[time-nuts] HP 5065A fault

paul swed paulswedb at gmail.com
Mon Aug 20 15:19:46 EDT 2018


John
Sorry to hear of the problem. Agree with a digging in and others will give
you good advice.
However if it just comes down to the very very difficult job of digging in.
Consider floating the heater with a isolated supply and optical switch
driver. Because the lamp heater uses the same common supply you would need
to do the same to that. Though perhaps the two heater +24V supply can be
easily separated.
The transistor may be operated in the linear mode at some point that adds a
wrinkle.
But heck if your in deep trouble then anything is reasonable.
I have had to float heaters like this twice. It works. Though they were on
xtal ovens.
Same with a CRT short.
Regards
Paul
WB8TSL

On Mon, Aug 20, 2018 at 1:50 PM, John Ponsonby <jebponsonby at gmail.com>
wrote:

> My HP 5065 has developed a fault. The LAMP OVEN heater winding has
> developed an internal short to ground. It is not a dead short (about 9
> ohms) and it is intermittent, developing when the oven is hot. I shall have
> to open the RVFR to fix it. I don't know what I'll find. I have no drawings
> to guide me. So I'd welcome any advice on what to expect, what precautions
> to take and what I shall need to effect a repair.
> John Ponsonby
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