Tektronix 495P Spectrum analyzer repair Help - Page 1
Forum section: electronics / repair

author: deepspace
author_rank: Contributor
timestamp: May 18, 2020, 03:54:59 pm
content: Hi,I acquire this SA and have some problems with it..1. when I want to do a calibration, calibration failed ,, "Calibrator SIGNAL NOT PRESENT", 100Mhz on CAL OUT is present2. REF OSC on screen still showing I-U instead of INT , I did not find the opportunity to change it.3. I cannot tune center frequency with knob to center marker, Curve jumping up and down around centerTek is B01 serial range, Caps on PSU changed.Can anyone help me with these problems ?Many Thanks for reply, and sorry for English , it's not my native language..Martin

author: bob91343
author_rank: Super Contributor
timestamp: May 18, 2020, 05:27:54 pm
content: Is there a RESET function? Check the manual.

author: deepspace
author_rank: Contributor
timestamp: May 18, 2020, 05:36:05 pm
content: Yes, I performed reset from front panel, this procedure only sets the values ​​as at startup.

author: tggzzz
author_rank: Super Contributor
timestamp: May 18, 2020, 06:00:51 pm
content: It might ne worth searching the groups.io TekScopes archive.https://groups.io/g/TekScopes/topicsIf necessary, join, and ask questions. They are friendly and knowledgeable, just like here.

author: deepspace
author_rank: Contributor
timestamp: May 18, 2020, 06:07:10 pm
content: tggzzz, Thank You, yes I did ..,still waiting for answer from TekScopes

author: KE5FX
author_rank: Super Contributor
timestamp: May 18, 2020, 06:54:30 pm
content: Unfortunately those symptoms are so broad that they could be caused by any number of things.What have you done to troubleshoot them so far?For instance, does your reference oscillator feel warm to the touch after it's been on for a while? If not, that would at least explain the I-U indication.

author: deepspace
author_rank: Contributor
timestamp: May 18, 2020, 08:38:06 pm
content: yes I understand .. reference oscillator is warm, I can't find out more yetOk, what I have done so far ..1. I read user manual2. I read Service manual Vol1, and Vol2., not all yet, it is too extensive3. I read the links about repair this SA,https://iz3kgj.jimdofree.com/realizzazioni/tektronix-495p-phaselock-failure-1st-lo-repair/Ind more useful service notes here ..http://www.ke5fx.com/49x_notes.pdfand all repairs have already been made.4. I did a check Aids from diagnostic menu - all Expected and measured Frequency and ofsets (1ST Lo, 2nd Lo, DAC ) are in tolerance.5. All PSU Voltages correspondent with Service manual, Power status LED is Green.6. I repaired Intermitted contact on 2nd LO, (SMA Connector)7. Visual inspected Whole boards for leak, corrosion etc..Result ..Basic calibration not working, Calibrator SIGNAL NOT PRESENT ..INT OSC shows I=U, sometimes when i change Center Frequency with knob for a moment shows INTWhen I change SPAN under 100kHz sometimes 1ST Lo , 2nd Lo error appears ..I will need more equipment to continue ..

author: KE5FX
author_rank: Super Contributor
timestamp: May 18, 2020, 11:06:39 pm
content: Quote from: deepspace on May 18, 2020, 08:38:06 pmHmm, sounds like you've made some good progress but not quite enough. Does the 100 MHz calibrator signal appear on the display? A fault in the 100 MHz oscillator assembly could cause most or all of these symptoms, so I would focus on making sure your 100 MHz calibrator output is present at the correct frequency and amplitude, and is stable.

author: deepspace
author_rank: Contributor
timestamp: May 30, 2020, 07:38:22 pm
content: The 100MHz oscillator looks fine, the frequency on the oscilloscope is stable at 99.9999 MHz, I found that the OCXO internal oscillator is defective. It drops out after heating. Unfortunately, this defect does not affect the INT-UNLK error. I need to get another ocxo module and we'll see.

author: KE5FX
author_rank: Super Contributor
timestamp: May 30, 2020, 11:31:24 pm
content: INT-UNLK just means that the internal 100 MHz oscillator that's located in the 110 MHz IF amp assembly isn't locked to the 10 MHz OCXO. That would be the expected symptom if the latter is defective. You may still be able to use an external 10 MHz source, in which case the CRT notation should change to EXT when you connect the 10 MHz source.Since the 100 MHz oscillator has a relatively wide tuning range, it also wouldn't be too surprising if it's impossible for the analyzer to calibrate the narrowband IF filters when there is no valid 10 MHz source for phase locking. It thinks there's no calibrator signal present because the peak is located too far offscreen. I'd recommend using an external 10 MHz reference for all further troubleshooting, until you are able to repair or replace the OCXO.

author: deepspace
author_rank: Contributor
timestamp: May 31, 2020, 09:02:13 am
content: Thanks for Your reply..,10 MHz OCXO inside is Vectron 217-5584-2. Unfortunately, I didn't find it anywhere. I know it could be replaced, but it has a specific pinout , SMA jack for output, two voltages and on-off input.Has anyone experienced with repairing this OCXO ?, is completly enclosed in metal housing.