Re: Short on the preAmp card

["Fernando J. Barbosa" <barbosa@jlab.org>]

Hall D Electronics:

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
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>>