[Test-Equipment] Hickok 539B with shorts light problem

[Kim Herron]

HI Pat!

    Don't know if this will help, but I'll pass it along anyway.  If you
put Daniel Schoo into google, you'll get to his website and in there
you'll find about 5 pages of repair and calibration info on the 539. 
It's still out there.  I was looking at it a few days ago.  I'm
guessing that you have an unresolved power supply issue and his info
does address some of those things.  Hope this helps.

> All:
>
> I have a Hickok 539B with a non-functioning shorts light.  I have a
> known "bad" tube that a BK600 and a TC162 flag as leaky that will not
> fire the bulb. Even using a simulated short using a 100K resistor at a
> socket will not fire the bulb. Fooling with the switches will not
> aggravate the lamp into firing. The switches and interior are still
> relatively clean.
>
> Here's what I've done so far:
>
> 1. tested the lamp by using a fixed series resistor and a variac, no
> problem, bulb is okay firing at about 60 volts
> 2. checked the three fixed resistors shown near the lamp in the
> schematic and tested the 250k sensitivity pot and toggle switch, all okay
> 3. checked plate supply, okay
> 4. checked screen supply, okay
> 5. general visual inspection for any cold solder joints, none found
> 6. replaced paper caps with mylar, none of the originals found leaky
> 7. none of the postage stamp caps were replaced
> 8. There were two 47 ohm 1/2 watt resistors embedded in the shorts
> switch assembly that don't show on my schematic, one was discolored,
> both were replaced
>
> The tester works but reads high due to the bias meter reading too low.
> Using a DVM to set bias gives a plausible reading.  I can measure a
> resistor across a tube socket on the gm meter but it is off about 100k.
>
> Is there anything that commonly goes bad after 50 years in this shorts
> test circuit that I have over looked? I've probably got about 20 hours
> of spare time into this thing already. I've not really been able to
> follow the schematic back to the voltage source. Perhaps someone already
> knows how to check that source.
>
> Pat
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-- 
Kim Herron
Golden Antique Radio Service
www.goldenradioservice.com
16141 24th Avenue
Coopersville, MI  49404
1-616-677-3706