Re: [time-nuts] OXCO Issues -- Latest
My guess is that there is a 'test case' that the unit (foam enclosed units minus the metal case) is placed into that has a hole through which adjustments can be made. Then, it is removed and installed in its 'final resting place' before sealing the unit. Joe -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Don Latham Sent: Sunday, May 12, 2013 5:16 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] OXCO Issues -- Latest If there's a pot set that's inside the case, indeed inside the "foam" then there has to be a procedure for setting it before final assembly, no? can't believe an engineering setup that requires tiny tweaks with assembly and disassembly. . . Don Bob Camp > Hi > > Several outfits made pot set OCXO's for a *long* time. As far as I > know there isn't any sort of premature end of life situation with > those designs. > > Bob > > On May 12, 2013, at 3:40 PM, "Al Wolfe" wrote: > >> Years ago we were taught that it was poor engineering practice to use >> pots to trim a DC value, especially if any appreciable current was to >> be drawn from the wiper. (Probably true for any kind of signal on a >> pot) It seems that current through the wiper would eventually erode >> away the material under the wiper. This is true especially for >> set-and-forget applications. If the wiper is used only as a voltage >> reference and very little current drawn then it is probably OK for >> most situations. >> >> The above info is mainly for carbon and ceramic pots. Wire wound ones >> tend to be somewhat more forgiving but they tend to be step-variable >> between the wire turns. Often the sweet spot is between the steps and >> they aren't very useful for fine tuning purposes. Sometimes we would >> use two pots in series. One was set up as a rheostat and was around 5 >> percent of the ohmage of the main one. It was used for fine tuning >> but the problem of DC current through the wiper remains and is >> exacerbated. >> >> Probably the best design is to use fixed resistors for most of the >> voltage divider circuit and the variable element be a small fraction >> of the total divider resistance. >> >> Al >> >> >>> Well, I decided to make the "Y" incision and pulled the circuit >>> board out of the oven. (Photos later after I crop them.) >>> >>> Yes, the trimpot is part of the circuit associated with the >>> thermistor. >>> >>> My plan is to check the resistors (surprisingly most are carbon film >>> except those in the thermistor circuit), look at the circuit board >>> under a magnifier, and stick it back in the foam for testing after >>> making any repairs. >>> >>> Thanks again for the continuing comments and advice. >>> >>> Fred >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > ___ > time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > -- "Neither the voice of authority nor the weight of reason and argument are as significant as experiment, for thence comes quiet to the mind." De Erroribus Medicorum, R. Bacon, 13th century. "If you don't know what it is, don't poke it." Ghost in the Shell Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OXCO Issues -- Latest
Hi They had cans with holes in them for the adjust process. There is no practical way to do the adjustment ahead of time. They turn hunt the parts first. Then a temperature test is done and they are adjusted again. The test / adjust process continues until they meet spec. The turn hunt gets things close, the test / adjust takes care of the (non trivial) contribution of temperature gradients and oscillator / buffer TC. Bob On May 12, 2013, at 6:45 PM, Frederick Bray wrote: > Interestingly, there is a hole in the foam to adjust the pot. There is no > corresponding hole in the can, only one for the piston capacitor adjustment. > It appears that the pot is part of the oven control circuit. Maybe Ovenaire > had a test fixture to make the adjustment before putting everything in the > can? > > I am about to the point where I will probably just reassemble it and drill a > hole for the pot. (That won't be hard to do after looking at the distance > between the two existing holes in the foam and figuring out where the hole in > the can should go.) > > I have looked at the board under a lighted magnifier and can't see any cold > solder joints or similar flaws. I suppose I could heat each one up with a > soldering iron to make sure. I have tested all the resistors while in > circuit and all values read less than or equal to the marked values. I > realize that it is still possible that one has increased but that due to > other circuit components the reading is still less than the value of the > resistor. Perhaps I should just shotgun the ones in the oven control portion > of the circuit? I have found no open diodes. I also have turned the pot 1/2 > turn in each direction and returned it to its original position in the hope > that this will have cleaned it. > > I will have to go back into the power supply anyway. There are a couple of > strange things, such as the previously mentioned fluctuations on the 12 volt > line. Then, there is the fact that the -7 volt supply is still a volt too > low. It came up after I replaced some electrolytic capacitors and some out > of value resistors but there's still more to do. This doesn't impact the > OCXO as it only uses 12 volts. > > Thanks again for all the suggestions. > > Fred > > > > > > On 5/12/2013 3:16 PM, Don Latham wrote: >> If there's a pot set that's inside the case, indeed inside the "foam" >> then there has to be a procedure for setting it before final assembly, >> no? >> can't believe an engineering setup that requires tiny tweaks with >> assembly and disassembly. . . >> Don >> >> > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OXCO Issues -- Latest
Interestingly, there is a hole in the foam to adjust the pot. There is no corresponding hole in the can, only one for the piston capacitor adjustment. It appears that the pot is part of the oven control circuit. Maybe Ovenaire had a test fixture to make the adjustment before putting everything in the can? I am about to the point where I will probably just reassemble it and drill a hole for the pot. (That won't be hard to do after looking at the distance between the two existing holes in the foam and figuring out where the hole in the can should go.) I have looked at the board under a lighted magnifier and can't see any cold solder joints or similar flaws. I suppose I could heat each one up with a soldering iron to make sure. I have tested all the resistors while in circuit and all values read less than or equal to the marked values. I realize that it is still possible that one has increased but that due to other circuit components the reading is still less than the value of the resistor. Perhaps I should just shotgun the ones in the oven control portion of the circuit? I have found no open diodes. I also have turned the pot 1/2 turn in each direction and returned it to its original position in the hope that this will have cleaned it. I will have to go back into the power supply anyway. There are a couple of strange things, such as the previously mentioned fluctuations on the 12 volt line. Then, there is the fact that the -7 volt supply is still a volt too low. It came up after I replaced some electrolytic capacitors and some out of value resistors but there's still more to do. This doesn't impact the OCXO as it only uses 12 volts. Thanks again for all the suggestions. Fred On 5/12/2013 3:16 PM, Don Latham wrote: If there's a pot set that's inside the case, indeed inside the "foam" then there has to be a procedure for setting it before final assembly, no? can't believe an engineering setup that requires tiny tweaks with assembly and disassembly. . . Don ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OXCO Issues -- Latest
Hi Inevitably there's a way to drill a hole in the outside case and get at the pot. The production cycle used one set of foam and covers for the adjustment. They were replaced with the final foam and cover once the units passed in the temperature test chambers. Bob On May 12, 2013, at 6:16 PM, "Don Latham" wrote: > If there's a pot set that's inside the case, indeed inside the "foam" > then there has to be a procedure for setting it before final assembly, > no? > can't believe an engineering setup that requires tiny tweaks with > assembly and disassembly. . . > Don > > Bob Camp >> Hi >> >> Several outfits made pot set OCXO's for a *long* time. As far as I know >> there isn't any sort of premature end of life situation with those >> designs. >> >> Bob >> >> On May 12, 2013, at 3:40 PM, "Al Wolfe" wrote: >> >>> Years ago we were taught that it was poor engineering practice to use >>> pots to trim a DC value, especially if any appreciable current was to >>> be drawn from the wiper. (Probably true for any kind of signal on a >>> pot) It seems that current through the wiper would eventually erode >>> away the material under the wiper. This is true especially for >>> set-and-forget applications. If the wiper is used only as a voltage >>> reference and very little current drawn then it is probably OK for >>> most situations. >>> >>> The above info is mainly for carbon and ceramic pots. Wire wound ones >>> tend to be somewhat more forgiving but they tend to be step-variable >>> between the wire turns. Often the sweet spot is between the steps and >>> they aren't very useful for fine tuning purposes. Sometimes we would >>> use two pots in series. One was set up as a rheostat and was around 5 >>> percent of the ohmage of the main one. It was used for fine tuning but >>> the problem of DC current through the wiper remains and is >>> exacerbated. >>> >>> Probably the best design is to use fixed resistors for most of the >>> voltage divider circuit and the variable element be a small fraction >>> of the total divider resistance. >>> >>> Al >>> >>> Well, I decided to make the "Y" incision and pulled the circuit board out of the oven. (Photos later after I crop them.) Yes, the trimpot is part of the circuit associated with the thermistor. My plan is to check the resistors (surprisingly most are carbon film except those in the thermistor circuit), look at the circuit board under a magnifier, and stick it back in the foam for testing after making any repairs. Thanks again for the continuing comments and advice. Fred >>> >>> ___ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > > -- > "Neither the voice of authority nor the weight of reason and argument > are as significant as experiment, for thence comes quiet to the mind." > De Erroribus Medicorum, R. Bacon, 13th century. > "If you don't know what it is, don't poke it." > Ghost in the Shell > > > Dr. Don Latham AJ7LL > Six Mile Systems LLP > 17850 Six Mile Road > POB 134 > Huson, MT, 59846 > VOX 406-626-4304 > www.lightningforensics.com > www.sixmilesystems.com > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OXCO Issues -- Latest
If there's a pot set that's inside the case, indeed inside the "foam" then there has to be a procedure for setting it before final assembly, no? can't believe an engineering setup that requires tiny tweaks with assembly and disassembly. . . Don Bob Camp > Hi > > Several outfits made pot set OCXO's for a *long* time. As far as I know > there isn't any sort of premature end of life situation with those > designs. > > Bob > > On May 12, 2013, at 3:40 PM, "Al Wolfe" wrote: > >> Years ago we were taught that it was poor engineering practice to use >> pots to trim a DC value, especially if any appreciable current was to >> be drawn from the wiper. (Probably true for any kind of signal on a >> pot) It seems that current through the wiper would eventually erode >> away the material under the wiper. This is true especially for >> set-and-forget applications. If the wiper is used only as a voltage >> reference and very little current drawn then it is probably OK for >> most situations. >> >> The above info is mainly for carbon and ceramic pots. Wire wound ones >> tend to be somewhat more forgiving but they tend to be step-variable >> between the wire turns. Often the sweet spot is between the steps and >> they aren't very useful for fine tuning purposes. Sometimes we would >> use two pots in series. One was set up as a rheostat and was around 5 >> percent of the ohmage of the main one. It was used for fine tuning but >> the problem of DC current through the wiper remains and is >> exacerbated. >> >> Probably the best design is to use fixed resistors for most of the >> voltage divider circuit and the variable element be a small fraction >> of the total divider resistance. >> >> Al >> >> >>> Well, I decided to make the "Y" incision and pulled the circuit board >>> out of the oven. (Photos later after I crop them.) >>> >>> Yes, the trimpot is part of the circuit associated with the >>> thermistor. >>> >>> My plan is to check the resistors (surprisingly most are carbon film >>> except those in the thermistor circuit), look at the circuit board >>> under >>> a magnifier, and stick it back in the foam for testing after making >>> any >>> repairs. >>> >>> Thanks again for the continuing comments and advice. >>> >>> Fred >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > -- "Neither the voice of authority nor the weight of reason and argument are as significant as experiment, for thence comes quiet to the mind." De Erroribus Medicorum, R. Bacon, 13th century. "If you don't know what it is, don't poke it." Ghost in the Shell Dr. Don Latham AJ7LL Six Mile Systems LLP 17850 Six Mile Road POB 134 Huson, MT, 59846 VOX 406-626-4304 www.lightningforensics.com www.sixmilesystems.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OXCO Issues -- Latest
Hi Several outfits made pot set OCXO's for a *long* time. As far as I know there isn't any sort of premature end of life situation with those designs. Bob On May 12, 2013, at 3:40 PM, "Al Wolfe" wrote: > Years ago we were taught that it was poor engineering practice to use pots to > trim a DC value, especially if any appreciable current was to be drawn from > the wiper. (Probably true for any kind of signal on a pot) It seems that > current through the wiper would eventually erode away the material under the > wiper. This is true especially for set-and-forget applications. If the wiper > is used only as a voltage reference and very little current drawn then it is > probably OK for most situations. > > The above info is mainly for carbon and ceramic pots. Wire wound ones tend to > be somewhat more forgiving but they tend to be step-variable between the wire > turns. Often the sweet spot is between the steps and they aren't very useful > for fine tuning purposes. Sometimes we would use two pots in series. One was > set up as a rheostat and was around 5 percent of the ohmage of the main one. > It was used for fine tuning but the problem of DC current through the wiper > remains and is exacerbated. > > Probably the best design is to use fixed resistors for most of the voltage > divider circuit and the variable element be a small fraction of the total > divider resistance. > > Al > > >> Well, I decided to make the "Y" incision and pulled the circuit board >> out of the oven. (Photos later after I crop them.) >> >> Yes, the trimpot is part of the circuit associated with the thermistor. >> >> My plan is to check the resistors (surprisingly most are carbon film >> except those in the thermistor circuit), look at the circuit board under >> a magnifier, and stick it back in the foam for testing after making any >> repairs. >> >> Thanks again for the continuing comments and advice. >> >> Fred > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OXCO Issues -- Latest
On 5/12/13 12:38 PM, Al Wolfe wrote: Years ago we were taught that it was poor engineering practice to use pots to trim a DC value, especially if any appreciable current was to be drawn from the wiper. (Probably true for any kind of signal on a pot) It seems that current through the wiper would eventually erode away the material under the wiper. This is true especially for set-and-forget applications. If the wiper is used only as a voltage reference and very little current drawn then it is probably OK for most situations. Probably the best design is to use fixed resistors for most of the voltage divider circuit and the variable element be a small fraction of the total divider resistance. Al This is what those EEPROM based electronic trimpots are great for. (assuming you fit within the other limitations of use). Basically, they're an array of FETs on a resistor network, and even with the power off, they have the same value. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OXCO Issues -- Latest
Years ago we were taught that it was poor engineering practice to use pots to trim a DC value, especially if any appreciable current was to be drawn from the wiper. (Probably true for any kind of signal on a pot) It seems that current through the wiper would eventually erode away the material under the wiper. This is true especially for set-and-forget applications. If the wiper is used only as a voltage reference and very little current drawn then it is probably OK for most situations. The above info is mainly for carbon and ceramic pots. Wire wound ones tend to be somewhat more forgiving but they tend to be step-variable between the wire turns. Often the sweet spot is between the steps and they aren't very useful for fine tuning purposes. Sometimes we would use two pots in series. One was set up as a rheostat and was around 5 percent of the ohmage of the main one. It was used for fine tuning but the problem of DC current through the wiper remains and is exacerbated. Probably the best design is to use fixed resistors for most of the voltage divider circuit and the variable element be a small fraction of the total divider resistance. Al Well, I decided to make the "Y" incision and pulled the circuit board out of the oven. (Photos later after I crop them.) Yes, the trimpot is part of the circuit associated with the thermistor. My plan is to check the resistors (surprisingly most are carbon film except those in the thermistor circuit), look at the circuit board under a magnifier, and stick it back in the foam for testing after making any repairs. Thanks again for the continuing comments and advice. Fred ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OXCO Issues -- Latest
Years ago we were taught that it was poor engineering practice to use pots to trim a DC value, especially if any appreciable current was to be drawn from the wiper. (Probably true for any kind of signal on a pot) It seems that current through the wiper would eventually erode away the material under the wiper. This is true especially for set-and-forget applications. If the wiper is used only as a voltage reference and very little current drawn then it is probably OK for most situations. The above info is mainly for carbon and ceramic pots. Wire wound ones tend to be somewhat more forgiving but they tend to be step-variable between the wire turns. Often the sweet spot is between the steps and they aren't very useful for fine tuning purposes. Sometimes we would use two pots in series. One was set up as a rheostat and was around 5 percent of the ohmage of the main one. It was used for fine tuning but the problem of DC current through the wiper remains and is exacerbated. Probably the best design is to use fixed resistors for most of the voltage divider circuit and the variable element be a small fraction of the total divider resistance. Al Well, I decided to make the "Y" incision and pulled the circuit board out of the oven. (Photos later after I crop them.) Yes, the trimpot is part of the circuit associated with the thermistor. My plan is to check the resistors (surprisingly most are carbon film except those in the thermistor circuit), look at the circuit board under a magnifier, and stick it back in the foam for testing after making any repairs. Thanks again for the continuing comments and advice. Fred ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OXCO Issues -- Latest
Hi If the oven is cycling enough to swing the frequency > 1 ppm, doing a turn hunt is going to be pretty tough. You are looking for small fractions of a ppm as you tweak the trimmer. The other minor point is that you need to do it with the foam and cover on the oscillator. Drilling a hole in the can is not all that hard. Bob On May 12, 2013, at 1:59 PM, Ed Palmer wrote: > When you've got it powered up again, you should try adjusting the trimpot. > You should be able to find a spot that gives you a frequency minimum, > assuming this is an AT crystal. This will minimize sensitivity to > temperature change. There's a slim chance that a shift in the temperature > set point could be at the core of your problem, but it would be a rather > extreme case. > > Ed > > On 5/12/2013 9:36 AM, Frederick Bray wrote: >> Well, I decided to make the "Y" incision and pulled the circuit board out of >> the oven. (Photos later after I crop them.) >> >> Yes, the trimpot is part of the circuit associated with the thermistor. >> >> My plan is to check the resistors (surprisingly most are carbon film except >> those in the thermistor circuit), look at the circuit board under a >> magnifier, and stick it back in the foam for testing after making any >> repairs. >> >> Thanks again for the continuing comments and advice. >> >> Fred > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OXCO Issues -- Latest
When you've got it powered up again, you should try adjusting the trimpot. You should be able to find a spot that gives you a frequency minimum, assuming this is an AT crystal. This will minimize sensitivity to temperature change. There's a slim chance that a shift in the temperature set point could be at the core of your problem, but it would be a rather extreme case. Ed On 5/12/2013 9:36 AM, Frederick Bray wrote: Well, I decided to make the "Y" incision and pulled the circuit board out of the oven. (Photos later after I crop them.) Yes, the trimpot is part of the circuit associated with the thermistor. My plan is to check the resistors (surprisingly most are carbon film except those in the thermistor circuit), look at the circuit board under a magnifier, and stick it back in the foam for testing after making any repairs. Thanks again for the continuing comments and advice. Fred ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OXCO Issues -- Latest
Hi If they are carbon film, I'd look for cracked end terminations. Hopefully the color codes are still readable. That should make the replacement process fairly easy. Another possibility - the thermistor bridge probably is / was regulated. If it's a zener diode, it may have opened up. That would boost the input voltage and increase the effective gain. Bob On May 12, 2013, at 11:36 AM, Frederick Bray wrote: > Well, I decided to make the "Y" incision and pulled the circuit board out of > the oven. (Photos later after I crop them.) > > Yes, the trimpot is part of the circuit associated with the thermistor. > > My plan is to check the resistors (surprisingly most are carbon film except > those in the thermistor circuit), look at the circuit board under a > magnifier, and stick it back in the foam for testing after making any repairs. > > Thanks again for the continuing comments and advice. > > Fred > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OXCO Issues -- Latest
Well, I decided to make the "Y" incision and pulled the circuit board out of the oven. (Photos later after I crop them.) Yes, the trimpot is part of the circuit associated with the thermistor. My plan is to check the resistors (surprisingly most are carbon film except those in the thermistor circuit), look at the circuit board under a magnifier, and stick it back in the foam for testing after making any repairs. Thanks again for the continuing comments and advice. Fred ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OXCO Issues -- Latest
Hi There should be a glass probe or bead thermistor on the oven. It's likely buried in epoxy. The epoxy may be silver loaded. Make sure the thermistor hasn't come loose from the epoxy. Give the leads of the thermistor a gentle tug. They can be sitting in solder, but not be fully wetted with solder. My guess is that the thermistor isn't the issue, but it's worth checking. Next up is that multi turn pot. If it's got a problem, the wiper is likely where it's at. Again, a long shot. Quick check is to mark the trimmer, rotate it, and return it to it's original position. Depending on when this one was made, it's either got a discrete transistor based error amp, or an op-amp in the loop. Either way there are resistors that set the gain. They may have changed value with age. My bet would be an op amp controller with a carbon comp feedback resistor across the amp. The poor thing may be 2X what it was when new. Gain is 2X what it should be, loop isn't stable…. With any troubleshooting, guessing like this isn't really the way to do it. My real point is that if you are careful, there's nothing crazy in there to work on. Bob On May 11, 2013, at 11:42 PM, Frederick Bray wrote: > Okay, I thought that perhaps the heating element wasn't working, so I pulled > the oven apart. > > In fact, the internal unit was warm and it got hot when I ran it for a couple > minutes w/o the foam around it. All of the solder connections which I can > see look good. I am not sure I want to try to remove the internal PC board. > > There are two adjustments visible once it is apart. One is a trimpot and the > one that you can normally adjust with the case closed appears to be a piston > type capacitor. It actually appears to be better constructed than I thought. > > I'll take a few pictures tomorrow for those who asked. > > Fred > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OXCO Issues -- Latest
Fred, Thanks for the info. I suspect the piston capacitor is on the oscillator board, along with the crystal. I suspect the trim pot is on the oven assembly. At least that was the way it was on the OSC 49-38C I opened. I did not have the courage to separate the oven control board from the oven assembly either. You would need to disconnect two heating coils along with a TO220 type transistor from the board and assembly. I suspect the trim pot adjusts the temperature to be able to find the lowest temp-co point of the crystal but I do not know. I would love to hear more about that circuit if anyone has ever 'autopsied' one. Joe -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of Frederick Bray Sent: Saturday, May 11, 2013 10:43 PM To: time-nuts@febo.com Subject: Re: [time-nuts] OXCO Issues -- Latest Okay, I thought that perhaps the heating element wasn't working, so I pulled the oven apart. In fact, the internal unit was warm and it got hot when I ran it for a couple minutes w/o the foam around it. All of the solder connections which I can see look good. I am not sure I want to try to remove the internal PC board. There are two adjustments visible once it is apart. One is a trimpot and the one that you can normally adjust with the case closed appears to be a piston type capacitor. It actually appears to be better constructed than I thought. I'll take a few pictures tomorrow for those who asked. Fred ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] OXCO Issues -- Latest
Okay, I thought that perhaps the heating element wasn't working, so I pulled the oven apart. In fact, the internal unit was warm and it got hot when I ran it for a couple minutes w/o the foam around it. All of the solder connections which I can see look good. I am not sure I want to try to remove the internal PC board. There are two adjustments visible once it is apart. One is a trimpot and the one that you can normally adjust with the case closed appears to be a piston type capacitor. It actually appears to be better constructed than I thought. I'll take a few pictures tomorrow for those who asked. Fred ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
