[time-nuts] LPRO-101 BITE (~lock) Signal Always Low

iovane at inwind.it iovane at inwind.it
Tue Mar 22 17:39:06 EDT 2016


Perfect !!
The swept voltage should not reach 14V, but only about 12.5V and then reverse. Your upper comparator is faulty. Check resistor R215 on the PCB bottom face, 100K SMD. You could chech it on board, and probably you will read more than 1 Mohm. I bet the trouble is there. R215 is near the longer slot and is of the smallest size.
Antonio I8IOV



From: Wayne Holder <wayne.holder at gmail.com>


I don't currently have a way to accurately measure the frequency of the output, but my assumption is that oscillator is running, but not locked.  I did some more poking around and found that the crystal volts monitor (pin 9) starts low (around 4 volts) and then slowly rises as the unit runs.  It rises to about 14 volts and then stops.  So, this may be a similar problem to what you described.  However, lacking proper schematics, I'm not sure where to look next.
Wayne
On Tue, Mar 22, 2016 at 8:43 AM, iovane--- via time-nuts <time-nuts at febo.com> wrote:
Wayne,



are you sure your LPRO actually locks? You say you have measured 10.000 MHz

but you don't mention the other decimals. Some years ago I characterized some

LPROs of mine, and from my notebook I take that, on one sample for instance,

prior to lock the frequency swept up and down between (about) 9.999860 and

10.000230. Such a span was rather typical among units. A faulty unit of mine

remained stuck at the upper limit without reversing the sweep. This was due to

a faulty resistor in one of the two (upper) voltage comparator circuits. Anyway

I don't know if this would affect the BITE, but I suggest you to check the

other decimals.



Antonio I8IOV



>

>The BITE signal is the only way to to know if it has a lock...

>

>Wayne

>

>> On Mar 22, 2016, at 4:37 AM, Bob Camp <kb8tq at n1k.org> wrote:

>>

>> Hi

>>

>> There are probably a dozen or more things that contribute to the BITE

output. It could be

>> a regulator out of range. It also could be the VCXO nearing tune limit. If

the unit locks up and

>> seems to work, I’d ignore it and move on.

>>

>> Bob

>>

>>> On Mar 21, 2016, at 9:42 PM, Wayne Holder <wayne.holder at gmail.com> wrote:

>>>

>>> I have a surplus LPRO-101 that seems to power up OK.  The power draw

starts

>>> at 1.7 Amps and then, after a few minutes, drops down to 600 mA, or so

and,

>>> after this startup, the output shows a 10.000 MHz signal thats 's

>>> accurately as I can measure it.  The lamp voltage is 6.2 volts, which

seems

>>> within spec.  However, the BITE signal that's supposed to indicate lock

>>> with a LOW level is always LOW and never changes.  The docs say that BITE

>>> signal should start at a HIGH level to indicate no lock and then drop to a

>>> LOW when lock is obtained.  So, this behavior seems all wrong.

>>>

>>> I opened the case and observed the purple glow of the lamp and probed

>>> around IC U401, which buffers the BITE signal, and saw the same signal LOW

>>> level.  U401 is getting 5 volt power and the inputs to the AND gate used

as

>>> a buffer for the BITE signal match what I'd expect.  But, lacking a proper

>>> schematic, I'm not sure how to trace this back to the problem.  Has anyone

>>> ever seen a symptom like this with an LPRO101?

>>>

>>> Wayne



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