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Re: HP34702A Ohms converter issues

 

I was just looking back at the schematic and OP - I see that you reported Q11 was bad and replaced, but not with the same type. This could be the problem, since JFETs all work more or less the same, but can vary greatly in characteristics. Check the Idss spec of your replacement versus the original type. It could be that Q11 simply can't cut off far enough with the available negative gate drive from U2. If you don't have the right one, or one close enough, you can help it out a bit by adding a shunt resistor from the gate to -12V, to drop the gate more, then U2 can lift off the rail and get control of the situation. Another option is to temporarily add a diode or two in the source lead to lift it, and help cut off. You should put the same or a proper equivalent part in once it's figured out.

Ed
Re: HP34702A Ohms converter issues

 

If U2 is railed negative, then Q11 should cut off. Are the parts in sockets? If so, try pulling Q13, which should drop the gain and the current to a very low value. If there's no effect, then try Q14. If Q13 or Q14 are bad, the current will be out of control. These two are exposed to the outside world in ohms range, so could have been damaged by over-voltaging, even though the Q12 circuitry is supposed to protect them somewhat (SOA-wise, but not much beyond Vcbo). They should both be fairly high Vcbo types (I'd guess 2N3440 or similar - an HP favorite), able to withstand momentary? specified fault conditions. They may test OK at low voltage, but if Q13 in particular is leaky, it could throw the current way off. For testing and diagnosis, you can replace them both with ordinary NPNs like 2N3904, then put the right ones in after you figure it out.

Also, you may want to recheck Q11 to be sure it's OK, and the of right type. It's easy to quick-check with a DMM - the D-S should look like a resistance with no gate connection, and the gate to D or S should look like a diode.

Ed
Prologix has updated the EZGPIB file and is working on the C++ example.

 

The title says it all.
You will find many examples in the folder when you download it.
Just click on EZGPIB.exe to run.
Investigate the?DF6JB Plotter as well.
No affiliation, I just like this software because it works.
PeterB?
Re: HP34702A Ohms converter issues

 

> I think we're getting close to the "Aha !" moment !!!

I hope so.? ;-)

In this setup (Q12 / CR13 out of circuit), the gates of Q15 are offset just a bit - A: -5.0V B: -5.8V? The drains are of course then far apart - A: 2.8V B: 8.46V? and the sources are tied together at -4.9V.

This means the inputs to U2 are both way off from the quiescent value of 5.7V.? U2 is not quite at the rail, but close: -10.9V and there's no drop across R43.

This should be trying to reduce the current from the current source by turning off the FET/darlington circuit, right?? Yet it isn't.? I can't quite believe that the replacement Q11 is also defective, but maybe...
Re: HP34702A Ohms converter issues

 

The problem is obviously revolving around the op-amp which is made up of Q15 and U2.
The two gates of Q15 should be balanced at all times, otherwise the output of U2 would be stuck at the +12 or the -12V supplies (because U2 is supposed to have infinite gain).
So you could do this: in a situation where the two gates of Q15 are NOT balanced, look at the output voltage of U2, does it saturate ? What are its two input voltages ?
Does it control the output current ? Are you seeing any voltage drop across R43 (in series with U2's output) ?
I think we're getting close to the "Aha !" moment !!!
Joel
Re: VNA advice wanted

 

Pat,

Thanks. I was pretty sure David had the A/B designations swapped, but confirmation greatly appreciated. And it would be very easy for someone reading the thread later to get things backwards with unhappy consequences.

Reg
Re: Interested in helping start/run a Wiltron/Anritsu group on groups.io?

 

Might take a few hours to be approved and propagate.


On Tue, Feb 12, 2019 at 2:50 PM bownes via Groups.Io <bownes=[email protected]> wrote:
[email protected] has been created.

Have fun!

On Tue, Feb 12, 2019 at 2:08 PM David Feldman via Groups.Io <wb0gaz=[email protected]> wrote:
Looking for person (one or more) interested in starting and running a Wiltron/Anritsu equipment group (possibly modeled after this HP-Agilent-Keysight-equipment group) on .

If you are interested in (or knowledgeable about) doing this via , please contact off-list. If you're aware of such a list (I could not find one), please let me know.

Thank you
Re: Interested in helping start/run a Wiltron/Anritsu group on groups.io?

 

[email protected] has been created.

Have fun!

On Tue, Feb 12, 2019 at 2:08 PM David Feldman via Groups.Io <wb0gaz=[email protected]> wrote:
Looking for person (one or more) interested in starting and running a Wiltron/Anritsu equipment group (possibly modeled after this HP-Agilent-Keysight-equipment group) on .

If you are interested in (or knowledgeable about) doing this via , please contact off-list. If you're aware of such a list (I could not find one), please let me know.

Thank you
Re: HP34702A Ohms converter issues

 

With the protection circuitry disabled, the 1K resistor reads 1.87K.

U3's inputs are both at -6.4V.? Its output is at -7.4V.

Q15 seems to depend on what I'm measuring; for this test, its inputs are at A:-5.5V B:-6.4V.? I was getting a fair match yesterday when testing the output current.? There is still a 1.9V drop across R55-R56.

U2 pin 6 (its output) is at -10.9V now.?

U2 and U3 outputs are both quite clean with the 1K resistor on the unit's inputs:
Interested in helping start/run a Wiltron/Anritsu group on groups.io?

 

Looking for person (one or more) interested in starting and running a Wiltron/Anritsu equipment group (possibly modeled after this HP-Agilent-Keysight-equipment group) on groups.io.

If you are interested in (or knowledgeable about) doing this via groups.io, please contact off-list. If you're aware of such a list (I could not find one), please let me know.

Thank you
Re: VNA advice wanted

 

On 2/12/19 12:36 PM, Eric Garner wrote:
In regard to the collet extractor for APC-7, where did you find one
cheap? I've been looking high and low for an inexpensive collet
extractor without success.
I bought mine from Globaltest a few years ago, I think I paid about
$40 for it.

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA
Re: VNA advice wanted

 

Dave,?

In regard to the collet extractor for APC-7, where did you find one cheap? I've been looking high and low for an inexpensive collet extractor without success.

-Eric

On Mon, Feb 11, 2019 at 9:00 PM Dr. David Kirkby from Kirkby Microwave Ltd <drkirkby@...> wrote:
On Tue, 12 Feb 2019, 04:04 Reginald Beardsley via Groups.Io <pulaskite=[email protected] wrote:

One question I have is how difficult is replacing the N connectors? on a 8753B with an external test set if they are worn out.? Part of what I'm trying to do is is acquire a self sustainable bench.? I want to have tools to fix things.? I can't do anything about the problem of sourcing parts? ?But first of all you have to have the tools to identify the fault.? I've done it with "flint knives and stone axes'" but that is *very* tedious.

To my knowledge all 50 ohm 3 GHz test sets (85046B) have APC7 connectors, not N connectors. If the test set has N connectors then it is almost certainly an 85046A which is a 75 ohm test set, and best avoided.?

Changing the connectors on the test set is unlikely to be practical without changing the complete bridge, although the collets in APC7 connectors can be easily changed if you get a collet extractor, which you could pick up cheaply. It is most unlikely the APC7 connectors are worn out. Most people put APC7 to N adapters and so the APC7 connectors are rarely used.?

Dave.?



--
--Eric
_________________________________________
Eric Garner
Re: Test fixture for dielectric measurements

Chris Trask - N7ZWY/WDX3HLB
 

Hmmm... If solid, you could hold the material in air away from the electrodes


Connecting to the material is a problem, especially above 1000 deg C.
Metals may react with fumes and change or melt. Many insulators and
dielectrics certainly will.
We are watching these exchanges with great interest.
Chris Trask
N7ZWY / WDX3HLB
Senior Member IEEE
Re: HP8714ET Impedance

 

Just going through my old emails.
You may find the attached useful. Don't even think about getting into the bridge to change the impedance. HP uses stripline on a saphire substrate (on the 85046A anyway) and the 75 ohm is a different dimension.
PeterB

On Tue, Feb 5, 2019 at 1:55 PM Steve Hendrix <SteveHx@...> wrote:
A fellow engineer raised a question re the 75 ohm characteristic impedance of the HP8714ET I just purchased off eBay. Although I have minimum-loss matching pads ordered and enroute, does anyone here know just what would be involved if I were to open up the unit and try to change the impedance with some part swaps? The firmware already supports a choice of 75 ohm or 50 ohms as the impedance, for Smith charts, etc. I suspect that before I do that, I had better get the service manuals, but that's for the future - thus far I'm less than 1/4 of the way thru reading the user manual, and I have a bunch of other documentation to read as well. I'm very pleased with my purchase, if only for the education I'm getting!

Steve Hendrix

HP 85046A Repair Log.pdf
HP 85046A Repair Log.pdf

Re: VNA advice wanted

Pete Manfre
 

With all this great talk about VNA's it reminds me¡­ I have an extra 8753ES,? 50ohm,? internal s-para,? working and looking beautiful¡­ 3ghz unit.? $3k and also an n8357a 6ghz pna for sale¡­ same condition.? ?Will do pics and details direct.? ?This post was just an after thought.? ?I am on a cruise in the caribbean now and can't give pics and full details at this time.?


Pete wa2odo


On Mon, Feb 11, 2019, 11:04 PM Reginald Beardsley via Groups.Io <pulaskite=[email protected] wrote:
Thanks.? I've got a lead on an 8753B with a 50 ohm 3 GHz S parameter test set at a comfortable price.? Gedas gave me a very succinct explanation of why an eternal test set is preferable from a hobbyist self repair? perspective.

Having spent my career in reflection seismology,? I am all too acutely aware of the problems caused by impedance mismatches..? Gedas linked some very helpful papers.which made clear that impedance matching is a significant headache. So I've got some mathematical chores to deal with.

One question I have is how difficult is replacing the N connectors? on a 8753B with an external test set if they are worn out.? Part of what I'm trying to do is is acquire a self sustainable bench.? I want to have tools to fix things.? I can't do anything about the problem of sourcing parts? ?But first of all you have to have the tools to identify the fault.? I've done it with "flint knives and stone axes'" but that is *very* tedious.

I'd greatly prefer to be an actively employed scientist, but that''s not possible in my field, so playing with electronics is the best alternative I can think of.
Re: HP34702A Ohms converter issues

 

¿ªÔÆÌåÓý

Hello Greg,

I think we're getting close to the root cause... but I thhink I need some more data.

First, temporarily unsolder the collector lead of Q12 and one lead of CR13, which will disable the overvoltage protection.

Then, with a 1K resistor across the Ohms input, and when switched on the 1K range:
- We know that the voltages at both inputs of U3 are -6.3V, which is OK.
- The output of U3 is -7.3V which is OK, too.
- If the two gates of Q15 are balanced at -6.3V, then there should be a 1V drop across R55-R56.
- But you have measured the output current to be 2mA, whereas it should be 1mA.

Then please let me know...

Also, I'd like to try a little bit of lateral thinking. Maybe we're dealing with some spurious oscillation, could you connect a 1K resistor across the Ohms inputs, and look at the outputs of U3, then of U2 with an oscilloscope ?

Joel

Virus-free.

Re: VNA advice wanted

Dr. David Kirkby from Kirkby Microwave Ltd
 

On Tue, 12 Feb 2019, 05:58 Patrick Manning <pbmanning@... wrote:
Just to be certain things don't get crossed up, the 85046A is a 50 ohm, 300 kHz to 3 GHz test set, and uses APC 7 connectors to interface with the DUT.? The 85047A is similar, but goes up to 6 GHz.

The 85046B is the 75 ohm version; it goes from 300 kHz to 2 GHz and uses 75 ohm N female connectors to interface with the DUT.

Yes, my error. I got the 85046A and 85046B transposed! The A is the 50 ohm version with APC7 connectors.

I doubt the RF source, A, B or R receiver N connectors would get damaged as they are rarely used.?
?
B
-Pat

Dave.?



On Tue, Feb 12, 2019 at 12:00 AM, Dr. David Kirkby from Kirkby Microwave Ltd wrote:

On Tue, 12 Feb 2019, 04:04 Reginald Beardsley via Groups.Io <pulaskite=[email protected] wrote:

One question I have is how difficult is replacing the N connectors? on a 8753B with an external test set if they are worn out.? Part of what I'm trying to do is is acquire a self sustainable bench.? I want to have tools to fix things.? I can't do anything about the problem of sourcing parts? ?But first of all you have to have the tools to identify the fault.? I've done it with "flint knives and stone axes'" but that is *very* tedious.

To my knowledge all 50 ohm 3 GHz test sets (85046B) have APC7 connectors, not N connectors. If the test set has N connectors then it is almost certainly an 85046A which is a 75 ohm test set, and best avoided.?

Changing the connectors on the test set is unlikely to be practical without changing the complete bridge, although the collets in APC7 connectors can be easily changed if you get a collet extractor, which you could pick up cheaply. It is most unlikely the APC7 connectors are worn out. Most people put APC7 to N adapters and so the APC7 connectors are rarely used.?

Dave.?
Re: Unleveled E4436B

 

Hi Tom,

At 4GHz, using my E4406 to measure its output from -90dBm to +13dBm, it appears to be within 0.5dBm of indicated.

Above 13dBm the power doesn't increase and the UNLEVELED indicator comes on at about 14dBm.

Using my HP438A and HP8481H to do the same test gives a similar result but with an additional -1dB offset.

So its "close" :) ... well at least at 4Ghz

None of this kit has been calibrated in years so take the result with a grain of salt!

Given a bit of time I could write a labview thing to make some nice measurements and plots some graphs

regards

Tim

On 12/02/2019 2:37 pm, Tom B wrote:
Hi Tim,

How accurate is the power output at 4GHz?

Tom Bryan
N3AJA


On 2/11/2019 7:05 PM, Tim Tuck wrote:
Hi Colby,

I can still change things via GPIB, no problem so far, my simple Labview(Student Edition) program still works :)

regards

Tim

de VK2XAX
Re: HP34702A Ohms converter issues

 

I see that the output of U3 is at -7.4V and the input is at -6.4V, so off from the specified value by 0.1 at each end.? The gate voltages of Q15 are finally balanced, which they weren't before, but the reading across R56-R55 remains at ~2V.? The voltage at the end of R52 starts to drop as you switch ranges, going from -5.4V to about -4.1V by the time you go to the 10M range; this agrees with the display error increasing at higher ranges.? That seems to point to U2, which I've already replaced.

R64 is fine - I tweaked it earlier to be sure that the value was in range since it's a 10K and there is no R69 on this board; it did change the displayed reading over a small set of values as you would expect.? Following the voltage from U3-6 back to U3-2 the voltage changes in steps as you check each resistor junction R58, R60, R61.? They don't seem to be a problem.
Re: VNA advice wanted

 

Just to be certain things don't get crossed up, the 85046A is a 50 ohm, 300 kHz to 3 GHz test set, and uses APC 7 connectors to interface with the DUT.? The 85047A is similar, but goes up to 6 GHz.

The 85046B is the 75 ohm version; it goes from 300 kHz to 2 GHz and uses 75 ohm N female connectors to interface with the DUT.

All three use 50 ohm N female connectors for the RF in, R, A and B connections to the 8753x, and a 50 ohm BNC jack for the DC Bias input.

-Pat


On Tue, Feb 12, 2019 at 12:00 AM, Dr. David Kirkby from Kirkby Microwave Ltd wrote:

On Tue, 12 Feb 2019, 04:04 Reginald Beardsley via Groups.Io <pulaskite=[email protected] wrote:

One question I have is how difficult is replacing the N connectors? on a 8753B with an external test set if they are worn out.? Part of what I'm trying to do is is acquire a self sustainable bench.? I want to have tools to fix things.? I can't do anything about the problem of sourcing parts? ?But first of all you have to have the tools to identify the fault.? I've done it with "flint knives and stone axes'" but that is *very* tedious.

To my knowledge all 50 ohm 3 GHz test sets (85046B) have APC7 connectors, not N connectors. If the test set has N connectors then it is almost certainly an 85046A which is a 75 ohm test set, and best avoided.?

Changing the connectors on the test set is unlikely to be practical without changing the complete bridge, although the collets in APC7 connectors can be easily changed if you get a collet extractor, which you could pick up cheaply. It is most unlikely the APC7 connectors are worn out. Most people put APC7 to N adapters and so the APC7 connectors are rarely used.?

Dave.?
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