Tektronix 7313 trace disapears... - Page 1
Forum section: electronics / repair

author: sadeoo7
author_rank: Contributor
timestamp: July 01, 2015, 03:06:03 am
content: first of all im sorry for my english i live in montreal and we speak french here. i bought the scope on craigslist a few months ago and it worked fine for a couple of weeks and after a bit of time the trace started to disapear an reapear while i was using it. and yesterday the trace completely disapeared however there is still some stuff on the dislplay like the time/div and the volt/div so its not the screen and when i press the locate/viewtime button the trace reapers faintly. i really dont know what it the problem. oh and i have the rackmount version of the 7313.the picture is when it was working now its like this but whitout the trace.

author: miguelvp
author_rank: Super Contributor
timestamp: July 01, 2015, 03:11:47 am
content: Can you post a picture of your time base module?Maybe you have it set to norm instead of auto, or some other setting that doesn't show the trace when it's not triggered, also knowing what time base module you have might help the rest know what the issue can be.Edit: and in case you didn't know about this link here you go, it might help you in the future.http://w140.com/tekwiki/wiki/7313

author: sadeoo7
author_rank: Contributor
timestamp: July 01, 2015, 03:25:13 am
content: on the picture you can kinda see a trace but its really faint and it disapears and reapears randomlyi knew about the wiki thanks.

author: miguelvp
author_rank: Super Contributor
timestamp: July 01, 2015, 03:39:36 am
content: Nice 7B92, I have a 7613 rack mount and a 7603 stand alone both using 7B53As with 7A18s, 7a26, 7d15 among another 7 modules.I always wondered if the mainframe limitations had an impact on the modules, because the 7313 mainframe is for 25MHz but your timebase is rated for 500MHzhttp://w140.com/tekwiki/wiki/7B92At first glance I can't see any bad setting and it seems your intensity is set to the highest.Maybe something is failing within the mainframe and might need fixing.Does it happen on all of the channels?

author: sadeoo7
author_rank: Contributor
timestamp: July 01, 2015, 03:44:36 am
content: yes it happens on all of themand yeah its interresting on what could be the limitation for the mainframe

author: miguelvp
author_rank: Super Contributor
timestamp: July 01, 2015, 03:44:45 am
content: Also you said:Quotehas that changed now?

author: sadeoo7
author_rank: Contributor
timestamp: July 01, 2015, 03:49:39 am
content: its still displays the v/div and the sec/div but the trace(s) appears and disapears.the trace is really nice for a bit and a few minutes later it disapears.

author: miguelvp
author_rank: Super Contributor
timestamp: July 01, 2015, 04:06:25 am
content: Set the scope mainframe to Vert Mode set on CHOP and Trig Source set to VERT MODE as seen here on the upper right.On the modules, set the 7A18 (sorry one of my knobs is broken (middle module) but its set the same as the one on the left.Edit: I see both of your DISPLAY MODE knobs on both 7A18s are starting to crack as well, maybe you can try to repair them before they go away.Set the Trigger Source to MODE on both dual trace amplifiers, and set the Display Source to CHOP on both as well. I did changed my input coupling to GND as you had but I would leave them on AC to test.Then I adjusted the 4 channel positions just to separate the traces.On my Time base module (mine is a 7B53A) I have the Mode set to AUTO, the Coupling set to AC and the Source set to INT, all of the rest should be like yours. I did change mine to 100nS but I don't think that would matter. Also mine doesn't have a contrast adjustment so I have no idea what that does on your 7B92Also on the mainframe the inner intensity knob controls the extra information (READOUT) like the 100mV or 100nS in the picture, the outer one is for the trace intensity.I would also check if your GRATICULE ILLUMINATION is affected as well.Here is a picture of my setup that shows all four traces:

author: sadeoo7
author_rank: Contributor
timestamp: July 01, 2015, 04:16:18 am
content: i it was working before and its still working after the manipulations but as i said the problem is intermittent and the trace(s) will disapear in a couple of minutes and what do you mean by the gratucule illumination???

author: miguelvp
author_rank: Super Contributor
timestamp: July 01, 2015, 04:24:52 am
content: Turn the scope off, take out the modules and re-insert them again. Maybe it's just a bad connection to the backplane.Otherwise, the link I posted and you already have has the service manual. So you could go through the troubleshooting.If you had more modules you could try to change them to see if one of the modules like the timebase is going bad. I think it's strange that both the trace and the readouts are faint in your picture, but you mentioned that sometimes the trace disappears but the readout is fine. So I don't know, could be the time base module or the mainframe.Edit: I see yours doesn't have a graticule illumination knob, but not sure what the other lower knobs do either on yours.

author: sadeoo7
author_rank: Contributor
timestamp: July 01, 2015, 04:30:37 am
content: i only have another 7a18 module and i doesnot make a difference when i try it. everything as been working right for an hour now but it will probably go out, anyway, hey do you want a knob to replace your broken one ?

author: miguelvp
author_rank: Super Contributor
timestamp: July 01, 2015, 04:33:47 am
content: Would love to get one, but like I said, yours are showing cracks already so you might want to keep it for yourselfEdit, mine is still operational I just have to count the clicks to know where is pointing to.

author: sadeoo7
author_rank: Contributor
timestamp: July 01, 2015, 04:35:25 am
content: i got a few of them as i have 2 other 7a18 modules for parts and a working one. since you helped me i can sand one to you if you want.

author: miguelvp
author_rank: Super Contributor
timestamp: July 01, 2015, 04:41:32 am
content: Well, thank you!, sent you a PM

author: miguelvp
author_rank: Super Contributor
timestamp: July 01, 2015, 04:57:48 am
content: I'm just glad to find someone else that is keeping the old gear still running. Here is my Tek gear, I also have a TM503 with a FG504 function generator (not pictured) that I have to repair but last attempt actually fixed the TM503 but the FG504 let out more magic smoke.I went nuts buying modules, I might get some more that I don't have if the opportunity arises.The older one (right under the Sony monitor) is a Tek 5110 (different modules than the 7000 series)The iCADE was a gift from my daughter for my birthday, but I don't have an iPad and doesn't seem to like my Android tablet, but I'm planning to do something with it eventually.

author: sadeoo7
author_rank: Contributor
timestamp: July 01, 2015, 05:08:55 am
content: cool collection, maaaan i waaaant this ''desktop'' mainframe on the left look at the pic to know why lol mine is suspended from the ceiling

author: miguelvp
author_rank: Super Contributor
timestamp: July 01, 2015, 05:15:48 am
content: You know it's 2 feet deep right? it will take your whole desktopActually that one is borrowed from a friend, but I can keep it until he needs it. It wasn't working too well when I got it but I managed to fix it:https://www.eevblog.com/forum/repair/repairing-tektronix-7603-oscilloscope/He might want it back eventually but at least I have my 7613 and the 5110 that I got for just $50 for both, they just needed some love and care:Edit: fixed last linkhttps://www.eevblog.com/forum/testgear/list-your-test-equipment-score-here!/msg645631/#msg645631

author: sadeoo7
author_rank: Contributor
timestamp: July 01, 2015, 05:25:02 am
content: i know my workshop is in my bedroom so i have to fit everything in it and i dont have mutch space...

author: miguelvp
author_rank: Super Contributor
timestamp: July 01, 2015, 05:34:31 am
content: Nice setup, mine is just 8 by 9 feet (2.44 by 2.75 meters) so I understand the dilemma, plus it seems like it has been designated as storage area by my wife, so I only have use of 3/4ths of it. the other 1/4th is just a bunch of boxes. I think I'll do a cleaning soon because I don't think we need anything that is in those boxes and I really want my space back.Old Chicago homes have really small rooms

author: sadeoo7
author_rank: Contributor
timestamp: July 01, 2015, 05:39:25 am
content: yeah your wife, for me its my mother... (im 16years old) she still wants my bedroom to actually look like a bedroom but i dont think i does anymore...

author: TerraHertz
author_rank: Super Contributor
timestamp: July 01, 2015, 08:21:44 am
content: Quote from: sadeoo7 on July 01, 2015, 03:06:03 amPossibly a silly suggestion, but if you turn the trace brightness knob slowly (when the scope is working) does the trace brightness vary evenly? Or does it flicker on and off while generally tracking the knob movement?The resistive films in those pots can develop dead spots, where wiper contact is very intermittent. It often happens with the trace vertical position pots for instance. The less you use the pots the more likely it becomes.The solution is to just sit there turning the knob back and forth rapidly over its range until it comes good. The repeated movement of the pot wipers seems to restore the resistive track evenness. Purely mechanical, the scope doesn't need to be on while doing this. Though it's nice to see whether the fix is working.Other than that, if the screen readouts stay normal while the beam goes, maybe there's something wrong with the beam gate signal from the timebase module?

author: sadeoo7
author_rank: Contributor
timestamp: July 01, 2015, 08:55:59 pm
content: Thanks i will try that

author: poot36
author_rank: Frequent Contributor
timestamp: July 02, 2015, 05:41:43 am
content: I think if you pull all of the modules out of the system and power it on then you should be left with just a dot on the screen. Lower the brightness so as to not burn the dot into the screen and see if the dot still goes away. If it does then the fault is in the mainframe. It almost seems like a loose soldier joint that is been affected by the temperature of the scope. If it happens on a cold power up then this is probably not the problem though.

author: sadeoo7
author_rank: Contributor
timestamp: July 02, 2015, 06:38:43 am
content: i think i could happen when its cold becose most of the time i power it up an it does the problem and i just turn i off but yesterday after 10 or 15 minutes of running the trace was nice and steady.

author: poot36
author_rank: Frequent Contributor
timestamp: July 03, 2015, 12:32:55 am
content: If it consistently does not work properly when cold try gently shaking it and see if you can make the trace go away or come back. If you can it is a loose connection somewhere in the scope. When the scope warms up everything expands just enough for it to continue working properly.

author: sadeoo7
author_rank: Contributor
timestamp: July 03, 2015, 03:01:42 am
content: i will try that when i get some time on my hands thanks

author: sadeoo7
author_rank: Contributor
timestamp: July 05, 2015, 06:38:29 am
content: its still works great now

author: miguelvp
author_rank: Super Contributor
timestamp: July 05, 2015, 03:40:19 pm
content: Maybe it was just some dust on the intensity knob and it has fixed itself with use, or any other thing due to the scope not being turned on for years. I'm glad it solved by itself.

author: sadeoo7
author_rank: Contributor
timestamp: July 06, 2015, 12:31:51 am
content: yeah i hope it was a supid thing like that i would have been ''scopeless'' for a few weeks if the problem was worst...

author: sadeoo7
author_rank: Contributor
timestamp: July 11, 2015, 02:31:12 am
content: nope still does the same thing and when i remove all the modules it atill does it so its a problem in the mainframe... crap!

author: Cyberdragon
author_rank: Super Contributor
timestamp: July 11, 2015, 05:02:20 am
content: Might just be a module issue. Also could be a bad sign that one of the power busses is failing. My 7603 was showing similar symptoms before blowing the psu without warning. Keep watching for any zoom or horizontal flicker, as this maybe a sign of faulty transistors in the power supply (they are usually all in sockets and changable without soldering).

author: sadeoo7
author_rank: Contributor
timestamp: July 11, 2015, 05:30:21 am
content: thanks ill go trought the troubleshooting section of the manual tommorow its going to take a loooong time but it worth it i need my scope lol

author: sadeoo7
author_rank: Contributor
timestamp: July 16, 2015, 12:11:18 am
content: the 12v rai is at 11v could it e a part of the prolem??

author: tautech
author_rank: Super Contributor
timestamp: July 16, 2015, 12:17:32 am
content: Quote from: sadeoo7 on July 16, 2015, 12:11:18 amQuite likely. All railsmustbe to spec.

author: sadeoo7
author_rank: Contributor
timestamp: July 16, 2015, 12:19:11 am
content: and i think it might be a 15 volt rail

author: poot36
author_rank: Frequent Contributor
timestamp: July 16, 2015, 01:50:45 am
content: As well as checking the rails for correct voltage check them for ripple by using the AC mode on your multimeter. The ripple usually should not exceed 200mV peak to peak unless otherwise specified in the service manual.

author: sadeoo7
author_rank: Contributor
timestamp: July 16, 2015, 02:55:20 am
content: yeah the ripple is fine i checked it