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I have an Agilent 34401A which I've used at my bench for many years.
Today I went to measure a 12 volt battery and it just started clicking.
I tried it on a power supply and auto ranging works fine up to 12 volts where it starts clicking about twice a second.? Trying manual range, going over the 10 volt range shows exactly zero volts to any input.
I am guessing it tries autoranging higher, sees the zero, then tries to go lower, then repeats.
This is only on DC volts.? AC volts and resistance (didn't check current) are fine, for example I can plug the leads into an outlet and it shows 120 VAC just fine.
Before I dig in, is anyone familiar with this fault?
Peter
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Hello Peter,
Try to run a Self Test and see if it passes it.
Could be anything but older 34401A have relay faults. The OMRON relays
can be found but not the COTO relay. Newer 34401A had a newer part
instead of the COTO one but from what I remember that is also unobtainable.
Regards,
Razvan
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On 05/03/2025 21:35, Peter Gottlieb via groups.io wrote: I have an Agilent 34401A which I've used at my bench for many years.
Today I went to measure a 12 volt battery and it just started clicking.
I tried it on a power supply and auto ranging works fine up to 12 volts
where it starts clicking about twice a second.? Trying manual range,
going over the 10 volt range shows exactly zero volts to any input.
I am guessing it tries autoranging higher, sees the zero, then tries to
go lower, then repeats.
This is only on DC volts.? AC volts and resistance (didn't check
current) are fine, for example I can plug the leads into an outlet and
it shows 120 VAC just fine.
Before I dig in, is anyone familiar with this fault?
Peter
|
Thanks.? I get 4 errors:
612, 613, 618, 619
Three of these have to do with resistance, maybe I needed to short the input, but as resistance works (I just tried with a range of high precision resistors from 1 ohm to 10 meg) and everything looks good so I will ignore those for now.
The 618 error is DC high voltage attenuator failure so that seems to be the issue.
Maybe it is a relay failure.
Thanks for this hint to get me in the right direction.
Peter
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Show quoted text
On 3/5/2025 3:44 PM, Razvan Popescu via groups.io wrote: Hello Peter,
Try to run a Self Test and see if it passes it.
Could be anything but older 34401A have relay faults. The OMRON relays
can be found but not the COTO relay. Newer 34401A had a newer part
instead of the COTO one but from what I remember that is also unobtainable.
Regards,
Razvan
On 05/03/2025 21:35, Peter Gottlieb via groups.io wrote:
I have an Agilent 34401A which I've used at my bench for many years.
Today I went to measure a 12 volt battery and it just started clicking.
I tried it on a power supply and auto ranging works fine up to 12 volts
where it starts clicking about twice a second.? Trying manual range,
going over the 10 volt range shows exactly zero volts to any input.
I am guessing it tries autoranging higher, sees the zero, then tries to
go lower, then repeats.
This is only on DC volts.? AC volts and resistance (didn't check
current) are fine, for example I can plug the leads into an outlet and
it shows 120 VAC just fine.
Before I dig in, is anyone familiar with this fault?
Peter
|
No problem. Let us know what was the faulty component just in case
somebody else will have the same issue in future.
Regards,
Razvan
toggle quoted message
Show quoted text
On 05/03/2025 21:57, Peter Gottlieb via groups.io wrote: Thanks.? I get 4 errors:
612, 613, 618, 619
Three of these have to do with resistance, maybe I needed to short the
input, but as resistance works (I just tried with a range of high
precision resistors from 1 ohm to 10 meg) and everything looks good so I
will ignore those for now.
The 618 error is DC high voltage attenuator failure so that seems to be
the issue.
Maybe it is a relay failure.
Thanks for this hint to get me in the right direction.
Peter
On 3/5/2025 3:44 PM, Razvan Popescu via groups.io wrote:
Hello Peter,
Try to run a Self Test and see if it passes it.
Could be anything but older 34401A have relay faults. The OMRON relays
can be found but not the COTO relay. Newer 34401A had a newer part
instead of the COTO one but from what I remember that is also
unobtainable.
Regards,
Razvan
On 05/03/2025 21:35, Peter Gottlieb via groups.io wrote:
I have an Agilent 34401A which I've used at my bench for many years.
Today I went to measure a 12 volt battery and it just started clicking.
I tried it on a power supply and auto ranging works fine up to 12 volts
where it starts clicking about twice a second.? Trying manual range,
going over the 10 volt range shows exactly zero volts to any input.
I am guessing it tries autoranging higher, sees the zero, then tries to
go lower, then repeats.
This is only on DC volts.? AC volts and resistance (didn't check
current) are fine, for example I can plug the leads into an outlet and
it shows 120 VAC just fine.
Before I dig in, is anyone familiar with this fault?
Peter
|
I replaced the bench unit with a spare which I had in a test setup that isn't being used at the moment.? Doing some quick checks revealed when switched to the front jacks resistance would vary from 5 to 2 k ohms with a shorting plug!? Oh no!? I then took the second spare out of the test setup and put that on my bench. It runs perfectly.
I opened the one with high resistance and got some De-Oxit into that switch which immediately fixed the problem.? It now reads 2 milliohms with a shorting plug (dual banana with a piece of wire).? Ok so now I am back to two working meters.
I opened the one with the DC issue and see a COTO relay.? I hope it isn't that.? Also the display has gotten rather dim from many years of being left on.? Pretty sur I have a new spare put away but I won't change it until I figure out what's wrong with the DC attenuator as I won't waste the new display if the problem is an unobtanium part.
Now I'll go find the schematic and service manual.
Peter
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Show quoted text
On 3/5/2025 3:44 PM, Razvan Popescu via groups.io wrote: Hello Peter,
Try to run a Self Test and see if it passes it.
Could be anything but older 34401A have relay faults. The OMRON relays
can be found but not the COTO relay. Newer 34401A had a newer part
instead of the COTO one but from what I remember that is also unobtainable.
Regards,
Razvan
On 05/03/2025 21:35, Peter Gottlieb via groups.io wrote:
I have an Agilent 34401A which I've used at my bench for many years.
Today I went to measure a 12 volt battery and it just started clicking.
I tried it on a power supply and auto ranging works fine up to 12 volts
where it starts clicking about twice a second.? Trying manual range,
going over the 10 volt range shows exactly zero volts to any input.
I am guessing it tries autoranging higher, sees the zero, then tries to
go lower, then repeats.
This is only on DC volts.? AC volts and resistance (didn't check
current) are fine, for example I can plug the leads into an outlet and
it shows 120 VAC just fine.
Before I dig in, is anyone familiar with this fault?
Peter
|
I have tracked this down to K104 and confirmed by bench test the relay has a bad side and won't make continuity to the DC high range attenuator.? With the relay removed I can jumper pins 9 to 13 and get a voltage reading on the higher range which confirms the rest of the meter works.
?
This is an Omron G6AK-274P-STLT-US-5VDC which is commonly available.? I will get one on order from Mouser.
?
Peter
|
Hi Peter,
If I am not mistaken there are 2 Omron relays on the board. If one
failed maybe the other one will fail soon so if you make an order and
have the unit open it is better to replace both.
Regards,
Razvan
toggle quoted message
Show quoted text
On 09/03/2025 20:17, Peter Gottlieb via groups.io wrote: I have tracked this down to K104 and confirmed by bench test the relay
has a bad side and won't make continuity to the DC high range
attenuator.? With the relay removed I can jumper pins 9 to 13 and get a
voltage reading on the higher range which confirms the rest of the meter
works.
This is an Omron G6AK-274P-STLT-US-5VDC which is commonly available.? I
will get one on order from Mouser.
Peter
|
I saw three and ordered two to have a spare.? Since I have three of this meter and now know about how they can fail I can just replace them as needed.
toggle quoted message
Show quoted text
On 3/9/2025 3:39 PM, Razvan Popescu via groups.io wrote: Hi Peter,
If I am not mistaken there are 2 Omron relays on the board. If one
failed maybe the other one will fail soon so if you make an order and
have the unit open it is better to replace both.
Regards,
Razvan
On 09/03/2025 20:17, Peter Gottlieb via groups.io wrote:
I have tracked this down to K104 and confirmed by bench test the relay
has a bad side and won't make continuity to the DC high range
attenuator.? With the relay removed I can jumper pins 9 to 13 and get a
voltage reading on the higher range which confirms the rest of the meter
works.
This is an Omron G6AK-274P-STLT-US-5VDC which is commonly available.? I
will get one on order from Mouser.
Peter
|
Update:
Relays arrived.? I replaced the failed relay and also put in a new display.
The instrument is back to proper operation with a nice bright display.
Thanks for the likely cause!
Peter
toggle quoted message
Show quoted text
On 3/9/2025 4:17 PM, Peter Gottlieb wrote: I saw three and ordered two to have a spare.? Since I have three of this meter and now know about how they can fail I can just replace them as needed.
On 3/9/2025 3:39 PM, Razvan Popescu via groups.io wrote:
Hi Peter,
If I am not mistaken there are 2 Omron relays on the board. If one
failed maybe the other one will fail soon so if you make an order and
have the unit open it is better to replace both.
Regards,
Razvan
On 09/03/2025 20:17, Peter Gottlieb via groups.io wrote:
I have tracked this down to K104 and confirmed by bench test the relay
has a bad side and won't make continuity to the DC high range
attenuator.? With the relay removed I can jumper pins 9 to 13 and get a
voltage reading on the higher range which confirms the rest of the meter
works.
This is an Omron G6AK-274P-STLT-US-5VDC which is commonly available.? I
will get one on order from Mouser.
Peter
|
Hi Peter,
I am glad you fixed it!
Best regards,
Razvan
toggle quoted message
Show quoted text
On 13/03/2025 21:01, Peter Gottlieb via groups.io wrote: Update:
Relays arrived.? I replaced the failed relay and also put in a new display.
The instrument is back to proper operation with a nice bright display.
Thanks for the likely cause!
Peter
On 3/9/2025 4:17 PM, Peter Gottlieb wrote:
I saw three and ordered two to have a spare.? Since I have three of
this meter and now know about how they can fail I can just replace
them as needed.
On 3/9/2025 3:39 PM, Razvan Popescu via groups.io wrote:
Hi Peter,
If I am not mistaken there are 2 Omron relays on the board. If one
failed maybe the other one will fail soon so if you make an order and
have the unit open it is better to replace both.
Regards,
Razvan
On 09/03/2025 20:17, Peter Gottlieb via groups.io wrote:
I have tracked this down to K104 and confirmed by bench test the relay
has a bad side and won't make continuity to the DC high range
attenuator.? With the relay removed I can jumper pins 9 to 13 and get a
voltage reading on the higher range which confirms the rest of the
meter
works.
This is an Omron G6AK-274P-STLT-US-5VDC which is commonly available.? I
will get one on order from Mouser.
Peter
|
Interesting observation.? The rear plastic piece (with the 2 screws) on the case cracked.? I went to glue it and found it to be completely brittle and crumbling with even the slightest pressure from my fingers.
Has anyone else seen this?? I wonder if all those plastic case pieces are going to fail?
Peter
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Show quoted text
On 3/13/2025 4:18 PM, Razvan Popescu via groups.io wrote: Hi Peter,
I am glad you fixed it!
Best regards,
Razvan
On 13/03/2025 21:01, Peter Gottlieb via groups.io wrote:
Update:
Relays arrived.? I replaced the failed relay and also put in a new display.
The instrument is back to proper operation with a nice bright display.
Thanks for the likely cause!
Peter
On 3/9/2025 4:17 PM, Peter Gottlieb wrote:
I saw three and ordered two to have a spare.? Since I have three of
this meter and now know about how they can fail I can just replace
them as needed.
On 3/9/2025 3:39 PM, Razvan Popescu via groups.io wrote:
Hi Peter,
If I am not mistaken there are 2 Omron relays on the board. If one
failed maybe the other one will fail soon so if you make an order and
have the unit open it is better to replace both.
Regards,
Razvan
On 09/03/2025 20:17, Peter Gottlieb via groups.io wrote:
I have tracked this down to K104 and confirmed by bench test the relay
has a bad side and won't make continuity to the DC high range
attenuator.? With the relay removed I can jumper pins 9 to 13 and get a
voltage reading on the higher range which confirms the rest of the
meter
works.
This is an Omron G6AK-274P-STLT-US-5VDC which is commonly available.? I
will get one on order from Mouser.
Peter
|
This does seem to be a problem, I have seen quite a lot go over time..
It must be the composition of the plastic...
I guess 3D print is the way forward as most other mouldings might suffer from the same degradation...
Regards
Nigel
Sent from my iPad by banging a nail into a piece of wood...
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On 13 Mar 2025, at 20:47, Peter Gottlieb via groups.io <hpnpilot@...> wrote:
Interesting observation. The rear plastic piece (with the 2 screws) on the case cracked. I went to glue it and found it to be completely brittle and crumbling with even the slightest pressure from my fingers.
Has anyone else seen this? I wonder if all those plastic case pieces are going to fail?
Peter
On 3/13/2025 4:18 PM, Razvan Popescu via groups.io wrote:
Hi Peter,
I am glad you fixed it!
Best regards,
Razvan
On 13/03/2025 21:01, Peter Gottlieb via groups.io wrote:
Update:
Relays arrived. I replaced the failed relay and also put in a new display.
The instrument is back to proper operation with a nice bright display.
Thanks for the likely cause!
Peter
On 3/9/2025 4:17 PM, Peter Gottlieb wrote:
I saw three and ordered two to have a spare. Since I have three of
this meter and now know about how they can fail I can just replace
them as needed.
On 3/9/2025 3:39 PM, Razvan Popescu via groups.io wrote:
Hi Peter,
If I am not mistaken there are 2 Omron relays on the board. If one
failed maybe the other one will fail soon so if you make an order and
have the unit open it is better to replace both.
Regards,
Razvan
On 09/03/2025 20:17, Peter Gottlieb via groups.io wrote:
I have tracked this down to K104 and confirmed by bench test the relay
has a bad side and won't make continuity to the DC high range
attenuator. With the relay removed I can jumper pins 9 to 13 and get a
voltage reading on the higher range which confirms the rest of the
meter
works.
This is an Omron G6AK-274P-STLT-US-5VDC which is commonly available. I
will get one on order from Mouser.
Peter
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