Topics

453 Sweep Problem

Bill
 

This 453 serial number is 25900 and Mod. 210H. It is very clean and was rescued from being scrapped about 15 years ago. Has always been dependable and accurate until now. It is an old IBM scope.

I can't get a good waveform with the Time/Div knob if the frequency is over 50khz. Even then it is very touchy. I'm using my Tektronix 191 Constant Amplitude Signal Generator. It has always been spot on in the past.

Here are some pics. The problem is the same on both A and B channels.
https://imgur.com/HLWA0aX
https://imgur.com/orjSHiN
https://imgur.com/dWuxr93
https://i.imgur.com/iFhu4Ie.jpg

From 1khz Cal connector on scope. There is no change in the waveform no matter where you set the Time/Div knob.
https://imgur.com/BB5qJkk
https://imgur.com/Ii1xLAa


Decided to first start checking all the voltages. The scope's Time/Div adjustments has no affect if the frequency is over 50khz. No being able to adjust for a square wave from the calibrator is confusing. I have a good grasp of basic electronics but new to Oscilloscopes.

What do you all think? I do have a manual for it with a full set of schematics. Need to get this problem resolved so I can check out my newly acquired 465 also in excellent condition.

Bill

Bill
 

Forgot to add that the sine wave was produced using the .35-.75 mHz position on the 191 Generator. The adjusting scale was set on a little past .6. Any frequency higher than this the scope can not slow down enough for you to see the waveform. I don't have a digital signal generator available.
Bill

Bill
 

On a hunch decided to check all the Tunnel Diode voltages as per the schematic test points. All but one checked ok. D705 on the B Sweep Generator board tested +1.1vdc at TP705 it's supposed to be -.1 vdc. The transistor Q704 base voltage is at +1.1vdc supposed to be -0.1 and the collector is at -4.4vdc as it should be.

Tomorrow I will check the recommended scope set up for these voltage checks to verify what I am seeing.

As soon as my new to me 465 scope is out of the virus quarantine I will use it to to check the voltages as per the schematic set up instructions.

Bill

Albert Otten
 

Perhaps the thread "453 no seep" a month ago contains useful information? Albert

Roger Evans
 

None of your pictures show the 'A sweep triggered' light illuminated, not even the first picture with an apparently steady trace.

If you set the sweep mode to 'normal' can you get a horizontal sweep by changing the trigger level? If you can then it might imply that the bulb or the driving circuitry for the 'A sweep triggered' light is not functional (not the main problem but a piece of the jigsaw).

If you connect the 1kHz calibrator to the ext trigger input and set the trig source to external can you get the 'triggered' light to illuminate?

There is another thread here relating to a 453 with some of the sweep speed wafer switches not moving. Is that the same scope? Normally the two knobs on the sweep speed shafts should be locked together and both the white dot on the main knob and the cursor lines on the transparent skirt move together when you change sweep speed. The manual is not entirely clear but it looks like the front half of the switch wafer stack controls one time base and the rear half controls the other. I would have thought that from a mechanical aspect the front half would have to be the outermost of the concentric shafts which I think is the transparent ring and the A sweep speed.

Regards,
Roger

Bill
 

If you set the sweep mode to 'normal' can you get a horizontal sweep by changing the trigger level?  If you can then it might imply that the bulb or the driving circuitry for the 'A sweep triggered' light is not functional (not the main problem but a piece of the jigsaw).Can get the sweep light to blink briefly by turning the Sweep Level knob back and forth.
If you connect the 1kHz calibrator to the ext trigger input and set the trig source to external can you get the 'triggered' light to illuminate?Trigger light will not come on.
Time/Div knob is ok.  I misunderstood how it worked.
Bill

On Thursday, April 9, 2020, 05:21:58 AM CDT, Roger Evans via groups.io <very_fuzzy_logic=yahoo.com@groups.io> wrote:

None of your pictures show the 'A sweep triggered' light illuminated, not even the first picture with an apparently steady trace.

If you set the sweep mode to 'normal' can you get a horizontal sweep by changing the trigger level?  If you can then it might imply that the bulb or the driving circuitry for the 'A sweep triggered' light is not functional (not the main problem but a piece of the jigsaw).

If you connect the 1kHz calibrator to the ext trigger input and set the trig source to external can you get the 'triggered' light to illuminate?

There is another thread here relating to a 453 with some of the sweep speed wafer switches not moving.  Is that the same scope?  Normally the two knobs on the sweep speed shafts should be locked together and both the white dot on the main knob and the cursor lines on the transparent skirt move together when you change sweep speed.  The manual is not entirely clear but it looks like the front half of the switch wafer stack controls one time base and the rear half controls the other.  I would have thought that from a mechanical aspect the front half would have to be the outermost of the concentric shafts which I think is the transparent ring and the A sweep speed.

Regards,
Roger