[Boatanchors] LK-500ZC Amplifier Help

[KA2PTE]

Yes the owner manual describes that board as I guess filament Inrush 
protection on the last page:
http://www.radiomanual.info/schemi/ACC_PA/Amp_Supply_LK-400_LK-500_series_user_1988.pdf

Apparently the relay didnt release. Could be the capacitor, or the resistor 
just got tired and gave out.

If its a DC relay, usually you see snubber diodes on the power coil, they 
are suppose to absorb counter EMF that
can damage or degrade whatever they are using to power the relay,usually
a transistor of some sort. Hard to say whats going on with this one tho.


--
Steve Hearns [ KA2PTE ]



----- Original Message ----- 
From: "Rob Atkinson" <ranchorobbo at gmail.com>
To: "Mark K3MSB" <mark.k3msb at gmail.com>
Cc: "Boatanchors List" <boatanchors at mailman.qth.net>
Sent: Saturday, May 07, 2022 4:19 PM
Subject: Re: [Boatanchors] LK-500ZC Amplifier Help


> It sounds like the blown resistor is an in-rush current limiting
> resistor.  The 2200 mfd cap probably has to do with a time delay.
> This is just a guess based on what you have posted.  The resistor is
> supposed to only be in use for a second at most.  When in-rush
> resistors burn up it's because they stay in series with the primary AC
> to the high voltage supply transformer.  A long tune up with the amp
> will pull too much current through that resistor and it will fry.  The
> relay isn't taking the resistor out of the circuit.  Something is
> wrong with the time constant circuitry, i.e. that 2200 µF cap or
> something else.  Look to see if the top of the cap is bulging out.  If
> the board isn't complex you can shotgun everything out that's
> associated with the relay coil and see what happens.  First replace
> the 20 ohm resistor and fire up the amp and see what the relay does.
> The resistor won't fry if the amp is unkeyed.
>
> The other use of a resistor like that is as a glitch where it's in
> series with the h.v. to the plate choke, but it doesn't sound like
> that's what it's doing.
>
> 73
>
> Rob
> K5UJ
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