Author Topic: Tek 2465 troubles  (Read 10260 times)

0 Members and 1 Guest are viewing this topic.

Offline DaxxinTopic starter

  • Regular Contributor
  • *
  • Posts: 213
Tek 2465 troubles
« on: October 05, 2014, 12:18:11 pm »
problems with my tektronix 2465 , when power on trig'd is blinking and - minus led on , pressing A/B trig all the front panel led will off
crt shows only 1 trace but incomplete  and some dots , only vertical pots working movig the partial trace , all voltages are perfect.
checking at first in A5 board looking at clock section seems not correct waveforms.




schematic waveform TP


number 1 , frequency is ok but amplitude is less than expected and waveform different shape


number 2 , here the same ..smaller amplitude but atleast similar waveform


number 3 , here totally different waveform of what expected , the timing maybe ok


alredy replaced the 74ls04 , tought failing but no changes , hope someone can help me to fix this.
 

Offline mij59

  • Frequent Contributor
  • **
  • Posts: 693
  • Country: nl
Re: Tek 2465 troubles
« Reply #1 on: October 05, 2014, 01:39:54 pm »
Hi,

Waveform 1 and 2 seem to be in frequency limited, 20 MHz bandwidth limit on the oscilloscope on  ?

The counter U2668 is free running, check the CNTR RESET signal.


 

Offline DaxxinTopic starter

  • Regular Contributor
  • *
  • Posts: 213
Re: Tek 2465 troubles
« Reply #2 on: October 05, 2014, 03:01:11 pm »
Hello mij59 , i think you are right about freerunning , have no signal at reset control , waveform n.4 , about the scope is set to full bandwidth.
what you think about lacking reset cntrl?
 

Offline mij59

  • Frequent Contributor
  • **
  • Posts: 693
  • Country: nl
Re: Tek 2465 troubles
« Reply #3 on: October 05, 2014, 03:30:49 pm »
Hello mij59 , i think you are right about freerunning , have no signal at reset control , waveform n.4 , about the scope is set to full bandwidth.
what you think about lacking reset cntrl?
The clock signal doesn't look right, +5VD ok ?.
Please check the signals on pins 11 , 18 , and 1 of U2034.
« Last Edit: October 05, 2014, 03:50:22 pm by mij59 »
 

Offline DaxxinTopic starter

  • Regular Contributor
  • *
  • Posts: 213
Re: Tek 2465 troubles
« Reply #4 on: October 05, 2014, 04:18:33 pm »
+5VD is ok , pin 1 and 11 this from scope ..look like DC with a bad ripple ..


pin 18 waveform changing costantly anyway this is a shot..
 

Offline mij59

  • Frequent Contributor
  • **
  • Posts: 693
  • Country: nl
Re: Tek 2465 troubles
« Reply #5 on: October 05, 2014, 04:52:51 pm »
+5VD is ok , pin 1 and 11 this from scope ..look like DC with a bad ripple ..


pin 18 waveform changing costantly anyway this is a shot..


There's no clock signal, check U2580.
 

Offline DaxxinTopic starter

  • Regular Contributor
  • *
  • Posts: 213
Re: Tek 2465 troubles
« Reply #6 on: October 08, 2014, 01:48:26 am »
U2580 is OK i have even swap with new one but no changes still same waveforms , back to the wf number 1 service man. says circa 4V pk-pk
but i get only 2.6V pk-pk maybe not enough level to make the logics IC working? lower than the minimal level? anyway i have check all components values
around the crystal osc. and V voltages all is fine the crystal also replaced with new one. No idea why the level still so small? the blinking trig'd
with minus led has fault code meaning but dont know wich device related to that error code.
« Last Edit: October 08, 2014, 01:51:05 am by Daxxin »
 

Offline mij59

  • Frequent Contributor
  • **
  • Posts: 693
  • Country: nl
Re: Tek 2465 troubles
« Reply #7 on: October 08, 2014, 04:40:01 am »
U2580 is OK i have even swap with new one but no changes still same waveforms , back to the wf number 1 service man. says circa 4V pk-pk
but i get only 2.6V pk-pk maybe not enough level to make the logics IC working? lower than the minimal level? anyway i have check all components values
around the crystal osc. and V voltages all is fine the crystal also replaced with new one. No idea why the level still so small? the blinking trig'd
with minus led has fault code meaning but dont know wich device related to that error code.

Waveform 1 is the clock for U2468A, waveform 2 is the output of U2468A, so the signal of waveform 1 is ok.

Are you sure the waveform's are correctly displayed by oscilloscope, what probe are you using  ?

Waveform 3 is derived from the microprocessor clock E, so this should also be ok.

Please probe the inputs of U2580.
 

Offline DaxxinTopic starter

  • Regular Contributor
  • *
  • Posts: 213
Re: Tek 2465 troubles
« Reply #8 on: October 08, 2014, 05:42:06 pm »
Yes all 3 wf is ok , i got  five inputs measures of U2580 (in order from pin 1 to 5 thats A6,A7,A8,E and Y14 output from U2770
with analogic scope just back from calibratio with new probe.











the last ..pin 5 very unstable
« Last Edit: October 08, 2014, 06:04:53 pm by Daxxin »
 

Offline mij59

  • Frequent Contributor
  • **
  • Posts: 693
  • Country: nl
Re: Tek 2465 troubles
« Reply #9 on: October 08, 2014, 06:36:19 pm »
Yes all 3 wf is ok , i got  five inputs measures of U2580 (in order from pin 1 to 5 thats A6,A7,A8,E and Y14 output from U2770
with analogic scope just back from calibratio with new probe.











the last ..pin 5 very unstable

Please check pin 14 of U2580 it should be low if the pins (4,5,1, and 3 are low) and pin( 2 is high).
 

Offline DaxxinTopic starter

  • Regular Contributor
  • *
  • Posts: 213
Re: Tek 2465 troubles
« Reply #10 on: October 19, 2014, 05:14:45 pm »
Partially fixed , the problem was 1 eprom 27c128 lost data , replaced the eprom finally boot up with diagnostic ALL OK
but still have a problem with readout board , flickering always and changing flickering speed turning the SEC/DIV knob
this the video on youtube , any help apreciated. http://youtu.be/t6aJclLUnrk
 

Online David Hess

  • Super Contributor
  • ***
  • Posts: 17477
  • Country: us
  • DavidH
Re: Tek 2465 troubles
« Reply #11 on: October 19, 2014, 06:41:17 pm »
...

but still have a problem with readout board , flickering always and changing flickering speed turning the SEC/DIV knob this the video on youtube , any help apreciated.

The way the 2465 determines when to draw some or all of the readout is pretty complicated.  I would very carefully study the theory section of the service manual which discusses it.

Does the readout flicker when no signal is present and AUTO mode is used so the sweep is fast?  What about with AUTO mode and slower sweep speeds?

The video looks like the 2465 is only updating the readout between sweeps.
 

Offline DaxxinTopic starter

  • Regular Contributor
  • *
  • Posts: 213
Re: Tek 2465 troubles
« Reply #12 on: October 19, 2014, 07:46:21 pm »
Is flicking all the times i tried to switch all possible configs but no changes ,  exactly looks like very slow refresh rate , with fast sweeps get even worst .
 

Online David Hess

  • Super Contributor
  • ***
  • Posts: 17477
  • Country: us
  • DavidH
Re: Tek 2465 troubles
« Reply #13 on: October 20, 2014, 12:01:46 am »
Is flicking all the times i tried to switch all possible configs but no changes ,  exactly looks like very slow refresh rate , with fast sweeps get even worst .

I would have to study the 2465B manual and read the theory section again to make a good suggestion about how to proceed.  As you surmise, it is not suppose to behave the way it does in your video.

Have you looked at the calibrator out using a different oscilloscope?  The way I remember it, the calibrator output is generated by the display sequencer which itself controls the readout timing.
 

Offline Bryan

  • Frequent Contributor
  • **
  • Posts: 633
  • Country: ca
Re: Tek 2465 troubles
« Reply #14 on: October 20, 2014, 08:55:45 am »
Is flicking all the times i tried to switch all possible configs but no changes ,  exactly looks like very slow refresh rate , with fast sweeps get even worst .

Daxxin

Does the flickering of the trace go away or improve if the Readout Intensity knob is turned off.?
-=Bryan=-
 

Online David Hess

  • Super Contributor
  • ***
  • Posts: 17477
  • Country: us
  • DavidH
Re: Tek 2465 troubles
« Reply #15 on: October 21, 2014, 01:19:25 am »
Is flicking all the times i tried to switch all possible configs but no changes ,  exactly looks like very slow refresh rate , with fast sweeps get even worst .

Daxxin

Does the flickering of the trace go away or improve if the Readout Intensity knob is turned off.?

The problem shown in the video is that the readout itself is intermittent.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf