Diode ID: Simpson 2701 DMM

A

Andy Cuffe

Guest
I'm working on an early digital multimeter (nixie tubes, from the late
60's). It's a Simpson 2701 which was actually made by a German
company:

http://www.radiomuseum.org/r/metrawatt_digitavo_hy_511_d.html

It has been having trouble with unstable and wildly inaccurate
readings in all ranges. I found an open diode on the amplifier board,
and I'm trying to figure out if it's anything special. It is labeled
"NT 9757 N".

http://wine-in-a-box.org/AK/simpsondiode.jpg

There is one other identical diode on the board that measures like a
normal silicon diode, but it looks like it could be something special.

For now, I've replaced it with an ordinary high speed silicon diode.
Things are working better, but it still has accuracy problems on some
ranges, and AC volts/amps aren't working at all.

If anyone is curious, I have what Simpson calls a service manual, but
it's not very detailed:

http://wine-in-a-box.org/AK/2701%20Service%20Manual.pdf
 
"Andy Cuffe" <acuffe@gmail.com> wrote in message
news:eefcs7lfr3v0dai1upejvm8a35ifnbvmhi@4ax.com...
I'm working on an early digital multimeter (nixie tubes, from the late
60's). It's a Simpson 2701 which was actually made by a German
company:

http://www.radiomuseum.org/r/metrawatt_digitavo_hy_511_d.html

It has been having trouble with unstable and wildly inaccurate
readings in all ranges. I found an open diode on the amplifier board,
and I'm trying to figure out if it's anything special. It is labeled
"NT 9757 N".

http://wine-in-a-box.org/AK/simpsondiode.jpg
Click to expand...

That looks almost big enough to be a stacked selenium pellet diode, possibly
about the right era too.
 
Andy Cuffe schrieb:

http://wine-in-a-box.org/AK/simpsondiode.jpg
Click to expand...
This is obviously a diode made by Nortron, AFAIK a German Manufacturer
of semiconductor devices.

Unfortunately, I can't find it in my 1969/70 catalog. The "nearest"
device as to the type number is NT 9779, a diode with logarithmic
reverse characteristic.

BTW, one of these meters belongs to my collection ...

HTH

Reinhard
 
Andy Cuffe <acuffe@gmail.com> wrote:
I'm working on an early digital multimeter (nixie tubes, from the late
60's). It's a Simpson 2701 which was actually made by a German
company:

http://www.radiomuseum.org/r/metrawatt_digitavo_hy_511_d.html

It has been having trouble with unstable and wildly inaccurate
readings in all ranges. I found an open diode on the amplifier board,
and I'm trying to figure out if it's anything special. It is labeled
"NT 9757 N".

http://wine-in-a-box.org/AK/simpsondiode.jpg
Click to expand...
are any of the semicondutors marked with logo or name of any sort?
 
On Wed, 30 May 2012 19:51:28 +0200, Reinhard Zwirner
<reinhard.zwirner@t-online.de> wrote:

Andy Cuffe schrieb:

http://wine-in-a-box.org/AK/simpsondiode.jpg

This is obviously a diode made by Nortron, AFAIK a German Manufacturer
of semiconductor devices.

Unfortunately, I can't find it in my 1969/70 catalog. The "nearest"
device as to the type number is NT 9779, a diode with logarithmic
reverse characteristic.

BTW, one of these meters belongs to my collection ...

HTH

Reinhard
Click to expand...

Thanks for the information. Knowing the manufacturer may help.

The good one has a forward voltage drop of about .65v, and reads open
in the reverse direction, but I haven't put much voltage across it
since I don't want to damage the only good one.

I don't suppose you have a full schematic, or any other information on
it?

I already have this, but it's not much more detailed than the Simpson
service manual:

http://www.rainers-elektronikpage.de/Sonstige-SM-und-SM---Infos/DIGITAVO.pdf
 
"Andy Cuffe" <acuffe@gmail.com> wrote in message
news:9ltcs71v7qegs65denkugfq1sik9ehgo5s@4ax.com...
On Wed, 30 May 2012 19:51:28 +0200, Reinhard Zwirner
reinhard.zwirner@t-online.de> wrote:

Andy Cuffe schrieb:

http://wine-in-a-box.org/AK/simpsondiode.jpg

This is obviously a diode made by Nortron, AFAIK a German Manufacturer
of semiconductor devices.

Unfortunately, I can't find it in my 1969/70 catalog. The "nearest"
device as to the type number is NT 9779, a diode with logarithmic
reverse characteristic.

BTW, one of these meters belongs to my collection ...

HTH

Reinhard


Thanks for the information. Knowing the manufacturer may help.

The good one has a forward voltage drop of about .65v, and reads open
in the reverse direction, but I haven't put much voltage across it
since I don't want to damage the only good one.
Click to expand...

Are there any the same type in places you could substitute with a common
silicon type without fear the different characteristics might be a problem -
such as relay back emf catch diode?

With a very cursory glance at the schematic, I noticed a transistor with a
vbe reverse clamp diode - if that diode just happend to be the one you want,
you could probably slide in a Shottky-barrier type and pinch that one for
the replacement you need.
 
Andy Cuffe schrieb:
[...]
Thanks for the information. Knowing the manufacturer may help.
Click to expand...
You're welcome.
The good one has a forward voltage drop of about .65v, and reads open
in the reverse direction, but I haven't put much voltage across it
since I don't want to damage the only good one.

I don't suppose you have a full schematic, or any other information on
it?
Click to expand...
You're absolutely right! In fact all my information I have got via those
both links you communicated here ...

Good night (it's almost midnight)

Reinhard
 
On Wed, 30 May 2012 21:17:38 +0100, "Ian Field"
<gangprobing.alien@ntlworld.com> wrote:

Are there any the same type in places you could substitute with a common
silicon type without fear the different characteristics might be a problem -
such as relay back emf catch diode?

With a very cursory glance at the schematic, I noticed a transistor with a
vbe reverse clamp diode - if that diode just happend to be the one you want,
you could probably slide in a Shottky-barrier type and pinch that one for
the replacement you need.
Click to expand...
Good idea, but there are only two of these diodes in it. I might try
swapping it into the other location to see if the symptoms change.

One problem is that they are in the middle of three boards sandwiched
together. It's a 10+ minute job to get to them, and they are
completely inaccessible while it's working. I might have to try
adding some extension wires.
 
On 5/30/2012 9:24 AM, Cydrome Leader wrote:
Andy Cuffe<acuffe@gmail.com> wrote:
I'm working on an early digital multimeter (nixie tubes, from the late
60's). It's a Simpson 2701 which was actually made by a German
company:

http://www.radiomuseum.org/r/metrawatt_digitavo_hy_511_d.html

It has been having trouble with unstable and wildly inaccurate
readings in all ranges. I found an open diode on the amplifier board,
and I'm trying to figure out if it's anything special. It is labeled
"NT 9757 N".

http://wine-in-a-box.org/AK/simpsondiode.jpg

are any of the semicondutors marked with logo or name of any sort?
Since you already know the bad diode is open, what is the voltage across
Click to expand...
the two leads? AC or DC? You know the voltage drop for the other good
diode indicates it is not germanium and probably silicon. So substitute
and old silicon diode with a voltage rating greater than what you saw
across the leads. You are not going to kill the device with another
diode and you will then know if the diode is something special, or a
common silicon device.

Paul
 
On Wed, 30 May 2012 15:29:54 -0700, Paul Drahn
<pdrahn@webformixair.com> wrote:

On 5/30/2012 9:24 AM, Cydrome Leader wrote:


are any of the semicondutors marked with logo or name of any sort?
Since you already know the bad diode is open, what is the voltage across
the two leads? AC or DC? You know the voltage drop for the other good
diode indicates it is not germanium and probably silicon. So substitute
and old silicon diode with a voltage rating greater than what you saw
across the leads. You are not going to kill the device with another
diode and you will then know if the diode is something special, or a
common silicon device.

Paul
Click to expand...
I already did just that, and things improved, but were still not
right. The diodes are located on the middle board of a 3 board
module, so access is difficult. Tonight, I disassembled the module
again and soldered some wires to the one working original diode, and
my substitute so I could take some reading with the module assembled.

I discovered that both diodes are reverse biased. The good one reads
17.8v, and the bad one that was replaced with a regular diode was
reading 22v, so clearly it's some kind of zener. I jumped the
replacement diode with an 18v zener and things are looking much
better. Without any calibration things all ranges are reading very
close, and the AC volts range is working. I think it's safe to say
that I have found the problem.

I would like to thank everyone who responded.
 
"Andy Cuffe" <acuffe@gmail.com> wrote in message
news:qj6ds7pgvaffmbgpjkko9f9um14fd1slcd@4ax.com...
On Wed, 30 May 2012 21:17:38 +0100, "Ian Field"
gangprobing.alien@ntlworld.com> wrote:

Are there any the same type in places you could substitute with a common
silicon type without fear the different characteristics might be a
problem -
such as relay back emf catch diode?

With a very cursory glance at the schematic, I noticed a transistor with a
vbe reverse clamp diode - if that diode just happend to be the one you
want,
you could probably slide in a Shottky-barrier type and pinch that one for
the replacement you need.


Good idea, but there are only two of these diodes in it. I might try
swapping it into the other location to see if the symptoms change.

One problem is that they are in the middle of three boards sandwiched
together. It's a 10+ minute job to get to them, and they are
completely inaccessible while it's working. I might have to try
adding some extension wires.
Click to expand...
Is that nested among the nixie boards? - a zener could easily be 180V in
that location!

In which case you may get random symbols lighting out of turn but not
innacurate readings as such, its also more common for zeners to fail S/C.
 
On May 31, 9:31 am, "Ian Field" <gangprobing.al...@ntlworld.com>
wrote:
"Andy Cuffe" <acu...@gmail.com> wrote in message

news:qj6ds7pgvaffmbgpjkko9f9um14fd1slcd@4ax.com...









On Wed, 30 May 2012 21:17:38 +0100, "Ian Field"
gangprobing.al...@ntlworld.com> wrote:

Are there any the same type in places you could substitute with a common
silicon type without fear the different characteristics might be a
problem -
such as relay back emf catch diode?

With a very cursory glance at the schematic, I noticed a transistor with a
vbe reverse clamp diode - if that diode just happend to be the one you
want,
you could probably slide in a Shottky-barrier type and pinch that one for
the replacement you need.

Good idea, but there are only two of these diodes in it.  I might try
swapping it into the other location to see if the symptoms change.

One problem is that they are in the middle of three boards sandwiched
together.  It's a 10+ minute job to get to them, and they are
completely inaccessible while it's working.  I might have to try
adding some extension wires.

Is that nested among the nixie boards? - a zener could easily be 180V in
that location!

In which case you may get random symbols lighting out of turn but not
innacurate readings as such, its also more common for zeners to fail S/C.
Click to expand...
Andy
Why not take the good one out and connect it up to a variable dc power
supply through say a 1K current limiting resistor. Then you can
increase the supply slowly while monitoring the voltage across the
diode and see where it clamps. I've cataloged all my odd ball diodes
I've had lying around here over the years that way.
Lenny
 
"klem kedidelhopper" <captainvideo462009@gmail.com> wrote in message
news:e6d9e392-4c3b-49a8-92b4-28d38f2f09f3@k5g2000vbf.googlegroups.com...
On May 31, 9:31 am, "Ian Field" <gangprobing.al...@ntlworld.com>
wrote:
"Andy Cuffe" <acu...@gmail.com> wrote in message

news:qj6ds7pgvaffmbgpjkko9f9um14fd1slcd@4ax.com...









On Wed, 30 May 2012 21:17:38 +0100, "Ian Field"
gangprobing.al...@ntlworld.com> wrote:

Are there any the same type in places you could substitute with a common
silicon type without fear the different characteristics might be a
problem -
such as relay back emf catch diode?

With a very cursory glance at the schematic, I noticed a transistor with
a
vbe reverse clamp diode - if that diode just happend to be the one you
want,
you could probably slide in a Shottky-barrier type and pinch that one
for
the replacement you need.

Good idea, but there are only two of these diodes in it. I might try
swapping it into the other location to see if the symptoms change.

One problem is that they are in the middle of three boards sandwiched
together. It's a 10+ minute job to get to them, and they are
completely inaccessible while it's working. I might have to try
adding some extension wires.

Is that nested among the nixie boards? - a zener could easily be 180V in
that location!

In which case you may get random symbols lighting out of turn but not
innacurate readings as such, its also more common for zeners to fail S/C.
Click to expand...
Andy
Why not take the good one out and connect it up to a variable dc power
supply through say a 1K current limiting resistor. Then you can
increase the supply slowly while monitoring the voltage across the
diode and see where it clamps. I've cataloged all my odd ball diodes
I've had lying around here over the years that way.
Lenny
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv

I have a home brew breakdown (onset of leakage) tester that wouldn't pass
any safety inspection - but its served me well.

Its entirely made from parts salvaged from monitor mains in/SMPSU sections.

For 240VRMS use; it has a pair of 68k 2W resistors in series (SMPSU chip
startup resistors) on the AC side of a moulded assy bridge rectifier block,
on the DC side is a pair of 180uF 380V caps in series with the junction
between the two connected to one AC arm of the bridge to make it a doubling
rectifier.

An important addition is a shorting switch to discharge the caps between
test - in series with a NTC inrush suppression thermistor to stop it blowing
the switch contacts away first time you use it.

Doubling the voltage gives about 600V for testing diode reverse leakage - it
also reduces the available current; I've tested the PIV of 1N4148 diodes
without damaging them.
 
"Ian Field" <gangprobing.alien@ntlworld.com> wrote in
news:luuyr.1266346$ed1.45472@fx04.am4:

"klem kedidelhopper" <captainvideo462009@gmail.com> wrote in message
news:e6d9e392-4c3b-49a8-92b4-28d38f2f09f3@k5g2000vbf.googlegroups.com..
. On May 31, 9:31 am, "Ian Field" <gangprobing.al...@ntlworld.com
wrote:
"Andy Cuffe" <acu...@gmail.com> wrote in message

news:qj6ds7pgvaffmbgpjkko9f9um14fd1slcd@4ax.com...









On Wed, 30 May 2012 21:17:38 +0100, "Ian Field"
gangprobing.al...@ntlworld.com> wrote:

Are there any the same type in places you could substitute with a
common silicon type without fear the different characteristics
might be a problem -
such as relay back emf catch diode?

With a very cursory glance at the schematic, I noticed a transistor
with a
vbe reverse clamp diode - if that diode just happend to be the one
you want,
you could probably slide in a Shottky-barrier type and pinch that
one for
the replacement you need.

Good idea, but there are only two of these diodes in it. I might
try swapping it into the other location to see if the symptoms
change.

One problem is that they are in the middle of three boards
sandwiched together. It's a 10+ minute job to get to them, and they
are completely inaccessible while it's working. I might have to try
adding some extension wires.

Is that nested among the nixie boards? - a zener could easily be 180V
in that location!

In which case you may get random symbols lighting out of turn but not
innacurate readings as such, its also more common for zeners to fail
S/C.

Andy
Why not take the good one out and connect it up to a variable dc power
supply through say a 1K current limiting resistor. Then you can
increase the supply slowly while monitoring the voltage across the
diode and see where it clamps. I've cataloged all my odd ball diodes
I've had lying around here over the years that way.
Lenny
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv

I have a home brew breakdown (onset of leakage) tester that wouldn't
pass any safety inspection - but its served me well.

Its entirely made from parts salvaged from monitor mains in/SMPSU
sections.

For 240VRMS use; it has a pair of 68k 2W resistors in series (SMPSU
chip startup resistors) on the AC side of a moulded assy bridge
rectifier block, on the DC side is a pair of 180uF 380V caps in series
with the junction between the two connected to one AC arm of the
bridge to make it a doubling rectifier.

An important addition is a shorting switch to discharge the caps
between test - in series with a NTC inrush suppression thermistor to
stop it blowing the switch contacts away first time you use it.

Doubling the voltage gives about 600V for testing diode reverse
leakage - it also reduces the available current; I've tested the PIV
of 1N4148 diodes without damaging them.
Click to expand...
you'd think some enterprising soul would come out with a budget curve
tracer to work with an o'scope.
It wouldn't have to have a very high V range.
IIRC,Heathkit used to have one.
I also recall a circuit for a simple XSTR curve tracer in an engineering
magazine's annual circuit collection issue.

Damn,I wish I had kept those books...along with everything else I had
ratholed while at TEK.... I coulda been somebody! ;-)

For that matter,I wonder if there's a hobbyist market for other budget
instruments like a scope-cal board(XTAL-controlled,divided Sq.Wave),or a
DMM cal-check reference board,stuff like that?


--
Jim Yanik
jyanik
at
localnet
dot com
 
On Sat, 2 Jun 2012 09:00:58 -0700 (PDT), klem kedidelhopper
<captainvideo462009@gmail.com> wrote:

Andy
Why not take the good one out and connect it up to a variable dc power
supply through say a 1K current limiting resistor. Then you can
increase the supply slowly while monitoring the voltage across the
diode and see where it clamps. I've cataloged all my odd ball diodes
I've had lying around here over the years that way.
Lenny
Click to expand...

Lenny,

I have already figured it out (see my reply on May 30).

Initially I was worried about destroying the only good once since I
had no idea what it was. For all I knew it could have been some
exotic diode that would be destroyed by much reverse voltage. Since
the diodes are completely inaccessible, I soldered wires to both of
them, and reassembled it. With the unit powered up, it only took one
measurement to find out that it's an 18v zener. I replaced the bad
one with an 18v zener, and everything appears to be working properly
at last.
 
On Jun 3, 1:25 pm, Andy Cuffe <acu...@gmail.com> wrote:
On Sat, 2 Jun 2012 09:00:58 -0700 (PDT), klem kedidelhopper

captainvideo462...@gmail.com> wrote:

Andy
Why not take the good one out and connect it up to a variable dc power
supply through say a 1K current limiting resistor. Then you can
increase the supply slowly while monitoring the voltage across the
diode and see where it clamps. I've cataloged all my odd ball diodes
I've had lying around here over the years that way.
Lenny

Lenny,

I have already figured it out (see my reply on May 30).

Initially I was worried about destroying the only good once since I
had no idea what it was.  For all I knew it could have been some
exotic diode that would be destroyed by much reverse voltage.  Since
the diodes are completely inaccessible, I soldered wires to both of
them, and reassembled it.  With the unit powered up, it only took one
measurement to find out that it's an 18v zener.  I replaced the bad
one with an 18v zener, and everything appears to be working properly
at last.
Click to expand...
Glad that you got it fixed. I recently found an intermittent cap in my
1970 Grundig portable radio. It's nice to see an old dog bark again.
Lenny
 
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