Re: Short on the preAmp card

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

Hall D Electronics:

Hi Yves,

    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.

    If you want to look at the outputs before the output connector, to 
the right of the ASICs (output connector is on the right), there are the 
output pads where the output resistors would normally go. These 
resistors are not installed. The left pads connect to the vias that 
connect to the ASICs and the output connector; the right pads connect to 
+1.25V. Additionally, one output pair (i.e. ch n) is on top,  the next 
output pair (i.e. ch n+1) is on the bottom, etc. You can access each 
output ch (+ or -) by carefully probing on the vias - they are small.

    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?

    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
>
>
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>                          /   Yves Van Haarlem
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