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Replace Neon NE-2 with Zener in 141T PSU?

 

Hi All,


I have recently acquired an HP-141T with the 8554B and 8552B plugins. Over the past month, the fuses in the plugins have blown three times. I've heard this can be an indication of an issue with the display section's PSU.?


Looking at the schematic and the board I have, I appear to have the older revision which uses neon lamps as a voltage reference. The lamp in my PSU board is pretty black looking -- that may be normal, I don't know.


At any rate, I wonder if I can replace the V1 neon with a 62 volt zener diode? Part number?2EZ62D5/TR8CT-ND from digikey, for example? I think any difference in the absolute level could be trimmed out using the +100V adjust pot. The biasing for the neon is a 5.6k resistor, I think that would work ok for the zener, but I could change it presumably.?


Thoughts??


Thanks,


--E



?
 

?
I have that circuit out in front of me trouble shooting that 100v supply on anothe system. My thought is that a 62v "zener" is not close enough to the 82v neon. You need another 20v?"zener" in series to make up the difference. R118 only has a swing of about 9v so not enough to make up for the lower voltage.?The 5.6k would deffinitely need increasing as the 62v?zener will be dissipating 400mW.
Good luck taking that pcb out is not a job to be undertaken lightly!!
?
Alan
G3NYK

----- Original Message -----
Sent: Wednesday, July 12, 2017 8:12 PM
Subject: [hp_agilent_equipment] Replace Neon NE-2 with Zener in 141T PSU?

Hi All,


I have recently acquired an HP-141T with the 8554B and 8552B plugins. Over the past month, the fuses in the plugins have blown three times. I've heard this can be an indication of an issue with the display section's PSU.?


Looking at the schematic and the board I have, I appear to have the older revision which uses neon lamps as a voltage reference. The lamp in my PSU board is pretty black looking -- that may be normal, I don't know.


At any rate, I wonder if I can replace the V1 neon with a 62 volt zener diode? Part number?2EZ62D5/TR8CT-ND from digikey, for example? I think any difference in the absolute level could be trimmed out using the +100V adjust pot. The biasing for the neon is a 5.6k resistor, I think that would work ok for the zener, but I could change it presumably.&n bsp;


Thoughts??


Thanks,


--E



?
 

If the part you're looking at is the voltage reference for the power supply, I believe you have some things to figure out. As I recall, the proper reference voltage is around 83-85V, produced by a miniature gas regulator tube that looks like a neon bulb, but much bigger. It's normally very stable, but does wear out eventually. I forget the part number, but it may be like Z1000, or 83A-something-something. It's definitely not supposed to be an NE-2, although someone may have put one there as an emergency substitute.

Once you figure out what's supposed to be there, you can replace it with a Zener or 431 circuit. This has been discussed a number of times over the years, so you may be able to find some info searching back, if it's possible anymore with this yahoo stuff - I think the last time the subject came up may be two years or so ago, so you'll have to dig pretty deep.

Ed
 

Are you sure it's a 62V zener that's needed?

My HP141T neon was 82V. ?I ?have recently replaced the Neon in mine with two series connected 1W Zeners of 39V and 43V. ?It drifts slightly for about 20 minutes but then stays in spec. ?I did make a PCB to put a stack of 6.2V Zeners in series to give a better tempco but the two series connected Zeners seem fine.

Denis
 

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I have two 141’s. One with the infamous VR tube, which consistently blows fuses on the IF’s, and one with a more recent power supply. I’ve not used the older unit in years, but I have purchased a zener, in case I ever get back to that unit.
?
The zener came from digikey - 1N5375BGOS-ND
?
It’s an 82 volt, 5W zener.
?
Gary Appel
?

Sent: Wednesday, July 12, 2017 9:12 AM
Subject: [hp_agilent_equipment] Replace Neon NE-2 with Zener in 141T PSU?
?
?

Hi All,


I have recently acquired an HP-141T with the 8554B and 8552B plugins. Over the past month, the fuses in the plugins have blown three times. I've heard this can be an indication of an issue with the display section's PSU.


Looking at the schematic and the board I have, I appear to have the older revision which uses neon lamps as a voltage reference. The lamp in my PSU board is pretty black looking -- that may be normal, I don't know.


At any rate, I wonder if I can replace the V1 neon with a 62 volt zener diode? Part number 2EZ62D5/TR8CT-ND from digikey, for example? I think any difference in the absolute level could be trimmed out using the +100V adjust pot. The biasing for the neon is a 5.6k resistor, I think that would work ok for the zener, but I could change it presumably.


Thoughts?


Thanks,


--E



?
 

Hi Gary, Denis, Ed, and Alan,

You are all correct, I read the value wrong. My printed schematic looks poor on paper!

Ok, so an 82 volt zener (or equivalent) would do the trick.?

Yes, that "bulb" does look rather large, perhaps an inch long or so.?

I will order a few from digikey next time I place an order.?

Thanks all,

--E
 

Here's an example:



If you make a replacement circuit that provides the same or close enough shunt regulator specs, it should drop in OK? without changing anything else. I think you can perform the surgery all from the component side without removing the PS board.

One nice thing about using a modern reference circuit is that the voltage won't overshoot. I'm convinced that many 141 failures were caused by temporary over-voltage while the gas tube had to reach striking voltage - significantly higher than running voltage.

Ed
 

Hello Gang,
First of all, I am not sponsored. But for such small orders, one or two parts and shit, use Arrow. Free shipping on literally everything.even to Slovakia. Just beware of customs...

Tam
--
With best regards
Tam Hanna
---

NEW: Enjoy electronics? Like seeing oscilloscopes get repaired? Please
subscribe to my new YouTube channel ->


On July 12, 2017 11:13:00 PM CEST, "w7qed@... [hp_agilent_equipment]" wrote:
?

Hi Gary, Denis, Ed, and Alan,


You are all correct, I read the value wrong. My printed schematic looks poor on paper!

Ok, so an 82 volt zener (or equivalent) would do the trick.?

Yes, that "bulb" does look rather large, perhaps an inch long or so.?

I will order a few from digikey next time I place an order.?

Thanks all,

--E
 

I have not compared this supply but remember it was discussed some earlier time in the past few years.

<<<
Old one - "neon tube" stabilized (pdf-page 35):
141T Display.pdf

New one - zenerdiode stabilized (pdf-page 10..12):
141T_changes.pdf

<<<
Hope it helps!

Dennis


--------------------------------------------
On Wed, 7/12/17, 'Alan Melia' Alan.Melia@... [hp_agilent_equipment] <hp_agilent_equipment@...> wrote:

Subject: Re: [hp_agilent_equipment] Replace Neon NE-2 with Zener in 141T PSU?
To: hp_agilent_equipment@...
Date: Wednesday, July 12, 2017, 4:48 PM

I have that circuit out in
front of me trouble
shooting that 100v supply on anothe system. My thought is
that a 62v "zener" is
not close enough to the 82v neon. You need another
20v?"zener" in series to
make up the difference. R118 only has a swing of about 9v so
not enough to make
up for the lower voltage.?The 5.6k would deffinitely
need increasing as the
62v?zener will be dissipating 400mW.
Good luck taking that pcb
out is not a job to be
undertaken lightly!!
?
Alan
G3NYK

----- Original Message -----

From:
w7qed@...
[hp_agilent_equipment]
To: hp_agilent_equipment@...


Sent: Wednesday, July
12, 2017 8:12
PM
Subject:
[hp_agilent_equipment] Replace
Neon NE-2 with Zener in 141T PSU?


Hi All,


I have recently acquired an HP-141T with the
8554B and 8552B plugins.
Over the past month, the fuses in the plugins have blown
three times. I've
heard this can be an indication of an issue with the
display section's
PSU.?


Looking at the schematic and the board I have, I
appear to have the
older revision which uses neon lamps as a voltage
reference. The lamp in my
PSU board is pretty black looking -- that may be normal, I
don't
know.


At any rate, I wonder if I can replace the V1
neon with a 62 volt
zener diode? Part number?2EZ62D5/TR8CT-ND from digikey,
for example? I
think any difference in the absolute level could be
trimmed out using the
+100V adjust pot. The biasing for the neon is a 5.6k
resistor, I think that
would work ok for the zener, but I could change it
presumably.&n
bsp;


Thoughts??


Thanks,


--E
arie schellaars
 

G'day Folks,
I cheated as I had removed the board several times before and didn't want that hassle
any more.
Snip the neon as close to the bulb envelope as possible and solder the zener(s) and resistor
to the left over wires. Keep the polarity of the zener in mind!
On both my units , that solution has been working for in excess of 5 years.
Cheers
Arie
VK3DBF
--------------------------------------------
 

Hi Arie,

I will definitely try that first, removing the board does look like a hassle.?

What value of resistor did you end up with for R21 (5.4k is stock)??

Thanks very much,

--E
arie schellaars
 

Hi from down under.
From memory I used an 8.2K 1 watt resistor as that is what I had on hand.
Also placed 68V and 14V zeners in series to make the necessary 82V level and again this is what was in
junk box.
Hope that helps.
Cheers and 73's
Arie
VK3DBF
--------------------------------------------

On Fri, 14/7/17, w7qed@... [hp_agilent_equipment] <hp_agilent_equipment@...> wrote:

Subject: Re: [hp_agilent_equipment] Replace Neon NE-2 with Zener in 141T PSU?
To: hp_agilent_equipment@...
Received: Friday, 14 July, 2017, 3:30 AM


?









Hi Arie,
I will
definitely try that first, removing the board does look like
a hassle.?
What value
of resistor did you end up with for R21 (5.4k is
stock)??
Thanks very
much,
--E









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Replacing the ZZ1000 - My Summary.

A high-voltage zener will add a lot of drift.

It's a hassle to ovenize it.

Nine 9V zeners is better but still pretty bad.
To meet spec you have to use what HP used, the 1N938, a special temperature-compensated part which costs over $10 each today.

That's too expensive.

It's a hassle to rework the board to use a single 1N938 the way HP did.

Ed Breya's TL431 suggestion is the only one that's cheap, easy, and pretty good.
That's a TL431 plus a 65-75V zener.
150k and 4.7k in the divider gets you 82V.
No other changes needed.

That's how I see it.

Dave Wise
 

Hi Dave,

In theory, ~18x 4.5v zeners would provide the lowest drift reference for a pure-zener design.

However, a single 82v zener has a tempo of around 0.073%. Compared to the 0.004% of the original reference bulb this is pathetic, however, looking at the dozens of carbon resistors, dried out caps, and of course the?potentiometer that sets the gain (and remember, new pots are generally not better than 100 PPM unless they are very expensive), I think the drift and tempo from a single zener will be the least of this circuit's problems!?

Thanks all for your input!

--E
W6EL
?
Bob Albert
 

Actually I think the lowest temperature coefficient is around 5V for zener diodes.? The 6.2 V units are very stable also so you don't need as many of those.

When you put zeners in series you invoke the concern of impedance.? Low voltage zeners have a fairly high impedance compared to just a few higher voltage ones.? So if the current through it changes, so will the voltage.

There are more elegant solutions to this 'problem' but the whole thread is probably more trouble than it's worth.

Let us know your results.

Bob


On Friday, July 14, 2017 1:00 PM, "w7qed@... [hp_agilent_equipment]" wrote:




Hi Dave,

In theory, ~18x 4.5v zeners would provide the lowest drift reference for a pure-zener design.

However, a single 82v zener has a tempo of around 0.073%. Compared to the 0.004% of the original reference bulb this is pathetic, however, looking at the dozens of carbon resistors, dried out caps, and of course the?potentiometer that sets the gain (and remember, new pots are generally not better than 100 PPM unless they are very expensive), I think the drift and tempo from a single zener will be the least of this circuit's problems!?

Thanks all for your input!

--E
W6EL
?
 

?
The thing is that most "zeners" do not depend on the Zener effect. That only occurs around voltages up to around 4volts, above 5v the process is Avalanche Breakdown , a bit like a gas tube. Then the temperature coefficient of these two processes have opposite senses so if you combine a true?Zener with a forward diode or an avalanche diode you can minimise the tempco.?The lowest tempcos are usually around 5 to 6v."zeners".
?
Alan
G3NYK

----- Original Message -----
Sent: Friday, July 14, 2017 9:16 PM
Subject: Re: [hp_agilent_equipment] Re: Replace Neon NE-2 with Zener in 141T PSU?

Actually I think the lowest temperature coefficient is around 5V for zener diodes.? The 6.2 V units are very stable also so you don't need as many of those.

When you put zeners in series you invoke the concern of impedance.? Low voltage zeners have a fairly high impedance compared to just a few higher voltage ones.? So if the current through it changes, so will the voltage.

There are more elegant solutions to this 'problem' but the whole thread is probably more trouble than it's worth.

Let us know your re sults.

Bob


On Friday, July 14, 2017 1:00 PM, "w7qed@... [hp_agilent_equipment]" wrote:




Hi Dave,

In theory, ~18x 4.5v zeners would provide the lowest drift reference for a pure-zener design.

However, a single 82v zener has a tempo of around 0.073%. Compared to the 0.004% of the original reference bulb this is pathetic, however, looking at the dozens of carbon resistors, dried out caps, and of course the?potentiometer that sets the gain (and remember, new pots are generally not better than 100 PPM unless they are very expensive), I think the drift and tempo from a single zener will be the least of this circuit's problems!?

Thanks all for your input!

--E
W6EL
?
 

开云体育

Go down to one of those 2nd hand store with your geiger counter and find a very old $5 watch with the glow in the dark? radium painted hands and dial. Peel of the minute hand and shrink tube it to the NE-2 :-)


Dave
manuals@...


On 7/14/2017 5:06 PM, 'Alan Melia' Alan.Melia@... [hp_agilent_equipment] wrote:
?

?

The thing is that most "zeners" do not depend on the Zener effect. That only occurs around voltages up to around 4volts, above 5v the process is Avalanche Breakdown , a bit like a gas tube. Then the temperature coefficient of these two processes have opposite senses so if you combine a true?Zener with a forward diode or an avalanche diode you can minimise the tempco.?The lowest tempcos are usually around 5 to 6v."zeners".
?
Alan
G3NYK
----- Original Message -----
Sent: Friday, July 14, 2017 9:16 PM
Subject: Re: [hp_agilent_equipment] Re: Replace Neon NE-2 with Zener in 141T PSU?

Actually I think the lowest temperature coefficient is around 5V for zener diodes.? The 6.2 V units are very stable also so you don't need as many of those.

When you put zeners in series you invoke the concern of impedance.? Low voltage zeners have a fairly high impedance compared to just a few higher voltage ones.? So if the current through it changes, so will the voltage.

There are more elegant solutions to this 'problem' but the whole thread is probably more trouble than it's worth.

Let us know your re sults.

Bob


On Friday, July 14, 2017 1:00 PM, "w7qed@... [hp_agilent_equipment]" wrote:




Hi Dave,

In theory, ~18x 4.5v zeners would provide the lowest drift reference for a pure-zener design.

However, a single 82v zener has a tempo of around 0.073%. Compared to the 0.004% of the original reference bulb this is pathetic, however, looking at the dozens of carbon resistors, dried out caps, and of course the?potentiometer that sets the gain (and remember, new pots are generally not better than 100 PPM unless they are very expensive), I think the drift and tempo from a single zener will be the least of this circuit's problems!?

Thanks all for your input!

--E
W6EL
?





-- 
Dave
Manuals@...

Virus-free.

 

开云体育

Or to a supermarket and find the "LoSalt". Replacing part of the NaCl with KCl inevitably includes K40 :)



On 14/07/17 22:15, Artek Manuals manuals@... [hp_agilent_equipment] wrote:

?

Go down to one of those 2nd hand store with your geiger counter and find a very old $5 watch with the glow in the dark? radium painted hands and dial. Peel of the minute hand and shrink tube it to the NE-2 :-)


Dave
manuals@...


On 7/14/2017 5:06 PM, 'Alan Melia' Alan.Melia@... [hp_agilent_equipment] wrote:
?

?

The thing is that most "zeners" do not depend on the Zener effect. That only occurs around voltages up to around 4volts, above 5v the process is Avalanche Breakdown , a bit like a gas tube. Then the temperature coefficient of these two processes have opposite senses so if you combine a true?Zener with a forward diode or an avalanche diode you can minimise the tempco.?The lowest tempcos are usually around 5 to 6v."zeners".
?
Alan
G3NYK
----- Original Message -----
Sent: Friday, July 14, 2017 9:16 PM
Subject: Re: [hp_agilent_equipment] Re: Replace Neon NE-2 with Zener in 141T PSU?

Actually I think the lowest temperature coefficient is around 5V for zener diodes.? The 6.2 V units are very stable also so you don't need as many of those.

When you put zeners in series you invoke the concern of impedance.? Low voltage zeners have a fairly high impedance compared to just a few higher voltage ones.? So if the current through it changes, so will the voltage.

There are more elegant solutions to this 'problem' but the whole thread is probably more trouble than it's worth.

Let us know your re sults.

Bob


On Friday, July 14, 2017 1:00 PM, "w7qed@... [hp_agilent_equipment]" wrote:




Hi Dave,

In theory, ~18x 4.5v zeners would provide the lowest drift reference for a pure-zener design.

However, a single 82v zener has a tempo of around 0.073%. Compared to the 0.004% of the original reference bulb this is pathetic, however, looking at the dozens of carbon resistors, dried out caps, and of course the?potentiometer that sets the gain (and remember, new pots are generally not better than 100 PPM unless they are very expensive), I think the drift and tempo from a single zener will be the least of this circuit's problems!?

Thanks all for your input!

--E
W6EL
?





-- 
Dave
Manuals@...

Virus-free.

 

开云体育

Would you guys slow down long enough for me to type a reply? ?:)


Tom,?Dave,


I wish. ?But the glass stops beta. ?The Kr-85 worked?because it was?inside.


Bob, Elliott,


So many parts in series... sometimes brute force is the best solution, but this one puts me off. ?That's just my personal taste; if you want to do it, knock yourself out.


Elliott,


HP used?1% metal film resistors. ?The pot is a weak point for long-term stability, but I think that since it's in a voltage divider the high-leg tempco compensates the low-leg tempco.


In a related thread, Alan Melia suggests adding a LED to illuminate the gas tube. ?If the problem was dark effect, brought on by Kr-85 depletion, that should work around it just dandy. ?I hope someone tries it. ?I can't, my ZZ1000 is still working. ?If I can find a flickering neon at home, I'll try to figure out what wavelength LED is the most effective. ?It will be visible light, not?UV, the glass blocks UV, same as external nuclear?radiation.


Dave Wise?


From: hp_agilent_equipment@... <hp_agilent_equipment@...> on behalf of Tom Gardner tggzzz@... [hp_agilent_equipment] <hp_agilent_equipment@...>
Sent: Friday, July 14, 2017 2:18 PM
To: hp_agilent_equipment@...
Subject: Re: [hp_agilent_equipment] Re: Replace Neon NE-2 with Zener in 141T PSU?
?


Or to a supermarket and find the "LoSalt". Replacing part of the NaCl with KCl inevitably includes K40 :)



On 14/07/17 22:15, Artek Manuals manuals@... [hp_agilent_equipment] wrote:
?

Go down to one of those 2nd hand store with your geiger counter and find a very old $5 watch with the glow in the dark? radium painted hands and dial. Peel of the minute hand and shrink tube it to the NE-2 :-)


Dave
manuals@...


On 7/14/2017 5:06 PM, 'Alan Melia' Alan.Melia@... [hp_agilent_equipment] wrote:
?

?

The thing is that most "zeners" do not depend on the Zener effect. That only occurs around voltages up to around 4volts, above 5v the process is Avalanche Breakdown , a bit like a gas tube. Then the temperature coefficient of these two processes have opposite senses so if you combine a true?Zener with a forward diode or an avalanche diode you can minimise the tempco.?The lowest tempcos are usually around 5 to 6v."zeners".
?
Alan
G3NYK
----- Original Message -----
Sent: Friday, July 14, 2017 9:16 PM
Subject: Re: [hp_agilent_equipment] Re: Replace Neon NE-2 with Zener in 141T PSU?

Actually I think the lowest temperature coefficient is around 5V for zener diodes.? The 6.2 V units are very stable also so you don't need as many of those.

When you put zeners in series you invoke the concern of impedance.? Low voltage zeners have a fairly high impedance compared to just a few higher voltage ones.? So if the current through it changes, so will the voltage.

There are more elegant solutions to this 'problem' but the whole thread is probably more trouble than it's worth.

Let us know your re sults.

Bob






Hi Dave,

In theory, ~18x 4.5v zeners would provide the lowest drift reference for a pure-zener design.

However, a single 82v zener has a tempo of around 0.073%. Compared to the 0.004% of the original reference bulb this is pathetic, however, looking at the dozens of carbon resistors, dried out caps, and of course the?potentiometer that sets the gain (and remember, new pots are generally not better than 100 PPM unless they are very expensive), I think the drift and tempo from a single zener will be the least of this circuit's problems!?

Thanks all for your input!

--E
W6EL
?





-- 
Dave
Manuals@...

Virus-free.



 

[resend in case it didn't get through email]

Would you guys ease off long enough for me to type a reply? ?:)


Tom,?Dave,


I wish. ?But the glass stops beta. ?The Kr-85 worked?because it was?inside.


Bob, Elliott,


So many parts in series... sometimes brute force is the best solution, but this one puts me off. ?That's just my personal taste; if you want to do it, knock yourself out.


Elliott,


HP used?1% metal film resistors. ?The pot is a weak point for long-term stability, but since it's in a voltage divider the high-leg tempco compensates the low-leg tempco. ?It's also a small fraction of the total divider resistance, so its tempco is a small part of the total.


In a related thread, Alan Melia suggests adding a LED to illuminate the gas tube. ?If the problem was dark effect, brought on by Kr-85 depletion, that should work around it just dandy. ?I hope someone tries it. ?I can't, my ZZ1000 is still working. ?If I can find a flickering neon at home, I'll try to figure out what wavelength LED is the most effective. ?It will be visible light, not?UV; the glass blocks UV. ?(Also external nuclear?radiation.)


Dave Wise?

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