Tektronix 7263A: [FIXED] Repaired, that's good but... trimmed? - Page 1
Forum section: electronics / repair

author: jmsc_02
author_rank: Regular Contributor
timestamp: January 13, 2016, 06:10:23 pm
content: DearToday i've received my last challenge: Put an old and dusty tektronix 7623A on.Note: This thread will be a long term theme. My resources are limited and I feel that I need to learn before dig more on the scope.the scope comes with seven modules listed below:- 3x 7A26 200MHz dual trace amplifier- 1x 7A18A 75MHz dual trace amplifier- 2x 7B53A 100MHz dual time base- 1x 7A13 100MHz differential comparatorFirst of all: Power on! The fan starts to run but nothing on the display and the power on indicator is not turned on.. hmm i will inspect all the voltage board in a first instance.After a while with the tek powered, an strange smell was felt, I guess was rubbish cooking(it seems to be a long time in a warehouse)I've checked the fuses and all were OK but one of the low voltage pcb seems not working fine (P855 fuse).Now I've downloaded the service manual and will check these other threads:https://www.eevblog.com/forum/repair/repairing-tektronix-7603-oscilloscope/https://www.eevblog.com/forum/testgear/tektronix-76037613-repairs/msg806718/#msg806718I've took some pictures to share. As a comment: It's impressive the quantity of Danger sticks around the scope...----------------Update 16/jan/2016EDIT -> After replace the C811 cap (14000uF, 25V electrolytic) and learn (and remember) about analog scopes, it works well but I want to study and review it and "look and find" bad components on the different boards. (this was the main reason why I bought it)

author: jmsc_02
author_rank: Regular Contributor
timestamp: January 13, 2016, 06:29:07 pm
content: Breaking news: It's alive! There is a random trace on the screen! The focus and the trace rotation is working but not fine, the intensity of the trace is hopeless...I've test the voltage connector and the 5volt rail is dead but the rest looks good at first glance.Something is noising when the trace is put on the screen... hmmmA pic of the random trace:PS-> It is not exactly a random trace, the scope repeats the figure regardless of the probe voltage...Edit: The text on the screen is responsive to the change of the rotative knobs of the plug-ins & the screen is about 5 second on and one off. I need to review the voltage section. There are ghosts of the numbers all aroud the screen too

author: jmsc_02
author_rank: Regular Contributor
timestamp: January 13, 2016, 08:04:17 pm
content: Well.. The +5V supply rail is faulty, and the -15V power supply measures -12V... There are fun to enjoyI'm surprised for the rest of rails, they are in tolerance values after 30 years...A moment of paniac: Male 8 pin connector vs Female 9 pin connector on the P1170 socket and I can't remember the correct position place...(luckily the connection diagrams appear on the schematics)

author: Anks
author_rank: Frequent Contributor
timestamp: January 13, 2016, 08:06:44 pm
content: Going of the picture it has a lot of ripple on one of the power rails.

author: jmsc_02
author_rank: Regular Contributor
timestamp: January 13, 2016, 08:17:49 pm
content: Quote from: Anks on January 13, 2016, 08:06:44 pmGreat answer, the -15V supply rail is faulty, the rest are ok (includes the 5V supply rail after I moved a connector)

author: Anks
author_rank: Frequent Contributor
timestamp: January 13, 2016, 08:25:36 pm
content: The right answer you are seeing bother side of the ac mains on the screen

author: tautech
author_rank: Super Contributor
timestamp: January 14, 2016, 08:32:02 am
content: http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

author: jmsc_02
author_rank: Regular Contributor
timestamp: January 14, 2016, 01:41:49 pm
content: Quote from: tautech on January 14, 2016, 08:32:02 amThanks for the info.Inspecting the power supply seems be serviced time ago... There are two big caps replaced and a LM7818 TO92 on the Q896 place instead of a 2N4888 TO103 as claims the service manual... I believe is a LM7818 but the mark on the IC is not clear, it's written F151 0228 7818 on the case.EDIT -> It's the same transistor... if I look on the service manual is typed something like "151-0228-00"

author: jmsc_02
author_rank: Regular Contributor
timestamp: January 14, 2016, 03:13:04 pm
content: C811, C806 and CR806 are kaput (Big capacitors & bridge rectifier of the rectifier board)

author: dom0
author_rank: Super Contributor
timestamp: January 14, 2016, 04:22:46 pm
content: Quote151-0228-00, datecode 78/18. Equivalent to 2N4888, the grade (-00) is often omitted for parts with only a single grade.

author: EPTech
author_rank: Regular Contributor
timestamp: January 15, 2016, 06:03:47 pm
content: Hey,great vintage scope. Hope you can repair it.I have recently repaired a Tek 465. It also did not power up and in the end it was a measly tantalum cap sitting between a power rail (don't remember which one) and GND on the edge of the top board, probably a local decoupling cap.Good hunting.

author: jmsc_02
author_rank: Regular Contributor
timestamp: January 15, 2016, 07:00:47 pm
content: Dear,Thanks for the answers.Today I ordered a 14000uF 25V cap, and having a while, I plug my DC Supply on the -15V rail to see what will happen when replace the cap. I took some snapshots but basically something is going very wrong because the screen is completelly green. There are traces and the plugins are responsive changing numbers on the screen, but all is covered by an intense green background.After a few minutes playing with the knobs, I restored the -15V supply to its original supply and the same AC coupling trace goes there.I need to mention that at the beginning, I could see the traces and move it around the screen but, on a second attempt, there was no trace to see, only the numbers :SI need to study more the scope

author: dom0
author_rank: Super Contributor
timestamp: January 15, 2016, 07:04:37 pm
content: Push NON STORE in.

author: jmsc_02
author_rank: Regular Contributor
timestamp: January 15, 2016, 07:10:33 pm
content: Quote from: dom0 on January 15, 2016, 07:04:37 pmlol... the green background fade to blackTHANKS!

author: jmsc_02
author_rank: Regular Contributor
timestamp: January 15, 2016, 07:34:33 pm
content: and the scope come back to life...Next time i promise read the operation instructions before do nothing

author: jmsc_02
author_rank: Regular Contributor
timestamp: January 16, 2016, 09:02:58 pm
content: Today I was testing the plugins, in general lines all were working reasonably well, but some modules needs new pots and switches. None was dead and some cal sticks has only twelve yearsI leave some pics of one of the 7B53A dual time base which I have. There is a problem with the rotary knob, it can't hold the push/pull position and the reason is a little and broken switch at the back of the plugin because it retain alone the state of the rotary knob (pulled or pushed).Edit --> The plugin is a great little work of art... I love it

author: ludek
author_rank: Newbie
timestamp: January 18, 2017, 01:48:43 am
content: Good job man! I love those old scopes and quality parts in those. Sorry for 1yr digging...I'm still wondering why tektronix decided to do it's own rebrander parts, confusing.

author: djnz
author_rank: Regular Contributor
timestamp: January 18, 2017, 03:50:17 am
content: A while ago, I found a PDF file on the web which cross-referenced tektronix part numbers with common, industry-standard part numbers. Perhaps people will find that useful, so here's the link:https://drive.google.com/open?id=0B-FOktb-HYpxdVp2NFBIaTQyUU0

author: tautech
author_rank: Super Contributor
timestamp: January 18, 2017, 06:19:05 am
content: Quote from: djnz on January 18, 2017, 03:50:17 amThat's a real gem dj, all 343 pages of it.There's some more better known ones at Sphere:http://www.sphere.bc.ca/test/tekequiv.htmlThere's some more at the bottom of the page that Sphere requests not to be linked.