Tektronix RTD720 resuscitation

[samofab]

Hello,

I recently acquired a Tektronix RTD720. The information about it is very limited. It appears to be a 500Mhz 2Gsa 4 channel digitizer that I think can be used as an oscilloscope. There is no manual on the internet. The unit that I got was (is) in unknown state, mostly because it is missing the cable that connects the main rack unit to the display. The status LEDs that were visible in the auction images instilled some hope that the unit is operational.

First impressions: it's big and heavy. The front panel is cast aluminium. It's not too loud and it didn't explode when I switched it to European voltage and plugged it in. Not for lack of trying on my part, though: after I opened the top cover I discovered that heat sink from one of the chips on the main AD board fell off. Luckily it didn't make any shorts. The unit responds to command over GPIB... The numbers on the PCB say that it was designed somewhere in 91' or 92'

First order of business is to make my own display cable.. or more precisely: hack it together first.

I'll post some pictures here... for starters I'm posting the image from the auction.

Any info on the unit would be appreciated.

[dom0]

tekwiki has a brochure about it. Looks like a transient digitizer mainly intended for physics experiments, so it has  2 GS/s real time sampling rate and segmented memory (at least that's what I understand from "Intelligent Memory Usage: Extremely fast multiple event capture"). It also seems to incorporate a somewhat high resolution time stamping unit ("time of arrival of each event is captured with time resolution as fine as 500 ps" -- probably runs off the acquisition clock).

The brochure also mentions it only supports IEEE488-1, so to make any use of the GPIB interface you'll absolutely need the programming manual...

[samofab]

I found original software disc on Tektronix website (the only thing there). The disk is meant to be directly bootable (DOS), but it also contains the BASIC source files for the capture and transfer of the forms. I didn't go into details, but copy pasting the commands to the unit resulted in sane responses. But yes, without real programming manual I'll be limited by the functionality in the BAS files. I really hope to get the display running.
Physics experiments focus was my presumption, too (in addition to military use of some sort)... I found an article about its use in an ultrasound experiment...

[daqq]

You should try talking to Tektronix directly - it's one of their more obscure pieces apparently, but they might dig out a manual if you ask them.

[samofab]

You should try talking to Tektronix directly - it's one of their more obscure pieces apparently, but they might dig out a manual if you ask them.

Actually I tried contacting support.. they said that they don't have anything. Perhaps it depends on the particular person handling the support request.

[samofab]

After some duct tape and soldering... the thing works. Buttons were sticking at first, causing the unit to lock, but after a few reboots it works kind of like it is 92' again. This particular unit apparently has 4M points memory... which I guess was quite a lot more than 20 years ago. No sin(x)/x yet...

Interface is slow as hell when capturing, otherwise it kind of works. Once I got over its byzantine organization, of course 

The thing makes funny noises when capturing.. possibly from power supply.

[rfincher]

Hello - anyone there after all this time?

I've also just acquired a Tek RDT 720A, and it has a more serious fault than those mentioned in the above posts. I wonder if other owners new to this device have learned more about resuscitating these rather nice instruments. I have a copy of the Operators Manual but not the Service Manual (which was an option for new buyers). It has quite good information about using a device which works, but has no faultfinding or troubleshooting content. As others have found, the Service Manual appears to be unobtainable, so I'm really looking for some helpful advice! The Service Manual for the sister model RTD710 is available, and gives some idea as to the complexity of these instruments.

My unit goes thru the self-diagnostic start-up, after which a System Status red fault LED lights up. Green LED's light up in the Front Panel and Active Interface sections of the front panel. A group of red LED's inside the instrument below the acquisition board also flash in some sequence or other during self-test, as do the GPIB status LED's on the rear panel. Voltages to the Acquisition board are -2.00v, +/- 5.00v and +/- 15.00v. The reference voltage at the rear panel terminals is 9.95 v. The flat panel Display Unit displays a raster, but no waveforms or text. None of the display unit buttons have any effect. There are 53.8 Hz and 11.6 kHz square pulses at the video out socket, but no other signs of video information.

In short, my machine is alive, but not well. Any help would be much appreciated.

[samofab]

If I understand correctly, the display unit is working and it is responsive. If that is so, you can run additional self tests. I just sold my unit so I can only help you "from memory" ;-).
If the display is not responsive, here are my very sketchy notes on what I saw on display cable: pin 5: 4MHz 3.3Vpp; pin 7: 13,4V; pin 8: -14V; pin 9: 13,4V.

[rfincher]

Hi Samofab,
Thanks for your reply. Although my display shows a raster, and the backlight and contrast controls work properly, the unit is not responsive in that there is no menu, text or cursors. The buttons on the display have no effect, so I can't run further self-tests via the display. I've just reassembled the display unit after inspecting the buttons for physical faults, but all seems fine. A check of the voltages on the display cable connector revealed plus and minus 15.0 volts, zero on the ground pins, and various DC voltages all less than 5 v. No sign of a 4 MHz sine wave. I don't think my problem is within the display unit itself.

Older Tek 'scopes could often be "brought to their knees" by a single faulty tantalum bypass capacitor somewhere across a DC supply. But there aren't many tantalums in the RTD 720, and they all tested OK. So it seems that I must start a serious hunt for a service manual. Do you remember who and how you made contact with Tek in your search for a manual? Perhaps an old-fashioned snail mail letter to their chief engineer might bear more fruit, as I simply don't believe that they no longer have at least one copy of a service manual, not only for the RTD720A, but for every single instrument they've ever produced.

Realising that you won't be too interested in these instruments now that you've sold yours, are there any more clues you might have, or any other contact people I should try to get in touch with? Many thanks.

Final question - the Operator Manual mentions an internal battery which is tested in the power-up diagnostic. Did you happen to discover where this particular battery is located? I didn't notice any battery when I dismantled the various circuit boards of the main unit, but I wasn't specifically searching for one at that stage.

[samofab]

I think I only used official support request on the Tektronix website. Direct contact with someone in engineering (not support) department seems like a very good bed. And sometimes it just depends on which particular person is solving your case. I once had a totally stellar support for obsolete product from Xantrex.. and a few years later they simply said "go away" on similar request (in a slightly more polite language).

If you don't see 4MHz clock on the cable, then the problem is very likely in your main unit. Looking at my photos, I think I see 68000 on the bottom board.. I guess you can check if you see clock on it. Perhaps the unit will power up properly with acquisition boards not installed. Very close to CPU I see something that looks like it might be a battery (next to 8-way DIP switch).

[rfincher]

Samofab,
Thanks again for your help - I'll keep exploring, and if I discover anything worthwhile, I'll report back under this post. Other commitments today, but will be back onto it tomorrow.

[rfincher]

Samofab,
Today I spent more time delving into my RTD720. I operated a few times the DIP switch on the rear panel which controls the powerup test, and lo and behold, I now have three green LEDs on the front panel. Supposedly this signifies no faults in the main unit. A test 'scope and probe revealed much digital activity on the lower board, and it seems that the circuitry around the 68000 CPU is active. However, I still have only a raster on the display panel, with no menu items, waveform or any other detail. This makes me think that the fault may well be in the display. A quick visual inspection doesn't reveal any apparent problems, but I'll investigate matters further - somehow the display unit seems nowhere near as intimidating as the main unit!! In an earlier post, you remarked that the display buttons were sticky, but eventually you coaxed them into operation - can you remember just what you did to "unstick" them? Any other thoughts on the behaviour of your display would be very helpful.
BTW, I did discover the battery in the same location as you said. It's a 3.5v lithium job (not bad for a 1989 product) and it's still delivering 3.65 volts after all this time.
Grateful that you're responding to my dumb questions.
Cheers

[samofab]

I think that the manifestation of stuck keys on my unit was manifested by not responding to commands and the screen was working otherwise. Still worth the shot, though: just remove the main display PCB (lots of screws) and use eraser/rubber to clean the PCB and the contacts on the rubber keyboard. Also wiggle the rubber keyboard in order to give it back some elasticity - and search this forum for additional advice, I'm sure this was better answered somewhere around here.

And of course measure voltages around the display board, check with oscilloscope that the signals are the same on both ends of the cable, try to locate clocks... and above all.. watch out for that back-light power supply - some painful genies live there.

[calmissile]

I ran across this thread during a search for a cable for the RTD720.

I am unable to locate the plugs necessary to make the cable that goes from the display to the main unit.  If someone would provide a cable, I would be very happy to copy and mail the two manuals I have.....

RTD 720A Transient Digitizer User Manual  070-8516-00

RTD 720A Transient Digitizer Programmer Manual  070-8518-00

[samofab]

I also couldn't find the cable or the connectors, so I removed the existing connectors and replaced them with VGA connector (it kind of fits, I had it lying around and it had enough pins). I guess it's about 2hrs job.

[Steve Dudley]

I have found the connectors on Digi-key website. Looking for wire cable.

I would love to get a copy of the two manuals that you have, and gladly pay you for the effort.