Tek 2465 troubles - Page 1
Forum section: electronics / testgear

author: Daxxin
author_rank: Regular Contributor
timestamp: October 05, 2014, 12:18:11 pm
content: 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 offcrt 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 TPnumber 1 , frequency is ok but amplitude is less than expected and waveform different shapenumber 2 , here the same ..smaller amplitude but atleast similar waveformnumber 3 , here totally different waveform of what expected , the timing maybe okalredy replaced the 74ls04 , tought failing but no changes , hope someone can help me to fix this.

author: mij59
author_rank: Frequent Contributor
timestamp: October 05, 2014, 01:39:54 pm
content: 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.

author: Daxxin
author_rank: Regular Contributor
timestamp: October 05, 2014, 03:01:11 pm
content: 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?

author: mij59
author_rank: Frequent Contributor
timestamp: October 05, 2014, 03:30:49 pm
content: Quote from: Daxxin on October 05, 2014, 03:01:11 pmThe clock signal doesn't look right, +5VD ok ?.Please check the signals on pins 11 , 18 , and 1 of U2034.

author: Daxxin
author_rank: Regular Contributor
timestamp: October 05, 2014, 04:18:33 pm
content: +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..

author: mij59
author_rank: Frequent Contributor
timestamp: October 05, 2014, 04:52:51 pm
content: Quote from: Daxxin on October 05, 2014, 04:18:33 pmThere's no clock signal, check U2580.

author: Daxxin
author_rank: Regular Contributor
timestamp: October 08, 2014, 01:48:26 am
content: 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-pkbut 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 valuesaround 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'dwith minus led has fault code meaning but dont know wich device related to that error code.

author: mij59
author_rank: Frequent Contributor
timestamp: October 08, 2014, 04:40:01 am
content: Quote from: Daxxin on October 08, 2014, 01:48:26 amWaveform 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.

author: Daxxin
author_rank: Regular Contributor
timestamp: October 08, 2014, 05:42:06 pm
content: 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 U2770with analogic scope just back from calibratio with new probe.the last ..pin 5 very unstable

author: mij59
author_rank: Frequent Contributor
timestamp: October 08, 2014, 06:36:19 pm
content: Quote from: Daxxin on October 08, 2014, 05:42:06 pmPlease check pin 14 of U2580 it should be low if the pins (4,5,1, and 3 are low) and pin( 2 is high).

author: Daxxin
author_rank: Regular Contributor
timestamp: October 19, 2014, 05:14:45 pm
content: Partially fixed , the problem was 1 eprom 27c128 lost data , replaced the eprom finally boot up with diagnostic ALL OKbut still have a problem with readout board , flickering always and changing flickering speed turning the SEC/DIV knobthis the video on youtube , any help apreciated.http://youtu.be/t6aJclLUnrk

author: David Hess
author_rank: Super Contributor
timestamp: October 19, 2014, 06:41:17 pm
content: Quote from: Daxxin on October 19, 2014, 05:14:45 pmThe 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.

author: Daxxin
author_rank: Regular Contributor
timestamp: October 19, 2014, 07:46:21 pm
content: 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 .

author: David Hess
author_rank: Super Contributor
timestamp: October 20, 2014, 12:01:46 am
content: Quote from: Daxxin on October 19, 2014, 07:46:21 pmI 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.

author: Bryan
author_rank: Frequent Contributor
timestamp: October 20, 2014, 08:55:45 am
content: Quote from: Daxxin on October 19, 2014, 07:46:21 pmDaxxinDoes the flickering of the trace go away or improve if the Readout Intensity knob is turned off.?

author: David Hess
author_rank: Super Contributor
timestamp: October 21, 2014, 01:19:25 am
content: Quote from: Bryan on October 20, 2014, 08:55:45 amThe problem shown in the video is that the readout itself is intermittent.