OCXO repair, is it possible? - Page 1
Forum section: electronics / repair

author: ZGoode
author_rank: Frequent Contributor
timestamp: August 31, 2024, 02:34:15 am
content: So I bought two Morion MV89A, one for use in a GPSDO and the other for upgrading the timebase in my 53131A. Turns out one of them is totally dead, of course its the one in better physical condition too, since the one that works had a completely sheared off ground pin. I ended up making a new pin on a lathe out of brass, which seems to have repaired the one with a missing pin, so I'm at 1 for 1 so far.The other one is a little more complicated, since it has zero signal output. It heats up, so the oven works, but no output. What are the odds this is salvageable? I saw some people mentioned I might be able to open it with a blowtorch or high power heat gun, but wanted some input before I did the irreversible.From anyone who has opened up a soldered case OXCO before what worked best for you?Edit: I did find a post by someone using the exact same OCXO as me, but would still love some input before getting out the torch.https://rbarrios.com/projects/mv89a/

author: ZGoode
author_rank: Frequent Contributor
timestamp: August 31, 2024, 04:27:26 am
content: Well, managed to crack it open with the power of a heater plate, FR301, and a heat gun. Now it's time for an autopsy and to see if we can figure out what is borked here.

author: smaultre
author_rank: Regular Contributor
timestamp: August 31, 2024, 06:29:39 am
content: They used acid flux that breaks the solder joints, on some series. You can try to open and clean\re-solder bad connections...

author: Stray Electron
author_rank: Super Contributor
timestamp: August 31, 2024, 01:35:06 pm
content: Quote from: smaultre on August 31, 2024, 06:29:39 amWTF? I've never heard of using acid flux to unsolder anything and I don't know why acid flux would work any better for that than any non-acid flux. Flux is intended to clean a surface before soldering to it, not as an aid for unsoldering. Furthermore, I would think that if you used acid flux on anything electrical that unless you can remove every trace of it (unlikely in the case of a soon to be sealed OCXO) that sooner or later the acid would creep into the electrical circuits and corrode and ruin them.There are several threads in this forum and online where people have opened OCXOs and repaired them.IMO acid flux has no place in electronics, period.

author: Gerhard_dk4xp
author_rank: Frequent Contributor
timestamp: August 31, 2024, 04:00:24 pm
content: This is what is inside:<https://www.flickr.com/photos/137684711@N07/49585174873/in/album-72157662535945536/>One of my MV-89A stopped oscillating when the tuning voltage was > 1V.The tuning range drifts when they age, and these MV89s on ebayalready had a life on a Chinese telecom tower behind them.I just took the 5 MHz SC cut crystal. Yes, the 10 MHz oscillator has afrequency doubler, and it shows on the output.Gerhard

author: ZGoode
author_rank: Frequent Contributor
timestamp: August 31, 2024, 07:30:50 pm
content: The solder joints on the inside are horrendous. I'm gonna add some good no-clean flux and reflow all the joints.Quote from: Gerhard_dk4xp on August 31, 2024, 04:00:24 pmGerhard, did you get pictures of the internal oven? Some of the solder joints are so bad on mine that parts are barely holding on, I want to make sure that the parts I put back are in the right places.

author: Gerhard_dk4xp
author_rank: Frequent Contributor
timestamp: August 31, 2024, 09:12:06 pm
content: Did you overheat the entire oven when removing the outer box?I did file the roof off (cold) and could then peel away the side walls.On Flickr, there are the pictures of the innards. Use the < and >for the others. Methinks the remains are still around. I could takemore photos if you want.Or I can send you the stuff, barring xtal and thermistor.No idea how to set that up for customs.The inner oven is not air-tight. More a folded piece of Alu.I do not see a point in repairing that stuff. It is probablyaged at 87°C for 20+ years. That could be OK just forthe XTAL, but the amount of other parts does not changethe statistics for success in your favor.All in all, my Chinese MV89A were not much of a success.SC crystals are not so easy to get. 20 years ago I asked aGerman company and the answer was as if I had asked ifI could lend the CEO's wife. Now DigiKey has at least some.(SC xtals, not wifes)Sooner or later, I ´ll try the univ of York oscillator with it.Gerhard

author: ZGoode
author_rank: Frequent Contributor
timestamp: August 31, 2024, 09:53:31 pm
content: Yeah, if you still have it, I woulb probably be interested in its guts to try and make a franken-OCXO out of the two. The weird little inductor/transformer things in the inner oven of mine are definitely borked since I broke those tiny little wires by accident when opening the inner oven. Unfortunately there was a rattling in the inner oven, so I had no choice.Any clue what those small little transformer/inductor things are or what they do? I might try and rewind them, but I have no clue what their pinout or ratios are.

author: Gerhard_dk4xp
author_rank: Frequent Contributor
timestamp: August 31, 2024, 10:02:05 pm
content: My guess is that they are part of the 5-> 10 MHz frequency doubler.Probably with 2 diodes. I did not check it.

author: ZGoode
author_rank: Frequent Contributor
timestamp: September 04, 2024, 08:53:38 pm
content: Quote from: Gerhard_dk4xp on August 31, 2024, 09:12:06 pmIf you're still open to the idea of sending me the parts you no longer need, I would greatly appreciate it. The little coil thingies on mine are not salvageable, so even if I could fix other possible problems, without those it probably won't work.

author: Gerhard_dk4xp
author_rank: Frequent Contributor
timestamp: September 04, 2024, 10:48:55 pm
content: Send me your post address by private message.It may take a little it of time; i have so search it.cheers, Gerhard

author: ZGoode
author_rank: Frequent Contributor
timestamp: September 04, 2024, 11:23:13 pm
content: Sounds good! Just sent you a PM with that information.Thank you!