A Guide to buying Tektronix 11000 Series Oscilloscopes

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Please scroll to the bottom to see updates: February 27, 2007

BANDWIDTH TABLE ADDED AT END

There seems to be an upsurge lately in buying Tektronix 11000 series mainframes, DSA mainframes, and 11000 series plugins. Perhaps many out there are beginning to realize the power built into these scopes. Or perhaps there are just a few of us, trying to get working units. I have purchased 9 units, three work completely. This is an area for buyer-beware.

DEATH ROW

There seems to be even more caution needed in the buying of these units than would be normally required when buying other Tektronix oscilloscopes, say, a 2465. If the 2465 is to be seen working, it is shown displaying a trace. This tells a prospective buyer that the unit basically works. There are many things that can be wrong with the 2465, but they are robust little scopes and usually work.

The 11000 and DSA scopes are a vastly different animal. The oscilloscope portion of the digital scopes (not the 11300 series) is like a TV set, turned sideways. It does not display a signal, but displays a memory representation of the signal. The mainframes have extensive self-checks and diagnostics. These are often used by a seller to establish that a mainframe is working, as opposed to the display of a trace. However, the self-tests, extended diagnostics, and enhanced accuracy calibrations are executed in a very specific way. IF THERE ARE NO PLUGINS IN THE UNIT, THE PLUGIN CHANNELS IN THE A5 ACQUISITION BOARD ARE NOT TESTED. The extended diagnostics and enhanced accuracy procedures are not executed FOR THE MISSING PLUGINS. If one or more plugins are installed, the extended diags and EA for the installed plugins are also performed. The only complete test is when ALL THREE plugin slots are filled, all diagnostics pass, and after a 20 minute warmup, enhanced accuracy is done and passes all calibration. There still could be problems that do not show up in these tests. If a test or diagnostic fails, other parts of the instrument can go untested.

A word about enhanced accuracy feature (EA). These units are able to calibrate themselves, including the plugins, to better than 1%. Whenever the configuration is changed, or the temperature changes by more than 5 degrees C, the unit attempts to get an EA done, either automatically or by operator request. The internal standards that it uses are much more accurate than what would normally be available and the full calibration is automatic.

What are some of the problems I have already found? First is that the condition of the units varies greatly. I still have not managed to remove all the grass and mouse droppings out of the first 11302 I bought. I have two other units which won't pass EA, and a plugin that also won't. One 11402 power supply went up in smoke, but appears to have recovered. On the other hand, the DSA602A I bought is quite good.

DSA602A

The cooling fans are a special item, and many are no doubt suffering from their age. These units run hot, and if the fan is slow, the temp sensors in the power supplies will shut the unit down until it cools. Or maybe they just shut the unit down anyway. These run hot, and cooling appears to be important. Good luck finding a replacement fan.

Often, the unit will just freeze. The 11402 manual suggests turning the power off and on again before calling for service. Kind of like my computer.

The power supplies apparently use the dreaded tantalum capacitors, which should all be replaced. Before they explode or catch fire. Twenty years seems to be about their limit. The power supplies are very modular and slide out easily for exchange or service. Power supplies may be interchangeable between the various models as well. Some other boards may interchange.

Another weakness is the warning in the instructions not to remove and install plugins with the unit power on. Yea, right. How many users of this type of equipment even read the manual, let alone follow it? So many mainframes and plugins may have damage  from wrongful removal of a plugin. This would only show up if the unit had a plugin installed in that channel when tested.

Speaking of the 50 gHz 11800 series, such as the 11801, sampling heads are required to use them. They can easily be ruined from over-voltage. Personally, I will wait until I can actually test a sampling head in my 11802A before purchasing it.

After studying the service manuals, I have to conclude that repair by the user was not an option. Tektronix identified the boards as Field Replaceable Units (FRU's). The user was supposed to identify which board was the likely cause of the problem they were having, and then remove it and send it to Tektronix for repair or replacement. Or Tek could fix the entire scope for you. I doubt if many of these boards were ever fixed, and I believe those units are still out there. The service manual does not describe the enhanced accuracy procedure, identify error codes or what problems they are detecting. If the unit fails EA, there is no way to know why.

Parts and service will be a problem. Boards from partly defective units perhaps could be used to repair other units with other defects. The problem is, what constiutes a "good board?" The board used must be later than the one it is replacing, and have the proper firmware on it. Without factory information, this is not going to be easy, or cheap. These boxes are all chock full of proprietary information, software, hardware and firmware. There are no schematic diagrams in the manuals. They were top-secret too, and only issued to the Tektronix module repair center. Training likewise. What was said to the Tek factory technicians in training must have been said in Las Vegas, because apparently, it stayed there.

Even new, these were not for the faint-of-heart. Today the units out there have been used and abused. It surely is the best case of buyer-bewareI have seen in a long time. We at The Oscilloscope Store currently have three working units and nine plugins, all of which we gurantee for 1 year from date of purchase.  I have manuals for the 401 and 402. These are soft copies from Artek Media. The set consists of 4 extended service and user manuals,  a good buy at $15. I would recommend these for anyone even looking at one of these units. Manuals are also available for the plugins.

The Good News

These are fabulous instruments. They have an excellent measurement system, which allows the operator to turn on the display of a variety of parameters from the acquired waveform, such as p-p, time , frequency, etc. As the measurement is taken from the data and not the display, accuracy is far better than measurements taken from the screen. Even the cursors are less accurate than the units measurement systems.

These oscilloscopes have a capability which is generally unmatched in any other type of instrument. That is the ability to view a waveform both PRE and POST trigger. A 11K or DSA acquires data continuously, and doesn't depend on a trigger event to initiate the sweep and display. The trigger event is simply a marker on the trace, so that data can be viewed both before and after the trigger. For example, if you are using the OVERLOAD or SHUTDOWN indicator on a power supply as a trigger, you can look at other points in the circuit BEFORE the failure event caused the indicator to activate.

A new DSA602A in 1991 cost over $37,000. It uses multiple microprocessors to acquire, process and display data. Does FFT at the touch of a button, instantly. The FFT processor produces both an amplitude and a phase FFT display, which the spectrum analyzer cannot do. The DSA601 has two 8-bit, 500 megasamples/sec digitizers. These can be configured through instrument controls to allow simultaneous, 500 MS/sec simultaneous single-shot from 2 channels. Or, they can be interleaved to obtain a 1 gigasample per second sample rate fromn a single channel. The DSA602 has four 8-bit digitizers, each capable of 500 ms/sec simultaneous single-shot acquisition on four independant channels. or 1 gs/sec on 2 channels, or 2 gs/sec on a single channel. Up to 12 channels can be acquired simultaneously for repetitive signals.

DSA602 with pulse train in time and frequency domains.

The touch screens are very interesting. The "touch" has really nothing to do with the "screen" which is probably good news. The little touch squares actually use an infrared beam, when your finger breaks it the scope can tell what intersection you are blocking, and reacts accordingly. I have seen no problems with the touch controls on any of my units. And there is no danger of damaging anything delicate because your finger is actually pressing against the glass front of the crt or its implosion shield.

In order of desirability, best to worst:

11403A + 11A81A - last of the line and good to 3gHz.

11403 - It does not have the analysis capabilities, but if that is not needed then the 403 is lighter, cheaper package.

DSA602A (same as a 602 but adds a disk drive for storing settings and waveforms)

DSA602

DSA601

11402A

The rest are less desirable. (Courtesy of Denis Cobley)

Plugins:

11A81A - only works in the 11403A

11A72 - 50 ohm, 1gHz X 2 channels

11A71 - 1 channel, 1 gHz

11A52 - 500 mHz, 2 channel early - not suitable for all mainframes

11A34 - 400 mHz, 4 channel, 1 meg / 50 ohm good general purpose module

11A32 - 400 mHz, 2 channel 1 meg / 50 ohm, good general purpose module

11A33 - Differential amplifier, 200 mHz, useful for differential and video work.

11T5H Multistandard Video Trigger (triggers on chosen line / field)

11A34V High Bandwidth Video Amplifier (4 channels, 75/1Mohm, 300MHz) . These do come up from time to time.

Mainframes available:

The 11000-series of Tektronix oscilloscopes consists of the following products:

ANALOG OSCILLOSCOPE MAINFRAMES

11301 Programmable Analog Oscilloscope 500 MhZ, USES 7000 AND 11000 SERIES PLUGINS.
11302 Programmable Analog Oscilloscope with Microchannel Plate (not the same on as the 2467) CRT, USES 7000 AND 11000 SERIES PLUGINS

                 11301

DIGITAL OSCILLOSCOPE MAINFRAMES

11201A I have only seen one of these, looks like a mini-401 with fixed preamps rather than plugins

               11201A

11401 Programmable Digitizing Oscilloscope - 500 MhZ, random equivalent time sampling USING 7000 AND 11000 SERIES PLUGINS.
11402 Programmable Digitizing Oscilloscope - 1 GhZ random equivalent time sampling USING 7000 AND 11000 SERIES PLUGINS.
11403 Programmable Digitizing Oscilloscope - 1 (3?) GhZ COLOR, 3 gHz in the A version, random equivalent time sampling USING 7000 AND 11000 SERIES PLUGINS.

                   11402

11801 Programmable Digitizing Oscilloscope - 50 gHz, sequential equivalent-time sampling USING SAMPLING HEADS. 4 slots.
11802 Programmable Digitizing Oscilloscope - 50 gHz, sequential sampling USING SAMPLING HEADS. 2 slots and delay line.

                    1802

DSA601 Digital Signal Analyzer - 1 gHz, real time sampling at 1 Gs/sec. No disk drive.
DSA602 Digital Signal Analyzer - 1 gHz,  real time sampling at 2 Gs/sec, color in A version. Disk drive in "A" version.

                DSA602A

All have (A) versions. Some ALSO have B and C versions, the higher the letter the more desirable the unit, all things being equal.

Some of these units will use 7000-series plugins. The useful 7000 series plugins are limited. The 7000 plugin needs to have the small plastic tab on the back filed or sawed off. This does not render the plugin useless for 7000 mainframe use. A 7000 plugin however cannot be calibrated, tested or have its accuracy enhanced by the 11000 series or DSA mainframe.

UPDATES: FEBRUARY 27, 2007

PLUGINS:

The plugins for these oscilloscopes are much more integrated with the mainframes than others like the 7000 series. Because the scope calibrates and operates the plugin, it can pass its woes on. Then, when you switch the plugin to another mainframe, the plugin may give errors. The DSA602A appears to be able to "fix" this problem, but the plugin sometimes cannot be "fixed" by the mainframe you wish to use it in. So one mainframe with a dedicated set of plugins seems to be the way to go. Switching plugins from one mainframe to another to another may turn out to be a frustrating experience.

FANS AND COOLING:

There appears to be a lot to the cooling of these units. The fan on the 11K sereis looks like it was an afterthought, to be kind. It is stuck on the back of the scope like a wart, a far cry from the very sophisticated fans used in the 2465 and other Tek scopes. It is a variable-speed, DC muffin fan, not plastic but metal. If you drop the scope or set it down on the back (not all that uncommon when carrying 60 pounds or so) the scope sits on the cover over the fan. There is a metal grill over the fan opening which gets flattened from the weight of the entire scope sitting on it, and it crushes against the fan. This binds the fan and prevents it from turning. If this goes unnoticed, the fan will burn out along with whatever parts of the instrument overheat. It is hard to notice because the fan is fairly quiet, but absolutely critical.

Inside the instrument, some of the processor chips have heat sinks clipped on. I received an 11802 where the heat sink had actually fallen off the chip. I believe the chip then overheated and failed. This would be a good check to make when powering up the first time. Or before buying.

The instruction manual says that for proper ventilation, ALL PLUGINS MUST BE INSERTED. ANY SLOTS NOT OCCUPIED BY A PLUGIN MUST HAVE A BLANK PANEL IN PLACE. YIPES!!

The 11301 and 11302 Analog Scopes

The 11301 and 11302 are different than the others, although they have many of the same storage and and gpib capabilities. They are both analog scopes, and operate much the same as a Tektronix 2465 or 2467. There are not many differences between the 301 and 302 except that the 302 has an MCP crt. The 302 is a very nice scope to work with, it only seems to have a few of the DSO idiosyncracies. It can store waveforms and setups, and transmit them over gpib. The menues are not as nice as the 401 or DSA. The menues are mixed into the screen with the waveforms and so are a bit harder to operate. Plus the screen is smaller than the 401, making it harder to hit the exact button you want. Still a very nice wideband oscilloscope.

Besides the MCP CRT, the 11302 shines because of its very accurate counting and measuring ability. The counter/timer readout is 7 digits (option 1T has 10 digits) and has a 2ns resolution.

 BANDWIDTH IN mHz OF MAINFRAMES WITH VARIOUS PLUGINS

PLUGIN                                          MAINFRAME

                   11301    11302    11401     11402     11403    DSA602   CH     INPUT IMPEDENCE                 COST

11A71           400       500        500        1000      1000       1000        1         50 OHM                                 2700

11A72           400       500        500        1000      1000       1000        1         50 OHM                                 2700

11A52           350       400        500        600         600         600         2         50 OHM                                 2405

11A32           300       350        350        400         400         400         2         50 OHM / 1 MEGOHM            2025

11A34           250       250        300        300         300         300         4         50 OHM / 1 MEGOHM            3525

11A33           150       150        150        150         150         150        + / -     50 OHM / 1 MEG / 1 Gig         3000

11A81            NA       NA         NA        NA         3000         NA         1        50 OHM                                  2700

11A16            50         50          50         50           50          50           2        CURRENT                              6000

COST           8550    12950    13000   15500      19950     34600

Software

There is still factory software available for free download. It is called Wavewriter. I have not set it up yet, when I do I will report. In order to talk to the scope, a National Instruments gpib card is needed for your computer. There is a PCI version which goes for about 200 bucks, but the ISA version works fine and sells for less than 50. A gpib cable connects the card in the computer to the scope. NI has a variety of drivers and other utilities on its website.

There are also some other utility programs on the Tektronix website.

We have an excellent video on the 11302 scopes for sale on our store. I also have some manuals for various units for sale. Please check the store.