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Huntron 1005B-1S display "focus"

Hoo

Huntron 1005B-1S display "focus"
« on: October 15, 2015, 03:12:35 pm »
I have the Maint manual and have glanced at the schematic, but before I jump in, anyone recognize this problem?

When all three range buttons are deselected there is a "bent loop" where there should just be a dot.

Otherwise, the box still functions normally, except it is tracing a loop instead of a dot, making a wide trace.   So I am guessing something in the 180V power spply, perhaps as simple as C12 bad?

But perhaps it is something in the 6V section.   Any recommendations on where to start?

HTR1005B-1S  S/N 21403860

Hoo

Re: Huntron 1005B-1S display "focus"
« Reply #1 on: October 15, 2015, 03:30:59 pm »
Also, side question I saw mentioned elsewhere on the forum.   To "unfix" the polarity of the display, can I just swap the wiring to the CRT deflection to get a "normal" IV curve?

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Re: Huntron 1005B-1S display "focus"
« Reply #2 on: October 16, 2015, 07:27:53 am »
You are correct that the CRT should show a dot with all switches deselected. I would try the simple approach first. Clean the switches thoroughly with some electronics cleaner.
What do the signatures look like with a range selected?

Not sure why you would want to reverse the polarity internally. The only case where polarity is shown is with semiconductors so just reverse your leads.

Thanks.
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The most important troubleshooting tool is your eyes.

Hoo

Re: Huntron 1005B-1S display "focus"
« Reply #3 on: October 21, 2015, 02:13:51 pm »
Indeed.   The deflection supply bulk cap C12 (10uF @ 350V) was open.   Replaced with larger cap @ 450V (what was available.)   Works great.

Also, FWIW, swapped pins 1 and 4 on the CRT connector (Horiz plates +/-) and now the display shows typical I/V curve for zeners.    This is handy when you're trying to quickly identify/verify polarity of tiny smt diodes and such for installation, instead of having to reverse your thinking or probes.

Thanks for the site and the "legacy" support forum....it speaks well for your commitment to your products!

jvthorsley

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Re: Huntron 1005B-1S display "focus"
« Reply #4 on: October 22, 2015, 03:46:59 pm »
On old equipment usually always comes down to capacitors developing high ESR and failing.
« Last Edit: October 22, 2015, 03:48:42 pm by jvthorsley »