[time-nuts] Thunderbolt question

[Chris Waldrup]

Hi,

I've changed the blown MMBT3904 in the antenna sense circuit and I still have no 5V to the antenna. I measure 0.5V DC on the F connector. 
There are two Murata filters (F2 and F3) on the RF path to the antenna. In between the two silver colored filters  is a 6 lead SOT package marked 51A. The PCB silkscreen says Q13. 
 I have measured the following voltages on this part:
Pin 1= 0v
Pin 2= 0v
Pin 3= 0.749V
Pin 4= 4.892v
Pin 5= 0v
Pin 6= 3.417v

The trace from pin 3 of this part goes to the F2 filter and the output of F2 goes to the F connector. I'm getting 0.5V on the output of this filter.   I'm suspecting this Q13 part may be bad but I'm not sure what the part is. Searching the net for 51A marking came up with a large 2 pin shottky which this isn't. 

Chris
KD4PBJ

> On Aug 4, 2017, at 5:27 PM, Chris Waldrup <kd4pbj at gmail.com> wrote:
> 
> Thanks guys. 
> I've opened up my T bolt and noticed a SOT23 packaged part has the top blown off. 
> The PPS BNC jack has U19 beside it. 
> The next part is blown. Could someone take a closeup of the five parts around U19?
> The intact parts are marked:
> 5Dz
> 1AM
> and two 2Az parts. 
> 
> 
> Chris
> 
>> On Aug 4, 2017, at 4:13 PM, Arthur Dent <golgarfrincham at gmail.com> wrote:
>> 
>> Actually that isn't my photo I linked to but one I just Googled. That is
>> probably a board revision most people don't have but it was the first one
>> I saw so I used it just to show that the GPS receiver is part of the
>> only circuit board and not another easily replaceable board like in some
>> other units.
>> 
>> I just took a couple of photos of the later revision of the board for
>> anyone interested in seeing what might be fried. In the photo of the
>> top of the board the signal comes into a filter then to a 25db amp
>> marked AM50002 by Macom. Above the filter near the input is where the
>> decoupled +5VDC for the antenna is connected. If you are only reading
>> 0.5VDC, if your're lucky it might only be the amp is fried and that
>> could be an easy fix. If the 5VDC is ok with the amp input pin lifted,
>> it might be the only problem. I wouldn't bet on it though. The 4031 I
>> believe is a 1575.42 SAW filter
>> 
>> The photo of the bottom of the receiver area shows a Sawtek filter and
>> other parts. At the bottom of the photo is C460, a feedthrough capacitor
>> and that might be where the receiver output is but where my Tbolts are
>> working I don't feel the need to look into whether you could connect
>> the output of a seperate GPS receiver there to make it work.
>> 
>> I do have one Tbolt that has no oscillator. I brought the EFC and 10Mhz
>> connections to SMA connectors on the back so I can test other oscillators
>> or GPSDOs that don't have an easy way to monitor of graph the stability
>> of those units and using Lady Heather gives me a good way to compare the
>> graphs to ones I'm used to. You might possibly be able to replace the
>> built-in receiver but it might be easier to buy a working Thunderbolt.
>> 
>> 
>> http://i906.photobucket.com/albums/ac262/rjb1998/GPS%20top%201_zpslgxunnyw.jpg
>> 
>> http://i906.photobucket.com/albums/ac262/rjb1998/GPS%20bottom%201_zpschvruppt.jpg
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