[time-nuts] Opening an Isotemp OCXO

Peter Reilley preilley_454 at comcast.net
Fri Oct 28 19:32:09 EDT 2016


Not S05 but S30.   A 74S30 is an 8 input NAND and the foot pint on the 
board, looking
at the inputs and outputs, seems to confirm it.

There is no 5 volt regulator.   The power pin is connected directly to 
the power
pin of a 74S30.

Pete.

On 10/28/2016 6:50 PM, J. L. Trantham wrote:
> I have emailed Peter separately earlier today.
>
> The top side marking of the chip appears to indicate it is a TI 74LS05D.
>
> The datasheet is here:
>
> http://www.ti.com/lit/ds/symlink/sn74ls05.pdf
>
> If it is indeed a 'HEX Inverter', perhaps another 'channel' can be wired in place to see if it would work without having to find another chip.
>
> Also, I, too, was wondering if it was 5 V or if there was a 5 V regulator on the board somewhere.
>
> Hope this helps.
>
> Joe
>
>
>
> -----Original Message-----
> From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Tom Miller
> Sent: Friday, October 28, 2016 4:18 PM
> To: peter at reilley.com; Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Opening an Isotemp OCXO
>
> Can you see the voltage on the yellow dipped tantalum under the board? I think that is what it is.
>
>
> ----- Original Message -----
> From: "Peter Reilley" <preilley_454 at comcast.net>
> To: "Discussion of precise time and frequency measurement"
> <time-nuts at febo.com>
> Sent: Friday, October 28, 2016 3:28 PM
> Subject: Re: [time-nuts] Opening an Isotemp OCXO
>
>
>> That seems the most reasonable thing to do.
>>
>> Pete
>>
>>
>> On 10/28/2016 3:20 PM, Tom Miller wrote:
>>> It looks like that is the only device that could be damaged by 12 volts.
>>> Can you find a replacement and try running at 5 volts?
>>>
>>>
>>> ----- Original Message ----- From: "Peter Reilley"
>>> <preilley_454 at comcast.net>
>>> To: "Discussion of precise time and frequency measurement"
>>> <time-nuts at febo.com>
>>> Sent: Friday, October 28, 2016 3:10 PM
>>> Subject: Re: [time-nuts] Opening an Isotemp OCXO
>>>
>>>
>>>> The reason that there was 12 volts on the unit was because I put it
>>>> there. I should
>>>> have tried 5 volts first but the only datasheet that I could find said
>>>> 12 volts.
>>>> All the eBay units that look the same say 12 volts.
>>>>
>>>> Pete.
>>>>
>>>> On 10/28/2016 12:53 PM, paul swed wrote:
>>>>> I confirmed the pin out matches a 74s30 also. An S30 is TTL. Great pix
>>>>> to
>>>>> look at.
>>>>> So 12 V on a 5 V chip is indeed a smoker. Find out why there was 12 V.
>>>>> OK crazy talk I see a 1K resistor next to the VCC chip. Would anyone be
>>>>> crazy enough to use a dropping resistor from 12 V to get 5?? Really bad
>>>>> engineering and I don't actually believe they would. But if true a open
>>>>> 74s30 would indeed show 12 V on pin 14.
>>>>> Good luck.
>>>>> Paul
>>>>> WB8TSL
>>>>>
>>>>> On Fri, Oct 28, 2016 at 12:48 PM, jimlux <jimlux at earthlink.net> wrote:
>>>>>
>>>>>> On 10/28/16 9:13 AM, Scott Stobbe wrote:
>>>>>>
>>>>>>> The OCXO82-59 datasheet lists 12V supply, 5V clock out, could also be
>>>>>>> a
>>>>>>> blown regulator in your ocxo, if it is indeed a 12v model.
>>>>>>>
>>>>>>> There you go..the design could use a 74S30 as a driver - it's fast,
>>>>>> fairly good drive, but runs off 5V.  If the regulator is shorted, and
>>>>>> you
>>>>>> put 12V on it, it will cook.
>>>>>>
>>>>>>
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