RE: LBA DAS problem at Hart
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From: Jonathan Quick <jon_at_email.protected>
Date: Wed, 17 Jun 2015 15:58:22 +0200
Hi Dick
It's been a while! I hope life is treating you well.
So the modules fans are all running and there are no over-temperature alarms.
If I swap either or both modules between channels the fault is always in the
first channel (ie. the modules are good), so it looks like is a connection
issue on the back plane. With no signal attached, both level and offset servos
are out of range, but the offset comes right when I put in a reasonable
signal.
The 5MHz and 1PPS signals show as being OK, so I don't think it's an input issue.
Unfortunately my control software doesn't allow setting manual control. So I
will need to spend some time getting a DOS emulator going on our control PC so
I can run LBA_DAS.EXE. It's been so long that this incarnation doesn't even
have an emulator installed!
Regards
Jon
On Sat, June 13, 2015 5:12 am, Dick.Ferris_at_email.protected
> Hi Jon,
>
> That's a new one on me. The only faults I'm aware of are fans stopping,
> usually due to a hairline crack in the Sampler PCB, and in one case an ADC
> chip which cooked due to said fan stoppage. Present symptoms seem to indicate
> the AGC circuit is running open-loop, which could arise from faults in either
> the Sampler or Filter modules, or the connections between them via the back
> plane.
>
> First up I suggest listening to the fans, then checking the module
> temperatures. If dead or slow, or hot then stop and remove the affected
> module to limit the damage.
>
> Next put the gain under manual control and see if you can set the gain such
> that the signal level is on scale. If so then you can continue to operate
> normally as the self adjusting thresholds on all of the outputs will keep the
> statistics spot on.
>
> To get a quick idea of the general health of the signal path connect in turn a
> CRO and a spectrum analyser to the BandSplitter monitor port and see if the
> signal looks normal, can display a test tone, looks the same on both IFPs etc.
>
> It must be going on 15 years since I last fired up a DAS so it's all a bit
> hazy! Come Monday I'll have a copy of the User Manual (Temporary) at hand and
> should be able to be more specific.
>
> Good luck,
> Dick
> ________________________________________
> From: Brett Reid [Brett.Reid_at_email.protected
> Sent: Friday, 12 June 2015 9:11 PM
> To: Jonathan Quick; vlbiobs_at_email.protected
> Cc: Ferris, Dick (CASS, Marsfield); Mirtschin, Peter (CASS, Narrabri); McFee,
> Jock (CASS, Narrabri)
> Subject: Re: LBA DAS problem at Hart
>
> Hi Jon,
> Although I am not aware of this problem, I am adding several people who
> may or may not be members of the LBA observers group, but I know have
> experience with the DAS hardware, since they have helped us at UTAS.
> They are Dick Ferris, Peter Mirtschin and Jock McFee.
>
> Also, I am at Ceduna currently, involved in H-maser and telescope
> maintenance, and I can easily refer to the DAS manual on the shelf here
> or make some measurements here if it would help. Our DAS manual does not
> have detailed schematics either though.
>
> If it were me I would be swapping Sampler 1 with 2 module positions to
> see if the behaviour swapped channels. Then if not changed I would be
> swapping filter 1 with filter 2 module positions. Also, I have learnt to
> not switch the red illuminated power switch off as the grease in the
> switch goes hard and prevents the contacts coming back to the on
> position nicely and burns the contacts sometimes. Best to leave the
> power switch on and switch it at the power outlet.
>
> Regards,
> Brett
>
> On 12/06/2015 8:11 PM, Jonathan Quick wrote:
>> Hi All
>>
>> My apologies if this is a little off topic for some. but I'm trying to tap
>> into collective wisdom here.
>>
>> One channel of our LBA DAS hardware appears to have developed some sort of
>> fault. The symptom is that the input level detector seems always to read
>> either too high or two low. To switch from one state to the other only
>> takes
>> a 0.1dB change in level and the level readout then takes a few seconds to
>> slide across from one end to the other. This problem seems to have
>> developed
>> spontaneously overnight last weekend,
>>
>> Has any one else ever encountered such behaviour in their DAS and if so how
>> did you fix it?
>>
>> We only have high level block diagrams and no extension cables so it is
>> going
>> to be extremely difficult for us to trace the fault ourselves.
>>
>> All advice welcome!
>>
>> Regards
>> Jon
>>
>> .
>>
>
> --
> Brett Reid
> Observatory Manager, Radio Astronomy Group
> University of Tasmania, School of Mathematics and Physics
> 03 6248 5285 Observatory 0407 955 283 mobile
> email brett.reid_at_email.protected
> web http://users.on.net/~cdadsl
>
>
> University of Tasmania Electronic Communications Policy (December, 2014).
> This email is confidential, and is for the intended recipient only. Access,
> disclosure, copying, distribution, or reliance on any of it by anyone outside
> the intended recipient organisation is prohibited and may be a criminal
> offence. Please delete if obtained in error and email confirmation to the
> sender. The views expressed in this email are not necessarily the views of the
> University of Tasmania, unless clearly intended otherwise.
>
>
Received on 2015-06-17 23:59:11
Date: Wed, 17 Jun 2015 15:58:22 +0200
Hi Dick
It's been a while! I hope life is treating you well.
So the modules fans are all running and there are no over-temperature alarms.
If I swap either or both modules between channels the fault is always in the
first channel (ie. the modules are good), so it looks like is a connection
issue on the back plane. With no signal attached, both level and offset servos
are out of range, but the offset comes right when I put in a reasonable
signal.
The 5MHz and 1PPS signals show as being OK, so I don't think it's an input issue.
Unfortunately my control software doesn't allow setting manual control. So I
will need to spend some time getting a DOS emulator going on our control PC so
I can run LBA_DAS.EXE. It's been so long that this incarnation doesn't even
have an emulator installed!
Regards
Jon
On Sat, June 13, 2015 5:12 am, Dick.Ferris_at_email.protected
> Hi Jon,
>
> That's a new one on me. The only faults I'm aware of are fans stopping,
> usually due to a hairline crack in the Sampler PCB, and in one case an ADC
> chip which cooked due to said fan stoppage. Present symptoms seem to indicate
> the AGC circuit is running open-loop, which could arise from faults in either
> the Sampler or Filter modules, or the connections between them via the back
> plane.
>
> First up I suggest listening to the fans, then checking the module
> temperatures. If dead or slow, or hot then stop and remove the affected
> module to limit the damage.
>
> Next put the gain under manual control and see if you can set the gain such
> that the signal level is on scale. If so then you can continue to operate
> normally as the self adjusting thresholds on all of the outputs will keep the
> statistics spot on.
>
> To get a quick idea of the general health of the signal path connect in turn a
> CRO and a spectrum analyser to the BandSplitter monitor port and see if the
> signal looks normal, can display a test tone, looks the same on both IFPs etc.
>
> It must be going on 15 years since I last fired up a DAS so it's all a bit
> hazy! Come Monday I'll have a copy of the User Manual (Temporary) at hand and
> should be able to be more specific.
>
> Good luck,
> Dick
> ________________________________________
> From: Brett Reid [Brett.Reid_at_email.protected
> Sent: Friday, 12 June 2015 9:11 PM
> To: Jonathan Quick; vlbiobs_at_email.protected
> Cc: Ferris, Dick (CASS, Marsfield); Mirtschin, Peter (CASS, Narrabri); McFee,
> Jock (CASS, Narrabri)
> Subject: Re: LBA DAS problem at Hart
>
> Hi Jon,
> Although I am not aware of this problem, I am adding several people who
> may or may not be members of the LBA observers group, but I know have
> experience with the DAS hardware, since they have helped us at UTAS.
> They are Dick Ferris, Peter Mirtschin and Jock McFee.
>
> Also, I am at Ceduna currently, involved in H-maser and telescope
> maintenance, and I can easily refer to the DAS manual on the shelf here
> or make some measurements here if it would help. Our DAS manual does not
> have detailed schematics either though.
>
> If it were me I would be swapping Sampler 1 with 2 module positions to
> see if the behaviour swapped channels. Then if not changed I would be
> swapping filter 1 with filter 2 module positions. Also, I have learnt to
> not switch the red illuminated power switch off as the grease in the
> switch goes hard and prevents the contacts coming back to the on
> position nicely and burns the contacts sometimes. Best to leave the
> power switch on and switch it at the power outlet.
>
> Regards,
> Brett
>
> On 12/06/2015 8:11 PM, Jonathan Quick wrote:
>> Hi All
>>
>> My apologies if this is a little off topic for some. but I'm trying to tap
>> into collective wisdom here.
>>
>> One channel of our LBA DAS hardware appears to have developed some sort of
>> fault. The symptom is that the input level detector seems always to read
>> either too high or two low. To switch from one state to the other only
>> takes
>> a 0.1dB change in level and the level readout then takes a few seconds to
>> slide across from one end to the other. This problem seems to have
>> developed
>> spontaneously overnight last weekend,
>>
>> Has any one else ever encountered such behaviour in their DAS and if so how
>> did you fix it?
>>
>> We only have high level block diagrams and no extension cables so it is
>> going
>> to be extremely difficult for us to trace the fault ourselves.
>>
>> All advice welcome!
>>
>> Regards
>> Jon
>>
>> .
>>
>
> --
> Brett Reid
> Observatory Manager, Radio Astronomy Group
> University of Tasmania, School of Mathematics and Physics
> 03 6248 5285 Observatory 0407 955 283 mobile
> email brett.reid_at_email.protected
> web http://users.on.net/~cdadsl
>
>
> University of Tasmania Electronic Communications Policy (December, 2014).
> This email is confidential, and is for the intended recipient only. Access,
> disclosure, copying, distribution, or reliance on any of it by anyone outside
> the intended recipient organisation is prohibited and may be a criminal
> offence. Please delete if obtained in error and email confirmation to the
> sender. The views expressed in this email are not necessarily the views of the
> University of Tasmania, unless clearly intended otherwise.
>
>
Received on 2015-06-17 23:59:11