8640b problem

[Steve]

We have an HP 8640b that will not work in phase lock mode. When you
turn on phase lock, the unit tries to phase lock for about two
seconds, then the display blinks. It does this on all frequency
ranges. Looking at the output, when phase lock turns on, the signal
jumps up in frequecy and keeps climing until the display blinks, then
the signal returns to the original frequency. I haven't opened this
one up yet, figured I'd ask if this is a normal problem before I dig
in.

I have checked for the obvious problems, i.e. cracked gears, loose
boards, burnt components..

All help appreciated.

Thanks,
Steve

 

[Ancient_Hacker]

We have an HP 8640b that will not work in phase lock mode. When you
turn on phase lock, the unit tries to phase lock for about two
seconds, then the display blinks. It does this on all frequency
ranges. Looking at the output, when phase lock turns on, the signal
jumps up in frequecy and keeps climing until the display blinks, then
the signal returns to the original frequency. I haven't opened this
one up yet, figured I'd ask if this is a normal problem before I dig
in.

I have checked for the obvious problems, i.e. cracked gears, loose
boards, burnt components..

All help appreciated.

Thanks,
Steve

Does the digital frequency readout work correctly? I've seen many of
these go intermittent or worse.
As you might expect, if the digital readout is flaky, the phase lock is
unlikely to work.

 

[[email protected]]

Does the digital frequency readout work correctly? I've seen many of
these go intermittent or worse.
As you might expect, if the digital readout is flaky, the phase lock is
unlikely to work.

The readout seems to work correctly, the frequency is accurate and it
isn't intermittent. It seems like the error amplifier is calculating
too high an error and overcorrecting, causing the frequency to drift
until it is no longer phase locked.

Thanks,
Steve Kamego
Calibration Specialty Inc.

 

[Ancient_Hacker]

The readout seems to work correctly, the frequency is accurate and it
isn't intermittent. It seems like the error amplifier is calculating
too high an error and overcorrecting, causing the frequency to drift
until it is no longer phase locked.

I've seen a high failure rate of the MECL IC's under the right circuit
board-- they normally run quite hot, which might have cut their life.
I wouldnt be surprised if the problem is in there.

If you have another 8640B you might try narrowing down the problem by
swapping those three boards in that area.

 

[[email protected]]

I've seen a high failure rate of the MECL IC's under the right circuit
board-- they normally run quite hot, which might have cut their life.
I wouldnt be surprised if the problem is in there.

If you have another 8640B you might try narrowing down the problem by
swapping those three boards in that area.

Thanks so much, I'll try that when I get it opened up again.

Regards,
Steve Kamego

 

[Jamie]

We have an HP 8640b that will not work in phase lock mode. When you
turn on phase lock, the unit tries to phase lock for about two
seconds, then the display blinks. It does this on all frequency
ranges. Looking at the output, when phase lock turns on, the signal
jumps up in frequecy and keeps climing until the display blinks, then
the signal returns to the original frequency. I haven't opened this
one up yet, figured I'd ask if this is a normal problem before I dig
in.

I have checked for the obvious problems, i.e. cracked gears, loose
boards, burnt components..

All help appreciated.

Thanks,
Steve

open the lid, look in the back, there is a power supply board plugged
in, actually boards! , they have LED's that indicates them being on.
you mostly will find one not on. flip the unit over, remove the bottom
lid, there is a can transistor there that likes to have it's screws in
the collector come loose. Tighten..
I have 2 of those units with all the options, they both have that
problem at times.

 

[Steve]

open the lid, look in the back, there is a power supply board plugged
in, actually boards! , they have LED's that indicates them being on.
you mostly will find one not on. flip the unit over, remove the bottom
lid, there is a can transistor there that likes to have it's screws in
the collector come loose. Tighten..
I have 2 of those units with all the options, they both have that
problem at times.

I'll give that a shot and let you know, I don't think I'm going to
open it up again this week, too much other work going on. Thanks for
the reply, come to think of it I didn't check all the supplies status
LED's, just made sure the boards were tight.

Regards,
Steve

 

[[email protected]]

open the lid, look in the back, there is a power supply board plugged
in, actually boards! , they have LED's that indicates them being on.
you mostly will find one not on. flip the unit over, remove the bottom
lid, there is a can transistor there that likes to have it's screws in
the collector come loose. Tighten..
I have 2 of those units with all the options, they both have that
problem at times.

I checked the supplies, all are present and in tolerance, I checked the
transistor and it's good and tight.

Thanks again,
Steve