Hello All,
Can someone point me in the right direction?
The HP 8640 has output on all ranges.
The frequency counter is accurate on the 4 to 8 MHZ range ONLY.
ALL other ranges are way off.
Any ideas?
73
Phil N6WKZ

I haven’t bought any of them so I cant attest to how well they work but $40 aint all that much money to give it a try

Some have reported great success using Tri-flow as a lubricant on hardened grease that TenTec used on their vfos.? Reports have it that TenTec used whatever tractor grease the farm store had on the shelf.
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Thanks,
Randy
randy.ab9go@...

Hello All,

I am thinking about getting a 3 GHz prescaler board for the HP 53181A from China.? They are only about $40US.? How well do they work?

Tom
N3AJA

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开云体育

Hi all,

Just obtained a rather sick HP3465A (the 4.5 digit one, not the big 6.5 digit unit). It is functioning but there is a one sided offset on measurements which is proportional to the divider/amplifier arrangement.?To clarify, if I short the inputs at 2V it floats reading +.0035. If I short at 20V range it sits around +0.648 volts. These measurements are much larger at turn on and drift down slowly. If I stick a 9V battery on the inputs it reads 9.995 in one polarity and -9.206 in opposite polarity as an example.

I am currently devoid of a scope and am working on this with a rather shonky Fluke 25 at my disposal so running through the SM diagnostics is problematic. I have a better DMM in flight (34401A) and am sourcing a scope at the moment.

I have checked the following things:

1. Power supply -> OK
2. input to Q16 -> seems ok (caveated)
3. input to U3 -> seems ok (caveated)?
4. COMPTP point -> seems ok (caveated)
5. AZTP point -> seems ok (caveated)

caveated = limited measurement capability here.

Any help appreciated. If anyone has any tribal knowledge or debugging approaches I would appreciate it.

Best regards,

Chris Smith

Greetings forum,

A synthesized sweeper is unfortunately beyond financial reach
but a cw-only synthesizer is. I have been using my 8510C with an 8350B
+ a 2-20GHz plug-in. It would be nice however, if it was possible to
inject a (low level) phase locked CW carrier (using a directional coupler) into
the test set before its own internal circuitry so that narrow band
circuitry could be measured on.

Anyone tried this?

Cheers

Ulf Kylenfall
SM6GXV

Hello we have three 8640, with varying amounts of shaft resistance, but all are OK to use.

I suggest that position the gen panel up, then apply alcohol or degreaser on the shaft to flush out the thick grease,

It may take some time to soak in the degreaser and dissolve the old congealed greases, gently warming the cavity and shaft and allowing it to sit a day may loosen it.

Finally re lubricate with a selected oil.

The cavity is a precision assembly and may require special tools and fixtures to disassemble and then realign. I am sure the frequency calibrations will be affected.

I would avoid disassembly if at all possible.

Bon Chance

Jon

Thanks for all the suggestions. I have been able to clean off the grease residue on the other bearings which are accessible for disassembly using isopropyl alcohol.

The problem with cleaning the tuning shaft bearing is that it is internal to the tuning cavity itself and not accessible unless the entire cavity assembly is taken apart. That's the real problem. So far, I have not found any info online regarding experience with disassembly, so it appears that no one has actually attempted (or posted info) on doing so. HP provides no info as they considered it a factory service only assembly.

What I will try first is to soak the visible end of the shaft in solvent and then follow with a light lubricating oil like ATF. Hopefully some will enter the bearing and this will do some good in loosening it up.

开云体育

As an observation:

Any time the presence or absence of a measurement probe (scope, meter, etc) makes a difference, you're dealing with a marginal situation.

Your probe represents at least a capacitor to ground paralleled by a resistor.? Analyze the circuit to see what's there (or what's not!) where this would make a difference.

It's subtle.

Harvey

On Sun, May 22, 2022 at 06:05 PM, John Quinn wrote:

Ozan, THANK YOU! The 100k resistor had failed open. I can’t believe it. I'm slightly embarrassed, because I was sure I had already checked these. It is always a great idea to have a second set of eyes look at things. I’ve been diagnosing this unit on and off for months. You have definitely helped keep an amazing piece of engineering out of the recycle pole for a 1 cent part.

Be well and have a wonderful week!

John Q

--------
Hi John,
Great news and congratulations for the repair. You already debugged it 99% of the way by identifying 1M-ohm from gate to ground makes a difference. That 100k resistor is not carrying any load so I wouldn't suspect it either if it wasn't for your observation with the 1M resistor.?

Ozan

Ozan, THANK YOU! The 100k resistor had failed open. I can’t believe it. I'm slightly embarrassed, because I was sure I had already checked these. It is always a great idea to have a second set of eyes look at things. I’ve been diagnosing this unit on and off for months. You have definitely helped keep an amazing piece of engineering out of the recycle pole for a 1 cent part.

Be well and have a wonderful week!

John Q

Roy is right.
In many greases, one of the major heavy components is soap. Look at what
happens when soap residue hardens. But, be careful; not all soaps dissolve
in water. Meths can sometimes help.
73 de Brian, VK2GCE

On Sun, May 22, 2022 at 12:45 PM, John Quinn wrote:

......

?

Now my bizzare observation: upon probing the gate drive signal for Q103 from U108, I found that the problem appears to go away! Unfortunately, replacing U108 (a LM393N) made no difference. Shunting that line to ground with a 10pf cap had no effect, but adding a 1 meg pulldown resistor does appear to make the problem disappear.?

?

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Are resistors R122 and R143 approximately correct and can you trace connectivity from TP104 to gate of Q103? The resistors don't need to be accurate but voltage at gate of Q103 should follow TP104 closely. Since adding 1M makes a difference in this state, comparator is not pulling its output to -18V and gate voltage of Q103 is set by TP104.

TP104 voltage should follow the star connection wired to bottom of R125 (first star summing node?) within few mV. Although an error there should impact other places but perhaps there is some offset and adding 1M to ground creates a voltage divider to make the voltage about right for Q103 in the test conditions you tried.?

Ozan

On Saturday 21 May 2022 07:14:21 am mondial wrote:

Other shafts and bearings in the instrument show the same symptoms of stuck bearings. The original grease seems to become like glue with age.

The issue here is the same thing that causes fans to not work well when they age. The original lubricant is made up of a number of different fractions, and over long periods of time the lighter ones evaporate, leaving the heavier ones behind.

The solution is to remove what's left of the original lube and put some new lube in there.

--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
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Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin