First check that you have good battery contacts and heavy test leads. Any resistance in leads will not let the meter zero. For test, remove your test leads and short the contacts right at the meter.
Norm
: I recently obtained a Simpson model 260 series 6P VOM
: in very good condition except I can't quite get it to
: zero on the Rx1 resistance scale. It still reads around
: 1 ohm with the zero pot turned all the way. I have replaced
: the 1.5v. D cell battery and checked the left side
: pointer zero. Also have cleaned selector switches which
: made minor improvement but not enough. Is this effected
: by one or more calibration pots? Is there a calibration
: procedure available on the web? Does this suggest any
: other problem? Any suggestions are appreciated.
: Bill
: First check that you have good battery contacts and heavy test leads. Any resistance in leads will not let the meter zero. For test, remove your test leads and short the contacts right at the meter.
: Norm
:
: : I recently obtained a Simpson model 260 series 6P VOM
: : in very good condition except I can't quite get it to
: : zero on the Rx1 resistance scale. It still reads around
: : 1 ohm with the zero pot turned all the way. I have replaced
: : the 1.5v. D cell battery and checked the left side
: : pointer zero. Also have cleaned selector switches which
: : made minor improvement but not enough. Is this effected
: : by one or more calibration pots? Is there a calibration
: : procedure available on the web? Does this suggest any
: : other problem? Any suggestions are appreciated.
This is going to sound a little insulting, especially after Norm
has already mentioned it, but I've been there before. Be sure
that you've replaced the 1.5 v battery with a known good (NEW)
one. The Rx1 range is the first to go with a mediocre "D" cell
and I've been burned when I made the assumption that my "new"
battery really was.
There is no calibration adjustment for the resistance function
on a 260. There should be four adjustements on the circuit
board, and they set the basic DC meter characteristics and
calibrate the rectifier to the meter movement on the ACV ranges.
Simpson does not have a calibration procedure for the 260 that
is not "internal corporate information only" as far as I know.
After working with lots of these meters in Navy PMEL, I ended up
developing a procedure which can help to set the meter "right on".
Take heed to Norm's suggestion to check battery and test lead
connections. Also don't forget that the two fuses in the meter
are in series with the COMMON test lead. Make sure that they're
making a good connection and that they're zero ohms themselves.
Be careful cleaning the switch. I'd tend to stick with isopropyl
alcohol only. Any conductive residue left behind on those
phenolic wafers can really goof up the high resistance and high
voltage ranges.
Assuming the battery is good, it would appear that someone before
you tried to "measure the number of ohms in a wall receptacle"
as we always used to say of someone who connected an ohmmeter
across a live circuit. It's likely that one or more resistors
have been shifted in value by a current overload. That is a little
surprising since this is a "P" model with the electronic overload
protection. It may not be working, either. Make sure that the
high-voltage ohmmeter battery is good, too, since it operates the
overload circuitry.
I have a schematic for a 6/6M here but not the 6P, but I think
the only difference is in the higher resistance ranges and the
electronic protection circuit. Assuming that, check R16 (11 ohms),
R17 (1.109K) and R19 (17.55K). Watch the schematic in your little
orange manual to verify those resistor values. Check these by
removing one end from the PCB or by making sure that the
function/range switch is in the 500V position so that your test
ohmmeter current has no chance or coursing through that 50µa meter
movement. Yeah, it has a protection diode assembly across it, but
we don't go deliberately slamming our car into a brick wall just
because we think the air bags are going to work. :•)
If you'd like the calibration procedure for the 260-series, let
me know on this thread. I'll be watching it for a couple of
weeks and will be happy to post it for anyone interested.
Dean
: This is going to sound a little insulting, especially after Norm
: has already mentioned it, but I've been there before. Be sure
: that you've replaced the 1.5 v battery with a known good (NEW)
: one. The Rx1 range is the first to go with a mediocre "D" cell
: and I've been burned when I made the assumption that my "new"
: battery really was.
: There is no calibration adjustment for the resistance function
: on a 260. There should be four adjustements on the circuit
: board, and they set the basic DC meter characteristics and
: calibrate the rectifier to the meter movement on the ACV ranges.
: Simpson does not have a calibration procedure for the 260 that
: is not "internal corporate information only" as far as I know.
: After working with lots of these meters in Navy PMEL, I ended up
: developing a procedure which can help to set the meter "right on".
: Take heed to Norm's suggestion to check battery and test lead
: connections. Also don't forget that the two fuses in the meter
: are in series with the COMMON test lead. Make sure that they're
: making a good connection and that they're zero ohms themselves.
: Be careful cleaning the switch. I'd tend to stick with isopropyl
: alcohol only. Any conductive residue left behind on those
: phenolic wafers can really goof up the high resistance and high
: voltage ranges.
: Assuming the battery is good, it would appear that someone before
: you tried to "measure the number of ohms in a wall receptacle"
: as we always used to say of someone who connected an ohmmeter
: across a live circuit. It's likely that one or more resistors
: have been shifted in value by a current overload. That is a little
: surprising since this is a "P" model with the electronic overload
: protection. It may not be working, either. Make sure that the
: high-voltage ohmmeter battery is good, too, since it operates the
: overload circuitry.
: I have a schematic for a 6/6M here but not the 6P, but I think
: the only difference is in the higher resistance ranges and the
: electronic protection circuit. Assuming that, check R16 (11 ohms),
: R17 (1.109K) and R19 (17.55K). Watch the schematic in your little
: orange manual to verify those resistor values. Check these by
: removing one end from the PCB or by making sure that the
: function/range switch is in the 500V position so that your test
: ohmmeter current has no chance or coursing through that 50µa meter
: movement. Yeah, it has a protection diode assembly across it, but
: we don't go deliberately slamming our car into a brick wall just
: because we think the air bags are going to work. :•)
: If you'd like the calibration procedure for the 260-series, let
: me know on this thread. I'll be watching it for a couple of
: weeks and will be happy to post it for anyone interested.
:
: Dean
Hi Dean,
If you could post that calibration procedure,
I'd sure be grateful. thanks, Lance.
Bill
: : in very good condition except I can't quite get it to
: : zero on the Rx1 resistance scale. It still reads around
: : 1 ohm with the zero pot turned all the way. I have replaced
: : the 1.5v. D cell battery and checked the left side
: : pointer zero. Also have cleaned selector switches which
: : made minor improvement but not enough. Is this effected
: : by one or more calibration pots? Is there a calibration
: : procedure available on the web? Does this suggest any
: : other problem? Any suggestions are appreciated.
Having spent years working on these in the Navy, I can tell you to measure the resistance of the fuses
and ensure you get one with the lowest possible resistance. This has a
direct reflection of resistance on the RX1 scale. Your fuse is probably
not as low as it should be.
Good Luck.