[time-nuts] Tbolt failure modes

[Said Jackson]

A radical procedure (short of replacing the Trimble Asic) is to take a brush and brush the pins on the pcb. Hard, but not hard enough to damage the board or the pins. Then clean the pcb with alcohol and compressed air.

Trimble uses RoHs solder, which will eventually generate tin whiskers that can short out adjacent pins etc. If your board is old enough to not be RoHs this should not be the cause of the problem.

You may be able to remove the whiskers with a brush. If that is your failure cause...

Sent From iPhone

On May 12, 2012, at 7:47, bg at lysator.liu.se wrote:

> Thanks everyone!
> 
>> On 05/12/2012 03:37 PM, Mark Sims wrote:
>>> 
>>> It sounds like the -12V supply is used to generate the DAC low voltage
>>> reference.  If it is floating,  the DAC output will be unstable.  If it
>>> is at a solid voltage,  the DAC output will be stable.  The standard EFC
>>> range for a tbolt is -5V to +5V,  but since almost all Tbolts are
>>> running the osc with a positive EFC voltage,  it will work with the -12V
>>> line grounded.
>>> 
>>> I suspect that  although it may appear to be working,  the DAC output
>>> may not be as stable as with a negative rail available since whatever is
>>> generating the negative DAC reference voltage will be well below its
>>> dropout voltage.
>>> 
>>> One thing to try is to do an oscillator autotune with the -12V line
>>> grounded  and at -12V.  Your DAC gain will probably double (or half)
>>> since the DAC output range is now 0V..5V instead of -5V to 5V.  The
>>> tbolt firmware knows what the expected dac voltages rails are (readable
>>> via an undocumented TSIP message) are and also has settings for what
>>> range to allow the EFC to swing.
>> 
>> Well, all this is well, but doesn't reflect well on Björns problems I
>> think, I did look at his postings in this thread and he seems to have
>> valid -12V.
>> 
>> What is an issue is that the big ASIC seems either powerless or kept not
>> running.
>> 
>> Either a 3,3V regulator went down, got shorted or something, or clock
>> failed or reset line not released.
>> 
>> I am a bit interested in this myself, but don't have the time to drive
>> down to him this weekend.
>> 
>> Cheers,
>> Magnus
> 
> I have checked the voltages. They are the same, measuring on the defect
> unit and a working one. Have also swapped the receiver boards between
> different PSUs. There is no problem running a working receiver with the
> PSU of the defect one. Hence I agree with Magnus and others suggesting the
> CPU (big Trimble asic) is not running.
> 
> Today I do not have access to the right instruments, but just measuring
> with a DMM - there are differences at TP8, TP9 and TP10. And as mentioned
> previously the CPU-chip is to cold, compared to a working unit.
> 
> I do not have time to pursue the CPU problem right now. Hope to come back
> later with an update.
> 
> thanks,
> 
>    Björn
> 
> 
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