Moscaps? Any ideas?...

J

JC

Guest
Hi, Anyone care to explain what the function is of the 2 FETS Q1 and Q2
in this Fluke calibrator and what might be the required parameters for a
replacement?

https://www.flickr.com/photos/40466580@N07/

It fails diagnostics with leakage caused by one of these. At the moment
I have them replaced with J210 FETS which I had to hand but I think
there\'s maybe more to it than that. I cant find any data on them, they
are marked IFC 07703
TIA JC
 
JC wrote:
Hi, Anyone care to explain what the function is of the 2 FETS Q1 and Q2
in this Fluke calibrator and what might be the required parameters for a
replacement?

https://www.flickr.com/photos/40466580@N07/

It fails diagnostics with leakage caused by one of these. At the moment
I have them replaced with J210 FETS which I had to hand but I think
there\'s maybe more to it than that. I cant find any data on them, they
are marked IFC 07703
TIA JC
Click to expand...

Protection diodes.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On Thu, 13 Oct 2022 16:40:18 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

JC wrote:
Hi, Anyone care to explain what the function is of the 2 FETS Q1 and Q2
in this Fluke calibrator and what might be the required parameters for a
replacement?

https://www.flickr.com/photos/40466580@N07/

It fails diagnostics with leakage caused by one of these. At the moment
I have them replaced with J210 FETS which I had to hand but I think
there\'s maybe more to it than that. I cant find any data on them, they
are marked IFC 07703
TIA JC

Protection diodes.

Cheers

Phil Hobbs
Click to expand...

Yes, jfets used as diodes. Terrible idea.

The c-b junction of a small transistor would be better all-around.
BFT25 has fA leakage... if you can get them. I could spare a few.

There\'s probably a common TO92 transistor with sub-pA leakage.
 
torsdag den 13. oktober 2022 kl. 22.52.31 UTC+2 skrev John Larkin:
On Thu, 13 Oct 2022 16:40:18 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

JC wrote:
Hi, Anyone care to explain what the function is of the 2 FETS Q1 and Q2
in this Fluke calibrator and what might be the required parameters for a
replacement?

https://www.flickr.com/photos/40466580@N07/

It fails diagnostics with leakage caused by one of these. At the moment
I have them replaced with J210 FETS which I had to hand but I think
there\'s maybe more to it than that. I cant find any data on them, they
are marked IFC 07703
TIA JC

Protection diodes.

Cheers

Phil Hobbs
Yes, jfets used as diodes. Terrible idea.

The c-b junction of a small transistor would be better all-around.
BFT25 has fA leakage... if you can get them. I could spare a few.

There\'s probably a common TO92 transistor with sub-pA leakage.
Click to expand...

https://youtu.be/BGcKjy_UNQ4
 
Lasse Langwadt Christensen wrote:
torsdag den 13. oktober 2022 kl. 22.52.31 UTC+2 skrev John Larkin:
On Thu, 13 Oct 2022 16:40:18 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

JC wrote:
Hi, Anyone care to explain what the function is of the 2 FETS Q1 and Q2
in this Fluke calibrator and what might be the required parameters for a
replacement?

https://www.flickr.com/photos/40466580@N07/

It fails diagnostics with leakage caused by one of these. At the moment
I have them replaced with J210 FETS which I had to hand but I think
there\'s maybe more to it than that. I cant find any data on them, they
are marked IFC 07703
TIA JC

Protection diodes.

Cheers

Phil Hobbs
Yes, jfets used as diodes. Terrible idea.

The c-b junction of a small transistor would be better all-around.
BFT25 has fA leakage... if you can get them. I could spare a few.

There\'s probably a common TO92 transistor with sub-pA leakage.


https://youtu.be/BGcKjy_UNQ4
Click to expand...
Oh no! It\'s Squeaky Dave!
 
torsdag den 13. oktober 2022 kl. 23.39.56 UTC+2 skrev Phil Hobbs:
Lasse Langwadt Christensen wrote:
torsdag den 13. oktober 2022 kl. 22.52.31 UTC+2 skrev John Larkin:
On Thu, 13 Oct 2022 16:40:18 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

JC wrote:
Hi, Anyone care to explain what the function is of the 2 FETS Q1 and Q2
in this Fluke calibrator and what might be the required parameters for a
replacement?

https://www.flickr.com/photos/40466580@N07/

It fails diagnostics with leakage caused by one of these. At the moment
I have them replaced with J210 FETS which I had to hand but I think
there\'s maybe more to it than that. I cant find any data on them, they
are marked IFC 07703
TIA JC

Protection diodes.

Cheers

Phil Hobbs
Yes, jfets used as diodes. Terrible idea.

The c-b junction of a small transistor would be better all-around.
BFT25 has fA leakage... if you can get them. I could spare a few.

There\'s probably a common TO92 transistor with sub-pA leakage.


https://youtu.be/BGcKjy_UNQ4

Oh no! It\'s Squeaky Dave!
Click to expand...

he doesn\'t drink, so his voice never gets lubricated ;)
 
Lasse Langwadt Christensen wrote:
torsdag den 13. oktober 2022 kl. 23.39.56 UTC+2 skrev Phil Hobbs:
Lasse Langwadt Christensen wrote:
torsdag den 13. oktober 2022 kl. 22.52.31 UTC+2 skrev John Larkin:
On Thu, 13 Oct 2022 16:40:18 -0400, Phil Hobbs
pcdhSpamM...@electrooptical.net> wrote:

JC wrote:
Hi, Anyone care to explain what the function is of the 2 FETS Q1 and Q2
in this Fluke calibrator and what might be the required parameters for a
replacement?

https://www.flickr.com/photos/40466580@N07/

It fails diagnostics with leakage caused by one of these. At the moment
I have them replaced with J210 FETS which I had to hand but I think
there\'s maybe more to it than that. I cant find any data on them, they
are marked IFC 07703
TIA JC

Protection diodes.

Cheers

Phil Hobbs
Yes, jfets used as diodes. Terrible idea.

The c-b junction of a small transistor would be better all-around.
BFT25 has fA leakage... if you can get them. I could spare a few.

There\'s probably a common TO92 transistor with sub-pA leakage.


https://youtu.be/BGcKjy_UNQ4

Oh no! It\'s Squeaky Dave!

he doesn\'t drink, so his voice never gets lubricated ;)
Click to expand...
A big of brake cleaner might help. ;)
 
John Larkin wrote:
On Thu, 13 Oct 2022 16:40:18 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

JC wrote:
Hi, Anyone care to explain what the function is of the 2 FETS Q1 and Q2
in this Fluke calibrator and what might be the required parameters for a
replacement?

https://www.flickr.com/photos/40466580@N07/

It fails diagnostics with leakage caused by one of these. At the moment
I have them replaced with J210 FETS which I had to hand but I think
there\'s maybe more to it than that. I cant find any data on them, they
are marked IFC 07703
TIA JC

Protection diodes.

Cheers

Phil Hobbs

Yes, jfets used as diodes. Terrible idea.

The c-b junction of a small transistor would be better all-around.
BFT25 has fA leakage... if you can get them. I could spare a few.

There\'s probably a common TO92 transistor with sub-pA leakage.
Click to expand...
Thanks for the replies.
JC
 
There are special low-leakage diodes, just Google for
\'picoampere diode\'.

The best-known is called PAD-1, from several manufacturers.

--

-TV


On 14.10.22 15.50, JC wrote:
John Larkin wrote:
On Thu, 13 Oct 2022 16:40:18 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

JC wrote:
Hi, Anyone care to explain what the function is of the 2 FETS Q1 and Q2
in this Fluke calibrator and what might be the required parameters
for a
replacement?

https://www.flickr.com/photos/40466580@N07/

It fails diagnostics with leakage caused by one of these. At the moment
I have them replaced with J210 FETS which I had to hand but I think
there\'s maybe more to it than that. I cant find any data on them, they
are marked IFC 07703
TIA JC

Protection diodes.

Cheers

Phil Hobbs

Yes, jfets used as diodes. Terrible idea.

The c-b junction of a small transistor would be better all-around.
BFT25 has fA leakage... if you can get them. I could spare a few.

There\'s probably a common TO92 transistor with sub-pA leakage.

Thanks for the replies.
JC
Click to expand...
 
On Fri, 14 Oct 2022 08:50:05 -0400, JC <Chipbee40_SpamNo@yahoo.com>
wrote:

John Larkin wrote:
On Thu, 13 Oct 2022 16:40:18 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

JC wrote:
Hi, Anyone care to explain what the function is of the 2 FETS Q1 and Q2
in this Fluke calibrator and what might be the required parameters for a
replacement?

https://www.flickr.com/photos/40466580@N07/

It fails diagnostics with leakage caused by one of these. At the moment
I have them replaced with J210 FETS which I had to hand but I think
there\'s maybe more to it than that. I cant find any data on them, they
are marked IFC 07703
TIA JC

Protection diodes.

Cheers

Phil Hobbs

Yes, jfets used as diodes. Terrible idea.

The c-b junction of a small transistor would be better all-around.
BFT25 has fA leakage... if you can get them. I could spare a few.

There\'s probably a common TO92 transistor with sub-pA leakage.

Thanks for the replies.
JC
Click to expand...

I would think that if this was a Fluke designed circuit, that it
wouldn\'t be something that wouldn\'t work.

The people I know that work in the Fluke calibration engineering
department are pretty smart.

boB
 
On Fri, 14 Oct 2022 17:32:42 +0300, Tauno Voipio
<tauno.voipio@notused.fi.invalid> wrote:

There are special low-leakage diodes, just Google for
\'picoampere diode\'.

The best-known is called PAD-1, from several manufacturers.
Click to expand...

The PADS are actually jfets. They are expensive, have crazy high
capacitance and series resistance, and leakage is huge compared to a
decent transistor c-b junction.
 
On Friday, October 14, 2022 at 4:44:20 PM UTC, John Larkin wrote:
On Fri, 14 Oct 2022 17:32:42 +0300, Tauno Voipio
tauno....@notused.fi.invalid> wrote:

There are special low-leakage diodes, just Google for
\'picoampere diode\'.

The best-known is called PAD-1, from several manufacturers.
The PADS are actually jfets. They are expensive, have crazy high
capacitance and series resistance, and leakage is huge compared to a
decent transistor c-b junction.
Click to expand...

https://www.interfet.com/pad/
I_r 1 pA, C_r 0.8 pF
was state of the art at one time :)
and maybe still \"OK\" for this application

node impedance ~ 1M so
1nA becomes 1mV offset.

= RS
 
On Friday, October 14, 2022 at 4:44:20 PM UTC, John Larkin wrote:
On Fri, 14 Oct 2022 17:32:42 +0300, Tauno Voipio
tauno....@notused.fi.invalid> wrote:

There are special low-leakage diodes, just Google for
\'picoampere diode\'.

The best-known is called PAD-1, from several manufacturers.
The PADS are actually jfets. They are expensive, have crazy high
capacitance and series resistance, and leakage is huge compared to a
decent transistor c-b junction.
Click to expand...

https://www.interfet.com/pad/
I_r 1 pA, C_r 0.8 pF
was state of the art at one time :)
and maybe still \"OK\" for this application

node impedance ~ 1M so
1 pA becomes 1 uV offset.

= RS
 
boB wrote:
On Fri, 14 Oct 2022 08:50:05 -0400, JC <Chipbee40_SpamNo@yahoo.com
wrote:

John Larkin wrote:
On Thu, 13 Oct 2022 16:40:18 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

JC wrote:
Hi, Anyone care to explain what the function is of the 2 FETS Q1 and Q2
in this Fluke calibrator and what might be the required parameters for a
replacement?

https://www.flickr.com/photos/40466580@N07/

It fails diagnostics with leakage caused by one of these. At the moment
I have them replaced with J210 FETS which I had to hand but I think
there\'s maybe more to it than that. I cant find any data on them, they
are marked IFC 07703
TIA JC

Protection diodes.

Cheers

Phil Hobbs

Yes, jfets used as diodes. Terrible idea.

The c-b junction of a small transistor would be better all-around.
BFT25 has fA leakage... if you can get them. I could spare a few.

There\'s probably a common TO92 transistor with sub-pA leakage.

Thanks for the replies.
JC


I would think that if this was a Fluke designed circuit, that it
wouldn\'t be something that wouldn\'t work.

The people I know that work in the Fluke calibration engineering
department are pretty smart.

boB
Click to expand...
I tend to agree and as this is an expensive repair/piece of gear
I think I might go with the PAD solution suggested by TV. They
are easily available and not that expensive in the world of Fluke parts :)
Thanks again for all the replies, much appreciated.
JC
 
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