Tek tds 3054b vs tds 744a

[cncjerry]

I posted this up on the tekscopes forum, no interest, so I thought I would try here.

I have a 744a that I love.  Yes, it is large, clunky, etc. but mine is a beauty, excellent shape, calibrated, etc and performs perfectly.  It has a crystal clear display and high contrast.  Having Glaucoma where lights bloom, the contrast is important to me.  I also got it for the cost of the probes alone (or better).

I recently had the opportunity to purchase a TDS 3054b again for a great deal.  I had read a lot about this scope and thought it would have a leg-up on my 744a.  Now I am starting to wonder and I guess the question I have is should I give it more time or is it truly below the 744a in features and functions?

Here's what I've found comparing the two: 

The 3054b is lighter, portable, with a larger display but it doesn't have near the contrast of the 744a.  The colors on the 744a are fully configurable and the 3054b your stuck.  This plays into the contrast again as I have more problems with some colors than others.  The variable DPO is interesting but I prefer the instaVue on the 744a as it uses color to differentiate the signal whereas the DPO uses intensity.  The 3054b has a higher sample rate compared to the 2GS/s on the 744, it has 5Gs/s across all four channels.

The acquire settings are missing hi-res and the average settings are stepped in powers of 2 whereas the 744a has unit variability from 2 - like 9000.   My 744 has the higher capture installed so I get more data as well though I haven't figured out how to get more than like 500 points into matlab.

Unless I am missing something, the 3054b doesn't really do probe compensation like the 744a but it has more splits in the probe pin contacts.

I use the keypad on the 744 a lot so that's gone on the 3054.  My 744 has GPIB where the 3054b has Ethernet which works pretty well. I have fixed IP addresses so my brother can see the scope across the internet.  I can add GPIB pretty cheaply but don't think I need it.

The FFT on the 3054 looks really grainy compared to the 744a.  Also, on the 744a I can set the persistence up higher and get nice impedance plots using a sweep or noise generator.  Haven't figured that out on the 3054 as the persistence doesn't seem to impact the FFT.

I guess I will be keeping both since having typed this I am starting to realize the 3054b is really just a decent portable scope and the 744a more of a bench model.

What am I missing?  By the way, I do like Agilent scopes, just never see a killer deal.

Jerry

[AndyC_772]

I used a couple of very similar scopes, a 3034B and a 754D, extensively for years, and for the most part I agree with you.

If you have the bench space to make the scope a permanent fixture, then the 700 series has a lot to commend it. I bought mine for home use as a budget alternative to the 3000 that I had at work, and rarely felt like I was using a machine that was second best.

I could have done without the noise and the heat, though. At over 400W, it made my lab an uncomfortable place to work in summer despite my best efforts to keep the place cool. Newer scopes don't have the same effect.

The reason I eventually sold it, though, was fear for how long it had left to live. The 'D' series models don't suffer the same capacitor rot as earlier units - and if you've not had the caps changed already then do it now! - but they do still have a CMOS memory module with a battery that'll be well past its expiry date by now.

When I started using my own gear to make a living rather than just as a hobby, I decided I couldn't afford to risk it dying in the middle of a customer job, and started looking around for newer alternatives. Now I have an Agilent 3000X with all options enabled, and other than the fact that I miss the equivalent-time modes, I couldn't be happier with it.

[Smokey]

After using the TDS3034B at work for years, the only real complaint I have is the small sample memory.  That's about the only thing that has gotten in the way of what I needed to do.  I've always thought the screen looked really good.  Well, ok and the floppy drive not being convenient sucks too.  I guess you can replace the floppy with a floppy-USB adapter thing, but I just grab screen shots from the Ethernet connected computer.

[cncjerry]

I'm going to replace the battery in my 744a now that you mention it.  Supposedly the 744 and 754 didn't save the cap problem like prior models.  Having said that though, the battery will die tonight and wHen I open it up the caps will pour out.

I can't believe how much you get for so little with these old scopes.  If people sat down with them and saw the features I think most would be impressed.  I see 5xx, 6xx and 7xx scopes on craigslist all the time for under $600.

The 3054 screen is nice but I prefer the high contrast of the 744, at least right now.  I guess I thought the 3054b would be better than it is, maybe it will take some time to get used to it.

These are the colors that I can see the best with the vision problems I have.

[nctnico]

Yeah make me regret selling my TDS744A 
I don't think the TDS3000 series are a good replacement due to their short memory. Did you look at the TDS5000 series? Or look at Lecroy; some say their higher end scopes are more geared towards signal analyses but I have no personal experience to back that up.

[Wuerstchenhund]

I guess I will be keeping both since having typed this I am starting to realize the 3054b is really just a decent portable scope and the 744a more of a bench model.

What am I missing?

I'd say you're missing that you're essentially comparing Apples vs Oranges. The TDS744 is a high end scope (even when it's old) while the TDS3000 is a better entry level scope. It's bit naff to expect the same features as you have in your TDS744 in a TDS3000, even though the TDS744 feature set is limited.

[MarkL]

The 3054 screen is nice but I prefer the high contrast of the 744, at least right now.  I guess I thought the 3054b would be better than it is, maybe it will take some time to get used to it.

These are the colors that I can see the best with the vision problems I have.

I have a TDS3054 I bought new 15 years ago and I never noticed how dim the display had become over the years.  I was able to replace the CCFL tubes with new ones and it made a huge difference in readability.

You can replace the CCFL tubes as slide-out FRUs, NEC part #65LHS–3L, or solder in bare CCFLs.  I did the latter with tubes from ccflwarehouse.com, part #CC26153.  There are two tubes and the display in your "B" version uses the same CCFLs according to the Tek service manual.

I've never used a Tek TDS7xx series, so maybe it has a better display anyway, but thought I'd point this out.

[tinhead]

you can even get more on tds700A series, with 4 resistors (in your case from 744A to 784A only one resistor on acq board) one can get 4GSa/s for single channel and 2GSa/s when 1or 2 and 3 or 4 ch enabled. The bandwidth increase to 1GHz must not work always.

One have of course to let calibrate somewhere (the cheapest way) or did it yourself (TDS700A Field Adjustment Software PN_063260100, NI GPIB controller and some signal gens, counters necessary to do that!).

In principle it does works as well when you burn the calibration data from other TDS784A, but only the missing
data for 4GSa/s not everything, it will not work 100% exact but sufficient. On the TDS700A series the call data is stored
in two X24C02 EEPROMs on bottom side of ACQ board (U1055, U1052). The data can be duped via GPIB, i wrote once
small app to dump that data, see attached code for TDS7x4A models (works similar to tektool from tek forum).

These board ID resistors (R1061<->R1064), whit which the model can be set, are near these EEPROMs as well. Soldered is 0.

TDS784A: 7,   0 1 1 1
TDS754A: 8,   1 0 0 0
TDS744A: 6,   0 1 1 0

interessting that these resistors are not on the TDS500B series schematic (well, they are marked as "exluded from").


on CPU board there are ID resistors as well (R12, R13, R15, R17). As far i remember there was no need to change
them when model was set on ACQ board to TDS784A.

744A - 12,17=0, other 1      0 1 1 0
754A - 17=0,    other 1      0 1 1 1

Btw, in principle one could take an TDS540B and change it to TDS784A, sure it will be still no color
(except on external monitor or custom display), but from sampling and bw point of view it would work.
I always liked these TDS700 series and wrked with them for long time, even if they loud and clunky.

And before i forget, similar hacks (with model change) are possible on TDS600B, TDS700C and TDS700D as welll,
but please don't ask me for details, use google to search for pcb pictures and you will find the differences.

[MarkL]

I guess I will be keeping both since having typed this I am starting to realize the 3054b is really just a decent portable scope and the 744a more of a bench model.

What am I missing?

I'd say you're missing that you're essentially comparing Apples vs Oranges. The TDS744 is a high end scope (even when it's old) while the TDS3000 is a better entry level scope. It's bit naff to expect the same features as you have in your TDS744 in a TDS3000, even though the TDS744 feature set is limited.

Well,  there must be something to the TDS3000 series.  Crazy prices aside, used TDS3054x units are selling for 2x to 3x the TDS744 on ebay.

I wouldn't put the TDS3000 series in the entry level category, but if you're looking for entry level I wouldn't be buying one of those anyway given the value you can get on some of the Rigols brand new.

[cncjerry]

I guess I will be keeping both since having typed this I am starting to realize the 3054b is really just a decent portable scope and the 744a more of a bench model.

What am I missing?

I'd say you're missing that you're essentially comparing Apples vs Oranges. The TDS744 is a high end scope (even when it's old) while the TDS3000 is a better entry level scope. It's bit naff to expect the same features as you have in your TDS744 in a TDS3000, even though the TDS744 feature set is limited.

Wait a minute, who's missing what here?  A 3054b an entry level scope?  :-) Don't make fun of my kids...

Granted it is old, but the price this sucker went for in it's day puts it a few notches up over entry level scopes.  I keep staring at this thing wondering who would have paid $8k for one new because as I struggled with above, when this was new the 744A and 754A weren't that old.   I still see 3054b's listed for 5k or even more.  Locally there are two 3052's that are listed at $5k and 5.6K and another 3054 (non b) that was listed at 6.6K.  I know nobody pays that much, but I haven't found one that works for under 2k.

[Wuerstchenhund]

I'd say you're missing that you're essentially comparing Apples vs Oranges. The TDS744 is a high end scope (even when it's old) while the TDS3000 is a better entry level scope. It's bit naff to expect the same features as you have in your TDS744 in a TDS3000, even though the TDS744 feature set is limited.

Wait a minute, who's missing what here?  A 3054b an entry level scope?  :-) Don't make fun of my kids...

Well, it's an upper entry-level scope ;-) The TDS3000 has always been on the lower end of Tek's offering, I'm not sure why this surprises you. In terms of capabilities it's a pretty primitive scope, low memory, poor maths and FFT, and that's about it. We still had several of them were I worked approx 10 years ago, they were fine for basic tasks but hardly luxurious in terms of capabilities or performance. Their main advantage was in their portability and the optional battery.

Granted it is old, but the price this sucker went for in it's day puts it a few notches up over entry level scopes. I keep staring at this thing wondering who would have paid $8k for one new because as I struggled with above, when this was new the 744A and 754A weren't that old.

Well, that was then, almost 15 years ago (the TDS3000 came out in 2000; IIRC the TDS744A is probably from around 1995 so quite a bit older), not today. Scope prices at the lower end of the spectrum have come down quite a bit since then. The TDS3000 is roughly where the Agilent DSO-X2000/3000 Series is today, and that is still the lower end of the market. Tek's midrange started with the TDS5000.

I still see 3054b's listed for 5k or even more.  Locally there are two 3052's that are listed at $5k and 5.6K and another 3054 (non b) that was listed at 6.6K.  I know nobody pays that much, but I haven't found one that works for under 2k.

There's all kinds of old stuff listed at exorbitant prices on ebay and elsewhere. That doesn't mean they sell for that amount, in fact many of the sellers that list kit at insane prices are happy to relist it year by year, waiting for someone stupid enough to buy at their asking price. This is however not specific to Tek scopes, you'll find these sellers for any other kit as well.

I'd say anyone who pays $5k or more for such a scope needs to have his head examined, seriously. $2k for a TDS3054 is still stretching it but I guess for some people it's important that a scope carries the name 'Tektronix', for which they apparently glady pay a premium. But even at $2k a TDS3054 is not really good value for money, considering the other options that are out there.

[cncjerry]

I agree with some and most of the points from Wuerstchendhund (some kind of dog?) except the comparison to the rigol et al.  Not to start a debate, and all you rigol fans, please note this is my thread, I know all there is to know about Rigol, Owon (have an SDS7102V), and the others.  I've read it all.  I am on the side with the people that think the Rigol hack-ability is a marketing ploy on their part.  Though that doesn't mean it isn't a great scope for the money. 

Also, as to the Agilent which I love by the way, I play with the 2000 series at Fry's every time I go in, I find it hard to believe that scope could keep up with the TDS3054b or even the 744a in the higher speeds.

I can give you 2 recent examples that compare my lower end scope to the lower end (yeah, right) TDS 3054b: 

1) Take a noisy 50mv RMS signal at 400hz.  Feed it into your typical asian scope that cost $500, +/- 100.  Set the coupling for ack and trig to AC and raise the trigger above zero to like .75 the positive peak.  Then take a measurement using their measurement function and tell me if you get the correct RMS value.  I don't on my SDS7102v but do on my 744a and the 3054b.  I also get the correct number on my ancient HP 427a.  On the SDS7102v, which I found to be a decent entry level scope, the signal tracks above zero as I move the trigger up and the RMS value drops.  Now in some ways this makes sense as the scope is triggering on the outlying signals above the zero line.  As there are fewer outlyers than there are correct signals, maybe the RMS should be lower?  Don't know, haven't thought about it much since last night.

2) The other thing I noticed is that with long but high quality 75 ohm cables (about 2M long) when I feed a signal into an old HP 427a voltmeter, that which I was calibrating above, I get more noise on the signal when I attach it to the meter and couple to the sds7102v.  So if I am looking at the signal coming from the generator and it is somewhat clean, then attach it to the old 427a, I see tons of noise;  If I do the same with the TDS scopes, I don't see half that much.  I don't know what this means.  Just found it last night.

These are the fist two inconsistencies I've seen on my sds7102v which I really like for the screen.  It might not apply at all to other entry level scopes.

Jerry

[Wuerstchenhund]

I agree with some and most of the points from Wuerstchendhund (some kind of dog?)

"Wuerstchenhund" is the direct German translation of "sausage dog", which in German is actually "Dackel" or "Dachshund".

except the comparison to the rigol et al. 

Well, when it came out the TDS3000 definitely was (better) entry-level, and so are Rigol scopes. It's certainly a fair comparison.

Also, as to the Agilent which I love by the way, I play with the 2000 series at Fry's every time I go in, I find it hard to believe that scope could keep up with the TDS3054b or even the 744a in the higher speeds.

I can't see why not. The TDS3000 is a scope of the same class from 14 years ago, and the TDS744A is (if my records are correct) somewhat 20 years old. None of them have any special capabilities or great features. The TDS744A was a very expensive and certainly a good scope at its days but sorry, technology has moved on a bit in these two decades.

I can give you 2 recent examples that compare my lower end scope to the lower end (yeah, right) TDS 3054b: 

1) Take a noisy 50mv RMS signal at 400hz.  Feed it into your typical asian scope that cost $500, +/- 100.  Set the coupling for ack and trig to AC and raise the trigger above zero to like .75 the positive peak.  Then take a measurement using their measurement function and tell me if you get the correct RMS value.  I don't on my SDS7102v but do on my 744a and the 3054b.  I also get the correct number on my ancient HP 427a.  On the SDS7102v, which I found to be a decent entry level scope, the signal tracks above zero as I move the trigger up and the RMS value drops.  Now in some ways this makes sense as the scope is triggering on the outlying signals above the zero line.  As there are fewer outlyers than there are correct signals, maybe the RMS should be lower?  Don't know, haven't thought about it much since last night.

I never had an Owon (and the ones I've seen made me glad I never bought one), but it's of course possible that there is a bug in how the scope calculates measurements. The Chinese have shown that they can produce decent hardware but in terms of software they still mostly suck.

The other thing is that your example doesn't say enough about the parameters you made the measurements under to determine what the issue was. For example, what was the noise floor on the 50mVrms 400Hz signal, what were its frequency components, what was your scope setup etc. I guess the Owon takes measurements from the screen content so how the scope was setup will have an impact on accuracy. Then there is the bandwidth difference (I assume the Owon os 100MHz? The TDS3054 is a 500MHz scope) which plays into that as well.

2) The other thing I noticed is that with long but high quality 75 ohm cables (about 2M long) when I feed a signal into an old HP 427a voltmeter, that which I was calibrating above, I get more noise on the signal when I attach it to the meter and couple to the sds7102v.  So if I am looking at the signal coming from the generator and it is somewhat clean, then attach it to the old 427a, I see tons of noise;  If I do the same with the TDS scopes, I don't see half that much.  I don't know what this means.  Just found it last night.

Again, too little details, but it might be that the Owon introduces more noise over the GND connection.

I'm not sure if those tests really show a problem with the Owon or with your setup.

[cncjerry]

I wasn't implying a problem with the Owon as I said, I like it for the money.  It's just something I would have to dig into.  I had the Owon on Battery without an external ground.  Many things can cause it, just that an unsophisticated user might not have recognized the problem that wasn't evident on the TDS scopes.  So from that perspective the TDS scope justifies itself.  At about 10x the cost used.   


And on that hacking the 744a, is that really feasible?  I wonder if I would get anything out of it.  I seldom work over 500Mhz.  All the bandwidth brings me is noise.

[Wuerstchenhund]

Many things can cause it, just that an unsophisticated user might not have recognized the problem that wasn't evident on the TDS scopes.  So from that perspective the TDS scope justifies itself. 

Not really. There's no evidence suggesting that the outcome was because the Tek is the better instrument or that these problems can be avioded by using a TDS3000 scope.

The only reasonable conclusion that can be drawn from this episode is that you'll measure crap if you don't know what you're doing or what the limitation of your equipment are. Simple as that. This "unsophisticated user" would have plenty of opportunities to get the similar crap results with the Tek scope.

[Smokey]

Fact!
You would be surprised how "smart" a person can be and still be an "unsophisticated user" by overestimating what a piece of equipment is capable of doing. 

[nctnico]

Many things can cause it, just that an unsophisticated user might not have recognized the problem that wasn't evident on the TDS scopes.  So from that perspective the TDS scope justifies itself. 

Not really. There's no evidence suggesting that the outcome was because the Tek is the better instrument or that these problems can be avioded by using a TDS3000 scope.

The only reasonable conclusion that can be drawn from this episode is that you'll measure crap if you don't know what you're doing or what the limitation of your equipment are. Simple as that. This "unsophisticated user" would have plenty of opportunities to get the similar crap results with the Tek scope.

Maybe even more. The TDS744A has a boat load of ways to acquire and display a signal. Modern scopes are dumbed down a lot.

[Wuerstchenhund]

Fact!
You would be surprised how "smart" a person can be and still be an "unsophisticated user" by overestimating what a piece of equipment is capable of doing.

Indeed. But this really is then an issue with the person and not the fault of the equipment.

[Wuerstchenhund]

The TDS744A has a boat load of ways to acquire and display a signal. Modern scopes are dumbed down a lot.

The TDS744A's manual only lists these:

• Sample Mode - the normal sample mode
• Envelope Mode - collecting Extrema over multiple acquisitions
• Average Mode - collecting average over multiple aquisitions
• Peak Detect - essentially Envelope Mode over only two acquisitions
• Hi-Res Mode - oversampling to increase the vertical resolution

It's certainly a good selection of options for a scope from 1994, but by today's standards none of these modes are anything special. What modes do you miss on modern scopes?

[David Hess]

The TDS744A's manual only lists these:

• Sample Mode - the normal sample mode
• Envelope Mode - collecting Extrema over multiple acquisitions
• Average Mode - collecting average over multiple aquisitions
• Peak Detect - essentially Envelope Mode over only two acquisitions
• Hi-Res Mode - oversampling to increase the vertical resolution

The TDS744A manual is very specific that peak detection occurs over one acquisition.  Two adjacent intervals are used to store the high and low values which I assume halves the record length.  Envelope mode uses multiple peak detection acquisitions.

InstaVu (DPO mode) combines with the sample or peak detect acquisition modes.

FastFrame (segmented memory) combines with most or all of the acquisition modes.

Depending on how one looks at it, that could be considered 12 different modes or too many ways to misconfigure the oscilloscope and confuse the user.

It's certainly a good selection of options for a scope from 1994, but by today's standards none of these modes are anything special. What modes do you miss on modern scopes?

A lot of modern DSOs inexplicably lack peak detection.  Maybe the designers figure having long record lengths makes it unnecessary.

[Wuerstchenhund]

The TDS744A manual is very specific that peak detection occurs over one acquisition.

That is not correct. From the TDS 684A, TDS 744A & TDS 784A Digitizing Oscilloscopes User Manual (070-8331-02 from 1994) page 3-22:

Peak Detect Mode. TDS 700A models only: Peak Detect mode alternates between saving the highest sample in one acquisition interval and lowest sample in the next acquisition interval. Peak Detect mode only works with real-time, noninterpolated sampling.

The manual says the following to Envelope Mode:

Envelope Mode. Envelope mode lets you acquire and display a waveform record that shows the extremes in variation over several acquisitions. You specify the number of acquisitions over which to accumulate the data. The oscilloscope saves the highest and lowest values in two adjacent intervals similar to the Peak Detect mode. But Envelope mode, unlike Peak Detect, gathers peaks over many trigger events.

InstaVu (DPO mode) combines with the sample or peak detect acquisition modes.

InstaVu is a Tektronix marketing term so it's obvious it's not found in other scopes. It's simply persistence mode with Peak Detect switched on.

FastFrame (segmented memory) combines with most or all of the acquisition modes.

FastFrame again is a Tektronix marketing term. Segmented memory which can be combined with other modes of course exists in many modern scopes.

It's certainly a good selection of options for a scope from 1994, but by today's standards none of these modes are anything special. What modes do you miss on modern scopes?

A lot of modern DSOs inexplicably lack peak detection.  Maybe the designers figure having long record lengths makes it unnecessary.

I've seen Peak Detect (which, as we hopefully have now established, is simply Envelope mode over only two aquisitions) on some newer scopes, particular those without Envelope mode.

Better scopes have Envelope mode and you get Peak Detect by setting the number of aquisitions to two.

[Ivan7enych]

Hi-Res Mode in Tek 744A produces 16bit samples, and I can transfer this 16 bit data via GPIB to analize it. That mode is very helpful to analyze slow and low voltage signals

My Rigol 2072 has Hi-Res Mode, but it is always 8bit.

[Ivan7enych]

you can even get more on tds700A series, with 4 resistors (in your case from 744A to 784A only one resistor on acq board) one can get 4GSa/s for single channel and 2GSa/s when 1or 2 and 3 or 4 ch enabled. The bandwidth increase to 1GHz must not work always.

Thank you very much for this detailed info! I'll try this mod on my 744a unit.

[Wuerstchenhund]

Hi-Res Mode in Tek 744A produces 16bit samples, and I can transfer this 16 bit data via GPIB to analize it. That mode is very helpful to analyze slow and low voltage signals

Most better scopes have high res modes that increase the sample size by an additional 2 or 3bit, which is the limit as to what is sensible in a scope with 8bit ADC hardware. For everything above that there are true (and fake) 12bit scopes.

My Rigol 2072 has Hi-Res Mode, but it is always 8bit.

If it's still 8bit, what makes it Hi-Res then?

[David Hess]

The TDS744A manual is very specific that peak detection occurs over one acquisition.

That is not correct. From the TDS 684A, TDS 744A & TDS 784A Digitizing Oscilloscopes User Manual (070-8331-02 from 1994) page 3-22:

Peak Detect Mode. TDS 700A models only: Peak Detect mode alternates between saving the highest sample in one acquisition interval and lowest sample in the next acquisition interval. Peak Detect mode only works with real-time, noninterpolated sampling.

Acquisition interval (Tektronix still uses this term.) is not the same as waveform acquisition.  When the real time samples are decimated for sample mode, peak detect mode, or high resolution mode, they produces acquisition intervals within the display record.  In peak detect mode, two adjacent acquisition intervals within the display record are used to hold the minimum and maximum values for the total duration of time those acquisition intervals represent.  This allows peak detection to operate on a single and every waveform acquisition:

From the same manual on page 3-21:

Provides the benefits of enveloping with the speed of a single acquisition.

And page 3-20:

Sample (the mode most commonly used), Peak Detect, and Hi Res modes
operate in real time on a single trigger event, provided that the oscilloscope can
acquire enough samples for each trigger event.

The manual says the following to Envelope Mode:

Envelope Mode. Envelope mode lets you acquire and display a waveform record that shows the extremes in variation over several acquisitions. You specify the number of acquisitions over which to accumulate the data. The oscilloscope saves the highest and lowest values in two adjacent intervals similar to the Peak Detect mode. But Envelope mode, unlike Peak Detect, gathers peaks over many trigger events.

Which means peak detect works over one trigger event and a single acquisition while envelope mode operates over two or more trigger events and multiple waveform acquisitions.  You can use peak detection with a single shot acquisition.  Envelope mode (without InstaVu or DPO) is done in post processing.

InstaVu (DPO mode) combines with the sample or peak detect acquisition modes.

InstaVu is a Tektronix marketing term so it's obvious it's not found in other scopes. It's simply persistence mode with Peak Detect switched on.

It is neither of those things.  When operating as a DPO, a histogram is generated in real time during decimation.  This is separate from persistence which is a separate step done after the acquisition record is transferred to the display record.  More modern DPOs may combine these steps although this may make them slower than the TDS744A.

It has been a while since I have used one of these oscilloscopes so I do not remember exactly how peak detection interacts with DPO mode but as I recall, it generates an envelope instead of a graded index.  This combination of modes always seemed pointless to me but at slower time/div settings I suppose it has utility.

It's certainly a good selection of options for a scope from 1994, but by today's standards none of these modes are anything special. What modes do you miss on modern scopes?

A lot of modern DSOs inexplicably lack peak detection.  Maybe the designers figure having long record lengths makes it unnecessary.

I've seen Peak Detect (which, as we hopefully have now established, is simply Envelope mode over only two acquisitions) on some newer scopes, particular those without Envelope mode.

We have not established it.  If peak detection required more than one acquisition, then it would require more than one trigger and would not work on a single shot acquisition.  There would also be nothing to distinguish it from envelope mode.

Are you thinking of peak detection as Rigol defines it on their older DSOs where they confound peak detection with envelope detection?  They work the way you describe when in peak detection mode which on a Tektronix would be envelope detection mode.

Better scopes have Envelope mode and you get Peak Detect by setting the number of acquisitions to two.

Better oscilloscope have both modes and on some, you get peak detect by setting the number of envelope acquisitions to one.

Some cheap DSOs have envelope detection without peak detection because the later requires dedicated hardware.

[tmbinc]

Though this stuff gets interesting on the low-end scopes, like the TDS2xx-series (and all the "modern" variants of it). They don't have high-speed ADCs, but a switched-capacitor array (which is whey they are limited to 2500 points; that odd non-power-of-two number) coupled with a slow ADC. That's why they exist with up to 2GS/s at moderate cost.

Now, the TDS224 for example also offers Peak-Detect. How would that work, given that the ADCs operate after "decimation"?

Point is, it doesn't. The manual states that "Peak Detect functions at SEC/DIV settings of 5us/div or slower. For SEC/DIV settings of 2.5us/div or faster, the acquisition mode switches to Sample automatically." 5us/div are 2500/50us = 50MS/s. That's the rate of the external ADC - at those slow sample rates, they don't use the SCA but sample the signal directly...

Upgrading from a TDS224 to a TDS2024 was a questionable decision (but I got the exchange for free). Upgrading from the TDS2024 to a DPO4034 (+software bandwidth hack) was a phenomenal (yet expensive) decision. I'm a happy DPO5034 (+hardware bandwidth hack) owner now, though the user interface sometimes drives me crazy.

[nctnico]

The TDS744A has a boat load of ways to acquire and display a signal. Modern scopes are dumbed down a lot.

The TDS744A's manual only lists these:

• Sample Mode - the normal sample mode
• Envelope Mode - collecting Extrema over multiple acquisitions
• Average Mode - collecting average over multiple aquisitions
• Peak Detect - essentially Envelope Mode over only two acquisitions
• Hi-Res Mode - oversampling to increase the vertical resolution

It's certainly a good selection of options for a scope from 1994, but by today's standards none of these modes are anything special. What modes do you miss on modern scopes?

On a TDS744A you can use 20 or so combinations of acquisition and display modes. Most with the ability to tweak some parameters.

[cncjerry]

Hotdog, Not sure if it is 20 because when you switch on InstaVue it doesn't allow Hi-res, for instance.  Also, InstaVue does it in full false color whereas the DPO is more like Z brightness.  From what I can tell, the DPO features are constant across all modes, but since it doesn't have hi-res which is disabled in InstaVue that isn't a fair statement.

So this morning I have the 3054b sitting on top of the 744a and I am looking at an old Instek GFG-8255A signal generator.  Should really be called a signal + noise + glitch generator.  What has always bothered me about this generator is that at the transition from up to down slope and the inverse, there is a little glitch. More obvious with a triangle, less so with a sine but still there.  I had to make some trade-offs in the two scope pictures but here they are below. 

Since this thread is getting to the point where people are putting on their mitres, I thought I would switch to that mode as well.

The first is from the 744a.  In this picture the step wouldn't be called out unless thou knew it was there.   I can see it a little as the slope is more acute at the top (maybe). The second is from the 3054b and though thou can see the glitch as that little down step, even after playing with the 3054b for 30 minutes and I am new to that scope, I can't get better resolution.  I left both in sample mode for the picture.  Thou will notice the step is more obvious on the 3054b.

No real conclusions here.  When I started this thread the intent was to garner opinions from thee (or is it thou?) on whether I should keep the 744a or sell it.  I don't need the $400 I would get for it (if lucky) but it does take up space.

If I had the cash, I would buy a 500Mhz or better Agilent or whatever they are called today.  Maybe Lecroy.  I think the value is in those brands more so than current Tektronix.  If I sold both of these scopes for lets say optimistically $2k total, I don't know if I could do better.


Thanks.

[nctnico]

You are using a shorter acquisition memory on the TDS744A which is why the distortion doesn't show when zoomed in. Just set the TDS744A to 25ksamples (or so) memory length and set 'fit to screen' to 'ON'.

[MarkL]

The first is from the 744a.  In this picture the step wouldn't be called out unless thou knew it was there.   I can see it a little as the slope is more acute at the top (maybe). The second is from the 3054b and though thou can see the glitch as that little down step, even after playing with the 3054b for 30 minutes and I am new to that scope, I can't get better resolution.  I left both in sample mode for the picture.  Thou will notice the step is more obvious on the 3054b.

One trick to getting "better resolution" is to use the scope's DC offset control to center the area of interest in the ADC's working range.

Below is an example on a TDS3054 using approx the same signal you used (12V Pk-Pk triangle at about 3.6kHz).  The DC offset is set to +5.5V and this allows the vertical sensitivity to be set to 100mV/div.  The delay has also been enabled and tweaked to bring the peak to the horizontal center.  Other settings of interest are "Avg 4", and trigger "HF Reject" to help stabilize the image.

100mv/div is as far down as you can go on the TDS3054 for this particular signal.  Any less and the offset range max changes to +/-1.000V, which isn't enough to bring the peak into range.

As you can see, this old FG504 function gen also has some transition issues at the peak, but you'll see that on any triangle generator to some degree.

[David Hess]

Though this stuff gets interesting on the low-end scopes, like the TDS2xx-series (and all the "modern" variants of it). They don't have high-speed ADCs, but a switched-capacitor array (which is whey they are limited to 2500 points; that odd non-power-of-two number) coupled with a slow ADC. That's why they exist with up to 2GS/s at moderate cost.

Most or all of their non-CCD oscilloscopes have non-power of 2 record and display lengths as well.  Their very early DSOs provide some interesting exceptions to this.  Some of their earlier CCD based DSOs had much higher record lengths but of course they were not expandable.

The TDS2xx series only samples at up to 1 GS/s per channel according to the documentation.

Now, the TDS224 for example also offers Peak-Detect. How would that work, given that the ADCs operate after "decimation"?

Point is, it doesn't. The manual states that "Peak Detect functions at SEC/DIV settings of 5us/div or slower. For SEC/DIV settings of 2.5us/div or faster, the acquisition mode switches to Sample automatically." 5us/div are 2500/50us = 50MS/s. That's the rate of the external ADC - at those slow sample rates, they don't use the SCA but sample the signal directly...

Take a look at a 2440 series service manual to get an idea about how this works in a CCD (charge coupled device) based FISO (fast in slow out) digitizer.  Peak detection is done in the analog domain before the analog shift register as a separate operation.  The cost reduced version of the 2432A, the 2431L, and the TDS600 series up to the B models dropped this capability.  I assume it was not until the B models of the TDS600 series that they were able to reimplement it to operate at sample rates higher than 500 MS/s.

I did not know that Tektronix continued to use FISO based sampling after the TDS600 series but it makes sense in low cost real time DSO designs if you already have the technology.  Tektronix had already divested itself of semiconductor manufacturing by the time that TDS220 series came out but it looks like they had National fabricate the ICs for them.  I wonder if Maxim made the ICs in the much faster TDS600 series.

This explains the rather odd TDS220 series specifications which indicate a maximum input bandwidth of 50 or 75 MHz when peak detection is used although the earlier TDS600 series lack such a limitation.

Upgrading from a TDS224 to a TDS2024 was a questionable decision (but I got the exchange for free). Upgrading from the TDS2024 to a DPO4034 (+software bandwidth hack) was a phenomenal (yet expensive) decision. I'm a happy DPO5034 (+hardware bandwidth hack) owner now, though the user interface sometimes drives me crazy.

I was not happy with the MSO/DPO5000 series interface either and a lot of other things about them as well.  They struck me as a good oscilloscope for ATE (automatic test equipment) environments.

[cncjerry]

nctnico,
I was using 5k points in 100 divs on the 744a.  Even moving it up to 50k in 1000, I get roughly the same picture.  I don't understand the difference in record length between the two scopes.  My 744a has options (depending on horizontal base) from 5k points in 100 to 50k in 1000. I had the 'fit to screen' turned on as well.  Since we are quoting chapter and verse :-), on page 3-12, Normal mode on my 3054b is 10k points but it doesn't say for instance, 10k in 10 divisions.   Since it displays 10 divisions, would it be 10k points in 10 divisions or 1k per?  Comparing to the 744a then, 50k in 1000 would be only 50, so that can't be correct, or maybe it is as the scope is so much older as everyone points out.  By the way, I'm getting a little tired of everyone saying how old my stuff is, it is all I can afford.  I don't have some monster company paying for my toys, it is all me!!!  Just kidding, I know the stuff is old but not as old as some of the things I have.

I was messing around the 3054b again and clearly I need to learn how to operate it better.  I wonder how many people on here make that statement every day? 

Anyway, success is in the pictures below.  The tds744 still has much higher contrast to me, again it could be just the vision defects I have playing into it.  The hardcopy mono prints look pretty much the same though there is variance in the sample time.  One thing that is obvious between the two scopes is the processing engine on the 3054b is much, much faster than the 744a at the same record length.

I do have to figure out how to change the battery in the 744 as one of the previous posters has me concerned now.  When I bought it, it was last serviced and calibrated in like 2011 so I wonder if they replaced the battery.  Also if anyone knows, is there a way to dump the calibration either to diskette or over GPIB in case I lose it the battery?

By the way, thanks for everyone's help.  It's been a very productive thread from my perspective.

Jerry

[cncjerry]

just noticed the difference in horizontal.  Here's the same 3054b at 400ns:

[David Hess]

By the way, I'm getting a little tired of everyone saying how old my stuff is, it is all I can afford.  I don't have some monster company paying for my toys, it is all me!!!  Just kidding, I know the stuff is old but not as old as some of the things I have.

Your TDS744A makes my newest oscilloscope, a 2440, look like an antique.  The the oldest oscilloscopes I regularly use were first produced in 1973 and one of those is still faster than anything Rigol makes for less than $4000.

The tds744 still has much higher contrast to me, again it could be just the vision defects I have playing into it.

The TDS displays were pretty nice and CRTs naturally have high contrast.  Tektronix used that weird LCD color shutter system because color CRTs would have sacrificed display resolution.

I would prefer your TDS744A to the alternatives simply because it supports magnitude/phase FFTs but that is a pretty esoteric feature.

[nctnico]

About the battery in the TDS744A: In the one I had I desoldered the NVRAM and backup it up using a $25 eprom programmer. I soldered the NVRAM in a socket and soldered a socket in the board. I never needed to replace the NVRAM. I still have a TS510A in which the NVRAM seems to be just fine (at least the last time I used it).

[Wuerstchenhund]

Acquisition interval (Tektronix still uses this term.) is not the same as waveform acquisition. 

You're right and I was wrong. My bad, I had a look at some other Tektronix documentation from that aera, which confirms what you said.

Are you thinking of peak detection as Rigol defines it on their older DSOs where they confound peak detection with envelope detection?  They work the way you describe when in peak detection mode which on a Tektronix would be envelope detection mode.

Possibly. The last time I have used a TDS700A scope was probably around 1997, and Peak Detect maybe a couple of times over a decade ago. For the type of work I did it didn't add any benefit. Most shops I worked were predominantly HP (and later Agilent).

But one point still stands, which is that the TDS700A Series was great in 1994 but even though some features like InstaVu work a bit differently than I remembered I can't see anything that can't be done in modern scopes (although I'm not saying that this is necessarily true for Rigols, though). After reading a it more about how the functions in the TDS700A work I can see why Tek had implemented it that way, considering that this is based on 1994 technology with very little processing power. And for a scope from 1994 it's a very good scope.

But I also see the limitations of the technology of that era, which in case of the TDS744A lies in the fixed combination of acquisition modes, the simple Hi-Res mode, the simple and slow math and FFT modes (although the TDS744A at least uses 10kpts for FFT which is much more than the the 700pts or less Rigol uses on their scopes), and the lack of any advanced analysis capabilities.

On a TDS744A you can use 20 or so combinations of acquisition and display modes. Most with the ability to tweak some parameters.

That sounds a lot (and for a scope from the 90's it is) but in comparison with newer scopes it's not much, especially when considering the limitations of most of these modes (i.e. Peak Detect works only on slow acquisitions). For example, if I'd count the possible combination of acquisition and display modes of my oldest scope (LT264M) then even in basic config I'd certainly get to at least 3x that number (and with the options I'd say its probably over 100 possible combinations), and that is a scope from 2003 which is positioned in the same spot as a TDS700/7000. A 9354 (which is from around 1995) should allow a similar number of combinations.

[cncjerry]

I would prefer your TDS744A to the alternatives simply because it supports magnitude/phase FFTs but that is a pretty esoteric feature.

Wait, magnitude, yes, phase?  I have to go back and dig thru my manual as I don't remember seeing phase.  Would that be a two channel math operation?  You have me thinking here tonight as for phase you would need I/Q, current, or a known impedance sense resistor, no?  Don't tell me I bought all that VNA, spectrum analyzer, etc, etc. stuff for nothing...  I wish it wasn't so late to go read-up on it.

[David Hess]

I would prefer your TDS744A to the alternatives simply because it supports magnitude/phase FFTs but that is a pretty esoteric feature.

Wait, magnitude, yes, phase?  I have to go back and dig thru my manual as I don't remember seeing phase.  Would that be a two channel math operation?  You have me thinking here tonight as for phase you would need I/Q, current, or a known impedance sense resistor, no?  Don't tell me I bought all that VNA, spectrum analyzer, etc, etc. stuff for nothing...  I wish it wasn't so late to go read-up on it.

The FFT function in the TDS500 and later series can display the phase information as well as the magnitude so if you have an impulse response measurement in the time domain (or differentiate the step response), then you can use the oscilloscope for low performance vector network analysis.  Some LeCroy oscilloscopes can do this as well (and probably better) and both Tektronix and LeCroy have application notes which discuss the procedure.

http://www.tek.com/document/application-note/fft-applications-tds

[Ivan7enych]

These board ID resistors (R1061<->R1064), whit which the model can be set, are near these EEPROMs as well. Soldered is 1.

TDS784A: 7,   0 1 1 1
TDS754A: 8,   1 0 0 0
TDS744A: 6,   0 1 1 0

Is there any mistake?
I opened my TDS744A and found another picture,
1061 soldered, 1062 open, 1063 open, 1064 soldered.
Can you help me here, what should I made to change it to 784? Can I brick if I make invalid ID?

[blacknoise]

Are all four placeble resistors "0-Ohm jumpers"?

Do all four mounting places for the resistors / jumpers share a common signal or a common level (e.g. GND, +5V, +3.3V...)?

Then i could not resist my curiosity to connect a rotary hex switch to the common line and the four ID select lines to start "turning out" all 16 possibilities... ;-)

Kind regards

[cncjerry]

Are all four placeble resistors "0-Ohm jumpers"?

Do all four mounting places for the resistors / jumpers share a common signal or a common level (e.g. GND, +5V, +3.3V...)?

Then i could not resist my curiosity to connect a rotary hex switch to the common line and the four ID select lines to start "turning out" all 16 possibilities... ;-)

Kind regards

as long as one of the 16 options isn't "CLRNVRAM".

[Ivan7enych]

Finally my TDS744A thinks it is 784A.

TDS784A: 7,   0 1 1 1
TDS754A: 8,   1 0 0 0
TDS744A: 6,   0 1 1 0

In this table, soldered is actually 0, open is 1.

The solution was to remove 0-resistor from R1061 place. Now I'm testing the scope...

[tinhead]

Can I brick if I make invalid ID?

oh well, even if, you made for sure EEPROM and NVRAM backup, right?

NVRAM and these two EEPROMs are protected by defualt, so as long you not change the switch position nothing can be saved there (except the profiles/setups, but they can be purged).

[cncjerry]

Finally my TDS744A thinks it is 784A.

TDS784A: 7,   0 1 1 1
TDS754A: 8,   1 0 0 0
TDS744A: 6,   0 1 1 0

In this table, soldered is actually 0, open is 1.

The solution was to remove 0-resistor from R1061 place. Now I'm testing the scope...

So it reports as a 784a but what happens when it switches to the higher rate, does it work correctly?  As in basically function setting aside that it might need calibration or must it be calibrated first?

[cncjerry]

I got a lot out of this thread and appreciate all the input, very helpful.  A couple more questions and I will move on:

1) on the 3054b, I read tektronix released/unlocked all the module software in version FV4.1.  I have 4.1 on my scope and don't see the advanced analytical functions under the math menu.  Were there two versions of 4.1 or was that not included?

2) I looked around and don't see anything, but was wondering if the 3054b could be hacked up to a 3064B?  It's only a marginal increase but why not if I could?

3) one thing has always bothered me a little on the 744a is the calibration signal seems really noisy.  It could be all the overshoot and I see the same noise testing it with the 3054b.  Both calibration signals on the scopes are the same frequency yet the rise time on the 744a calibration signal is much faster than that on the 3054b: 1.320ns on the 744a;  206.5ns on the 3054b. 1/1.32E-9 is .75Ghz on the 744a and 1/206.5ns is 4.8Mhz on the 3054b.  I'm not using the correct terms, what would 1/(rise time) be called? I don't think this means anything, just trying to get a better understanding of the scopes.

I use my scopes for RF work approaching 1G today and higher in the future.  I've been looking at the low end Agilent scopes, MSOX2024a for example, and the displays look good to me with my vision problem.  I doubt they are special in any way, I think it is more how they present the trace than the display.   If someone made a high contrast OLED display I would jump on it if it was within the reach of a typical independent inventor, say less than 4k or so. 

I completely lost a little over half of my vision. The remaining has two aspects: The first can be described by us technical types as low dynamic range hence the need for high contrast.  If I make the scope bright enough then it washes out other details like the grid and text.  The second problem is that bright lights have blooming, not unlike cranking the trace up too high on an analog scope.

Anyway, thanks again.  If anyone ever needs high end CNC work done, parts made, drilling, etc, please send a PM.  I generally do work gratis for people that share my interests, especially if the need is one-off and interesting.  I don't make parts that can be bought elsewhere unless they Are ridiculously expensive and/or made of unobtanium.

Jerry

[EV]

..
1) on the 3054b, I read tektronix released/unlocked all the module software in version FV4.1.  I have 4.1 on my scope and don't see the advanced analytical functions under the math menu.  Were there two versions of 4.1 or was that not included?
..

I do not know about 3054b modell but in TDS3032 only Adv trigger and FFT modules are unlocked with the latest FW, nothing else.

[Ivan7enych]

Can I brick if I make invalid ID?

oh well, even if, you made for sure EEPROM and NVRAM backup, right?

No. I still have no idea where the battery is inside this scope. Is it possible to read both with GPIB commands? I looked at your source code, and I see some commands there, but I don't have any native GPIB adapter to run your code wihout modifications. I have prologix GPIB adapter, which works as if it is a com port.

[Ivan7enych]

So it reports as a 784a but what happens when it switches to the higher rate, does it work correctly?  As in basically function setting aside that it might need calibration or must it be calibrated first?

Main difference, there appears 4GS\s for single channel and 1GS\s for 4 channels. Analog bandwith, high frequiency rolloff (above 500-600MHz), rise time didn't change at all.

Also, second improvement - now I can see in FFT signals up to 1.6..1.8GHz. There is a significant rolloff, but many radio signals are visible there.

There appears some misaligment between ADCs when I switch single channel aquisition from 2GS\s to 4GS\s, but after warming and self calibration (from scope menu) everything in general looks fine.

[tinhead]

Can I brick if I make invalid ID?

oh well, even if, you made for sure EEPROM and NVRAM backup, right?

No. I still have no idea where the battery is inside this scope. Is it possible to read both with GPIB commands? I looked at your source code, and I see some commands there, but I don't have any native GPIB adapter to run your code wihout modifications. I have prologix GPIB adapter, which works as if it is a com port.

to backup nvram you can use tektool

http://www1.tek.com/forum/viewtopic.php?f=5&t=5527

or this backup tool (booth are working ok)

https://groups.yahoo.com/neo/groups/TekScopes/conversations/topics/79198

There are two nvram chips, one doing clock and what so ever, and the second to store settings.
They mapped to :

straddr = 0x04000000L; /* Start of TDS700A DS1486 - clock chip */
endaddr = 0x0407FFFFL; /* End of TDS700A DS1486 - clock chip */

straddr = 0x04080000L; /* Start of TDS700A DS1650/DS1250 NVRAM */
endaddr = 0x040FFFFFL; /* End of TDS700A DS1650/DS1250 NVRAM */

the cal data, as already said, is in EEPROM on TDS700A, so use that code which posted already (or part of it) with your GPIB adapter.

[David Hess]

3) one thing has always bothered me a little on the 744a is the calibration signal seems really noisy.  It could be all the overshoot and I see the same noise testing it with the 3054b.  Both calibration signals on the scopes are the same frequency yet the rise time on the 744a calibration signal is much faster than that on the 3054b: 1.320ns on the 744a;  206.5ns on the 3054b. 1/1.32E-9 is .75Ghz on the 744a and 1/206.5ns is 4.8Mhz on the 3054b.  I'm not using the correct terms, what would 1/(rise time) be called? I don't think this means anything, just trying to get a better understanding of the scopes.

The calibration signal is usually only intended for checking and adjusting passive probe compensation (and gain and offset on the 744A) so there is little reason for it to have a fast transition time.  I have noticed before though that Tektronix calibration outputs sometimes have fast transition times but there seems to be no pattern as to why.  Some of the LeCroy ones are fast enough to be suitable for TDR applications.

The noise seen on the calibration signal is usually just ambient RF noise picked up by the probe because of its long ground lead.  On oscilloscopes which use a coaxial connection for the calibration signal output, it will be noise free.

[cncjerry]

I bought an NI PCI-GPIB adapter card from a guy in Sweden.  It as $50USD shipped and works perfectly.  He had 4 left a few weeks ago, I am buying another one today so you better hurry...

I am opening up  my 744a as I type, going to try to the mod.

Thanks again.

[MarkL]

..
1) on the 3054b, I read tektronix released/unlocked all the module software in version FV4.1.  I have 4.1 on my scope and don't see the advanced analytical functions under the math menu.  Were there two versions of 4.1 or was that not included?
..

I do not know about 3054b modell but in TDS3032 only Adv trigger and FFT modules are unlocked with the latest FW, nothing else.

That's interesting your scope is running 4.1.  According to Tek's web site, the latest firmware for both the TDS3000 and TDS3000B is 3.41.  Is 4.1 available for download somewhere?

Even for the TDS3000C (latest is v4.26), Tek is still selling the same Math, Limit, Telecom, and Video keys so I assume those have not been unlocked in any version of the firmware.

[cncjerry]

Yes, I mistyped the version number, it is 3.41, not 4.1 as stated.  Tek calls this FV3.41. 

I took out the resistor as the previous posted suggested in the 744a.  It now presents as a 784a and moves smoothly into 4Gs/s sampling.  Pretty cool.

This doesn't make sense, though and I wonder if it is calibration related:   The risetime on the probe calibration signal now reports as 1.183 after the change where it was 1.340 before. All the settings are the same with the exception of the 4Gs/s mod.  I have repetitive signal turned on and the ET is reporting as 250Gs/s.  I don't remember it being that high in the past.

Another question:   On the 744a there is what looks like a thin PC board sensor around the BNC jacks.  It looks like the probe pin wore the surface coating off a little.   Is this considered a problem?    I've seen those PC board/cables for sale, and thought they were a little expensive.

[nctnico]

Hmm. I'm starting to regret selling my TDS744A even more  . TiN has told me about the 1GHz hack before but I never got round to try and more or less forgot all about it.

[David Hess]

This doesn't make sense, though and I wonder if it is calibration related:   The risetime on the probe calibration signal now reports as 1.183 after the change where it was 1.340 before. All the settings are the same with the exception of the 4Gs/s mod.  I have repetitive signal turned on and the ET is reporting as 250Gs/s.  I don't remember it being that high in the past.

I doubt this could be related to any increase in sample rate.  The original transient response calibration of the oscilloscope was probably only done up to 500 MHz so when configured to 1 GHz, it results in a peaked response which will make the transition time look faster than it really is.  You could test for this using a leveled signal generator or reference flat top pulse generator.

[nctnico]

AFAIK there is a programmable bandwidth filter in the input stage which is disabled by the hack. If you look in the TDS520B component service manual you'll see the input stage has several bandwidth setting pins.

[tinhead]

one of the calibration steps is HFCal, which is unique for 500MHz ang 1GHz. Check the fied adj software, and all these *.con files and you will see all the differences during clibration for different models. So yeah, sampling as said before is getting increased, but one can have bigger skew between channels and of course bw is not given. Only calibration can change this. When there are errors due unmatched input hybrids during calibraion, one can comment out hfcal in field adj software and run it again. I don't have any TDS700x anymore, so can't help more that this what i already did in the past.

Attached cal data from perfect working TDS754A. It would be still great if someone with TDS784A could dump the cal data.

[cncjerry]

Hmm. I'm starting to regret selling my TDS744A even more  . TiN has told me about the 1GHz hack before but I never got round to try and more or less forgot all about it.

Nicotine,  Yes, let me tell you, most people that come in my lab look around and their eyes settle on one of two things: my 744a; or, my perfect, and I mean perfect, HP-4815a RF Vector Impedance Meter with probe, original cardboard Impedance calculator and manual, I might add. It would be a toss-up between my first born and the 4815a if I had to catch one or the other.  Not to get to far off track,  but I could power on 4815 and measure multiple circuit nodes before I find the cables for my  Advantest r3131a and tracking generator.

And since I am rambling as usual, the other thing I get a lot of comments on is my retro Dekabox.  The picture doesn't do it justice as I cleaned it since.

I'm was going to bid on a TDS5034a that just went for $1,017 on ebay.  It has an error though and I have a stack of errors waiting to be fixed already.  I like that scope.  Another one went for about $1000 a few months ago and all it needed was the software  CD (that Tek wanted  $350 for, by the way).

[MadTux]

Anyone here has the schematic for the attenuators of the TDS 744A/754A/784A?

I'm now a happy owner of a 744A that became a 784A by removing the R1061 resistor from the back of the acquisition board.

Works great apart from the damaged LCD shutter and a problem with the CH1 attenuator. The guy on ebay said something about purple spots on the screen and I was unfamiliar with the LCD shutter technology and therefore thought that somebody was playing with magnets or spilled some ink as I believed that Tek used a normal color CRT.
But I can live with that, since the CRT itself is still in perfect condition and a few purple spots don't really bother me in seeing the traces on screen. If the problem gets worse, I'll simply cut the shutter off and use it in monochrome white mode. Not really nice, but usable.

The other problem I'd like to fix is the broken attenuator of CH1. The relays are still clicking, but I loose the signal if I switch between 100mV/div and 200mV/div and only see small capacitive spikes in 200mV/div mode.
This makes me think that those numerous gold pins in the plastic connector, the amp, ADC ... of CH1 is fine and one of those 4 yellow relays has bad contacts. Switching between AC/DC doesn't change it.

Since there's a black chip on the ceramic assembly and I'm unsure if it has anything do do with the relays, I don't want to use my usual method of cleaning relays by  applying 20V@100Hz _|¯|_|¯|_ from a function generator for a few minutes to a few h until the oxides on the relay have vibrated off.
Maybe someone has the schematic, so I can see which relay I need to torture or unsolder

[cncjerry]

There's a guy on the tek scopes forum that replaced his 744a display with a standard LED type and it looks and works great.  He listed the parts and it was like $150. There are some guys over there in that forum that know that scope inside and out and could help with the attenuator problem.

Jerry

[curiosu]

Dear Tek wizards, I've got a TDS 724A, is there any hack/mod that will increase the sample rate ?

 Many thanks, MC

[dnmeeks]

you can even get more on tds700A series, with 4 resistors (in your case from 744A to 784A only one resistor on acq board) one can get 4GSa/s for single channel and 2GSa/s when 1or 2 and 3 or 4 ch enabled. The bandwidth increase to 1GHz must not work always.

I love this! I have a TDS754C, and wanted to try this mod. I didn't see any jumper settings (R1061-1064) for that particular model / hack, so I mapped all of the settings, just in case anyone else needs them:

R1061 R1062 R1063 R1064 is the order.
1 = INSTALLED
0 = Not Installed
The text (ie "TDSxxx") is the model displayed on the CRT after booting. TDSxxx is literally what some of them said, so I assume this is either a test mode or just not supported / unpredictable.

0000: TDSxxx
0001: TDS784C
0010: TDSxxx
0011: TDSxxx
0100: TDSxxx
0101: TDS724C
0110: TDS794
0111: TDS794
1000: TDS754C
1001: TDS754C
1010: TDS724C
1011: TDSxxx
1100: TDSxxx
1101: TDSxxx
1110: TDS754C
1111: TDS754C

In my case I left them at 0001 for TDS784C.
I verified rise times: before: 480psec, after: 270psec!!! That equates to >1GHz analog bandwidth!
I am going off to figure out how to calibrate this thing now.
Great hack, I can't believe it was there the whole time.
Dan

[eKretz]

I know that this is a very old topic, but there is missing relevant information regarding upgrading the TDS scopes to higher bandwidth versions in case anyone runs across it. The ID jumpers/resistors are NOT the only thing that needs to be done in order to upgrade the scopes. There are coupling capacitors in the signal path also that need to be removed to achieve the higher bandwidth. These are listed in another more recent post which can be readily found if you do a search here at EEVB. Several posters in this thread have apparently performed only half of the work, (the jumper swaps) which is why they see no significant improvement in risetime numbers. After the coupling caps are removed also and the calibration is performed the scopes will indeed achieve 1GHz B/W.