Re: tek 7904A...


You are headed in this direction, but I would suspect filter caps that have dropped in value. At light load, they would still work okay, but at heavier loads the ripple may get so large that regulators either drop out of regulation or otherwise pass the ripple along. I have had this same symptom with TM5xxx mainframes.

Having said that, I know nothing about the guts of a ‘7904 – whether the mainframe has rectifier / filter banks or not.


Good luck –



From: TekScopes@... [mailto:TekScopes@...] On Behalf Of Jim
Sent: Tuesday, December 22, 2009 5:09 AM
To: TekScopes@...
Subject: [TekScopes] Re: tek 7904A...



On Tuesday 22 December 2009 2:43:05 am d.seiter@... wrote:
> My 7904 (non-A) has no fan. The non-A's appear to have a picky power
> supply; my non-A is in tick mode(which has been resisting repair... and my
> -A is behaving nicely :-))

Does anyone have any advice on the "picky power supply" issue? My power supply
seems to be within spec. The plug-ins I'm using work fine on a 7514 and a
7704A. But on the 7904, if I try to use a full complement of four plug-ins
things usually get flaky (readout becomes garbled on some plug-ins, the 7D14
counter stops working, etc.). It works with three plug-ins, but does "tic" a
couple of times at start up.

I've been considering recapping the regulated supplies to see if that helps.


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