Re: Short on the preAmp card (fwd Yves)

[Elton Smith <elton@jlab.org>]

Hall D Electronics:


---------- Forwarded message ----------
Date: Sat, 8 Dec 2007 16:29:54 -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 21:59:54 -0500
Resent-From: "Curtis A. Meyer" <cmeyer@ernest.phys.cmu.edu>
Resent-To: halld-electronics@jlab.org

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
>> (|  ||__|   ==   |  |) \
>>  |  |[] []  ==   |  |   \           Tel.:   +1 412 268-6949
>>  |  |____________|  |    \                  +1 412 641-9252
>>  /__\            /__\     \          Fax.: +1 412 681-0648
>>   ~~              ~~       \-----------------------------------
>>
>