right side of the box, the backplane is to the left of the power supply, and the modules go in from the left.

* On Mon, May 14, 2012 at 09:42:31AM +0200, Pontus Pihlgren <pontus at Update.UU.SE> wrote: Well... I'm of two minds about it. Part of me actually thinks the challenge is fun. The other part is frustrated that it will be so much work and expense, and just wants to play with a working PDP-11/35. I did take a step toward the repair already - Someone on eBay had an H744 +5V regulator for a very reasonable price, so I bought it. Since the H744 seems to be the most disgustingly rotten part, I think it might get me a long way toward a working power supply. -Seth

Not at all, alas. It is possible to put the 11/40 backplane/CPU into the BA11-K (I think that's the number) which was used with the 11/34, but Seth's photos show a totally different supply to that one. The 11/44 PSU is totally different again. -tony

And you call them that? I am sure you have high voltage insualtion testers, but I wasn't sure if you call them soemthing else. The term 'Megger' is of course a contraction of Megaohmmeter, a device that measures resistances of a million ohms or more. The important thign is that they apply a fiarly high voltage across the 'resistor' under test (which may well be the leakage from a transformer widing to its core) and thus will cause any marginal insulation to spark over and show a low reisstance. I beelive that the normally-quoted requirement is that insulation should stand at least twice the voltage it's goign to run at, so for UK mains test at 500V or so. I normally test at 1kV, because my instrument can do it and anything that can't stand 1kV to groudn probably shouldn't go on the mains. Origianlly a 'Megger' ahd a hand cranked generator to provide the high voltage. It ws a trade name (I forget who). Therr was a competing instrument called a 'Hum Metrohm' which used a battery-powered vibrator and step-up tranformer (the former producing the 'hum') to give the high votlage. The think I normally use now is Austrian (I forget the manufacturer) and uses a transistor oscillator and transformer (so it's a bit more modern, but still not all that new :-)). The nice thign about it is that it can be set to provide 100V, 250V, 500V, or 1000V. So I can use the first to test a little 12V motor I've just reound and the last to check the insulation on a mains transformer. For the real enthusiasts there's something caled a 'Bridge Megger' This has 2 modes of operation. One is a normal megger, the other is a wheatstone bridge usign the generator as the supply (there is a built-in 4 decade resistance box). These normally work at a couple of hundred volts (so not really suitable for checking stuff to go on the mains) and were used to detect fualts in telehpone lines and the like. Not all that useful for classic computer work (the high vbotlage prevents their use on IC-based circuitry!), it's the sort of thing you buy if you see one cheap and if, like me, you collect obscure measuring instruments. Quite why soemthign that insists on jumping on your workbench and scattering bits everywhere, and which is one of the best static electricity generators known should be a hacking companion is illogical, but I agree with oyu. I love Muon and Tigger... -tony

On 05/14/2012 04:28 PM, David Riley wrote: Ahh, youngn's. ;) Meggers are everywhere. I suppose such disclaimers ARE probably necessary on this list. Very sad. One of my beloved purring beasts, Kramer, destroyed quite a bit of stuff with pee when he first came to adopt me. I very nearly twisted his head off. It stopped IMMEDIATELY and PERMANENTLY, uncannily so, after The Big Snip(tm). Balls on cats are very bad things. -Dave -- Dave McGuire, AK4HZ New Kensington, PA

I am suprised they;'re a high enough voltage for that, I seem to remeber using about 3.5kV to 5kV to power a PM tube, so you'd want ot megger it at at least that (HV leaks are nsty thigns that tend not to appear until you get close to the working votlage. This is, of ocurse, Murphy's Law...) Well, obviously you dont; use them anywhwere near the logic (unless you work on vlaved machines :-)). But I do chekc the isulatuion fo mains transfiormers, fans, etc with one. It's better to find the leak.breakdown that way than by having the mains ps thotuh you (or worse, the logic boards!) -tony

A good current limiting cirucit (or trip) is _essential_ on V power supplied. I indirectly owe my existnace to one, my father managed ot touch the output of an 10kV (or so) PSU he was using in his resarch with one hand while his other hand was resting on an earthed metal sink. Fortuately the supply was a Fluke, so the trip actually worekd properly. This was before I was born, so if it hadn't tripped, I would not be here... I always test verything before I conenct it to the mains. it only takes a few minutes ,and I reckon my life is worth that (yes, OK< the safety earth should protect me, but I prefer that it doens't have to!). When I say 'everyything' I mean old and new. And I will tell you I've found many mroe dubious new things than classic computers... -tony

On 15 May 2012 at 19:41, Tony Duell wrote: That's certainly a term that I'm familiar with--"Megger". Perhaps that's only for old fogies like yours truly. Another related term is "Hipot". An adjustable high-voltage source with an insulated probe. Indispensible for testing (sometimes destructively) susceptibility to ESD, although I suspect a cat and a pair of rubber-soled shoes might work as well. --Chuck

On May 15, 2012, at 2:41 PM, Tony Duell wrote: Oh yes, he's fixed. He's just scared of everything, including (not entirely unjustifiably) the other cat, who keeps him from getting to the litterbox until it's far too late. Alas! The next step is kitty Prozac, but we're not entirely out of options yet. - Dave

On 05/16/2012 12:54 AM, Chuck Guzis wrote: Peeing...on...the...tubas? Seriously? -- Dave McGuire, AK4HZ New Kensington, PA

On Tuesday (05/15/2012 at 07:41PM +0100), Tony Duell wrote: A friend was just telling the story of how is four year old son climbed up on top of the audio system subwoofer and pee'd into the large screen TV that was operating nearby. Seems like maybe that kid should have had his private parts adjusted/removed too. -- Chris Elmquist

If urine conducts electricity (I have no idea if it does), that really might hurt if it's a CRT. Honestly though, why would you have a sub woofer right next to a TV? I would be afraid of magnet field interfering with the TV if the speakers aren't shielded.

I would be very suprised if urine was a perfect insulator :-). More seirously, I am sure there are some ionic compounds disolved in it. I am not going to test this by urinating on a high votlage point, though ;-) If it was a flat screen (LCD or plasma) TV, then a magnetic field has little effect on the picture. With a CRT, of course, stray magnetic fields defelct the elctron beams jsut as well as the desired field sform the defleciton yoke. -tony

Given all the ionic salts the body dumps via that route, I'd be astonished if it _weren't_ pretty conductive. Possibly excepting someone who's been forcing fluids, but even then it'd surprise me. Of course, the kid on the TV probably wasn't very grounded with respect to the potential shock, unlike the guy on the tractor. (Not that that'd be something I'd bet a kid's life on. Not even close. :-/) /~\ The ASCII Mouse \ / Ribbon Campaign X Against HTML mouse at rodents-montreal.org / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B

On Wed, May 16, 2012 at 10:58:51AM -0700, Christopher Satterfield wrote: It most likely does, since various salts are usually dissolved in it. Depends on the TV. I would expect modern LCD TVs to be most unimpressed by magnetic fields. A CRT - especially a color one - would probably not like it. Quick way to screw up the picture on a CRT color TV: run a magnet over the front of the tube, thus magnetizing the beam mask. The degaussing pulse on power up eventually clears it up again (after a few repetitions). Kind regards, Alex. -- "Opportunity is missed by most people because it is dressed in overalls and looks like work." -- Thomas A. Edison

Seriously? I've never seen a CRT-based colour TV or monitor without a degaussing coil around the CRT flare and a little posistor circuit to produce a decaying AC field at switch-on. Even cheap brands, like Amstrad, had them over here. -tony

Sure (Like fitting a fuse is much cheaper than paying out when the thing catches fire and the house burns down). More seriously, I was only disputing the OP's claim that some colour CRT TVs /monitors were sold without degaussing coils. Can anyone poitn me to a service sheet/schematic for such a set? -tony

As am I. Yes, some monitors degauss with quite a lound 'clang' (I assume it's the shaddowmask. flexing. I've never heard a TV that does that. -tony

In-line gun CRTs (whether used i nTVs or monitors) rarely had an external magnetic shield over the CRT flare, delta gun ones, again both TV and monitor, often did. If you don't rememebr those, start fixing Philips G8s, etc :-) But I've heard this clang on in-line gun nonitors too. And there doesnt' seem to thew that much metal near the degaussing coil to make any noice. But maybe it is just the chassis flexing. No, I always had better things to do than watch TV. I do remewmebr articles, letters, etc in electronics magazines about it. Maybe Everyday Electroncis (long befroe it merged with Practical Electronics [1]) in the mid 1970s. [1] I acutally took inspiration from a circuit in a 1972 issue of Practical Electronics yesterday. I needed a simple distinctive noise-maker and for various reasons I didn't want ot use any ICs. The ;Hooting Owl' in the December 1972 issue was a starting point. I got the circuit down to 4 transistors, 7 resistors, 5 cvapacitors and a transducer. -tony

On 22 May 2012 at 13:53, ben wrote: I wonder if you substitute a memristor or two for the transistors and cvapactiors... --Chuck

It belongs the general class of components the ytpo. Regards ? Rod Smallwood ? -----Original Message----- From: cctech-bounces at classiccmp.org [mailto:cctech-bounces at classiccmp.org] On Behalf Of Tony Duell Sent: 23 May 2012 19:01 To: cctalk at classiccmp.org Subject: Re: CRT degaussing coil (was Re: PDP-11/35 power supply woes) Same as a condenser. And if you're not careful, I'll start giving the values in jars.... -tony

David Riley wrote about color CRTs: No, if a color CRT TV or monitor doesn't have a degaussing coil, it will have color problems every time you physically reorient it with regard to the earth's magnetic field, or any other ambient magnetic field. My friends that did TV repair for a living for many years say that they have *never* seen a commercially sold color CRT TV or monitor that didn't have a built-in degaussing coil, even in the cheapest ones. The degaussing coil in the monitor is relatively weak. If a strong external magnetic field is applied, it may affect the CRT more than the built-in degaussing coil can correct. In that case a more powerful external degaussing coil is required. People that did TV service had those. If a *very* strong external magnetic field is applied, it can permanently warp the shadow mask or aperture grille, in which case no amount of degaussing will fix it. This was sometimes seen when people accidentally discovered that holding magnets near the face of the tube produced interesting visual effects, without realizing that they could permanently damage the tube.

Makes/Models (and pointers to the service sheets)? I am very dubious about this. The internal degaussing coils are not that powerful, and it's easily possible to use a permanent magnet to magnetise the mask so strongly that it is not cured b ya dew degausing cycles. But I would be suprised if there was no internal degaussing at all. No, but turning off a vacuum cleaner under the set (e common cause of accidental magnetisation) probably would be. -tony

On Wednesday (05/16/2012 at 09:19PM +0100), Tony Duell wrote: Ya... some new fangled HDTV thing with probably max of 3.3V. Kids don't know how easy they have it now days... -- Chris Elmquist

[Urinating in TVs, for some strange reason] Mind you, there's probably an SMPSU in there, with a nice live heatsink o nthe shopper transistor... -tony

On 17 May 2012 at 16:28, Chris Elmquist wrote: My late father used to tell about a neighbor who got tired of dogs urinating in his flowerbed. Apparently, he placed a metal plate mounted on a board in the dogs' favorite spot and connected the plate to the hot side of the 115V line--and that cured the problem. --Chuck

In article <20120514204135.GA13870 at mail.loomcom.com>, Seth Morabito <lists at loomcom.com> writes: uk> wrote: . I don't think Hantavirus is a real risk unless your equipment was stored in the desert southwest. -- "The Direct3D Graphics Pipeline" free book <http://tinyurl.com/d3d-pipeline> The Computer Graphics Museum <http://computergraphicsmuseum.org> The Terminals Wiki <http://terminals.classiccmp.org> Legalize Adulthood! (my blog) <http://legalizeadulthood.wordpress.com>

In article <201205142259.q4EMxZZ19044154 at floodgap.com>, Cameron Kaiser <spectre at floodgap.com> writes: My point is that the risk of Hantavirus is vastly overstated compared to say getting in car. <http://www.cdc.gov/hantavirus/surveillance/> Agreed. I just don't think hantavirus is really all that likely. -- "The Direct3D Graphics Pipeline" free book <http://tinyurl.com/d3d-pipeline> The Computer Graphics Museum <http://computergraphicsmuseum.org> The Terminals Wiki <http://terminals.classiccmp.org> Legalize Adulthood! (my blog) <http://legalizeadulthood.wordpress.com>