[time-nuts] HP5370 Error 04

John Allen john at pcsupportsolutions.com
Mon Jun 8 18:12:24 UTC 2015

Hello Matthias - I had this problem on my 5370B - it turned out that the fan wasn't running, which resulted in overheating.

I hope this helps.

Regards, John K1AE

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Matthias Jelen
Sent: Monday, June 08, 2015 9:28 AM
To: time-nuts at febo.com; dk4yj at gmx.de
Subject: [time-nuts] HP5370 Error 04

I´ve got a question to the 5370 experts on the list.
I just received my new (old...) HP5370a. It performed fine for abt. one hour, then it started to display error 04 which means "PLL out of lock".
A look in the service manual revealed that there are several reasons for this. I checked the VCO voltage on both interpolator cards, and indeed, one of them is out of the specified -6V..-3V, it runs to the rail (-12V). Even if the error is not there, the voltage is at abt. -7 V, so I guess it´s just on the edge. The other card is fine.
Normally, I´d try the alignment procedure, but I´m missing the exotic HP pulse generator used for the alignment and I have no clue how I could easily substitute this one.
Did anyone encounter this problem before? Is there a cure for this problem known to the experts? Any hints are highly appreciated...
Thanks a lot,
Matthias, DK4YJ
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