Fault on Tektronix TDS694C - Page 1
Forum section: electronics / testgear

author: sportq
author_rank: Regular Contributor
timestamp: March 17, 2014, 11:42:47 am
content: We have this scope at work, it's been in a cupboard for years with a 'Faulty - Do not use" sticker on it so I thought I'd have a look at it.I downloaded the service manual and ran through the diagnostic and troubleshooting procedures but according to the flowchart in the manual my scope is workingExcept it's not. It boots up, front panel lights come on, I see the Tektronix splash screen then the screen displays the picture attached, a horizontal bar with short vertical lines at the end (apologies for the terrible camera phone picture). It then hangs at this point and is unresponsive to all keys on the front panel.Any ideas what's wrong with it? I'm hoping some recognises this from another scope in the TDS7xx,6xx series.Pete

author: vaualbus
author_rank: Frequent Contributor
timestamp: April 25, 2014, 11:30:11 pm
content: Check all the caps on both the acq board (the bottom one) and the processor one.This capicitor tend to leak and the acid could demage the PCB.Clean the PCB and change the caps.Best regards, Alberto.

author: nctnico
author_rank: Super Contributor
timestamp: April 26, 2014, 10:16:55 am
content: AFAIK this scope doesn't have electrolytic capacitors. A major problem on these scopes is that the trigger chip tends to burn out. Tek forgot to put a heatsink on it. There is a 'TDS520B component service manual' which has schematics and deeper troubleshooting procedures.

author: Whales
author_rank: Super Contributor
timestamp: April 26, 2014, 12:33:22 pm
content: Did the diagnostic procedures you went through involve any interaction with the software, or just point measurements?EDIT: Ie is there a way to get some form of software-mode working on the screen, or does it always end up in that frozen state?

author: vaualbus
author_rank: Frequent Contributor
timestamp: April 26, 2014, 01:56:17 pm
content: the TDS520B schematics aren't so usefull because the C revision change the board layout (tek used even more integration).Can you please give which digit the seven display, on the top board, show during the startup?Also on the board there is two nvram one contains the calibration data and options and the other contains the real time clock.Sometimes if the first nvram is bad the system stop.Also build the following adapter for the console port that allow to use the rs232 optional board to see the system startup log.link:http://www1.tek.com/forum/viewtopic.php?f=5&t=5526&st=0&sk=t&sd=a&hilit=tds+rs232

author: sportq
author_rank: Regular Contributor
timestamp: April 27, 2014, 09:15:51 am
content: Thanks for the suggestions,I will look at it again tomorrow at work.Whales, the diagnostic flow I followed from the Service Manual didn't require me to measure any voltages so it was ALL software interactions and dip switch flipping. It always ends up frozen at the screen shown and no button presses can change it.vaualbus, I'll note the diagnostic digits as it boots and post tomorrow. That adapter looks pretty complex to build, I have a bunch of logic analyser grabbers and jumper wires so I could maybe use them?Pete

author: skennedy
author_rank: Contributor
timestamp: April 27, 2014, 10:23:02 am
content: It certainly looks a lot like a distorted top of screen you would expect from a Tek TDS Scope. I would connect a VGA monitor to the port on the back just to check it isn't a dead screen or driver board. Might be an easy way to eliminate any acquisition board issues that plague these scopes.Simon

author: vaualbus
author_rank: Frequent Contributor
timestamp: April 27, 2014, 12:44:18 pm
content: Is not ddifficult to built If you have the option 13 installed you just need two connector and follow the wiring connection like in the post. Of course you could use you a logic analyzer but you need to figured out how to connect it (there some signal that the option 13 send to processor board).

author: sportq
author_rank: Regular Contributor
timestamp: April 27, 2014, 03:56:16 pm
content: Quote from: skennedy on April 27, 2014, 10:23:02 amI should have mentioned that I connected a VGA monitor and the picture is exactly the same.Pete

author: max-bit
author_rank: Frequent Contributor
timestamp: April 27, 2014, 07:13:31 pm
content: dead cpu board, rather he did not fix ...and ..dead cpu board, it is difficult to fix, you do not have access to the player.check voltage, oscillators, can cold solder joints?

author: nctnico
author_rank: Super Contributor
timestamp: April 27, 2014, 07:24:32 pm
content: Quote from: vaualbus on April 26, 2014, 01:56:17 pmPerhaps but the idea is the same. Every bit helps. Sometimes I fix equipment on componenent level using a block diagram.

author: vaualbus
author_rank: Frequent Contributor
timestamp: April 27, 2014, 09:39:18 pm
content: ya but If the problem is inte processor board I think that the processor board isn't change so much.The acquisition board is change a little bit.For the schematics try to ask to tek support.For me it works and I have the true schematics of the TDS 540.

author: sportq
author_rank: Regular Contributor
timestamp: April 28, 2014, 01:04:03 pm
content: Just took a look at it.When powered on the figure of 8 LED rapidly cycles through 2,3,4,5,6,7 then starts alternately lighting the top center segment and the bottom center segment at around 2Hz. Looks like a simple heartbeat diagnostic, is that normal for a Tek scope?I don't think the CPU board is dead, it manages to display splash screen for a few seconds before displaying the screen in the first post.Pete

author: vaualbus
author_rank: Frequent Contributor
timestamp: April 28, 2014, 02:34:43 pm
content: could you make a video on the seven segment display?Excute all the diagnistic you found on the TDS520B component level schematics and let us know the result.Here there is a video on what my TDS540 scope do when power up:https://www.dropbox.com/s/tbzle2lwyi292mg/2014-04-28%2013.52.06.mp4Best regards, Alberto