[time-nuts] Z3805

[Bob Camp]

Hi

There often are series resistors / inductors ahead of the power bricks in all these designs. I have found several of them fried. After replacement, everything seems to work ok. I have no idea why they cook out, but they do…

Bob

On Nov 16, 2012, at 2:50 AM, Charles P. Steinmetz <charles_steinmetz at lavabit.com> wrote:

> Bob wrote:
> 
>> I've heard much talk in this group about the power supplies on the Z3805.
>> *   *   *   my Z3805   *   *   *   started producing a real bad smell after a
>> few hours, the classic burnt transformer type.  *   *   *   I opened the
>> unit and found the 25W 5V, +/-15V (made by AT&T) was real, real hot.
>> 
>> Is this the supply driving the heater inside the 10811?
> 
> There appear to be quite a number of different boxes available labeled "Z3805" these days, so information you get may or may not apply to the particular unit you have.  My Korean-made Z3805A takes nominally 24-27 V DC power and has a dual-oven 10811 OCXO.  I presume -- but do not know for sure -- that the ovens run from the raw DC supply, not from a DC-DC converter.
> 
> If the smell did come from the DC-DC converter block, it suggests a failure either in the converter itself or in the circuitry that is powered by the 15 V supplies.  I think the former would be more likely -- the converter should have internal protection that would step in before it got hot enough to smell, in case of a load fault.
> 
> A failed oven controller in the 10811 could also produce a burnt smell.
> 
> Whatever it was, it will very likely give a repeat performance at some inopportune time, unless you chase down the trouble first.  Not easy with an intermittent fault, but particularly if it was one of the 10811 ovens acting up, it would be nice to catch it before it happens again.
> 
> Hints:  (1) use your nose, up close.  Does one part have a residual smoky smell?  (2) Look very carefully, using a magnifier.  Does one part have ID markings that look faded or scorched, or small cracks?  Is anything leaking out of the DC-DC converter?  Also look carefully at resistors and polar capacitors.
> 
> Best regards,
> 
> Charles
> 
> 
> 
> 
> 
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