2215 problem found

A couple of days ago I reported that I’d let the magic smoke out of my Tek 2215 oscilloscope. I was playing around with it last Friday evening, heard some arcing, and then saw a puff of smoke exit the back of the instrument. Oddly enough, the scope still seemed to work, though.

To get some help, I joined the TekScopes Yahoo Group and described my problem. Almost immediately, I got a couple of responses. One guy suggested:

I would take a look at surge suppressor VR901 and line to neutral capacitor C901 at the AC input before the preregulator. Either could have failed without significantly affecting operation of the oscilloscope.

Another said:

I’ll wager that your Tek 2215 has a failing AC-inlet filter. Visit the following site: http://www.vintage-radio.net/forum/showthread.php?t=88137, which discusses failures of Schaffner AC-inlet EMI filters due to a certain type of capacitor manufactured by Rifa…http://www.vintage-radio.net/forum/showthread.php?t=69128

One commentator mentions incompatible rates of expansion between the epoxy encapsulant and the capacitor innards. Another explanation (which I like better) is that microcracks in the encapsulant allow moisture to get into the metallized paper that forms the capacitor’s innards. The innards expand, which applies stress and makes more cracks, and the deposited metallization corrodes and forms conductive compounds with the moisture. Before long…pffffft!

Neither was completely correct, but they both were close. See the photo and schematic below:

2215-problem

2215-problem-schematic

It looks like the problem is indeed a capacitor in the filter section, but my scope does not have a Schaffner AC filter, like they used on some of the earlier (and more expensive) scopes. Instead, this filter is right on the main board. I’m guessing that the 0.068 uF cap shorted out,which led to the resistor burning out.

One odd thing about troubleshooting this problem is that while it looks pretty obvious from the photo, it wasn’t that obvious right off the bat. As you can see from the schematic L925 is not on the board. Instead, it’s mounted in a little housing that sits right above these two components. I had to remove that housing before I could see them.

At any rate, now I just have to find a suitable replacement capacitor and solder it all back together.

Station Notes: June 6 – June 9, 2014

While going through some boxes last Friday, I came across a Heathkit IG-102 signal generator. It was in pretty good shape, so I thought I’d fire it up and see if it was still working. I fired up my Tek 2215 scope and connected to to the IG-102. Unfortunately, I wasn’t getting any output.

I pulled the cover off the signal generator, and was going to start poking around, when I heard some arcing, and then saw a puff of smoke come out the back of the scope. I quickly pulled the scope plug, but of course, the damage had probably already been done.

Today, I finally got around to getting the Torx screwdriver that I needed to take the covers off the Tek. After removing more than a half dozen screws, I was finally able to get the power supply shield off to look for damage. Oddly enough, I couldn’t find any obvious signs of arcing or burnt components, and the scope seems to power up and work.

Even so, I’m hesitant to just button it up and start using it again. There must be a problem in there that’s just waiting to happen. If you have any experience with Tek 2215s, I’d love to hear from you.

Museum ships ahoy!
On Saturday, I operated the Museum Ships Weekend special event. This was a lot of fun. In a couple of hours, I worked 15 of the museum stations, which qualifies me for some kind of certificate.

One of the more interesting contacts was with AC0TX, operating from the SS Grandcamp Memorial. This ship was the site of one of the worst industrial disasters in the U.S. The Grandcamp had docked in Texas City to pick up a load of ammonium nitrate fertilizer.

Just before the longshoremen finished loading the fertilizer, a fire broke out aboard ship. It eventually got so hot that the ammonium nitrate exploded. Hundreds of employees, pedestrians and bystanders were killed. This was truly a disaster.

Alabama QSO Party
Kind of surprisingly, I was the high scorer from Michigan in the 2013 Alabama QSO Party. I don’t think I’m going to repeat this year. Last year, I scored over 2,000 points. This year, I barely broke 200. I guess I spent too much time working the museum ships.

Press release: RF Test Blog

From time to time, I get press releases that might be of interest to radio amateurs. Here’s one.

Making RF measurements can be difficult, especially if you need to make high-precision measurements. Fortunately, most amateur radio operators don’t need to make such measurements, but you can always learn something by reading articles by those who do it for a living…Dan

Agilent Technologies Announces Availablity of RF Test Blog – A Resource for Making Better Measurements

The RF Test Blog is a resource for finding ways to make better RF measurements. With over 10,000 visits since 2013, this popular blog includes information on equipment and measurement techniques that improve accuracy, measurement speed, dynamic range, sensitivity, repeatability, and more. Ben Zarlingo, an applications specialist for Agilent Technologies, shares what he has learned through several decades of working as an electrical engineer in test and measurement.

From my inbox: 100 years of ham radio, spectrum analysis, mesh networks

Celebrating 100 years of ham radioThis month marks the centennial of the American Radio Relay League, the largest ham radio association in the United States. That means it will be a special year for the hundreds who converge annually on W1AW, a small station known as “the mecca of ham radio” in Newington, Conn., to broadcast radio signals across the globe.

Spectrum Analysis Basics - Application Note 150Spectrum Analysis Basics – A Resource Toolkit. Learn about the fundamentals with Agilent’s most popular and recently updated application note, Spectrum Analysis Basics – Application Note 150, which is now paired with a toolkit of app notes, demo videos, web/mobile apps, and related material.

When the Internet Dies, Meet the Meshnet That Survives. The art and technology nonprofit center Eyebeam recently staged a small-scale scenario that mimicked the outage that affected New York after Superstorm Sandy hit in 2012. As part of the drill in Manhattan, a group of New Yorkers scrambled to set up a local network and get vital information as the situation unfolded.

My Dayton purchases

I didn’t buy a lot at Dayton this year, but I did pick up a couple of cool things:

I'm not sure if this cap will actually help me sell more study guides, but it looks cool.

I’m not sure if this cap will actually help me sell more study guides, but it looks cool.

scope-cart

I bought this Tek Model 3 scope cart from a guy in the far reaches of the flea market. Then, I had to roll it through the crumbling asphalt of of the Hara Arena parking lot to get it to my car. As you can see, it was made for a bigger scope, but my 2225 fits nicely on the top shelf, while my bench DMM fits nicely on the shelf that was made to house the plugins. The drawer down below is plenty big for all the DMM and scope probes and accessories that I have. A bonus is a four-outlet power strip on the back of the cart.

 

From my Twitter feed: Trash Talk, Android antenna analzyer, Oinker

DIYEngineering's avatarDIY Engineering @DIYEngineering
Trash Talk – Trash Talk is a prototype for an inexpensive, mesh-networked, democratic public address system. Each … ow.ly/2Gx8z5

 

RadioGeek's avatarKKØHF @RadioGeek
Amateur radio more Space Age than Digital Age gaining popularity reviewjournal.com/life/recreatio… pic.twitter.com/sNti1HxhXD

 

W2MDW's avatarMatthew Williams @W2MDW
Interesting, and fairly cheap antenna analyzer that has Android support. ebay.com/itm/Sark100-HF…

 

DIYEngineering's avatarDIY Engineering @DIYEngineering
Oinker is Twitter for HAMs – Have you ever wanted to send a quick message to your HAM radio buddies over the … ow.ly/2GDOlL

From the trade magazines: Beagle Bone add-ons, DIY 555, using digital scopes

Giant 555Build Your Own Giant 555. This is definitely not practical, but it is fun. It’s educational, too!

BeagleBone: 9 Add-Ons That Power It Past Raspberry Pi. I have a BeagleBone, and while I haven’t played around with it a lot yet, I am liking it. I think it’s a better choice for amateur radio apps than the Raspberry Pi.

How to Use a Digital Oscilloscope. Now that scopes are so cheap, more and more hams have them. They do work differently than analog scopes, and this course will help you use yours better, if you have one.

From my Twitter feed: SDR, spider coils, smart scope

vielmetti's avatarEdward Vielmetti @vielmetti
decoding radio digital modes without a radio, using WebSDR and fldigi /cc @kb6nu #hamr bit.ly/1o678qG

mike_n8wc's avatarMike Comer @mike_n8wc
@kb6nu great info! Back to radio after several years. Enjoy how the internet has enhanced enjoyment of a great radio hobby.

AK6L's avatarRobert Liesenfeld @AK6L
Taught myself PostScript and wrote a template generator for making spider-wound coils. Inspired in part by .@vk2zay. github.com/xunil/spider_c…

DH1TW's avatarTobias @DH1TW
“SmartScope – Kickstarter campaign for an open source 100MS portable oscilloscope #hamradio #diy feedly.com/k/1gr8jQm

LC100 LC meter seems like a good deal

I recently bought an LC100A LC meter from eBay, like the one shown below. If you search eBay, you’ll find them on sale anywhere from $20 to $40. Yesterday, I finally got around to playing with it a little.

lc100

To power the device, you need to supply +5V. It comes with a cable that has a USB connector on one side and a power connector on the other. Obviously, it’s meant to be powered by a USB port. I used a power adapter that I purchased to charge an iPod. It worked great.

As a quick test, I measured the capacitance of ten 0.33 uF caps that I purchased for a project. I first measured the capacitance with the LC100A and then with the fancy-schmancy Keithley 2110 that I purchased about a year ago. Below are the results:

LC100 2110
1  .35 .339
2  .33 .326
3  .33 .318
4  .33 .322
5  .33 .324
6  .34 .328
7  .34 .330
8  .34 .329
9  .34 .330
10  .33 .316

Now, this wasn’t a very scientific test, but I am pleased with the results. I also measured the value of some 330 uH chokes that  I had. They all measured between 315 and 320 uH.

So, all in all, I think this is a good deal for the money. I’m looking forward to using it on some of my projects. The next step is to find a box to put this in. I’m surprised that no one seems to have found one yet.

2014 Tech study guide: Basic repair and testing

The addition of T7D12 is the only change to this section…Dan

The most common test instrument in an amateur radio shack is the multimeter. Multimeters combine into a single instrument the functions of a voltmeter, ohmmeter, and ammeter. Voltage and resistance are two measurements commonly made using a multimeter. (T7D07)

You use a voltmeter to measure electric potential or electromotive force. (T7D01) The correct way to connect a voltmeter to a circuit is in parallel with the circuit. (T7D02) When measuring high voltages with a voltmeter, one precaution you should take is to ensure that the voltmeter and leads are rated for use at the voltages to be measured. (T7D12)

An ohmmeter is the instrument used to measure resistance. (T7D05) When measuring circuit resistance with an ohmmeter ensure that the circuit is not powered. (T7D11) Attempting to measure voltage when using the resistance setting might damage a multimeter. (T7D06) What is probably happening when an ohmmeter, connected across a circuit, initially indicates a low resistance and then shows increasing resistance with time is that the circuit contains a large capacitor. (T7D10)

An ammeter is the instrument used to measure electric current. (T7D04) An ammeter is usually connected to a circuit in series with the circuit. (T7D03)

In addition to knowing how to make electrical measurements, knowing how to solder is an essential skill for amateur radio operators. Rosin-core solder is best for radio and electronic use. (T7D08) A grainy or dull surface is the characteristic appearance of a “cold” solder joint. (T7D09)