OT - Simpson 260, series 6P won't zero on all resistance scales


Dave Seiter
 

I'm stumped- I've gone through the four Simpson 260s I've manage to acquire over the years, and now three work correctly, but the last, a 6P, can't zero all three resistance scales.  The resistors are all nominal (usually they are either open or very high on these units), the protection circuit is working AND the relay contacts have been cleaned (another common issue).  After a lot of searching on various forums, etc,  it seems like an ohm zeroing failure occurs on any one of the three settings, or sometime two, but all three is unheard of (or at least no one's posted it yet.)  The only I haven't tried yet is the zero pot itself (and this just occurred to me):  while the end to end resistance is good, maybe the the wiper isn't seeing the full range for some reason (I know these pots can shed resistive material, but that usually results in an open pot.
If you've seen this behavior before or know the probable cause, please respond to my email directly.  Yes, the batteries have been checked...  ;-)
Thanks!
-Dave


Jean-Paul
 

suggest you scrap the battery contacts with wire brush, check for cold solder joints and on the zero contr use a good control cleaner like Miller Stephenson or De Oxit.

jon


 

As Jean-Paul wrote- verify that the battery contacts (and batteries) are
OK.  I had similar issues on my 260 (series 2); I found that a can of
compressed air applied to the zero pot and the range switch contacts,
followed by some deoxit on the zero pot, worked wonders.  And make sure
that the set screw on the range switch is secure- I had a bid of
"wiggle" on my range switch knob which I initially ignored, but the
"wiggle" was indeed part of the problem that I was experiencing.

On 8/28/21 2:35 AM, Jean-Paul wrote:
suggest you scrap the battery contacts with wire brush, check for cold solder joints and on the zero contr use a good control cleaner like Miller Stephenson or De Oxit.

jon




Charles Plunk
 

I emailed Dave direct about this as I had a similar issue. My series 3 developed resistance between contacts on the rotary range switch. It was the contacts underneath thus almost inaccessible. Contact cleaner &  DeOxit would not help. I finally took a chance and tried some other potent chem's letting them soak for a while stuffing small pieces of soaked cloth under there and to tell the truth don't remember for sure what cured it. Removing the switch would have likely meant its destruction. Its been working a year now though just fine. My guess is battery acid got to it but not sure. Some sort of crude was all over much of the circuit board.

Chuck

W4NBO

On 8/27/21 7:37 PM, Dave Seiter wrote:

I'm stumped- I've gone through the four Simpson 260s I've manage to acquire over the years, and now three work correctly, but the last, a 6P, can't zero all three resistance scales.  The resistors are all nominal (usually they are either open or very high on these units), the protection circuit is working AND the relay contacts have been cleaned (another common issue).  After a lot of searching on various forums, etc,  it seems like an ohm zeroing failure occurs on any one of the three settings, or sometime two, but all three is unheard of (or at least no one's posted it yet.)  The only I haven't tried yet is the zero pot itself (and this just occurred to me):  while the end to end resistance is good, maybe the the wiper isn't seeing the full range for some reason (I know these pots can shed resistive material, but that usually results in an open pot.
If you've seen this behavior before or know the probable cause, please respond to my email directly.  Yes, the batteries have been checked...  ;-)
Thanks!
-Dave




Roy Morgan
 

Two comments offered to help:

Soldering short wires from the battery to the terminals will ensure good connection.

Caig De-Oxit is best for metal to metal sliding contacts as in switches and wire wound rotary resistors. If may damage resistive film controls.

Caig Fader Lube is best for rotary controls that have resistance tracks as in most potentiometers.

Caig used to sell a Sample Kit of small tubes of three of their products. Not sure if they still do.

Roy

Roy Morgan
K1LKY Western Mass

On Aug 28, 2021, at 2:36 AM, Jean-Paul <jonpaul@ix.netcom.com> wrote:

suggest you scrap the battery contacts with wire brush, check for cold solder joints and on the zero contr use a good control cleaner like Miller Stephenson or De Oxit.

jon


Dave Hills
 

Have you checked the movement calibration?
Do you get full deflection with 1.0 volts applied to the +1V input?
This bypasses all the switch contacts and connects directly to the
movement via a 15K resistor.
I ask this because I have an older Series 3 that will not swing to
full scale with 50 uA applied to the movement terminals. This of
course makes it read low on all ranges. I suspect mine has
a weak field magnet.

Dave

On Fri, Aug 27, 2021 at 05:37 PM, Dave Seiter wrote:


I'm stumped- I've gone through the four Simpson 260s I've manage to acquire
over the years, and now three work correctly, but the last, a 6P, can't zero
all three resistance scales.  The resistors are all nominal (usually they are
either open or very high on these units), the protection circuit is working
AND the relay contacts have been cleaned (another common issue).  After a lot
of searching on various forums, etc,  it seems like an ohm zeroing failure
occurs on any one of the three settings, or sometime two, but all three is
unheard of (or at least no one's posted it yet.)  The only I haven't tried
yet is the zero pot itself (and this just occurred to me):  while the end to
end resistance is good, maybe the the wiper isn't seeing the full range for
some reason (I know these pots can shed resistive material, but that usually
results in an open pot.
If you've seen this behavior before or know the probable cause, please respond
to my email directly.  Yes, the batteries have been checked...  ;-)
Thanks!
-Dave


Jean-Paul
 

Rebonjour on a few 260 and Triplett VOM, the coil insulation can flak or a microscopic bit of dust or debris enters the D'Arsonval movement

Symptoms are movement sticking at a certain point on every range

the flake may be removed, place meter on face, a few gentil whacks may clear it

Bon Chance

Jon

PS the old analog meters are invaluable for high voltage work,
or if high energy transients are present. We tested 7000 12kv Aviation PSU
with five Simpson 260s over 10 years.


DaveH52
 

Since it won't zero on some ranges suggests to me that either 1 - the meter movement isn't zeroed properly; or 2 - there is some extra resistance in the probe circuit like the probe jacks, range switch, wiring, or resistors R61 through R21 have changed values.


Richard Knoppow
 

The meter mechanical zero is easily checked and adjusted. The meter is usually zeroed laying flat on its back. If the meter counterbalances are correctly adjusted the zero should remain when the meter is placed upright.
   If the meter is mechanically zeroed you should be able to zero it on all ranges. Most of the time when I have had problems its due to one or the other battery being weak. More often the high voltage battery for the high range. Depends on which ranges are off. If the ranges that don't zero are not exclusively the high or low ranges, i.e. if the batteries are OK, then you have a bunch of stuff to look for. The zero pot is probably the first place but you could have a bad resistor in one of the dividers. First a visual inspection for a resistor that looks burned or otherwise damaged. I am not sure what kind of resistors the 260 uses, my meters are Triplet but look for problems at the leads. Many precision resistors have end caps that can corrode. Also wire wound resistors may have corroded connections at the ends of the windings. Typically a bad resistor will be far off value.
   It may be tedious to find. If the ranges that are off are scattered try to find what is common to them.
   Someone mentioned corroded battery terminals, worth looking for. If there was ever a leaky battery in the meter it can have left residue that might take quite some time do do its damage. Should be visible. This meter and the Triplet 630 are probably the most widely used VOMs out there and both are good meters.

On 8/29/2021 11:13 AM, DaveH52 wrote:
Since it won't zero on some ranges suggests to me that either 1 - the meter movement isn't zeroed properly; or 2 - there is some extra resistance in the probe circuit like the probe jacks, range switch, wiring, or resistors R61 through R21 have changed values.



--
Richard Knoppow
dickburk@ix.netcom.com
WB6KBL


Dave Hills
 

The OP stated, "but the last, a 6P, can't zero all three resistance scales."
"Zero" on the resistance scale of a "260" is full scale deflection of the meter movement.
Of course incorrect mechanical "Zero" on the voltage scale will affect the full scale
meter deflection, "Zero Ohms", as well.

Dave


Dave Seiter
 

I thought I had found something- I was focussing on the zero ohm pot, and found that it didn't go all the way to zero, but stopped at 8 ohms.  Sadly, shorting the pots' terminals didn't make any difference.  The batteries/clips/leads are also ok; even though I had to make a new clip to replace one that had been eaten through, there is no voltage drop or resistance in that part of the system.  
I'm beginning to wonder if the movement is bad.  On the 1V setting, a source which reads 1.00V on my Tek DMM, reads .62V on the Simpson.  The only resistor in that part of the circuit s/b 15K and is 15.16K; technically out of spec, but close enough.  
Ok, I think the only problem this meter has is that it needs a cal, BADLY.  Tweaking the shunt pot allowed both the 1V and zero ohms to read correctly.  I'm pretty sure I have the mil cal manual for this thing somewhere.
Thanks for everyone's suggestions!
Dave

On Sunday, August 29, 2021, 01:46:06 PM PDT, Richard Knoppow <dickburk@ix.netcom.com> wrote:

   The meter mechanical zero is easily checked and adjusted. The
meter is usually zeroed laying flat on its back. If the meter
counterbalances are correctly adjusted the zero should remain
when the meter is placed upright.
   If the meter is mechanically zeroed you should be able to
zero it on all ranges. Most of the time when I have had problems
its due to one or the other battery being weak. More often the
high voltage battery for the high range. Depends on which ranges
are off. If the ranges that don't zero are not exclusively the
high or low ranges, i.e. if the batteries are OK, then you have a
bunch of stuff to look for. The zero pot is probably the first
place but you could have a bad resistor in one of the dividers.
First a visual inspection for a resistor that looks burned or
otherwise damaged. I am not sure what kind of resistors the 260
uses, my meters are Triplet but look for problems at the leads.
Many precision resistors have end caps that can corrode. Also
wire wound resistors may have corroded connections at the ends of
the windings. Typically a bad resistor will be far off value.
   It may be tedious to find. If the ranges that are off are
scattered try to find what is common to them.
   Someone mentioned corroded battery terminals, worth looking
for. If there was ever a leaky battery in the meter it can have
left residue that might take quite some time do do its damage.
Should be visible. This meter and the Triplet 630 are probably
the most widely used VOMs out there and both are good meters.

On 8/29/2021 11:13 AM, DaveH52 wrote:
Since it won't zero on some ranges suggests to me that either 1 - the meter movement isn't zeroed properly; or 2 - there is some extra resistance in the probe circuit like the probe jacks, range switch, wiring, or resistors R61 through R21 have changed values.




--
Richard Knoppow
dickburk@ix.netcom.com
WB6KBL


Michael W. Lynch
 

Here are 2 great resources for Simpson 260:

On You Tube: w2aew at https://www.youtube.com/user/w2aew/ Search for Simpson 260. He has several videos about the instrument.

and on the web at: http://simpson260.com/

I have several Simpson 260's and Triplett 630's , they are both fine instruments. Well worth the effort to fix.

Good luck with your repairs.

--
Michael Lynch
Dardanelle, AR


Jean-Paul
 

If every range is affected the D'Arsonval movement may be bad.

Set meter level on bench, carefully set mechanical zero.

On 1 v range get calibrated source, or PSU with know good dvm, increasing V 0-1.0 V eg

0 100,200, 300......1000 mV

is pointer smoothly indicating both increasing and decreasing 0-1 and 1-0

Bon Chance

Jon


Brent W8XG
 

Just happened to watch this video on Youtube, from the AllAmericanFiveRadio channel https://www.youtube.com/watch?v=6PluFphrRVw
this weekend. He had good reading on some ohm values but not on another. There are separate fuses for the various values and it turned out to have a fuse with resistance in it. If I remember the low ohm values fuse had about 80 ohms in it, creating a mess.

I would have never thought to look there!. It's probably not your problem, but it's sure worth checking, as it's easy to verify. I've got a series 8, which has the backwards banana plugs, but you can get really nice ones from Probe Master for it. I love the unit.

Brent W8XG


Dave Hills
 

Dave,

Proper calibration of a Series 6 depends upon the resistance seen across
the 50uA/250mV terminals being precisely 5000 ohms. All of the meter's
ranges depend on this. You have to adjust both the series and shunt pots,
R2 and R1, respectively, to simultaneously achieve a full deflection and
250mV across the 50uA and common terminals.
It can be rather tedious and in the case of my Series 3, impossible. This
scheme requires the meter movement's sensitivity be less than 50uA
and with mine it proved to be around 58uA, thus making calibration impossible.

Dave

On Tue, Aug 31, 2021 at 05:24 PM, Dave Seiter wrote:


I'm beginning to wonder if the movement is bad.  On the 1V setting, a source
which reads 1.00V on my Tek DMM, reads .62V on the Simpson.  The only
resistor in that part of the circuit s/b 15K and is 15.16K; technically out of
spec, but close enough.  
Ok, I think the only problem this meter has is that it needs a cal, BADLY. 
Tweaking the shunt pot allowed both the 1V and zero ohms to read correctly. 
I'm pretty sure I have the mil cal manual for this thing somewhere.
Thanks for everyone's suggestions!
Dave


Dave Hills
 

One more thing. The protection device V1 could be leaky,
stealing some of the movements current. Easily checked
by removing it and retesting with 1.00v applied. If you get a
higher reading than with V1 installed, it's leaky. Be careful not
to apply more than 1.00 volts with V1 disconnected, you
could easily damage the movement.

Dave


Jim Ford
 

Hmmm...  my 260, a series 6XLP, says "Taut Band Suspension" on the face and has a yin-yang-like drawing near the text.  Not that I know diddly-squat about taut band or D'Arsonval movements.  Can somebody enlighten me please?   TIA, Jim Ford Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: Jean-Paul <jonpaul@ix.netcom.com> Date: 9/1/21 5:55 AM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] OT - Simpson 260, series 6P won't zero on all resistance scales If every range is affected the D'Arsonval movement may be bad.Set meter level on bench, carefully set mechanical zero.On 1 v range get calibrated source, or PSU with know good dvm, increasing V 0-1.0 V eg0  100,200, 300......1000 mVis pointer smoothly indicating both increasing and decreasing 0-1 and 1-0Bon Chance Jon


SCMenasian
 

Before taut band, most meter movements had a spiral hairspring to return the pointer to the zero position. This posed many problems. For example, if subjected to a minor shock, the loops of the hairspring could become entangled - requiring a delicate repair process. The entire pointer assembly was supported by two jeweled bearings which were finicky to adjust and could become sticky if not abslutely clean.

Taut band movements solved these problems and provided greater overall stability by replacing the spiral hairspring with a torsion spring passing through the rotation axis of the pointer. Since there were no loops to become entangled, the first problem was eliminated. The not-quite-friction-free jeweled bearing was completely eliminated, resulting in greater general overall stability and ease of adjustment.


Jim Ford
 

Thanks, SC.  Interesting stuff!          JimSent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: SCMenasian <scm@menasians.com> Date: 9/1/21 10:24 AM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] OT - Simpson 260, series 6P won't zero on all resistance scales Before taut band, most meter movements had a spiral hairspring to return the pointer to the zero position. This posed many problems. For example, if subjected to a minor shock, the loops of the hairspring could become entangled - requiring a delicate repair process. The entire pointer assembly was supported by two jeweled bearings which were finicky to adjust and could become sticky if not abslutely clean.Taut band movements solved these problems and provided greater overall stability by replacing the spiral hairspring with a torsion spring passing through the rotation axis of the pointer. Since there were no loops to become entangled, the first problem was eliminated. The not-quite-friction-free jeweled bearing was completely eliminated, resulting in greater general overall stability and ease of adjustment.


Dave Seiter
 

I have three 6's (one being the 6P), and a 7 with the reverse plugs.  I find the plugs to be annoying (because I tend to grab the closest set of leads), but at least they are in good shape.
-Dave

On Wednesday, September 1, 2021, 06:14:29 AM PDT, Brent W8XG <brent@pwg.net> wrote:

Just happened to watch this video on Youtube, from the AllAmericanFiveRadio channel https://www.youtube.com/watch?v=6PluFphrRVw
this weekend. He had good reading on some ohm values but not on another. There are separate fuses for the various values and it turned out to have a fuse with resistance in it. If I remember the low ohm values fuse had about 80 ohms in it, creating a mess.

I would have never thought to look there!. It's probably not your problem, but it's sure worth checking, as it's easy to verify. I've got a series 8, which has the backwards banana plugs, but you can get really nice ones from Probe Master for it. I love the unit.

Brent W8XG