[hpsdr] Is Penelope U6 Toast?

[Mike F]

Scotty, Phil

I looked at U6 using my stereo SMD assembly microscope and, although I 
can blow it up to what ever size I need, I can't read the markings on 
the chip.  As though they have been burnt off.  No holes, and no other 
obvious problems.

In this case I was driving a 50 ohm load (in-line termination with a 
connector at each end) and connected to a scope.  I believe that the 
amplitude was about 5.6 vrms (15.8 v p-p), around 0.6 watts.  I know 
this sounds high, especially when my T2 is one of the reversed ones.  I 
can't guarantee the accuracy of my old (Tek 475) scope at 28MHz.  The 
signal died away in about a second.  The info below is incorrect in that 
the drive level at JP2 is about 1.3v p-p and the output is 88mv p-p.

Based on the above it looks like I will be replacing U6, but I am still 
not sure what caused the problem.  My PA (the PA from a FT-900 
transceiver) was developing bad distortion on the input when powered.  I 
believe I have traced it to a bad transistor in one of the push-pull 
stages.  I didn't have the amplifier connected when the problem 
occurred, but U6 may have been stressed earlier by the distortion.

Thanks for the responses

Mike, K7SR

> Hi Mike,
>
> One pretty easy way to tell if you smoked U6 is to see if it gets
> warm during TX.
>
> I have managed to let the smoke out of one, and the result was
> visible damage to the chip.  Maybe a good visual inspection would
> give you an indication.
>
> 73,
> Scotty WA2DFI
>
>
>
>
>
>
> At 08:52 2012-02-10 +0800, Phil Harman wrote:
>>***** High Performance Software Defined Radio Discussion List *****
>>
>>Hi Mike,
>>
>>Penelope is fine into a 50 ohm load - she does not like a short circuit.
>>
>>It does sound like you have let the smoke out of U6.
>>
>>73 Phil...VK6APH
>>
>>
>> > ***** High Performance Software Defined Radio Discussion List *****
>> >
>> > I had a 50 ohm load on Penelope output and was changing the output when
>> > it disappeared.  I am wondering if Penelope doesn't like a 50 ohm load
>> > and therefore I need to change U6.  I do see output when I crank the
>> > scope gain way up, but it is now about the same level as what I measure
>> > at JP2.
>> >
>> > Thanks
>> >
>> > Mike, K7SR
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