Basic electronics lab questions. - Page 1
Forum section: electronics / beginners

author: TK0130
author_rank: Contributor
timestamp: January 30, 2017, 02:10:57 am
content: So to start off: I am a jr in college planning to study electrical engineering (Possibly a bit of computer science as well) and have been tinkering with electronics for at least 5 years now and have some basic questions about the lab equipment: (Hopefully it is correct to group multiple questions into one topic)What test equipment i have so far:100mhz dual channel tektronix scopeFluke 117 (No mA range)3x Genaric inexpensive multimeter used for secondary/unimportant measurements.HP laboratory power supply. 0-39.99v 2A 40Wratedmax. has current limiting(Tested to 1% at 40v but under 20v it is spot on. $5 at a hamfest)LM317/377 based 30V 2A dual rail linear supply (almost done building, Working on current limiting. finding 30+v transformers isn't easy.)USAF frequency counter 50mhz. ($5, really only on my bench because it has a 9 digit nixie display)(re-capped PSU and fan replacement. ) It is WAY out of spec but has an external 1mhz input I plan to use someday.Now for my questions:Question #1:I have a tektronix 434 storage oscilloscope that the trigger doesn't work. Tracked it down to a quad transistor dip and replaced it but it still didn't work. So i followed the circuit further (Service manuals from tektronix are amazing!) and there is a tunnel diode missing completely from the board. (Pulled to fix another scope?) Is it worth trying to get an almost $15-$40 NOS replacement to a 24mhz scope (Assuming this is the only problem left!) or is there a modern replacement? (If i am going to replace it I want to do so with a modern part, but from what i read that will be more trouble than it is worth)(snippet from the service manual attached It is CR644. it is supposed to be a 1n3716)Or am I better off starting to save for a digital or areputableUSB scope? I have had many a situation where i wanted to single shot capture something.Question #2:The other tool that I have wanted on many an occasion is a function generator. I have some old XR function generator ICs that would be fun to use however they (And every other function generator ic) are obsolete so i don't really want to use them in a piece of equipment i am going to build and use for a while.So the two options as i see it are: A micro-controller with a DAC or discrete components. The discrete would be fun but less practical (And more time consuming) So i plan to do it SMD with a micro. (I have made a few PCBs before, soldering 0402 and SOT-23 isn't much fun on a radioshack iron)Is a crystal good enough accuracy for general use or do I need better? Can i just have an opamp as the output? What other stuff should it have? dual channel? max voltage?Question #3:Is there any other equipment that I should look out for? I couldn't think of much else.

author: Basileus
author_rank: Regular Contributor
timestamp: January 30, 2017, 01:06:30 pm
content: Quote from: TK0130 on January 30, 2017, 02:10:57 am3If you didnt, i would suggest you to check out the two videos dave made about setting up an electronics lab on the EEVblog yt channel. They are pretty good.Imho, dont think "what do i need next". This isnt talking about buying shoes, its about buying TOOLS, which allow you to do what you wish to do or do it better/faster. Get what you need when you need it. It also spreads the costs on a larger time window.I know myself that getting new gear is compelling, but i... erm... you, must resist the temptation

author: danadak
author_rank: Super Contributor
timestamp: January 30, 2017, 01:25:04 pm
content: If you look on Ebay there are a number of low cost DDS based f()generators.Logic analyzer, these work pretty good, but do not have overvoltage protectionon inputs, That you can do pretty easily with diode/R network/pin.This link just one of many -http://www.ebay.com/itm/24MHz-8-Channel-USB-Logic-Analyzer-8-CH-Logic-Analyzer-for-Arduino-MCU-vv/272455617430?_trksid=p2045573.c100505.m3226&_trkparms=aid%3D555014%26algo%3DPL.DEFAULT%26ao%3D1%26asc%3D20150817211623%26meid%3Deb2239fc6a424b669682e5ddd64732d3%26pid%3D100505%26rk%3D1%26rkt%3D1%26Scope. I do not know your financial situation, one of the best buys is theRigol DS1054Z. Its a scope that will be useful to you for a long time forgeneral purpose work. And people have been hacking it to 100 Mhz witha simple procedure.If thats out of reach look for the early DSOs on Ebay. Some of the Tek TDS seriesfall < $ 200.Regards, Dana.

author: rstofer
author_rank: Super Contributor
timestamp: January 30, 2017, 06:53:21 pm
content: There are so many alternatives, it is hard to know where to start. If you need a function generator to make common waveforms at lower frequencies, the FG085 is an interesting choice:https://www.amazon.com/Function-Generator-DIY-Tech-FG085/dp/B00C5UO8U6Before you blow it off, you might want to read through the manual. It got my attention:http://www.jyetech.com/Products/085/Manual_085F.pdfIt is NOT a full featured Arbitrary Waveform Generator (AWG) but if you just need signals for small project, it's an attractive alternative. I like mine! And it will even do a very short arbitrary waveform (256 points).A feature of the modern DSO (like the Rigol DS1054Z, among many others) is the single shot capability. You can trigger on a single event and get a stable display. Of course, advanced triggering, measurements and decoding come along in the deal. I'm happy with mine. Now I just have to RTFM to see what it will do.However, within it's specs, the Digilent Analog Discovery (AD) is an attractive alternative. It has a dual channel scope, a dual channel AWG, 16 bits of binary input/output with Logic Analyzer capability including decoding. It also has +-5V supplies and in version 2, they are capable of a decent amount of current. This thing is really a 'lab in a box'. Again, I like mine!http://store.digilentinc.com/analog-discovery-2-100msps-usb-oscilloscope-logic-analyzer-and-variable-power-supply/You can download and install the Waveforms software and run the demo to get a sense of the capabilities.http://store.digilentinc.com/waveforms-2015-download-only/Pay careful attention to the capabilities before you blow past this thing. It is amazing! I might want to provide external power to my projects if they had high current or high voltage requirements but just about everything else can be handled by the AD.After decades of messing around with this stuff, I still don't have a stand-alone AWG. I'm looking at the Siglent SDG2042X but I just can't come up with the justification. I have the AD and the FG085 plus I can make any digital scheme I want with an FPGA. I can't convince myself to spend the money. Maybe...There is also the Test Equipment subforum which focuses on equipment.Question 1: Yes, fix the scope. Even if you get a DSO, an older analog scope is handy to haveQuestion 2: Discussed above and yes, for all practical purposes, a crystal oscillator is 'good enough'. If you need better, you will already know about it.Question 3: There is always more equipment. Spectrum Analyzer, Logic Analyzer, Bench DMM, and so on. When you can't get along without it, buy it!A 24 MHz scope will do a lot but... You need about 5 to 7 harmonics to reproduce a decent looking square wave. So, somewhere around 3 MHz is all it's really good for. For square waves... Sine waves are no problem. That's why the DS1054Z, after unlocking, at 100 MHz is pretty much an entry level scope. I have had an older Tek 485 (350 MHz) for the last 13 years but I added the 1054 to get the extra channels and decoding. The 485 sits under the bench and ready to use if I should happen to be looking at higher frequencies.Well, this should keep you thinking for a while.

author: james_s
author_rank: Super Contributor
timestamp: January 30, 2017, 07:27:31 pm
content: Personally I would fix the scope, but then I have a soft spot for older Tek gear and can't bring myself to scrap one that is in decent shape. I would probably also be looking for another more capable scope but really it depends on what you plan to do. There are a lot of applications where a relatively low bandwidth scope is still just fine. Personally my favorite scope is my old Tek 465b, it's nearly as old as I am, it's an analog instrument so there are some things it can't do, but it's a joy to use and has never let me down. Personally I like the instantaneous response and "real" feeling of an analog scope, you have to spend a lot on a high end DPO to come close to providing that feel. I also have an older Bitscope DSO that I got a good deal on, it's handy for when I need to capture an event or analyze a non-repeating waveform, I tend to use it for digital stuff but when I'm working on audio gear I pull out the 465.Anyway to get to the point, decide what sort of projects you want to work on, and then look into what sort of test equipment will make your life easier. It's always fun to pick up more gear, but there's no sense in spending money on esoteric equipment that collects dust, or buying high end gear and then only ever just scratching the surface of what it can do.

author: TK0130
author_rank: Contributor
timestamp: January 31, 2017, 03:00:36 am
content: Thank you! I didn't really expect that much feedback.I didn't really feel like I needed any other equipment other than a way to capture waveforms and a function gen.I just repaired the PCB on a windows 10 tablet i got for $25 so once i sell it maybe i can get an entry level digital scope.It looks like you can get a 100mhz dual channel digital scope for under $200 on e-bay.I thought about a good USB scope but I like a dedicated piece of lab equipment. The analog discovery does do a lot but it is still rather expensive considering i would live in constant fear of killing. (+/-25v?) as I like the ability to go upwards of 30-50V for a lot of stuff i repair.As i said in my first post i have a 100mhz dual channel analog scope, It does most of what i need but not everything.The issue with fixing the tektronix is my skill in diagnosing the problem, The hope is that the missing tunnel diode is the only problem remaining as i don't really want to waste money replacing parts and then not ending up with a working product.The nice thing is the prior owner kept the original service manual, probes and several replacement transistors with it. (Brand new in box) There are also some rectifier diodes as well as some flux on the diodes on the board so they have been replaced.Is there any way i can test functionality of the rest of the board without replacing that tunnel diode? If not is there any way I can make a replacement using modern parts?(I would rather not use obsolete parts if possible/economical.)

author: rstofer
author_rank: Super Contributor
timestamp: January 31, 2017, 03:53:27 am
content: Quote from: TK0130 on January 31, 2017, 03:00:36 amUse a 10x probe on the BNC Adapter Board:http://store.digilentinc.com/bnc-adapter-board-for-the-analog-discovery/You would want to do this even with a DSO or analog scope. 1x probes aren't used much.

author: julian1
author_rank: Frequent Contributor
timestamp: January 31, 2017, 05:54:28 am
content: > Is there any other equipment that I should look out for?Don't overlook a humble Transistor tester, they're great value,https://www.google.com.au/search?q=GM328R&newwindow=1&source=lnms&tbm=ischBasic parameters of Bjts, mosfets, diodes, zeners, caps, inductors etc. Also works for sot-23.

author: julian1
author_rank: Frequent Contributor
timestamp: January 31, 2017, 05:57:44 am
content: QuoteIf he pulled the tunnel diodes, but left you the service manual, then I'm not sure how nice he really is!

author: james_s
author_rank: Super Contributor
timestamp: January 31, 2017, 08:10:34 am
content: Is there a way to approximate a tunnel diode well enough to determine that the rest of the circuit is more or less functional? Those are something that are a bit before my time and I'm not entirely familiar with how they work.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: January 31, 2017, 10:49:20 am
content: http://excelworks.info/Tek.htmlhttp://www.ebay.com/itm/4x1I304A-GI304A-Military-USSR-Germainium-Fast-Switching-Tunnel-Diode-/192056709825?hash=item2cb778d2c1:g:VYwAAOSwk1JWcYK0

author: David Hess
author_rank: Super Contributor
timestamp: January 31, 2017, 11:57:29 pm
content: Quote from: james_s on January 31, 2017, 08:10:34 amThere is a three transistor substitute which can be used if one side of the tunnel diode is held at a fixed potential like in this case but performance can never be as good.Quote from: rstofer on January 30, 2017, 06:53:21 pmWhile they are not as convenient or capable, this is also a feature of old analog storage oscilloscopes like the Tektronix 434 being discussed.

author: EEVblog
author_rank: Unknown
timestamp: February 01, 2017, 05:24:53 am
content: Quote from: TK0130 on January 30, 2017, 02:10:57 amThere is nothing better or more valuable than being able to capture a single shot event.Save up for that.

author: james_s
author_rank: Super Contributor
timestamp: February 01, 2017, 06:00:14 am
content: Quote from: EEVblog on February 01, 2017, 05:24:53 amI would say it depends on what you're doing. There are times when capturing a single shot event is essential and nothing else will do. Plenty of other times that isn't necessary and it's more useful to just have a peek at what is going on in real time.At any rate the old Tek 434 he has can capture a single shot event, not as well as a fancy modern DSO but sometimes the best equipment is the stuff that's already in your hands and paid for. It all depends on the situation, primarily the budget and whether or not the equipment is being used to earn money or just having fun.

author: David Hess
author_rank: Super Contributor
timestamp: February 01, 2017, 03:50:46 pm
content: Quote from: james_s on February 01, 2017, 06:00:14 amOne of the reasons I bought a 7834 is because it can capture faster single shot events for less cost than an inexpensive 100 MHz DSO and it has much faster effective acquisition rate of 250k to 500k waveforms per second to capture rare glitches. The 434 has a bistable storage CRT so its storage is not very fast and that is why its bandwidth is low; it could not take advantage of high bandwidth anyway. But it is still much faster than necessary to diagnose common but difficult things like power supply startup and sequencing problems.For a number of reasons however, I would not recommend an analog storage oscilloscope in place of a digital storage oscilloscope unless you already have one like in this case and tunnel diode repairs are one of the easier things to deal with.

author: rstofer
author_rank: Super Contributor
timestamp: February 01, 2017, 05:27:50 pm
content: Quote from: james_s on February 01, 2017, 06:00:14 amThe OP's 434 can capture and store ONLY if he can get it working. Missing, obsolete, parts is not a good omen. Perhaps the eBay Tunnel Diodes will work; it's worth a try for the cost. Otherwise, it's off to the electronics recycler... Or, buy another for parts and hope that somebody hasn't already cannibalized it. At some point, a decision will have to be made. There's a "For Parts" 434 on eBay right now for $129 + $30 shipping.I have one of the old Tek 4006-1 terminals that uses a similar storage technology. I bought it back around '78 and I haven't used it lately (like the last 35 years) but I suspect it still works. I had a lot of fun with UCSD Pascal Turtle Graphics and this terminal - way back when.

author: james_s
author_rank: Super Contributor
timestamp: February 01, 2017, 07:57:53 pm
content: Well hopefully if he decides not to repair it, he will offer it to someone else rather than simply recycle it. If the CRT is good then it has value, that's about the only truly irreplaceable consumable part.Those old Tek storage terminals are amazing. They are sought after collectible retro tech.

author: David Hess
author_rank: Super Contributor
timestamp: February 01, 2017, 08:32:14 pm
content: Quote from: rstofer on February 01, 2017, 05:27:50 pmThat is the dilemma. With experience and another oscilloscope to help with diagnosis and calibration, restoring the 434 will likely be an easy task. Otherwise a novice is likely to find themselves lost and wasting enough time that new but cheap DSO is a better bargain.If the CRT, X-Y mode, and the sweep works, then the tunnel diodes were probably pulled to repair some other instrument. However I have read that the 434 is a difficult oscilloscope to work on because of mechanical access issues.

author: TK0130
author_rank: Contributor
timestamp: February 03, 2017, 04:44:57 pm
content: Most of the time just a good multimeter or even an analog scope is perfect, however there are times where it is impossibly to fix something without the ability to single shot capture.Agreed.The x-y mode and sweep works it is just that it won't auto trigger. (It i put it in single shot capture and rapidly move the pot the noise it it will trigger the scope and i will get a single sweep)The tunnel diode had to be de-soldered to be removed. I suspect it was pulled as a replacement part.If i knew for sure it was the only problem replacing it would be a no-brainer.Quote from: David Hess on February 01, 2017, 08:32:14 pmYou said it, It is hard to get at multiple areas of the circuit (Compared to my other thee analogs) AND ALL THE SCREWS ARE ALUMINUM! Why would anyone use non-magnetic screws!?! It is just a pain.You also cannot pull the horizontal/sweep board without taking half the scope apart.It is funny that the tunnel diode is just going directly from the 5v rail to that point in the circuit that is the signal just offset by ~4.2v.Thanks for all the advice, (I even got Mr, Jones's input) I think I will hold onto the old 434 and hope to find a replacement part at a hamfest/historical society and start saving up for a digital scope.No way will I be getting rid of it, I love old tech. Amazing to think that this thing was routed by hand, designed by hand and built mostly by hand. And to have it calibrated only cost $300 (converted for inflation) If shipping wasn't so crazy from the US I would send it in for a tear-down/repair.Looks like I can get some name brand 100mhz dual channel digital scopes for under $220 (usd) used on e-bay. Should I save for that or keep saving for a newer one? I have run into a very few cases where i need to watch 3-4 points at once.Also on a more current topic: I had my original tektronix probe break a few months ago. I have a cheap Chinese probe and an unlabeled probe that came with it, Where do you guys get probes?

author: vpetrog
author_rank: Contributor
timestamp: February 03, 2017, 05:44:07 pm
content: As i' m currently designing an low cost AWG i should advice not to use a uC with DAC, even in parallel it's not fast enough. (Except if you want signals of 10Khz at most, but i highly doubt )

author: David Hess
author_rank: Super Contributor
timestamp: February 03, 2017, 06:18:22 pm
content: Quote from: TK0130 on February 03, 2017, 04:44:57 pmUsually removal of the trigger tunnel diode results in very low or no trigger sensitivity and/or a screwed up operating point for other circuits. In this case, replacing the missing CR644 with a resistor with a value of about 86 ohms to restore the operating point of the driving circuits might restore some operation. The real trigger tunnel diode is CR678 shown on schematic 6; is it missing also?QuoteWhat I remember reading is that the 434 is difficult to work on for all of the reasons you identify but that they do perform well as a bistable storage oscilloscope.QuoteThe Russian germanium tunnel diodes of the appropriate operating current (4.7mA for both diodes?) should be direct replacements; higher capacitance diodes will be slower but I doubt that would be a problem in this case. The other Russian tunnel diodes can be used if the operating current in the circuit is adjusted but this will not be trivial to do.QuoteI definitely would not pay $100s of dollars to have a 434 rebuilt and/or calibrated; better to buy something new or at least modern. Several 434s could be bought for parts or even working one for that much or something better like a 2230 or 2232 analog/DSO.QuoteI buy cheap Chinese probes off of Ebay. The common switchable x1/x10 100 MHz probes are not mechanically reliable but the high bandwidth Texas x10 probes work well; among others, Keystone/Agilent uses them.

author: james_s
author_rank: Super Contributor
timestamp: February 03, 2017, 07:06:28 pm
content: It's not always about the money. More than once I've spent more to refurbish something than it was worth, simply because I knew what was wrong with it and wanted to save it. I admire the engineering that went into this stuff and look at it as a work of art.

author: TK0130
author_rank: Contributor
timestamp: February 05, 2017, 04:08:26 am
content: Quote from: David Hess on February 03, 2017, 06:18:22 pmThe other tunnel diode is there. I shall try tossing in a 68 ohm resistor tomorrow. (Whoever desoldered this one added a TON of solder and flux when they did do it...)If i can get this one working to single shot capture slower waveforms I can use it until I feel the need to get something better.(faster)

author: David Hess
author_rank: Super Contributor
timestamp: February 05, 2017, 04:36:23 am
content: Quote from: TK0130 on February 05, 2017, 04:08:26 am25 MHz is fast for a bistable storage oscilloscope.68 ohms is just a rough value; experiment with the exact value for best performance. Triggering will work best on square waves.

author: Messtechniker
author_rank: Frequent Contributor
timestamp: February 05, 2017, 07:18:49 am
content: Quote from: TK0130 on January 30, 2017, 02:10:57 amReading this, I'd go for a very good soldering iron before spending any money onanything else. Yes, it will be expensive but it will be a lifetime investment.Yours Messtechniker

author: james_s
author_rank: Super Contributor
timestamp: February 05, 2017, 07:32:12 pm
content: You don't have to spend a lot on a good soldering iron, one of my favorites is still the old Hakko 936, those were only about $100 and perform very well.Something I've found even more valuable is a good *desoldering* iron, my Hakko 808 is one of the best tools I've ever bought. I do a lot of repair work on older through-hole gear though.