[time-nuts] HP 106B quartz frequency standard...the story so far

[Magnus Danielson]

GandalfG8 at aol.com wrote:
>  
> In a message dated 08/08/2009 11:56:59 GMT Daylight Time,  
> magnus at rubidium.dyndns.org writes:
> 
> Please  also note that it is not necesserilly that transistor which could 
> be bad,  but the driving curcuit may have gone bad.
> 
> 
> 
> Exactly:-)

In one case, the buffer transistor driving the regulating transistor (as 
a Darlington stage) had gone bad, it had burned into a short, so the 
regulating transistor was conducting full force while the output of the 
741 was at full voltage. Fortunatly, all the powered curcuits survived 
and some faults disappeared as voltage levels became as expected.

Focusing on a single component can be quite missleading, even after 
emitting smoke.

I have had to move components and restore PCB tracks to overcome that a 
design error created a "heat pocket" on the PSU, slowly cooking and 
aging it in a faster rater than intended.

Cheers,
Magnus