Tektronix 7603 Oscilloscope Sweeping Issue. - Page 1
Forum section: electronics / repair

author: jack001214
author_rank: Contributor
timestamp: August 02, 2018, 09:55:55 am
content: I found this scope inside the basement of the house and when I fired it up I noticed a problem, straight away.It has come to me that the horizontal sweeping has an issue (preferably the timing plugin failed) and where the vertical sweeping is fine.I believe it works as I rapidly shake my head and i could see the signal producing on the CRT display. Any help provided would really be appreciated.https://youtu.be/a_Cx27IrzSs

author: particleman
author_rank: Regular Contributor
timestamp: August 02, 2018, 12:06:10 pm
content: Try moving the time base over one bay and see if you get a sweep although it wont be horizontal it will be vertical.

author: Tom45
author_rank: Frequent Contributor
timestamp: August 02, 2018, 02:44:49 pm
content: It looks like the 7603 mainframe's trigger source has both left and vert mode pressed in. I don't think that is right. Perhaps it interferes with the horizontal plugin's output. Try each of the Left, Vert Mode, Right buttons to see if you can get the buttons back to where only a single button is active at a time.

author: jack001214
author_rank: Contributor
timestamp: August 02, 2018, 05:33:53 pm
content: Thanks for the response Tom and particle.I have tried all different possible functions but it just wont sweep horizontally!

author: Johnny10
author_rank: Frequent Contributor
timestamp: August 02, 2018, 05:47:08 pm
content: It is not a tv set.You shouldn't just willy nilly press all the buttons and switch all the knobs.Most of these old units need to be set up.They have three slots and they are defined by selecting the push buttonsLeft Vertical, Center and Right Horizontal.Than find the manual for your horizontal plugin and set the proper push-buttons for triggering than set the time base properly.You are just spinning knobs hoping to find the right combination. That is not going to work.

author: jack001214
author_rank: Contributor
timestamp: August 02, 2018, 06:45:19 pm
content: I also have noticed that scope has a burned readout Ic.As i deep further i see why it was put in the store in the first place.I found the right manual for the scope and set my scope to time mode instead of X Y mode i sort of got a different result. The beam would move up an down but not left and right(as before) at a controlled rate. Could there be possibly another burned Ic ?. Another information to account is that the weather is very humid and warm and where i am keeping that scope its the same as outside(humid and warm). Could that be effecting the way it functions?

author: particleman
author_rank: Regular Contributor
timestamp: August 02, 2018, 09:13:02 pm
content: You are going to have to start with low voltage and ripple measurements.

author: Johnny10
author_rank: Frequent Contributor
timestamp: August 02, 2018, 09:22:50 pm
content: I had a problem with a 7000 series scope one time.Pull out the plugins and clean the contacts with contact cleaner check the female connectors for tightness.I have three 7800 series scopes and had a connector problem with two of them.Worth a try, I am in Florida and the units I purchased were kept in very humid conditions also.

author: jack001214
author_rank: Contributor
timestamp: August 02, 2018, 09:26:18 pm
content: doesn't that require another scope? and how am i supposed to take measurements when switched on? the cover does not come off even when the screws are taken out. i am complete newbie to this machine and practically got no idea where to begin troubleshooting

author: jack001214
author_rank: Contributor
timestamp: August 02, 2018, 09:27:49 pm
content: Will try

author: jack001214
author_rank: Contributor
timestamp: August 02, 2018, 09:40:08 pm
content: Alright after cleaning and making the pads shiny again, the results were still the same

author: tautech
author_rank: Super Contributor
timestamp: August 02, 2018, 09:53:22 pm
content: Quote from: jack001214 on August 02, 2018, 09:40:08 pmFor starters you'll need this:http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdfThen find the SM for the timebase pluginandprovide the link to it.Then do some reading for understanding......lots.You might need an extender card or cable so you can operate the plugin out of the scope.IMO the problem is a dead sweep generator and it should be straightforward to fix. If you're lucky you might even do it with a DMM and if you have a analog meter they can be better at showing the sweep voltage sawtooth at slow timebase settings.First check all LV PSU rails then understand what you're trying to fix, why and exactly where to start.

author: Johnny10
author_rank: Frequent Contributor
timestamp: August 02, 2018, 10:25:24 pm
content: Patience, grasshopper.Your journey has just begun.

author: Tom45
author_rank: Frequent Contributor
timestamp: August 03, 2018, 03:23:08 am
content: Try removing the horizontal time base plugin from slot 3 and then put one vertical plugin in slot 1 and the other vertical plugin in slot 3. Leave slot 2 empty. Set the same sensitivity on both of the plugins in slots 1 and 3.Then feed the same sine wave of a few volts and a low frequency into both of the plugins.If you then see a circle or an oval on the screen the main frame is OK and the horizontal plugin is faulty. If you just see a vertical line the mainframe's slot 3 has a problem of some kind.

author: jack001214
author_rank: Contributor
timestamp: August 03, 2018, 05:57:46 am
content: Thanks for the response. There is no oval or circular shape at all and just a line going up and down ,so i think its save to say the the time base is ok and something is wrong in the mainframe

author: jack001214
author_rank: Contributor
timestamp: August 03, 2018, 05:59:18 am
content: Interesting will see for sure

author: jack001214
author_rank: Contributor
timestamp: August 03, 2018, 06:43:08 am
content: Alright another newbie thing i must say.How to open it? the manual does not refer to it

author: tautech
author_rank: Super Contributor
timestamp: August 03, 2018, 07:18:22 am
content: Quote from: jack001214 on August 03, 2018, 06:43:08 amWhich manual ?The service manual will have a exploded parts view and that will give clues do dismantle it.Manual and useful links:http://w140.com/tekwiki/wiki/7603But you problem is not in the mainframe, instead it's in the timebase plugin.

author: jack001214
author_rank: Contributor
timestamp: August 03, 2018, 07:50:03 am
content: Tom45 suggested me to replace the timebase with a vertical plugin and remove it completely. I have followed it and it creates a line on vertical line but not horizontal possibly suggesting that the mainframe has an issue.

author: tautech
author_rank: Super Contributor
timestamp: August 03, 2018, 08:00:18 am
content: Quote from: jack001214 on August 03, 2018, 07:50:03 amSure but did you supply a sine wave as he suggested ?From your video (if you have all the settings correct), no sweep is a timebase issue.From what I can see the plugin is a 7B53A.Web page and manual link:http://w140.com/tekwiki/wiki/7B53Read all manuals in detail for the correct operation and then work through the fault finding sections.Take notes. Read, read and then some more.

author: jack001214
author_rank: Contributor
timestamp: August 03, 2018, 08:07:28 am
content: yes but not a stable one. Closely resembling a square wave but i think that shouldn't be much of an issue though

author: tautech
author_rank: Super Contributor
timestamp: August 03, 2018, 08:22:58 am
content: See TP560 on P137/193http://w140.com/smb/7b53a_an_svc_sm.pdfIf you haven't got a sawtooth waveform there you won't have a sweep, period.Slooooow the timebase setting right down and check for a rising voltage there with a volt meter, analog is best if you don't have another scope. It needs to swing 4V, -2 to +2.Read, study, rest, read, study.......You have a top of the line scope from its day and it's worth the effort to lean about it and repair it.If fixing this timebase is beyond you get another from eBay.

author: jack001214
author_rank: Contributor
timestamp: August 03, 2018, 09:29:01 am
content: https://youtu.be/hmGPV15MAQcThe readings are taken from the SAWTOOTH OUTPUT at the back and set the time base knob slightly above the lowest.

author: tautech
author_rank: Super Contributor
timestamp: August 03, 2018, 10:03:30 am
content: Quote from: jack001214 on August 03, 2018, 09:29:01 amLooks like it.Now you need measure the CRO horizontal amplifier stages (mainframe) with the dot centered but still at that nice slow timebase setting. Check the mainframe schematics to see if there's waveforms to reference against and possible test points to check. Follow the sweep from source (timebase plugin) through the stages until the CRO horizontal plate output stage to find the point where the sweep ramp stops. Then check components around there.Good luck.

author: slbender
author_rank: Regular Contributor
timestamp: August 03, 2018, 10:19:07 am
content: Hi, I have a Tektronix7603 mainframe and it would fail after about an hour. I learned that the power supplies can fail, or rather they get thermal and basically there are pass transistors, (2n3055 selected parts) where the solder joints go bad over time, so you may be missing a power supply voltage. Check old PS caps and resolder those big power transistors. Then see if those plug-ins work. My mainframe is being used with a Wavetek 7530 Spectrum Analyzer/ Oscilloscope plug-in that takes up all three slots.Steven

author: Johnny10
author_rank: Frequent Contributor
timestamp: August 03, 2018, 12:25:27 pm
content: Give us a photo of unit with all your front panel settings.

author: Tom45
author_rank: Frequent Contributor
timestamp: August 03, 2018, 03:53:51 pm
content: Quote from: jack001214 on August 03, 2018, 05:57:46 amWhat kind of signal did you feed into both slots 1 and 3?This test won't tell whether the time base is OK or not, but certainly it looks like the mainframe has a problem with the horizontal signal path.

author: jack001214
author_rank: Contributor
timestamp: August 03, 2018, 04:31:16 pm
content: https://imgur.com/a/SViZfzb

author: jack001214
author_rank: Contributor
timestamp: July 31, 2019, 09:11:11 pm
content: I have finally(a year later) got around to open the scope and inspect it further. According to the troubleshooting guide if the beam finder is working then there is a issue with the timebase. I have measured the SAWTOOTH output pin again and its rising and falling. However, when connecting a multi-meter too GATE out pin,the voltage seems to be stuck at 10VDC and wont budge while the +VERT SIGNAL is changing respective to the 'POSITION' knob. What magical pin should be inspected now? and is there a a way to switch the vertical and horizontal signals(for clearing doubts)