EEVblog #1185 - Dumpster Tek TDS540D Scope

[EEVblog]

Will this dumpster 500MHz 4 channel Tektronix TDS540D scope work?
Teardown included of course.

[Deodand2014]

Is this episode 1185? The last episode was 1184 as well.

[FERCSA]

One vote for a repair video!

Good news is the CRT has some kind of sign of life, so it should be something with the controller board.

[SilverSolder]

Looks challenging to repair without being able to power it up - maybe an external video signal generator would come in handy?

I like the LCD upgrade idea.  Especially if it can be coaxed into making a colour picture!

[Brumby]

Is this episode 1185? The last episode was 1184 as well.

Indeed




EDIT: It's been fixed 

[johnlsenchak]

Hey Dave

Please  do a  repair  video  on that oscilloscope  with a   1080P  or VGA  display

[snoopy]

You still can't buy a cheap decent 4 channel 500Mhz scope which is why these are still sort after apart from the earlier models with cap problems. And with the Tek active probes this makes it an even more valuable combination

Dave when you get a chance try measuring the waveform update rate. You'll be shocked at the performance of these things considering their age. I have a TDS784 and with Instavu or DPO switched on I managed to clock about 390,000 waveforms per second with a 1 MHz signal on the input. They really were way ahead of their times 

cheers
david

[MT]

Repair CRT then do the upgrade to LCD

[EEVblog]

Is this episode 1185? The last episode was 1184 as well.

Err, yeah, 

[EEVblog]

Please  do a  repair  video  on that oscilloscope  with a   1080P  or VGA  display

1080p is not possible, it's only 640x480 VGA output

[EEVblog]

Looks challenging to repair without being able to power it up - maybe an external video signal generator would come in handy?

Yep, would be really annoying.
First step might be remove and electrically check caps and other things and hope to get lucky before having to try and power it up and feed in a signal.

I like the LCD upgrade idea.  Especially if it can be coaxed into making a colour picture!

I'd love to know if it can be colour. The other models are, and the firmware and hardware obviously supports it in some way. Anyone know anything?

[tsman]

I'd love to know if it can be colour. The other models are, and the firmware and hardware obviously supports it in some way. Anyone know anything?

Need to change 1 part, modify the strap resistors and add more VRAM but it looks like you can upgrade your TDS520D to be a colour TDS754D. It would make a very nice colour scope with a new VGA LCD fitted.

[snoopy]

Looks challenging to repair without being able to power it up - maybe an external video signal generator would come in handy?

Yep, would be really annoying.
First step might be remove and electrically check caps and other things and hope to get lucky before having to try and power it up and feed in a signal.

I like the LCD upgrade idea.  Especially if it can be coaxed into making a colour picture!

I'd love to know if it can be colour. The other models are, and the firmware and hardware obviously supports it in some way. Anyone know anything?

I used to repair TV's a long time ago before they went to LCD. Typically a fault like this could be traced to the yoke coupling capacitor on the horizontal yoke windings. From memory usually a metalized polyester type capacitor or poly carbonate of around 3.3uF is what they used on old 12inch B&W TV's. Does anyone have a schematic of the monitor section ? Sometimes even a dry joint was the culprit around the line output transformer etc

cheers

[EEVblog]

I'd love to know if it can be colour. The other models are, and the firmware and hardware obviously supports it in some way. Anyone know anything?

Need to change 1 part, modify the strap resistors and add more VRAM but it looks like you can upgrade your TDS520D to be a colour TDS754D. It would make a very nice colour scope with a new VGA LCD fitted.

Cool!

[tsman]

More upgrades possible

You can enable all the options via GPIB.

It may be possible to upgrade it to 1GHz as well by removing some caps and altering the strapping resistors. Guide is for an A model though not the D model. It'll be a hassle to recalibrate it though.

[IanB]

Sometimes even a dry joint was the culprit around the line output transformer etc

"It's always a dry joint around the line output transformer"

...says me from personal experience 

[DaJMasta]

Those memory controller QFPs attached to the ADCs are real beauties! 

[Moshly]

Only just finished converting a TDS310 to LCD. (dead flyback)

LCD was this one from ebay ~$100 AUD
https://www.ebay.com.au/itm/VGA-AV-LCD-controller-board-with-5-6inch-640x480-AT056TN52-lcd-panel/251590018265?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

[nueron]

The TDS monochrome CRT schematics are at the very end (pg 366+) of the TDS520B Mod CM Service Manual. Do a search for "TDS520B Mod CM" and you should be able to download the pdf.

You should also be able to test the CRT outside of the frame via the ribbon cable only. However, I would make sure that everything is properly grounded (e.g. metal strap around the front of the CRT is grounded to the chassis!) as you don't want high voltages flapping around in the breeze...

[AndyC_772]

It's not that long ago I was making a living with a TDS754D as my main bench scope. They might be old, but performance was exceptional for the time. A solid workhorse of an instrument if ever there was one.

I eventually switched to an Agilent MSO-X3054A for two reasons:

- The Tek was an old scope, and I was always worried that it might finally expire at an awkward moment. Not such an issue if you're using it for a hobby, but when your livelihood depends on it, reliability is key

- One hot summer the combination of a south facing lab and a scope chucking out ~400W became too much to bear. The scope itself doesn't "run hot" as such, thanks to that massive fan and heat sinks, but it does warm a small lab alarmingly effectively.

The new scope has given me back a fair amount of desk space, and the lab is much quieter and more comfortable - but in performance terms there's not a huge amount to choose between them. Serial decoding and much faster horizontal pan/zoom are about the only differences I notice in day to day operation.

I still miss equivalent time sampling. Not sure if anyone's doing that any more

Also: I had a TDS540 for a short while too, and its CRT driver board went bad in much the same way. I tried replacing every cap on the board with no luck, and eventually replaced the whole board with a donor. I think the flyback transformer had failed, and they're unobtainium.

LCD kits used to be too expensive to really be an economical repair given the value of the scope. Has that changed now?

[snoopy]

Only just finished converting a TDS310 to LCD. (dead flyback)

LCD was this one from ebay ~$100 AUD
https://www.ebay.com.au/itm/VGA-AV-LCD-controller-board-with-5-6inch-640x480-AT056TN52-lcd-panel/251590018265?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

That's a great retrofit

cheers

[CJay]

As always, I need a dumpster like that...

The Schaffner gadget, I think I have plugs for it, they look like the ones used on Motion control hardware, I've got one sat on my desk, if there's an intention to get it running I could post a secondhand one over?

[bsfeechannel]

Dave is so lucky, it is contagious. I was walking a few blocks from home the other day when I noticed a small cardboard box tossed to the curb. It was full of NOS tubes. It was not a Tek scope, but I had never found anything before watching Dave's dumpster dive videos. Unbelievable.

[David Hess]

I still miss equivalent time sampling. Not sure if anyone's doing that any more

There is a lot to be said for 100 GSamples/second or higher to remove all doubt about what the DSO is showing but if I am reading the specifications right, the TDS500D series is real time only and the TDS700D series is needed to support equivalent time sampling.

Some high end DSOs still support equivalent time sampling but it requires extra hardware outside of the vertical signal chain and digitizer which is not amendable to integration unlike faster digitizers so ETS became relatively more expensive as Moore's Law marched on.  Implementing ETS after the ADC is a contradiction.

Update:

The tear-down video seems to show that ETS is supported but the documentation says otherwise.  I wonder what the story is with that.

[David Hess]

Dave, the Dallas nVSRAMs routinely last about 20 years so those are close to the end of their life.  Before getting too involved in repairing the display, know that the calibration data is stored in the nVSRAMs and the calibration procedures are very involved requiring special equipment and software.

Replacing the nVSRAMs is not too difficult however I have not successfully been able to read a nVSRAM which is that old.  If you try this, I suggest testing your read and write procedures on an expendable nVSRAM of the same type before removing the ones inside the instrument.