Author Topic: Tektronix 468 B sweep unblank or enable issue  (Read 7349 times)

0 Members and 1 Guest are viewing this topic.

Offline Addicted2AnalogTekTopic starter

  • Frequent Contributor
  • **
  • Posts: 508
  • Country: us
Re: Tektronix 468 B sweep unblank or enable issue
« Reply #25 on: January 25, 2016, 10:30:40 pm »
probably would help to post this, too.
« Last Edit: January 25, 2016, 10:39:17 pm by Addicted2AnalogTek »
 

Offline Addicted2AnalogTekTopic starter

  • Frequent Contributor
  • **
  • Posts: 508
  • Country: us
Re: Tektronix 468 B sweep unblank or enable issue
« Reply #26 on: January 31, 2016, 04:22:45 am »
There are multiple out of tolerance resistors on the timebase board, all of which coincide with the settings one would expect to see used most frequently.   I am considering putting in the timebase board from my other 468 until I get new resistors for both, but may not since it is one revision earlier than the one that belongs in this scope. 

I am wondering if there may also be an issue with the A sweep start comparator (Q987A/B 151-0354-00) since the A sweep waveform from the scope under test is 400uS longer than the other scope's A sweep waveform on most timebase settings.  This would coincide with A sweep starting too early, which seems to be what I am dealing with here instead of the B sweep not unblanking correctly. 

For now I will just order and replace the out of tolerance resistors that I've found and  go from there.  I also intend to check the timing capacitors as best I can with the meters I have.   On another note, the trigger level adjust on the 465 I use is no longer working, so I now feel the need to get one of these repair pile scopes done so I have one to troubleshoot/cal my 465 with.
 

Offline tautech

  • Super Contributor
  • ***
  • Posts: 28136
  • Country: nz
  • Taupaki Technologies Ltd. Siglent Distributor NZ.
    • Taupaki Technologies Ltd.
Re: Tektronix 468 B sweep unblank or enable issue
« Reply #27 on: January 31, 2016, 05:27:11 am »
On another note, the trigger level adjust on the 465 I use is no longer working, so I now feel the need to get one of these repair pile scopes done so I have one to troubleshoot/cal my 465 with.
Yep, know that feeling from the past....fingers crossed for you.  ;)
 :scared:
Avid Rabid Hobbyist
Siglent Youtube channel: https://www.youtube.com/@SiglentVideo/videos
 

Offline Addicted2AnalogTekTopic starter

  • Frequent Contributor
  • **
  • Posts: 508
  • Country: us
Re: Tektronix 468 B sweep unblank or enable issue
« Reply #28 on: January 31, 2016, 07:25:50 am »
Interesting.... replacing the A sweep start comparator has 'cleaned up' the end of the A sweep.  Previously, when in ALT mode, there was a period approx half of a division at the end of A sweep that coincided with the intensity of the B sweep (as the beginning of A sweep does).  This is now gone entirely.   

Of course upon removing it, I checked it with DMM diode check and hFE and compared it against a NOS one and ones out of a 365 I use for parts.  It appeared to be rather degraded but not entirely bad, but apparently not good enough for this circuit.

In order to determine whether or not my remaining sweep issues lie in the timing circuitry, I have decided to swap timing boards since there is only minor difference between the 00 and 01 revisions. Specifically in the A sweep high speed timing caps, which I have the parts to change over if I decide to keep it in.
 

Offline Addicted2AnalogTekTopic starter

  • Frequent Contributor
  • **
  • Posts: 508
  • Country: us
Re: Tektronix 468 B sweep unblank or enable issue
« Reply #29 on: January 31, 2016, 09:43:50 pm »
I have swapped out the A13 timebase board and A12 trigger gen/sweep logic boards with my other 468 (one at a time of course) and now know that it is something on the A15 main interface board.  Now to isolate it further...
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf