[time-nuts] HP-5370A update

Magnus Danielson cfmd at bredband.net
Mon Jul 24 13:03:02 EDT 2006


From: "Jose V. Gavila" <eb5agv at ctv.es>
Subject: [time-nuts] HP-5370A update
Date: Mon, 24 Jul 2006 18:28:30 +0200
Message-ID: <5.2.0.9.0.20060724180439.0269c990 at pop.wanadoo.es>

> Hello my friends!

Jose,

> It is time <pun intended> for some update...

Hehe...

> OK, I said, go back to the basics: is the CPU clock working?. Some 
> oscilloscope probing later showed that it was not. Good point to start!. So 
> I went to A8 (REFERENCE FREQUENCY BUFFER) assembly troubleshooting, as it 
> is the source of the 10MHz clock to the CPU clock circuit. Manual shows 
> some waveforms and yes!, one of them was bad... obviously, the one which 
> has to do with the 10MHz CPU oscillator. Some more probing later I decided 
> one of the transistors in the circuit could be bad. But I replaced them 
> (both 2N2904) to not avail... Then I saw a couple tantalums and a 
> suspicious small resistor which seemed overheated. Looking at the manual it 
> was no less than a fuse resistor. And it was open... and one tantalum was 
> shorted. Yes, this supply goes only to the 10MHz CPU clock generator circuit!
> 
> After replacing the burnt resistor and the tantalum (with a 105C 10uF/50V 
> electrolytic as I hate tants!), I powered up the unit... and IT WORKED!!!

Whee! Good thinking and good that you had a simple and classic problem which
you could resolve easy enougth!

> I think I made a good buy :-)!

You did. May I congratulate you both on the buy and repair effort! It must give
you much joy! ;O)

> Unit has some cosmetic damage and one button does not work properly (it 
> sticks) but with a careful cleaning and some front panel work it should end 
> as an 8.5+ looking instrument.
> 
> Now I have to learn how to properly use it. I will sure ask you ;-)

I am pretty sure the necessary knowledge is here on the list.

> Best regards and sorry for the ramblings but I am a very happy camper today!

I bet you are, if your not then we better come and spank you. You made a good
buy and a good repair-effort. As I very recently had the same experience with
my Cs-beam and really understand you. I was however not set back as much as
57 EUR, but that is another matter. I am however deeply in depth to a fellow
time-nut for his contributions in time, money and spare part, so I will have to
compensate him at some time, maybe a beer session or something.

Cheers,
Magnus



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