Author Topic: Tektronix 7603 Oscilloscope Sweeping Issue. (Read 5621 times)

jack001214 · « **on:** August 02, 2018, 09:55:55 am »

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

particleman · « **Reply #1 on:** August 02, 2018, 12:06:10 pm »

Try moving the time base over one bay and see if you get a sweep although it wont be horizontal it will be vertical.

Tom45 · « **Reply #2 on:** August 02, 2018, 02:44:49 pm »

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.

jack001214 · « **Reply #3 on:** August 02, 2018, 05:33:53 pm »

Thanks for the response Tom and particle.I have tried all different possible functions but it just wont sweep horizontally!

Johnny10 · « **Reply #4 on:** August 02, 2018, 05:47:08 pm »

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 buttons

Left 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.

jack001214 · « **Reply #5 on:** August 02, 2018, 06:45:19 pm »

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?

particleman · « **Reply #6 on:** August 02, 2018, 09:13:02 pm »

You are going to have to start with low voltage and ripple measurements.

Johnny10 · « **Reply #7 on:** August 02, 2018, 09:22:50 pm »

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.

jack001214 · « **Reply #8 on:** August 02, 2018, 09:26:18 pm »

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

jack001214 · « **Reply #9 on:** August 02, 2018, 09:27:49 pm »

Will try

jack001214 · « **Reply #10 on:** August 02, 2018, 09:40:08 pm »

Alright after cleaning and making the pads shiny again, the results were still the same

tautech · « **Reply #11 on:** August 02, 2018, 09:53:22 pm »

Quote from: jack001214 on August 02, 2018, 09:40:08 pm

Alright after cleaning and making the pads shiny again, the results were still the same

For starters you'll need this:
http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

Then find the SM for the timebase plugin and provide 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.

Johnny10 · « **Reply #12 on:** August 02, 2018, 10:25:24 pm »

Patience, grasshopper.
Your journey has just begun.

Tom45 · « **Reply #13 on:** August 03, 2018, 03:23:08 am »

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.

jack001214 · « **Reply #14 on:** August 03, 2018, 05:57:46 am »

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

jack001214 · « **Reply #15 on:** August 03, 2018, 05:59:18 am »

Interesting will see for sure

jack001214 · « **Reply #16 on:** August 03, 2018, 06:43:08 am »

Alright another newbie thing i must say.How to open it? the manual does not refer to it

tautech · « **Reply #17 on:** August 03, 2018, 07:18:22 am »

Quote from: jack001214 on August 03, 2018, 06:43:08 am

Alright another newbie thing i must say.How to open it? the manual does not refer to it

Which 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/7603

But you problem is not in the mainframe, instead it's in the timebase plugin.

jack001214 · « **Reply #18 on:** August 03, 2018, 07:50:03 am »

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.

tautech · « **Reply #19 on:** August 03, 2018, 08:00:18 am »

Quote from: jack001214 on August 03, 2018, 07:50:03 am

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.

Sure 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/7B53

Read all manuals in detail for the correct operation and then work through the fault finding sections.
Take notes. Read, read and then some more.

jack001214 · « **Reply #20 on:** August 03, 2018, 08:07:28 am »

yes but not a stable one. Closely resembling a square wave but i think that shouldn't be much of an issue though

tautech · « **Reply #21 on:** August 03, 2018, 08:22:58 am »

See TP560 on P137/193
http://w140.com/smb/7b53a_an_svc_sm.pdf

If 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.

jack001214 · « **Reply #22 on:** August 03, 2018, 09:29:01 am »

https://youtu.be/hmGPV15MAQc

The readings are taken from the SAWTOOTH OUTPUT at the back and set the time base knob slightly above the lowest.

tautech · « **Reply #23 on:** August 03, 2018, 10:03:30 am »

Quote from: jack001214 on August 03, 2018, 09:29:01 am

The readings are taken from the SAWTOOTH OUTPUT at the back and set the time base knob slightly above the lowest.

Looks 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.

slbender · « **Reply #24 on:** August 03, 2018, 10:19:07 am »

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


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Author Topic: Tektronix 7603 Oscilloscope Sweeping Issue. (Read 5621 times)

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