Tektronix 7603 + 7D20 Digitizer - Page 1
Forum section: electronics / testgear

author: david77
author_rank: Frequent Contributor
timestamp: May 04, 2014, 01:38:42 pm
content: A 7603 mainframe and the digitizer plugin 7D20 are on their way to me, should arrive sometime next week.I've always lusted for a 7000 series Tek scope, now that it's on its way I'm wondering what I've let myself in for this time.Apparently the scope works for most of the time, but the seller told me the CRT gets dim from time to time also the digitizer plugin works but sometimes says "Calibration failed" or some similar message.Any thoughts?

author: wn1fju
author_rank: Frequent Contributor
timestamp: May 04, 2014, 03:09:16 pm
content: I have the 7603/7D20 (which fortunately works fine). It is a very nice arrangement, particularly for lower frequency (<50 MHz) waveforms and can do averages, envelopes, storage of waveforms, cursor readout/measurements, etc. It automatically switches to a strip chart at slow time bases, which is kind of cute. Unfortunately, it is a little hard to diagnose what could be wrong with yours. While (free) service manuals are available on-line, your biggest problem will be working on the 7D20 which is a 3-slot plug-in. That means ideally you need three extender cables or extender plug-ins, although it might be possible to get to some of the guts in-place if you take off the side panels of the host scope. Occasionally, one will see the extenders for sale on eBay. The prices are prohibitive because the sellers know that people need these things desperately and are willing to pay exorbitant prices. It is rumored (google it) that you can make your own extender cables in a pinch. Good luck.

author: MadTux
author_rank: Frequent Contributor
timestamp: May 04, 2014, 07:15:41 pm
content: I like my 7D20. Very useful if you are a fan of the 7k series and already have some 7xxx mainframes standing around and you need a plugin for slow single shot signals, e.g. for old slow speed microcontrollers.I only had problems with the attenuator relays. Since it's fully digital unit, the V/div knobs is read by a microcontroller that operates 4 relays on each channel.Over time, the traces on the ceramic PCB substrate, on which these relays are placed, collect some dust and oxidation, so that the attenuator sometimes fails.Another problem is that the leaf spring contacts of the relays are bent too much and won't make contact on the PCB surface.http://pcbunn.cithep.caltech.edu/jjb/tektronix/7D20/tektronix_7d20.htmProblem #1 can be solved by carefully cleaning the PCB (inside the plugin, very complicated to remove it since the whole 7board plugin needs to be taken apart to remove it) with 70%/30% isopropanol/water and a very fine brass wire brush pencil to remove dust and oxides on the PCB.Problem #2 is solved by swapping each relay between one bad and one good channel to identify bad relay and carefully straightening the bad spring contacts of the bad relay

author: david77
author_rank: Frequent Contributor
timestamp: May 05, 2014, 06:41:18 pm
content: Thank you guys.I didn't think about how to fix the plugin while it's plugged in. I'm still hoping it won't be neccesary, may only be dirty contacts - one can hope.

author: edavid
author_rank: Super Contributor
timestamp: May 05, 2014, 07:10:53 pm
content: The 7D20 is a heavy load that will show up any weakness in the 7603's power supply. When you get the scope, check the supply voltages.

author: david77
author_rank: Frequent Contributor
timestamp: May 06, 2014, 02:59:38 am
content: Quote from: edavid on May 05, 2014, 07:10:53 pmOk. Will do.

author: David Hess
author_rank: Super Contributor
timestamp: May 06, 2014, 03:12:20 am
content: We have had some interesting discussions over on the Yahoo Tektronix email list about the 7D20 which led to me studying its design in detail. When I went hunting for an inexpensive DSO, I only avoided it because of its lack of peak detection.

author: david77
author_rank: Frequent Contributor
timestamp: May 07, 2014, 09:51:07 pm
content: I haven't yet received the scope but I did some research on it and on the 7D20. It seems it's even possible to take screenshots off of it via the GPIB interface. There are drivers for LabView available and I also found thishttp://www.hakanh.com/dl/ScopeWFM.htm.Has anybody taken waveform data from a 7D20? Would be nice to know before I go out getting a GPIB card.

author: david77
author_rank: Frequent Contributor
timestamp: May 11, 2014, 09:48:56 pm
content: The paket with the scope was waiting for me at home when I came back from work a couple of days ago. I have to admit I was a bit shocked by the size of it. And by the size of the scope that came out of that box, I didn't expect it'd be that bloody deeeeeeeeeeeeeep. Where the hell am I going to put that beast?Optically the 7603 and also the 7D20 are in good/very good condition, no broken knobs or major dents or scuffs.Electrically it basically worked as advertised, there is some intermittent fault with the brightness of the scope that appears everytime you knock the right side of the case a bit. Also the brightness pot on the front needs cleaning. These issues may be related.The 7D20 sometimes doesn't pass the self test, I reckon there are some dirty contacts involved. I've already cleaned the input attenuator relay contacts, which has improved reliability drastically.Three of the caps in the PSU looked a bit dodgy ESR wise, so I decided to replace them all.That ugly blue contraption is only a temporary fix, I've already ordered a suitable 22000µf/16V cap and also the others.The black cap to the left is already a replacement for the original Mallory caps. The originals were two 1800µf/75V types that I replaced with those Matsushita 2200µf/100V caps I had knocking about in the junk bin.

author: David Hess
author_rank: Super Contributor
timestamp: May 11, 2014, 10:39:32 pm
content: Quote from: david77 on May 11, 2014, 09:48:56 pmLonger CRTs have greater deflection sensitivity so Tektronix used all of the depth available in a deep rack mount frame.

author: tcleavela
author_rank: Contributor
timestamp: May 19, 2014, 08:24:25 pm
content: Quote from: david77 on May 05, 2014, 06:41:18 pmJohn Griessen sells a flexible extender kit for Tek 7000-series mainframe scopes, or at least he did back in 2011: john at ecosensory dot com.

author: casinada
author_rank: Frequent Contributor
timestamp: May 19, 2014, 08:36:54 pm
content: For the 7D20 you would need 3 extender plugins and that would be very expensive.You can find Extenders on ebay form $199 and up that would make it at least $600 in extenders.(can buy many 7D20s)You can buy a 7D20 for less than $100

author: PaulAm
author_rank: Frequent Contributor
timestamp: May 19, 2014, 09:01:50 pm
content: I just got one of those in with a bunch of 7603s. Very similar to the 468, although the specs are different. I think that's the largest screen in the 7000 series.Where to put it? Get a 7000 series scope cart and you can wheel it out of the way. That will also give you a place to store your plugins. What plugins? The ones you can start collecting that will turn your 7603 into anything from a curve tracer to a spectrum analyzer to a mutli GHz sampling scope.

author: David Hess
author_rank: Super Contributor
timestamp: May 19, 2014, 11:07:53 pm
content: The interface operation may be similar but the 7D20 digitizer is very different from the 468 digitizer. It lead to the 2430 series of DSOs which use CCD based acquisition while the 468 lead to the 2220, 2221, and 2230 DSOs which use an analog channel switch and flash ADC. The CCDs used in the 7D20 were originally intended for things like timebase correction and comb filtering in television applications.

author: tcleavela
author_rank: Contributor
timestamp: May 20, 2014, 01:25:53 pm
content: John Griessen's extender kit cost USD 28/per, although that was in 2011. Here's what the assembled version looks like:http://ecosensory.com/tek/TEK_7K_FLEX_assy-013-sm.jpgAgree that the official Tek extenders are prohibitively expensive.

author: casinada
author_rank: Frequent Contributor
timestamp: May 21, 2014, 06:16:43 am
content: I almost purchased one of Griessen's kits, but I found a tek extender very cheap and forgot about it.All the pictures of the kit can be found here:http://ecosensory.com/tek/as posted by tcleavela.Probably he lurks around on the TekScopes Yahoo group

author: david77
author_rank: Frequent Contributor
timestamp: May 22, 2014, 09:57:17 pm
content: The mainframe now works perfectly again, I fixed a couple of issues it had like ageing caps and a few bad contacts.The 7D20 is still giving me a bit of grieve, though.It has an intermittent problem I'm unable to pin down exactly. Sometimes both channels stop working and the trace moves vertically on the screen, sometimes slowly up or down and sometimes it jumps around like mad. When the digitizer is in this condition the self test gives me errors 65432 and 654321. Everything else continues to work like normal.65432 is test 62: CCD Multiplexer see page 133654321 is test 63: CCD A/D ConverterI haven't got the extenders to check the boards outside of the scope, soldering wires on the boards and running them outside works but is quite tedious. So before I continue doing test I'd like to ask what others think would be the right way to continue.So far I've checked voltages and resoldered everything around U1050 and U930. I thought that did it, it worked now for days but just now when I screwed the 7D20 back together it went straight back into that failure mode.The circuit diagrams I'm interested in are of the A5 board, thats on page 257 and 260 in the manual. I'm using the manual downloaded from BAMA.