Re: Short on the preAmp card (fwd from Yves)

[Elton Smith <elton@jlab.org>]

Hall D Electronics:


---------- Forwarded message ----------
Date: Sun, 9 Dec 2007 14:22:21 -0500 (EST)
From: Yves Van Haarlem <yvhaarle@ernest.phys.cmu.edu>
To: Fernando J. Barbosa <barbosa@jlab.org>
Cc: Gerard Visser <gvisser@indiana.edu>,
     Curtis Meyer <cmeyer@ernest.phys.cmu.edu>
Subject: Re: Short on the preAmp card
Resent-Date: Mon, 10 Dec 2007 22:00:14 -0500
Resent-From: "Curtis A. Meyer" <cmeyer@ernest.phys.cmu.edu>
Resent-To: halld-electronics@jlab.org

Hi Fernando,

I tested the cable and found no short, so it has to be on the preAmp. I
only have channel 1 and 2 connected to the postAmp (I soldered them to a
17-ch flat-cable connector and connected it to the postAmp) all the other
channels I left open, so next thing to do is to connect all signal cables
that are populated to the postAmp (in that way they are terminated) and
see if there are still oscillations. I connected the heatsink to the
ground of the HV-distribution board with a cable that has alligator
clamps.

Cheers,
 	Yves



On Sun, 9 Dec 2007, Fernando J. Barbosa wrote:

> Hi Yves,
>
>   You are right, the unpopulated channel 9 should be open. The short may be
> either on the cable, where it is crimped to the connector, or the preamp due
> to assembly. I would check the cable first as I didn't test the cables.
> However, this should not impact your measurements.
>
>   I checked every output on the cards, OUTA and OUTB, directly with a scope
> as I didn't have any signal cables at the time. I didn't see any oscillations
> in this manner. I will try tomorrow with a cable. How are the outputs
> connected? Are all the outputs terminated into 100 Ohm resistors? Any
> reference to ground?
>
>   Thanks for your feedback and keep me posted.
>
> Best regards,
> Fernando
>
>
>
> Yves Van Haarlem wrote:
>> Hi Fernando,
>>
>> Thanks for your reply, my answers/findings are below:
>>
>>>   I don't quite understand your last paragraph but channels 9 through 16
>>> are not populated. The two ASICs on top populate channels 1-8 and 17-24.
>> Here are the resitance I measure (I connect the signal cable to the preAmp
>> and measure the resistance between OUTA and OUTB on the end of the signal
>> cable) :
>>
>> - 16 channels have a resistance of 950 Ohm -> those are the populated ones
>> - 7 channels are open -> the not populated channels
>> - 1 channel(#9) has a resistance <5 Ohm (shorted) - I believe this channel
>> should be open because it is not populated.
>>
>>
>>>   You also note a block of pulses of 200 mV at 10 MHz. Is this
>>> oscillation? Do you see such oscillation with the preamp card and
>>> interposer powered but not attached to the  HV board?
>> Yes - if i do not connect the interposer to the HV-distribution board I
>> just see noise (looking like bursts) with an amplitude of 25 mV.
>>
>>
>> Cheers,
>>     Yves
>>
>>
>>
>>>
>>>   Please let  me know what you find. Thanks and best regards,
>>> Fernando
>>>
>>>
>>> Yves Van Haarlem wrote:
>>>> Hi Fernando, Gerard,
>>>>
>>>> The PreAmp card and the interposer reached CMU yesterday, thank you.
>>>>
>>>> Today i tried to get it to work. At first i applied 3.2 V on the preAmp
>>>> card only (no transposer) - the board was drawing 280 mA of current -
>>>> good! After attaching the signal cable to it the current went up to 500
>>>> mA. Apparently the heat-sink was touching the end of the signal cable
>>>> that was sticking out of the connector, i could solve this by cutting
>>>> this end of as close as possible to the connector. After that the board
>>>> was drawing a current of 290 mA wich is OK i figure.
>>>>
>>>> Next thing I did was connecting the preAmp to the transposer and
>>>> connected the transposer to our HV-distribution board. I used the signal
>>>> cable you sent to go to our postAmp and then read out one channel on the
>>>> scope. I saw block pulses of 200 mV with a frequency of 10 MHz. So I
>>>> suspected another short somewhere; after visually inspecting the preAmp -
>>>> I found a short on the output connector (a picture was taken but is not
>>>> available yet), it was a piece of soldering that was easy to remove.
>>>> However, it did not solve the problem.
>>>>
>>>> I start measuring the signal cable(s) for shorts - no shorts were
>>>> measured, then i did the same measurement but now with the signal cable
>>>> connected to the preAmp and there it was: channel 9 (starting from 1) is
>>>> shorted. Problem is that after again inspecting the preAmp visually I
>>>> could not find anything. So my question - is there an obvious candidate
>>>> for this short (the connector looks fine to me) - are there certain
>>>> points i can measure on the board to figure this out?
>>>>
>>>> Thanks.
>>>>
>>>> Have a nice weekend,
>>>>     Yves
>>>>
>>>>
>>>>                           /--------------------------------
>>>>                          /   Yves Van Haarlem
>>>>        _--~~--_         /
>>>>      /~/_|  |_\~\      /      Carnegie Mellon University
>>>>     |____________|    /        Department of Physics
>>>>     |[][][][][][]|:= /          Wean Hall room 8404
>>>>   __| __         |__ \            Pittsburgh, PA 15213
>>>>  |  ||. |   ==   |  | \           USA
>>>> (|  ||__|   ==   |  |) \
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>>>>  |  |____________|  |    \                  +1 412 641-9252
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>>>>   ~~              ~~       \-----------------------------------
>>>>
>>>
>