8640b issues

[sck0006]

I have an 8640b with issues. As frequency is increased in each range,
it falls off to nothing or very low at the high end. Low end seems to
work ok. I aligned the two seperate detents on the range selector
switch, but still the same problem. Is this a common failure, or am I
going to have to dig deeper? Sorry this is so vague, I really haven't
had time to tear it up, but I can't keep up w/ all the customer
equipment and repair all of ours at the same time, you know how it
is..
Steve

 

[Thomas Hejl]

I have an 8640b with issues. As frequency is increased in each range,
it falls off to nothing or very low at the high end. Low end seems to
work ok. I aligned the two seperate detents on the range selector
switch, but still the same problem. Is this a common failure, or am I
going to have to dig deeper? Sorry this is so vague, I really haven't
had time to tear it up, but I can't keep up w/ all the customer
equipment and repair all of ours at the same time, you know how it
is..
Steve

Steve
Do you have any numbers? What falls off - the frequency or the output
levels in dbm? Do you have a repair manual? (You can download one at BAMA:
http://bama.sbc.edu/index.html ) I wish I was in your shoes, I have all the
time in world to repair test equipment - aka lack of customers.

Tom

 

[sck0006]

Sorry, output level (dBm) falls off. Yes, we have a manual, I just
haven't gotten too involved yet (our spec an needs adjustment first,
so it's just waiting in line).
Steve

 

[Thomas Hejl]

Steve,
Is this unit the standard civilian or the military version (AN/USM 323-
black face plate)? I will try to trouble shoot it for you long distance from
here.
Tom

 

[Thomas Hejl]

Steve,
Just another added thought - You might want to post you request for
assistance in the news group:

sci.electronics.equipment

There might be more equipment repair techs visiting there then here.

Tom

 

[**THE-RFI-EMI-GUY**]

Also QEX (ARRL Publication) has had an article in past few months about
repairing them, with letters in the followup issues about errors in the
first article,

Steve,
Just another added thought - You might want to post you request for
assistance in the news group:

sci.electronics.equipment

There might be more equipment repair techs visiting there then here.

Tom


<sck0006> wrote in message

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P

 

[Thomas Hejl]

Any particular date(s) on that article?
Also QEX (ARRL Publication) has had an article in past few months about repairing them, with letters in the followup issues about errors in the first article,

Thomas Hejl wrote:

Steve,
Just another added thought - You might want to post you request for
assistance in the news group:

sci.electronics.equipment

There might be more equipment repair techs visiting there then here.

Tom


<sck0006> wrote in message
Sorry, output level (dBm) falls off. Yes, we have a manual, I just
haven't gotten too involved yet (our spec an needs adjustment first,
so it's just waiting in line).
Steve





--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P

 

[Alt Beer]

Steve,
Just another added thought - You might want to post you request for
assistance in the news group:

sci.electronics.equipment

Also Yahoo group http://groups.yahoo.com/group/hp_agilent_equipment

 

[sck0006]

Civilian version, I believe. Standard grey case, I can get the s/n
and other specifics on monday.

Thanks,
Steve

 

[Fred McKenzie]

I have an 8640b with issues. As frequency is increased in each range,
it falls off to nothing or very low at the high end. Low end seems to
work ok. I aligned the two seperate detents on the range selector
switch, but still the same problem. Is this a common failure, or am I
going to have to dig deeper?

Steve-

The only common problem I've heard of, is cracked or broken nylon gears in
the tuning mechanism. I've never had mine apart, so can't tell you what
to look for.

I imagine that there could be additional circuits that must be tuned to
track frequency. If a gear was broken, it would mess up the tracking and
could explain low output at one end of the range.

The person who told me about this indicated that he had custom metal gears
made for one(s) he repaired. They may not be commonly available.

Fred

 

[Ancient_Hacker]

There are sooo many stages and parts in these nice old generators, it
could be most anything.

If it happens on EVERY range, then it's most likely in the big
rocket-shaped oscillator. Too bad as that's acccording to HP a
non-user-repairable unit.

IMHO the whole thing is a non-repairable unit! There are so many
custom IC's in there it's a big crap-shoot. I was able to make ONE
working unit out of three sick ones, but that's not terribly
economical. The nylon gears, the digital readout, and the voltage
regulator modules, the FAN, the lever knobs, the slide switches, all
seem to be very weak points on these units. They're very ruggedly
built otherwise, lots of gold-plating, heavy-duty castings. But too
many weak points IMHO. You might consider parting it out! I'd sure
bid on a working digital readout module!

Regards,

 

[Ancient_Hacker]

Oh I forgot a few shaky things: The power transformer, the power
diodes, the Pc board they horridly mounted the power transformer ON,
the many dipped-tantalum capacitors that tend to short out on the
hidden motherboard and modulation boards, the board handles that crack
off, the unobtainable power output IC's hidden under a ton of
allen-head bolts, the modulation meters that stick or fail, the
gold-plated slide switches that switch all the lc filters, under a ton
of screws, the u-joints and flexible couplings that break, the
often-charred output attenuator that is almost unrepairable. I could
go on but I think you get the idea.

 

[sck0006]

Thanks for the replies everyone. I had it apart a while ago, I
remember checking out the gears, but don't remember the condition they
are in. If memory serves, it does fall off on every range. We do
have a working one that we use as the standard, so we'll probably keep
this one as a part unit, I was just wondering if it was a quick-n-easy
so we could have two (as is I have to run an 8 ft coax to a test bench
whenever I do power meters). Again, thanks for the replies, I'll
probably just leave it in the stock-pile of old stuff for future use,
there's other things that need fixin that get priority.

Thanks,
Steve

 

[**THE-RFI-EMI-GUY**]

Check Google; There was a problem with ECL divider chips that affected
the high end of each range.

Thanks for the replies everyone. I had it apart a while ago, I
remember checking out the gears, but don't remember the condition they
are in. If memory serves, it does fall off on every range. We do
have a working one that we use as the standard, so we'll probably keep
this one as a part unit, I was just wondering if it was a quick-n-easy
so we could have two (as is I have to run an 8 ft coax to a test bench
whenever I do power meters). Again, thanks for the replies, I'll
probably just leave it in the stock-pile of old stuff for future use,
there's other things that need fixin that get priority.

Thanks,
Steve

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P