At 1:53 PM -0700 1/6/06, Richard wrote: I rather like my Tektronix TDS-220 Oscilloscope, small and very easy to use. I also had a Tek 465B, but gave it away as it wasn't working right, and I needed the space. Of the two, the TDS-220 was definitely nicer. IIRC, it was also Tek's recommended replacement for a 465B. I purchased the 465B used and cheap, I got what I paid for, a scope that didn't work right :^( As a result, I purchased the TDS-220 new, of course it helped that at the time I could afford it. In any case, I always recommend Tek scopes :^) Zane -- -- | Zane H. Healy | UNIX Systems Administrator | | healyzh at aracnet.com (primary) | OpenVMS Enthusiast | | MONK::HEALYZH (DECnet) | Classic Computer Collector | +----------------------------------+----------------------------+ | Empire of the Petal Throne and Traveller Role Playing, | | PDP-10 Emulation and Zane's Computer Museum. | | http://www.aracnet.com/~healyzh/ |

"Dave Dunfield" wrote: I'd second this. I have a TDS-2024 which I like very much. But's overkill for what you are trying to do (I need 4 traces and 200mhz for what I do). The 220 would work fine. I've used most of the TDS line and always find them easy to use and reliable. (but I always lust for the the higher end models ;-) the nice thing about the TDS smaller size scopes is they are really easy to bring into the field. I've spend time under desks at gas stations with mine :-) -brad

At 3:32 PM -0800 1/6/06, Don North wrote: Ouch! Thanks for the warning! Thankfully that's before I bought my TDS-220, but I just double-checked, and I'm in the clear. Zane -- -- | Zane H. Healy | UNIX Systems Administrator | | healyzh at aracnet.com (primary) | OpenVMS Enthusiast | | MONK::HEALYZH (DECnet) | Classic Computer Collector | +----------------------------------+----------------------------+ | Empire of the Petal Throne and Traveller Role Playing, | | PDP-10 Emulation and Zane's Computer Museum. | | http://www.aracnet.com/~healyzh/ |

. the 545B is a good scope, 30Mhz bandwidth (with the right plug-in). I use my "classic" 500 series scopes for a lot of things, mainly because the trigger is very reliable. The 547 (50MHz), with tunnel diode trigger, will trigger on 1GHz pulses - very useful for catching glitches (you don't see the glitch, but you do get a trace "bright-up" to show an event). The 549 analogue storage would be good for a lot of vintage work (anyone in the UK got one they don't want.....) Jim.

I hate t osay this again, but the most important tool for debugging is a brain :-). I feel that a good engineer/hacker armed with an LED+resistor logic probe is likely to do rather better than an idoit or novice (these are NOT THE DAME THING!) armed with the most expensive 'socpe and analyser available. As to test gear, the main instruments I think you need are : 1) A multimeter. Digital or analogue, the choice is yours (I have, and use, both). It is rare to need to make accurate measurements in classic computer work, so analogue is OK, and in fact better when you want to 'peak' the voltage at some test point or something like that. If you go digital, I would certainly consider a Fluke. A Very useful feature is a continuity buzzer, a beeper that sounds if the resistance between the probes is less than a certain, fixed, value. But make sure it repsonds quickly (and doesn't, for example, take the time for the autoranging system to work and then for the instrument to take a couple of samples). You will want, quite often, to clip one probe onto, say, a wire at one end of a cable, and run the other probe down the pins at the other end. You don't want to have to stop and wait on each pin. 2) A logic probe. HP have made some nice ones over the years (I've seen them on E-overpay from time to time). Actually, a cheap one (Radio Shack used to sell them) is all you need for most work. This is very useful for fioding a signal that's stuck high, or something like that. If you are a rich enthusiast, consider attempting to find an HP 'Advanced Logic Probe' aka LogicDart. It's a handheld thing that acts as a digital voltmeter, frequency meter, logic probe and 3-channel logic analyser. A word of warning, if you ever use one of these you will be 'hooked'.... 3) A 'scope. I would always consider Tektronix here. Actually, I rarely use a 'scope, other than for disk drive alignments and PSU repairs, neither of which need a particularly highly spec'ed instrument. Mine is a very old, valved, Tektronix 555 with an assortment of plug-ins. If I was buying now, I'd consider getting a second-hand 7000 series or 460 series. Nothing much more recent, IMHO Tektronix went way downhill when they stopped putting schematics in the user manual. A typical spec for most classic computer work would be dual trace, at least 20MHz. External trigger -- and a good trigger system -- is essential, if you can't keep the trace still you can't measure from it. Delayed timebase (or a second timebase which can be used as a delay) is very useful. Storage is useful, but by no means essenital. 4) A logic analyser. Tektronix made a reasonable one as a plug-in for the 7000-series 'scopes. HP and Gould also made analysers, either stand-alone or as plug-ins for 'scopes. I would say at least 50MHz and preferably 100MHz is fine for classic computers. 16 channels is enough (you can get away with fewer if you have to). Make sure you get the probes/pods with the instrument, they are _hell_ to find on their own and often get lost/separated from the unit. The ability to transfer the captured data to another computer for more analysis (often via an RS232 or GPIB port) is very useful I have several analysers, but the main one is a Gould K100D (I think the manual is on Bitsavers). 16 channel, 100MHz. I have never needed anything more 5) An EPROM Emulator. I put this under test equipment because it's very useful to replace the ROMs in a system with an emulator containing a little test program (even something as simple as a jump to itself), and see what happens. I built my own, they are not complicated. -tony

On Friday 06 January 2006 06:13 pm, Dave Dunfield wrote: I forget where I ran across it on the 'net, but there was a design out there where the tone would change somewhat for differing low values of resistance, to the point where you could find that aspect of it real useful. I keep thinking I'm going to get around to building one of those one of these days.. <...> Got one here that was back when "Global Specialites" was still in their earlier incarnation as "Continental Specialties", if I'm remembering right. And another one I got at Yamaha that also gives an audible indication, which I thought was pretty nifty when I saw it demonstrated, though I haven't given it as much use as I thought I would. <...> I need to build one of these sometime. In the meantime, jamming a NOP on the data bus when practical is often useful. I troubleshot a z80-based board that way by removing one buffer chip and tack-soldering a bit of wire across the bus pins, and watched the address lines cycle through the address space. A bit more difficult with some other chips, but... I have one that I'm waiting to put into a box, 15-0-15A. What sort of rates do you find most useful? Sounds to me like this would be easy enough to build. -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, a critter that can be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin

Yes. It's interesting that the design spec for the HP LogicDart specified a repsonse time for the continuity beeper (I have an idea it was a few ms), so you could use it i n the way I described. HP engineers found a 'slow' continuity tester to be very irritating too. I am not sure what my Fluke uses as the threshold, it's less than that, I think, but still fixed. A variable setting would be very useful. For example, at the moment, I am looking at a PCB which has series termination resistors of 220 Ohms in series with some of the signals. It's SMD, components on both sides, and 80 pin PQFP chips. Tracing out signals would be a lot easier if I could take 220 Ohms to be 'continuity', and then later figure out where the termination resistors are. At this point I just want to know that a given pin goes to the CPU Wr/ line, not worrying about a series resistor. I should get round to making something like that.... A freind of mine had a nasty problem with a cheap DMM. The range switch wenter intermittant (without him realising it), and it claimed the input voltage was 0, when in fact it was full mains (he was working on some mains wiring, and wanted to check it was dead. Yes, I know the _correct_ procedure is to check with it live, check again when you've isolated it, then check the meter on a seperate live source to guard against this, but how many people do that?). After being thrown across the room by the shock, he went out and bought a Fluke. They're cheaper than funerals :-). He could only afford the cheapest model, which didn't even have current ranges, but as he said, current is the least-often measured quantity. Voltage and resistance the ranges I (and most people I know) use all the time. I've never found this to be a real problem. If you're seriously worried about the voltages, then use the 'scope. The logic probe is a useful instrument to look for sillies, like a data pin shorted to ground or something. It'll also tell you if a memory chip is ever being enabled, if the clocks are running, and so on It;'s not common for a chip to fail in a way that it gives illegal output voltagess, although I have had 74Hxxx parts do this. If you know what your instrument is doing, you can do a lot with a cheap logic probe. Most logic analysers have one threshold. Anything over it is a '1', anything under it is a '0'. The LpgicDart is good in that it has 0, 1, illegal states for the inputs, you set 2 thresholds (it has pre-set ones for TTL, 5V CMOS, 3.3V CMOS, ECL). I use a 'scope a lot less than I should, mainly because the 555 is rather hard to move around. It's a matter of taking the problem to the 'scope rather than the reverse. I think it's what you're used to using. I prefer the analyser, since I can look at many signals (an entire microcode address bus, for example) at once. The triggering on aq good analyser is more versatile too. But if you prefer the 'scope, use it.. Absolutely. Read the manual (old HP and Tek came with very fine manuals that are well worth reading), play with the instrument. Use it on stuff where you know what you should be seeing. Misuse it too. I don't mean applying the mains to the input of the logic analyser. I mean things like on a DSO, applying a signal of a higher frequency than it claims to handle. What does it do. If it aliases it down in to the passband, beware. It'll do this sometime 'for real' and you will get confused (yes, I have seen a DSO that does this sort of nasty, no I wouldn't want to use it!). Yep. Mine is the Velleman kit one. 30V, 8A continuous (10A for 20 minutes). It's a really old-fasioned design, using 723 regulator chips and 5 trnasiostor in parallel (with emitter resistors, of course), 7107s (or do I mean 7106s, the one that drives LEDs) for the voltmeter and ammeter. But it does the job. I als have a homebrew 5V, 1A supply (useful to power a few TTL chips when I have the larger supply in use for, say, running the motors in whatever I'm working on) and a Heathkit 50V, 1A one that sometimes gets pressed into service. Ah yes... The former to save expensive blow-ups when rebuilding SMPSUs, amongst other things... And of course dummy load resistors/bulbs for testing PSUs before connecting the logic board to them. -tony

Nor would I, actually. The 'correct' procedure for high voltages (or so I am told) is to measure the voltage with the circuit live (and make sure you get a reading), then turn off the power/pull the fuse and check again (make sure you get zero), and then to check the meter again on a similar high voltage source to make sure you get a reading there (just in case the meter decides to fail at the wrong moment). Even then, with mains, I'd touch it with the back of my hand first, so if it is still live it'll throw me off (I hope). Incidetnally, on most DMMs (including my Fluke), the fuse is for the current ranges only. The voltage and resistance ranges work fine with the fuse blown. But of course there are plenty of other faults that can cause a zero reading with a voltage on the input. Heck, even test leads can go open-circuit. Something I was taught early on (in a different context, but it applies to electronics too). 'It is much easier to make measurements than to know what you are measuring'. With most 'socpes, if you touch the probe on a point in your circuit and twiddle the knobs you will get _some kind of trace_. It may well mot be any use in actually tracking down the fault, though. It may not even be a true representation of the signal at that point. -tony

Right... And as I said, even if the fuse wouldn't cause the voltage ranges to fail, plenty of other things could, starting with the leads themselves. NEVER assume the meter is working if your life could depend on it. Check it on a known voltage source of the same sort of voltage. Yep, I always check the PSU (prefereably on dummy load) first, too. So many problems are traced to PSU problems. I once spent a long time doing battle with the Unibus logic in a PDP11/45, the fault turned out to be that the PSU was sitting at 4.2V( should have been 5V, of course). The darn machine would work most of the time, and then do some really odd things. Having been brought up on analogue meters where you have to set the zero on the resistance range by hand, I do this too. Force of habit. Just as, if I'm using the continuity beeper in my DMM, I tap the probes together when I've selected it (just to check I've pressed the right buttons). And then tap them together every so often thereafter, just to make sure it's still working. It's a releated statement, not directly 'for' you, but on that side of things, and I agree with what you're saying My point is that it's very easy to get readings. They may or may not be meaningful, they may or may not help with the problem you'r trying to solve. Experience (and knowing what you expect) will help you to take meaninful readings, and to interpret them correctly. If you get a reading that disagrees with what you expect, then there are 2 posibilities. Either you've not measured what you thought you measured, or there is a fault. You then need to investigate which (and not to assume the second always!). If the rteading agrees with what you expect it's likely everything is OK (yes, it could be a fault _and_ a mismeasurement, but that's very unlikely). Oh sure. Many times there's _something_ on the testpoint, bnt it's not what it should be. -tony

On 1/7/2006 at 4:35 PM Ethan Dicks wrote: Was that the little hand-held logic analyzer that Agilent came out with and then, almost at the same time, discontinued? It looked like a very handly little gizmo. Why did HP/Agilent drop them? I've seen some inexpensive USB logic analyzers (USB pods, I think) that might be worthwhile having. Cheers, Chuck

In message <m1Ev2mD-000IyIC at p850ug1> ard at p850ug1.demon.co.uk (Tony Duell) wrote: Yeah, LED+resistor debugging is fun. Downclock the CPU to a few Hz and watch the data bits fly by :) Avoid the cheap little "pocket" meters though. If it isn't a Fluke, it's likely to be horrendously inaccurate at best. I once had a cheapie DMM that was about 1.5V out on the 3V scale, and 5V out on the 30V scale. Fluke 25 and 27 ruggedised DMMs are starting to appear on the surplus market; seems most of them are ex-military stock. They're pretty rugged, but also rather heavy. I've got a Fluke 25 that's been dropped a fair few times, and still works perfectly. I've also got a Solartron 7150plus. Very nice bench DMM, but watch out for the power line filter module. The capacitors inside are getting old and tend to go bang, leaving a thick coating of soot on virtually all the power supply circuit when they blow. Schaffner still sell them (via RS), but they're ?45 a throw IIRC. You could replace the capacitors, but good luck getting the case open. *drool* Or if you don't want to buy one, design your own. I've got (somewhere) the schematics for a 20MHz 8-channel logic analyser/logic probe based on a Gameboy. I still need to write the software, but the logic side of things looks OK. The 466 is a nice little scope. 100MHz, dual channel, dual timebase and analogue storage. Not as nice as a DSO, but a hell of a lot cheaper, and just as usable. The trace is a little fuzzy though, thanks in part to the storage CRT. Still perfectly usable, though, and the storage function makes it easier to get photos off the screen. HP 1651Bs are very nice - 32 channels, but make sure it comes with the pods and grabbers! Agilent still sell pod/grabber kits, but they charge insane amounts for them - upwards of $400. On e-OverPay, they're hard to find at the best of times. I've got two pods, two of the woven pod-to-analyser cables, a pack of grabbers (only enough for one pod though) and a bag of replacement probe cables. System disks can be rebuilt with a DOS PC and a copy of ImageDisk (it's actualy faster than LIFUTIL). As long as the machine passes the powerup self-test, it's probably fine. The 1651B can do this, but I haven't made an attempt to decode the acquisition data that it passes over GPIB. Inverse Assemblers are also fun to play with - I've got one that I threw together for the 6502, and IIRC Jim Kearney has done one for the 8008. I had a Gould analogue oscilloscope at one point - an OS1100A. Very nice machine, 30MHz dual-trace with delay-sweep. Lovely little machine. A little sensitive to cold though - if the temperature goes below 10 C, it won't even power up. Same here - there's nothing like the sense of achievement you get when building your own test equipment. Plus the fact that having designed and built it, you also have all the information you need to repair it. I've put full schematics for my EPROM emulator online - I actually entered it into the PICLIST.com design contest last year. <http://www.piclist.com/images/boards/EPROMemuMk2index.htm> The Mk1, BTW, was a very fussy parallel-port thing that emulated a printer. It had the annoying quirk of running fine on my laptop, but refusing to work with anything else. Hence the swap to RS-232 on the Mk2. Yes, there's a PICmicro running it, but the source code is available and pretty well commented. -- Phil. | Acorn RiscPC600 SA220 64MB+6GB 100baseT philpem at dsl.pipex.com | Athlon64 3200+ A8VDeluxe R2 512MB+100GB http://www.philpem.me.uk/ | Panasonic CF-25 Mk.2 Toughbook ... I will not steal this tagline, it eez scratched.

And now, I'm going to post the *correct* URL... *sigh*. 100 lines, "I will always check the URLs in my messages *before* I post them" :) Thanks to Roy Tellason for pointing out my stupid mistake... -- Phil. | Acorn RiscPC600 SA220 64MB+6GB 100baseT philpem at dsl.pipex.com | Athlon64 3200+ A8VDeluxe R2 512MB+100GB http://www.philpem.me.uk/ | Panasonic CF-25 Mk.2 Toughbook ... Things are not as bad as they seem - they're worse

Ah yes, fine instruments. I have an old Model 8 (I can't remember the version), a DA114 (early digital meter) and, of course, a Valve Characteristic Meter Mk 4. For the people across the Pond, AVO, of course, comes from the initals of Amps Volts, Ohms. It was the brand name of one of the first multimeters in the UK (the 'Universal AVOmeter' was around before WW2 I think, 'Universal' meaning it had AC and DC ranges). Amongst older engineers and scientists, 'AVO' is used as a generic name for any multimeter over here. So would I. And an HP3468. I think that's the model, the one with an HPIL interface on it. I have an HP3421 logger which is very nice, but you need a computer/calculator to control it. It has no front panel controls or display. -tony

From: "Tony Duell" <ard at p850ug1.demon.co.uk> AVO was a trade mark of "The Automatic Coil Winder and Electrical Company", who made measuring instruments and coil winders. The instruments included meters, valve testers, signal generators, transistor testers and LCR bridges. I have a few manuals for meters and coil winders on my site: www.g1jbg.co.uk/service.htm if anyone needs them. Jim.

http://www.peakelec.co.uk/acatalog/jz_lcr40.html Is a nifty, affordable piece of kit. I use one for L & C measurements on home brew coils ... With some nifty cousins. Martin -----Original Message----- From: cctalk-bounces at classiccmp.org [mailto:cctalk-bounces at classiccmp.org]On Behalf Of Roy J. Tellason Sent: 11 January 2006 21:28 To: General Discussion: On-Topic and Off-Topic Posts Subject: Re: Recommended logic analyzer/scope tools? On Tuesday 10 January 2006 04:43 pm, Jim Beacon wrote: It's an interesting list, there. I didn't see much on the main page that was of immediate interest but on http://www.g1jbg.co.uk/manuals2.htm I see a thing or two. In particular, this one: Heathkit CL-1 Crystal calibrator And on this one: Wayne Kerr B221 Universal Bridge I'm wondering if that's one of those LCR bridges you mention? I'm intersted in something of the sort, mostly as a means of measuring inductance, a capability currently lacking from my test equipment. -- Member of the toughest, meanest, deadliest, most unrelenting -- and ablest -- form of life in this section of space, a critter that can be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters" - Information is more dangerous than cannon to a society ruled by lies. --James M Dakin