EEVblog #1139 - OCXO Oven Oscillator Repair

Well, repair-ish. Fixing the adjustment issue in the Systron Donner oven crystal oscillator. More issues found though.

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[johnwest]

I don't know what stability tricks the new ovenized oscillators have implemented, but an ovenized oscillator that has been running for years is noticeably more stable than it was when it was new. The internal mechanical stresses have stabilized over the years, reducing drift components. In other words, and old one is better than a new one, and one that's been running for 20 years is best.

[UpcycleElectronics]

I really like the positivity as of late ;)
I've left with a smile and having learned a thing or two for a few uploads in a row. Much appreciated. Thanks Dave.

[RedwoodRhiadra]

How to use a frequency counter as a gravity detector: Drop it. If it falls, then yep, there's gravity.

[atose_offline]

nobody sees the broken resistance near pin 14 of the IC ?? 7:31

[Subgunman]

OCXO's require a minimum of ten minutes of warm up when they are working. Tantalum capacitors are a type of electrolytic capacitor. You cannot replace them with non polarized Mylar film capacitors. Tantalums are usaually very accurate as to their ratings unlike a standard electrolytic and used in precision circuits.Try finding a tantalum of equal value for precise calibration or substitute an electrolytic if precision is not of importance. Not much can go wrong with these units unless the heater element has gone open circuit. Love your videos and the great commentary! CHEERS!

[nerdful]

I just took out my systron donner 7014 1970 year. Made in USA Concord California.
Been sitting a few years unpowered, so powered it up to prevent decay.
Small ac fans were used such as boxer or muffin fans.
Typically heavy rotors, sort of like my Revox reel motors.

Spins really freely by hand, probabaly lubed by my test and measurement repair team.
Takes a bit to spin up, but totally free spinning.

Some friends would say when is it going to take off?
A few years ago I took it back from storage hoping it was not tossed. It was my instrument, and was going to be used in a reflex timing exhibit.

Got dragged to Maine following new wife's job.

So refreshing to see real 5's rather than upside down 2's. All nice and bright.

[EmilHarder]

I really enjoy your repair(-ish) videos. You have a good way of showing how to understand a circuit and find the failure.
And it seems you videos in general have been more positive as of lately. It really suits you and your channel!

[Tommyinoz]

So this is a 1970's Australian designed and built device? Then where is the beer holder and ashtray attachments?

[zxztv]

Fix the heater dave, have patience for the old beast, loverly old counter.

[Nexfero]

Atleast its from an era where service personnel were expected to solder and the manual actually tells you everything you need to know if not more.

[jorno]

and of course it was a god damn tantalum

[iamdarkyoshi]

The tantalum shorting is probably what caused the resistor to get hot

[Damien.D]

Working, more or less, not reassembled properly, I'd call this a professional fix.

[CoolMusicToMyEars]

I had the same problems with old worn out temperature controlled oscillators, to remove the case I find it better to use a hot heat plate and carefuly use a small gas soldering iron & stanley blades to go between the bottom of the soldered area, suck off as much solder as you can, use flux make the solder run down to one spot, as long as the main case is hot the gas soldering iron should work, I tried this on a Truetime GPS XL-DC 10MHz oscillator, must admit its not easy takes ages to remove the base depends on how much solder you can get off...

[dalehorton]

Is it actually fixed? the frequency was dropping on it's own from temperature, sure the adjustment pot actually did something, and wasn't just it warming up? :/

[davidv]

Not asbestos, it would be white and very flaky in its raw form and would probably have been wrapped. That looks like glass wool insulation. Please take the "Recycle Rate" control (gate delay) off of infinity so the poor gate circuit can do its job... Also, consider donating it to somebody new, in its day that counter was considered the ducks cuts - I used one like it for many years.

[bryant]

Lots and lots of flux helps when unsoldering surfaces like that can. The rest of the electronics are magic to me. That's why I watch Mr. Jones do it.

[JismalJamal]

Glass wool, I seen them in very large oven.

[Rob]

I don't think you have repaired it... you found a failed component and replaced it, but after that the frequency was still off and not well reacting to the trimmer. The frequency dropped, but it continued to drop without you touching the trimmer. That is because of the oven heating up (thermal coefficient of the oscillator as a whole is usually negative).
Furthermore, the failure of the tantalum 2.2u capacitor which likely is some supply decoupling in the heating circuit would not at all explain why the trimmer was ineffective.
There must be some other fault like a break in the connection between the trimmer and the oscillator circuit, or failure of another (small ceramic) cap in the oscillator.

[sincerelyyours]

Dave, if you have no further need for this Systron-Donner freq counter and feel like donating it to a worthy cause, I could take it off your hands. The nixie tube display alone would make a welcome edition to my struggling vintage electronics repair shoppe...