Tektronix 11402 calibration and gain voltage problem.  - Page 1
Forum section: electronics / repair

author: WKibler
author_rank: Contributor
timestamp: March 04, 2019, 10:13:05 pm
content: I recently purchased a Tektronix 11402 for next to nothing. It powers up and passes all self tests. I plugged in two calibrated 11A52 modules which work perfectly in my 11301, yes I know I have a problem.Besides hoarding boat anchors. I am in need of a service manual for the 11402.Here is a screen shot of the errors I get with both 11A52’s when installed in the 11402.My next step is likely re-capping the crap out of the thing but I’d like to have a service manual to go off of and google has yielded no results.Any help would be appreciated. Thank you.Sent from my iPhone using Tapatalk

author: tautech
author_rank: Super Contributor
timestamp: March 05, 2019, 08:05:28 am
content: You might find something in the Tek Wiki:http://w140.com/tekwiki/wiki/11402

author: WKibler
author_rank: Contributor
timestamp: March 05, 2019, 08:14:49 am
content: Been there. No dice. Many other places also. All I can find is a print from eBay or documentation for models with similar components.

author: WKibler
author_rank: Contributor
timestamp: March 05, 2019, 08:16:41 am
content: Quote from: tautech on March 05, 2019, 08:05:28 amThere isn’t a service manual there.Sent from my iPhone using Tapatalk

author: tautech
author_rank: Super Contributor
timestamp: March 05, 2019, 08:38:05 am
content: Quote from: WKibler on March 05, 2019, 08:16:41 amAnd the 11A52 info doesn't help ?http://w140.com/tekwiki/wiki/11A52Any hints to the errors in the 11A52 manuals ?

author: WKibler
author_rank: Contributor
timestamp: March 05, 2019, 09:38:31 pm
content: Quote from: tautech on March 05, 2019, 08:38:05 amThank you. I went through the service manual for the module I’m using and it says the error is linked to a stage of the testing that uses voltages from the scope. I found reference to where those voltages are adjusted in an 11801 which is similar but I am unable to locate the test points.I am going to buy an actual service manual off of eBay. I was hoping someone here had one. I have been to all the usual places in search of a download. Including all the sites listed in the sticky forum posts.I collect and repair old Tektronix hardware and w140.com and the boat anchors site are places I frequent.Thank you for your help. Incidentally, when I measure a 1v p-p using my 2440 I get 1v p-p. When I use the 11402, using the graticule and internal measurement I get 820mV p-p. No I am not using rms measurements. Both inputs are 50ohm terminated and I’m using the same bnc cable. Since the traces are drawn smaller than they really are I’m guessing the 10v reference voltage is off. Inside a 2440 the voltages are easy to locate and measure, inside the 11402 not so much. But this is what I find fun, I enjoy the challenge of repairing these relics.Sent from my iPhone using Tapatalk

author: Johnny10
author_rank: Frequent Contributor
timestamp: March 06, 2019, 03:52:00 am
content: Hasn't someone else on here worked on this unit?I can't remember.I have this unit, it worked perfectly for a few days and then died with lots of DAC errors.After searching for information and service manuals I bought one and guess what....FRU descriptions only. Field Replaceable Boards only.It did identify Test point locations and Reference voltage troubleshooting but no board schematics.I will look around the lab see if I can find it and have a look again.Have 2- DSA602 units, the Big Big Brother to the 11402.No schematics for those either.There are Service Manuals with schematics and parts lists for the 11A52 Plug-ins online.Diagnostic error L144111A52 Plug-inStep Gain ErrorChannel 1L stands for the Left UnitU310 and U410 are Vertical Preamps Tektronix # 165-2129-02You might try switching units around see if error follow Left - Center- Right slotsI have gotten errors from the plugin sockets inside the unit.

author: edavid
author_rank: Super Contributor
timestamp: March 06, 2019, 04:30:20 am
content: The 11402 extended service manuals are available cheaply from Artek:http://artekmanuals.com/manuals/tektronix-manuals/

author: Johnny10
author_rank: Frequent Contributor
timestamp: March 06, 2019, 04:33:35 am
content: From 11A52 Service Manual

author: WKibler
author_rank: Contributor
timestamp: March 06, 2019, 05:16:25 am
content: Quote from: Johnny10 on March 06, 2019, 03:52:00 amI wouldn’t doubt if someone has had this unit on here. I have seen signs of repair in it. Good repairs.I have tried moving the 11A52’s to other slots and the error does follow but the same 11A52’s in an 11301 work flawlessly.Sent from my iPhone using Tapatalk

author: WKibler
author_rank: Contributor
timestamp: March 07, 2019, 10:17:32 am
content: Update: I got a hold of the extended service manual with schematics. PM me if you want a copy.The voltages are all good and you guys were right the amplifier M377 chips are all four bad. To within 100mV in some cases. Statistically improbable I know. But when I throw those same 11A52’s in the 11301 they throw enhanced accuracy calibration errors I never really cared about. So while the 11301 can calibrate itself around the problem the 11402 cannot.Thank you Johnny10, you were the most help IMHO.Time to purchase some 11k series plugins. Anyone know a good source besides eBay?Sent from my iPhone using Tapatalk

author: Johnny10
author_rank: Frequent Contributor
timestamp: March 07, 2019, 12:44:02 pm
content: Great!Glad to help.I keep my 7000 series and 11000 series scope around mostly for the differential plugins.Saved me and my equipment on a number of projects

author: WKibler
author_rank: Contributor
timestamp: March 07, 2019, 12:49:30 pm
content: Quote from: Johnny10 on March 07, 2019, 12:44:02 pmI plan on doing something similar, grab some old differential amps and probes. I may not stick with the 11402 but it is fun to repair.Do you happen to know if a 7000 series vertical amp will work in the 11402? When the right slot is empty the hardware id says “7K” where left and center say 11A52.Sent from my iPhone using Tapatalk

author: Johnny10
author_rank: Frequent Contributor
timestamp: March 07, 2019, 12:58:35 pm
content: 7000 series plugins will work in 11402 but are lacking some function.The 7000 series case must be modified to allow the plug-in to slide all the way in. (From what I remember you have to remove a bit of plastic)Researching this on Tek sites will give you the procedure.You will find many 11000 series plugins for around 25 dollars.For information on TEK scopes and plugins:http://www.barrytech.com/tektronix/tek.html

author: WKibler
author_rank: Contributor
timestamp: March 07, 2019, 12:59:41 pm
content: Quote from: Johnny10 on March 07, 2019, 12:58:35 pmThank you!Sent from my iPhone using Tapatalk