Tektronix R7103 Scope teardown (also 7A26) - Page 1
Forum section: electronics / general

author: muvideo
author_rank: Frequent Contributor
timestamp: May 09, 2012, 08:32:49 pm
content: Hello, recently I was searching some "new used" scope.The requirements were high bandwidth, more than 2 traces and not too costly,this drove me immediately to old tektronix 7000 units.These are wonderful scopes that can be found cheap and have huge possibilitieswith their flexible plugins. I was enlightened on this forum not long ago when I askedinfo about a tek 7934.The only problems I see with these machines is that they are big, and I mean BIG,and that are old, full of custom components, so the servicing isn't easy.On the positive side is that tektronix documentation is the best I've seen,and easy available and there are people around that know these machines in all details.On the Tekscopes Yahoo groups there was a message from a nice guy saying thatsome ebay seller had some R7103 units, sold as defective units.The same seller sold before some working units at a very good price and the peoplethat bought these reported that these units had very clean internals and good tubes.I tried and got a good offering from the seller: the delivery cost was higher than theasking price. I bought it, I think that this decision was also conditioned by thereading of app notes of Jim WilliamsWhen it arrived I realized why tektronix called the 24xx series "portables":because that ones didn't need two persons to carry around like this.To put things in perspective:The tube in these units (like the 7104) is particular and delicate, it's screen is slightly smallerthan the usual: 8mm per division instead of 10mm.At sub nanosecond per division the beam becomes very dim, and this tube contains amicro channel plate that intensifies the beam. This can be a problem at slow scans becausethe beam power can destroy the phosphors easily.There is also a timer that limits the use of the scope in order to save the tube working hours.This is the tag that reports the defect "no crt", bad sign :Here is the plugins bay:Here the top cover removed:And the bottom with the high voltage board:More to come...

author: muvideo
author_rank: Frequent Contributor
timestamp: May 09, 2012, 08:56:21 pm
content: This is the tag on the tube reporting calibration data, I suppose:These are some desoldered connectors, an important hint,here can be seen the channels switch bottom, the psu left, and theside of the readout board on the right:On the top there is the mode switches board:On the top back near the the psu there is the vertical channel switch:On the top of the tube the Horizontal amplifier:On the side of the tube the Vertical amplifier:And under the tube the Z-axis:And the High voltage circuitry:

author: muvideo
author_rank: Frequent Contributor
timestamp: May 09, 2012, 09:09:00 pm
content: More details:this is the route of the vertical channels from the plugins to the switch hybrid to the delay lines and at last to the tube:This is the channels switch hybrid:These are two 51nanoseconds:delay lines.

author: muvideo
author_rank: Frequent Contributor
timestamp: May 09, 2012, 09:17:07 pm
content: Later or tomorrow I will describe the symptoms, for now I don't want to gain access to the tube,there is a possibility that the tube is good and I don't want to risk to damage it.This is a wonderful piece of equipment, and my knowledge is too little to appreciate allthe particularities. I make my best and hope that the knowledgeable people that read this treadcan correct me and contribute with more details of the internal features and working principles of the scope.Fabio.

author: muvideo
author_rank: Frequent Contributor
timestamp: May 10, 2012, 08:17:46 am
content: Now the description of the problems.the scope arrived with signs of having been opened before:it lacked screws from top and bottom plates, and one from power supply on the back.The psu had some connectors bent like if it was extracted not too gently.The internals are very clean, and there were some wires unsoldered on the back, thesecame from the connectors of probes power supplies on the back.I put these wires in a safe position, changed the voltage range to 220V, inserteda new fuse and fuse cap that were absent and powered up.The graticule lighted up at max but not responded to the regulation pot,and the cooling fan was silent. Powered down and started reding the service manual.First thing I checked the psu voltages: +-50V and 5V were ok and very well regulated,but +-15 were almost zero. Powered down and waited for the input capacitors todischarge and measured the dual 15V rails with an ohmmeter and they were dead short to ground.Started disconnecting the cables, beginning from the psu, and the short went away oncedisconnected the cable that was going to the readout board.At this point tried starting without this connector and the fan started (in it is loud!)now the graticule illumination responded to the pot and the voltages were all ok.I gained access to the readout board on the side and here it was showing some signsof precedent working, two capacitors were bent down and two pots had signs offused plastic from soldering iron. The wires that were desoldered came from this boardand the pads have the signs of (dirty) desoldering process.The funny thing is that once removed the board I tried mesuring the 15V rails and theshort simply wasnt there. I reconnected the board to the scope and the scope startedwith all the voltages ok. I only reseated two caps with hands and nothing else.This is the readout board, tektronix partnumber 670-8622, it's different from theone in the R7103 service manual but the detailed schematic can be foundin the servicemanual of the 7934 scopein the final part of the service manual, section MANUAL CHANGE INFORMATIONS,probably because is a more recent unit.Now I don't know if there are other problems, and I dont like the fact thatthe rails problem disappeared with apparent self healing.My other concern is the tube, given thelong shipping and all the movement it was subjected during the delivery.Now I'm waiting for two plugins, probably they will arrive next week,I bought a pair of generic ones: 7A26 and 7B92A, if the scope will comeback to life I'll start searching info about suitable probes, and willtry to complete the setup with a 7B15 7A29 7A29/opt04,and another 7A26 for high impedance work.If there are ways to test the tube without the plugins let me know.Fabio.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 10, 2012, 09:07:24 am
content: "When it arrived I realized why tektronix called the 24xx series "portables":because that ones didn't need two persons to carry around like this."I'm not calling "wimp",but I remember carrying 545Bs solo,& on one memorable occasion,a 524AD!When the 7000 series came out,we were thrilled at how lightweight they were!

author: muvideo
author_rank: Frequent Contributor
timestamp: May 10, 2012, 09:25:06 am
content: Quote from: vk6zgo on May 10, 2012, 09:07:24 amWell, I was exaggerating, it weights a little less than 20kg an I imagine substantially less than a 5xx monsterthe fact is that it's also voluminous and uncomfortable to grab.I was thinkin to a discussion I had with a guy that was searchin info about a portable scopefor field use, not too costly and with a battery, I said him to consider the owon but he saidnooo tooo BIGFabio.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 10, 2012, 10:46:25 am
content: It was really a bit "tongue in cheek"--20kg or so is quite heavy enough!I bought a 7613 at a Hamfest a year or so back,& had to carry it way down the street.By the time I got to the car,my arm felt a bit stretched---Not too good for an Old Codger!As to the 5xx series,we were a bit silly & macho when we were young,strong,lads!

author: tekfan
author_rank: Frequent Contributor
timestamp: May 10, 2012, 11:29:14 am
content: Here's a funny picture of the old and new scopes in the old days:That looks like some piece of engineering right there. I had similar problems with the readout board in my 7904. Check all the peltola connectors and see if one of the thin wires of the shield of the coax isn't somehow touching the inner conductor.I would strongly suggest that you shouldn't try to see if the CRT works untill you get the plugins. All you can do for now is check the HV power supply with a HV probe to see if the volages are there.It is amazing when you think about what would be needed these days to capture a single 1GHz event. A +100,000 USD digital scope with at least 10 gigasamples/second. Or you could just use one of these Teks with the MCP accelerator and a camera to record the single shot event.

author: firewalker
author_rank: Super Contributor
timestamp: May 10, 2012, 11:45:53 am
content: MCP accelerator? Any infos?Alexander.

author: BravoV
author_rank: Super Contributor
timestamp: May 10, 2012, 11:52:00 am
content: Quote from: firewalker on May 10, 2012, 11:45:53 amhttp://en.wikipedia.org/wiki/Microchannel_plate_detectorMost high end tek analog scope has it, its considered rare & exotic crt technology for scope.

author: firewalker
author_rank: Super Contributor
timestamp: May 10, 2012, 12:08:51 pm
content: Thanks m8!Alexander.

author: muvideo
author_rank: Frequent Contributor
timestamp: May 10, 2012, 01:08:10 pm
content: Quote from: BravoV on May 10, 2012, 11:52:00 amThe ones I know of that use the intensified beam are the 7100 and 2467 "portable"Quote from: tekfan on May 10, 2012, 11:29:14 amIn that picture seem that Tektronix trusted their handles, if they failed the one under the stairs was doomedDon't know why but this image made me think to atomic Bill with the first atomic wristwatch :http://leapsecond.com/pages/atomic-bill/Fabio.

author: tekfan
author_rank: Frequent Contributor
timestamp: May 10, 2012, 01:37:22 pm
content: Quote from: muvideo on May 10, 2012, 01:08:10 pmDon't forget the Tektronix 11302. It also has the MCP. Although its bandwidth is ''only'' 400MHz it is probably the most complex analog oscilloscope ever built.The early versions of the Tek 11000 series had problems with the handles. They would rip off when two people were holding the scope in mid air. I wouldn't want to know what happened to the feet of the poor people moving the 40kg oscilloscopes.The later versions of the 11000 series scopes don't have the handles for this exact reason.

author: muvideo
author_rank: Frequent Contributor
timestamp: May 10, 2012, 02:35:10 pm
content: Quote from: tekfan on May 10, 2012, 01:37:22 pmDidn't know this.QuoteI can imagine:- "Bill, do you wear the safety shoes?"- "Yes"- "Ok go grab a pair of helmets, we have to move the scope "Also if the feet were ok I couldn'd imagine their faces contemplating 15kUSD new scope destroyed down the stairsFabio.

author: muvideo
author_rank: Frequent Contributor
timestamp: May 11, 2012, 06:11:47 pm
content: It seem that I'm lucky, today i received the plugins and tested the tube,it works !and the screen is not too bad, here a screen capture obtained defocusing and moving the beam offscreen,you can see some slight defects: two faint horizontal lines two divisions below center, and some residuefrom the readout on the right high and low.The readout seem to have some problems- it doesnt regulate the intensity, turning the readout intensity pot the readout is off until before thedetent on the "pulsed position", when it shows for a moment at maximum intensity, probably the pot is gone.on pulsed mode it works ok.- the readout writes only on the right side of the screen, the text on the left is grouped in two vertical lineson the centerhere the readout associated to the right plugin:and here associated to the left:The 7A26 plugin also has some problem, but this will be another story and another teardown

author: bingo600
author_rank: Super Contributor
timestamp: May 12, 2012, 02:28:19 pm
content: @MuvideoI have 2 HP 6632B PSU's , and noticed your PSU bracket on the below pic.https://www.eevblog.com/forum/product-reviews-photos-and-discussion/tektronix-r7103-scope-teardown/?action=dlattach;attach=24135Would you care to describe them a bit , and maybe snap a pic. or two of the backside (PSU & Bracket) ?TIA/Bingo

author: muvideo
author_rank: Frequent Contributor
timestamp: May 12, 2012, 02:47:41 pm
content: Quote from: bingo600 on May 12, 2012, 02:28:19 pmHello, not much to write about and not much proud of it, I didnt make a clean work there, it was a little rushedAnyway I simply had a pair of L shaped aluminium plates that nicely fitted on the side of the hp6632.I made the holes for the rack mount screws and put on the front face 5 binding posts, one double pole switchand a DB9 connector for serial interface (I use them mostly driven by a pc to test batteries).The 5 banana posts are GND, OUT+ OUT- Sense+ and Sense-, the switch connects Sense+ to Out+ andSense- to Out- when I dont want to use 4 wire up to the load, and this is all.All the wires (3 thick for OUT 2 thinner for SENSE and a shielded multipole for serial link) run externally onthe side to the back of the instruments.While connecting the load and using 2 wire (switch closed) only be careful to connect it to OUT + and -to the correct banana posts, otherwise you risk to pass all the load current trough the switchI hope it's clear.Fabio.

author: bingo600
author_rank: Super Contributor
timestamp: May 13, 2012, 04:59:55 pm
content: I think i got it/Bingo

author: muvideo
author_rank: Frequent Contributor
timestamp: May 13, 2012, 10:49:49 pm
content: After a little work the scope seem to be ok, the CRT bias voltage needed a little tweaking.Edit: forgot to mention the wonderful help I han on the TekScopes yahoo group, there arevery helpful people that sure know these scopes like their own pocketsNow it's the turn of the 7A26 plugin,this plugin is a dual channel vertical amplifier:The one I have has one of the channels not working, or better disconnected.In the photo the defective upper trace.I opened the unit, it contains two attenuator boards and one amplifier board.On the back there is the readout board that communicates to the mainframethe setting to show them properly as text on the screen.The signal is attenuated and later amplified.The attenuator boards are made of PPO plastic material that has less heat tolerancethan standard epoxy, and tektronix warns:The attenuator board has a series of attenuators that are switched in combinationto obtain the desired ratio: x2 x5 x10 x10.The switching is operaded by some gold plated contacts, operated by cams underthe board.The mechanical construction is a joy to see, after opened I started turning theselectors on the front while watching the cams and various switches move forseveral minutesThis is the input stage with input capacitor:The attenuator are resisteve/capacitive dividers, can be seen the laser trimmedresistors, and the trimmer capacitors for calibration.Problably I'm having problems with the solder joints in the attenuators,seem that the solder is embrittled, the solder itself seem very low temperaturebut doesnt wet anymor the surfaces. I'll try to rejuvenate all the joints underthe microscope.Edit: just finished recovering the joints, now the thing seem to work,here a closeup of the attenuater where the bad joints can be seen:Fabio.

author: eldude5972
author_rank: Newbie
timestamp: September 15, 2021, 02:10:54 am
content: The black bezel attach around the screen do you know it’s purpose?

author: xrunner
author_rank: Super Contributor
timestamp: September 15, 2021, 02:20:07 am
content: Quote from: eldude5972 on September 15, 2021, 02:10:54 amI believe it is there to affix a film camera.

author: eldude5972
author_rank: Newbie
timestamp: September 15, 2021, 05:30:47 am
content: The black bezel around the screen do you know what is for?

author: Vince
author_rank: Super Contributor
timestamp: September 15, 2021, 12:50:50 pm
content: Yes that bezel is designed to hold a camera so you can take pictures of the screen... this is an analog scope you can't just press the " Hardcopy " button and print it out !Here is what the Tektronix camera looked like, for this 7000 series scope :https://w140.com/tekwiki/wiki/C-50_series_cameras