Power On since a log period of not use my Tek 7L12 Spectrum analyzer, and bang a problem. I couldn't turn the nice coarse tuning dial, it is barely move and jammed...
Time to open up the beast, used to calibrate and repair these guys 35 years ago... These Tek modules are so dense that it is not a work in the park to work inside them, and the spectrum analyzer are the worst!
I had to completly removed the front panel and the thousand buttons and dial, and the IF module to be able to pry open the front section wide enough to extract the frequency dial assy. Guess what I found? a little custom gear was unglued and cam apart. It was no longer turning the mechanical dial and YIG tuning pot...
Put some glue, let it tried and put it back to try. But surprise! naturally it was not working fine, dial was still difficult to rotate at some position, and jam at others. Removed it and using a magnification glass look at the little gear teeth, bingo some where slightly bent, and some other where not straight. Using a fine plier I straighten and realigned the incorrect teeth. Put it back and Voila! working like a charm again.
Time to open up the beast, used to calibrate and repair these guys 35 years ago... These Tek modules are so dense that it is not a work in the park to work inside them, and the spectrum analyzer are the worst!
I had to completly removed the front panel and the thousand buttons and dial, and the IF module to be able to pry open the front section wide enough to extract the frequency dial assy. Guess what I found? a little custom gear was unglued and cam apart. It was no longer turning the mechanical dial and YIG tuning pot...
Put some glue, let it tried and put it back to try. But surprise! naturally it was not working fine, dial was still difficult to rotate at some position, and jam at others. Removed it and using a magnification glass look at the little gear teeth, bingo some where slightly bent, and some other where not straight. Using a fine plier I straighten and realigned the incorrect teeth. Put it back and Voila! working like a charm again.
Attachments
But then I reassembled everything, and the multiple dials and buttons like for gain/step attenuator and the complex Span/BW/Resolution. Put it back into the frame, nothing!
Put it back on the bench, and looking insde I saw a few small wire/cables going to the IF module that were not connected... Re-open it, corrected the wirings and put it back.
The Span/BW/Resolution is intermittent and barely making contact to the multiple time base inside. For those that know the infamous little Tek finger contact used in their time base cam switches, well it is a real pleasure to adjust and repair...
Re-opened the beast again, remove the very long and complex BW/Time/Span selection can switch cover, using a high intesity light and a magnifier I look at all the little switches. Looking at their operation I can see that some contacts were not making contact and needed to be gently bent to correct it. But Oh no! one of the little finger was broken and was just standing there on the pcb...
Dissambled again a part of the unit to gain access to this large switch, remove it with the variable scan pot. Then using very gentle touch, a tweezer and magnication I resoldered in place the loose contact. Took ma couple of try but I was able to get it near perfectly aligned. I repaired Tek gear like this in the past, and it last.
Then I check all switch finger, bent some to regain the spring. put back the large cam, and screwed the cam support block, making sure the little finger were aligned with the cams. Then I double check all the switches. Looking good. Put some 'Luberex' lubricant grease on the cam ball crank, they were quite dry after at least 40 years.
Put back everything, and turn it on. It is working now! Calibrate the front adjustments and working almost as new.
Until next time I guess...
Put it back on the bench, and looking insde I saw a few small wire/cables going to the IF module that were not connected... Re-open it, corrected the wirings and put it back.
The Span/BW/Resolution is intermittent and barely making contact to the multiple time base inside. For those that know the infamous little Tek finger contact used in their time base cam switches, well it is a real pleasure to adjust and repair...
Re-opened the beast again, remove the very long and complex BW/Time/Span selection can switch cover, using a high intesity light and a magnifier I look at all the little switches. Looking at their operation I can see that some contacts were not making contact and needed to be gently bent to correct it. But Oh no! one of the little finger was broken and was just standing there on the pcb...
Dissambled again a part of the unit to gain access to this large switch, remove it with the variable scan pot. Then using very gentle touch, a tweezer and magnication I resoldered in place the loose contact. Took ma couple of try but I was able to get it near perfectly aligned. I repaired Tek gear like this in the past, and it last.
Then I check all switch finger, bent some to regain the spring. put back the large cam, and screwed the cam support block, making sure the little finger were aligned with the cams. Then I double check all the switches. Looking good. Put some 'Luberex' lubricant grease on the cam ball crank, they were quite dry after at least 40 years.
Put back everything, and turn it on. It is working now! Calibrate the front adjustments and working almost as new.
Until next time I guess...
Attachments
At the cal lab we used to say, Spectrum are Hewlett-Packard, scope are Tek. Never had the money at the time to buy an HP, but I had the opportunity to get the 7L12. Just hope it doesn't break down!
As for the surgeon thing, I repaired once one of the bigger HP Spectrum analyzer, two large chassis affair, digital display, tracking generator, a beauty. The bright tech that damaged it plug the poor specturm directly at the output of a radar, and then after complained that the instrument was showing nothing. No wonder, after sending 200Kw peak into the poor beast rated probably a few mw it was dead.
I started from the instrument input; everything was blown up, first 3dB pad, step attenuator, first mixer, IF amp, it goes on. Took me 2 days to dissassemble the beast, test the parts, and to find up to where it was blown up. At the end there were boxes of screws, bolts, small flex and rigid coax, RF assy modules everywhere. There was 6 service manuals to work with.
Took an other 2 days to put it back and calibrate/check everything once I had all the replacement parts. Costed an arm and a leg to fix, but the instrument for about easily 50K$ in the 80's, so it was worth it.
Spectrum analyzer were always a mystery for most techs, and big powerful radars blown countless spectum analyzer and power sensors, that's for sure... Good thing now we have digital scope with FFT.
SB
As for the surgeon thing, I repaired once one of the bigger HP Spectrum analyzer, two large chassis affair, digital display, tracking generator, a beauty. The bright tech that damaged it plug the poor specturm directly at the output of a radar, and then after complained that the instrument was showing nothing. No wonder, after sending 200Kw peak into the poor beast rated probably a few mw it was dead.
I started from the instrument input; everything was blown up, first 3dB pad, step attenuator, first mixer, IF amp, it goes on. Took me 2 days to dissassemble the beast, test the parts, and to find up to where it was blown up. At the end there were boxes of screws, bolts, small flex and rigid coax, RF assy modules everywhere. There was 6 service manuals to work with.
Took an other 2 days to put it back and calibrate/check everything once I had all the replacement parts. Costed an arm and a leg to fix, but the instrument for about easily 50K$ in the 80's, so it was worth it.
Spectrum analyzer were always a mystery for most techs, and big powerful radars blown countless spectum analyzer and power sensors, that's for sure... Good thing now we have digital scope with FFT.
SB
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