[Amps] LK-500 ZB problem

[MU 4CX250B]

Vic is correct that most vacuum relay problems result from hot
switching. You can often repair vacuum relays whose contacts have been
welded shut by holding a magnet against the body of the relay.
Surprisingly, after the relay contacts have been freed up by the
magnet, the relays are usually quite reliable.
73,
Jim w8zr

Sent from my iPad

> On May 28, 2014, at 10:09 PM, Vic Rosenthal K2VCO <k2vco.vic at gmail.com> wrote:
>
> Mike,
>
> I can't answer most of your questions, but in general the most likely cause of vacuum relay failure is hot-switching. This could be due to the design of the amplifier, or the transceiver used to drive it.
>
> K4MGS (Max Gain Systems) <http://www.mgs4u.com/index.html> often has suitable vacuum relays at reasonable prices.
>
>> On 5/28/2014 6:47 PM, mike stokes wrote:
>> I bought a used Amp supply LK-500ZB.  Met the ham on his way to Dayton so I
>> wasn't able to check it out beforehand.   So of course it has a problem.
>>
>>
>> This amp has the QSK board with a qsk switch on the back.  All the
>> schematics I have seen have 5 relays on the qsk board  while this one only
>> has 3 relays.
>>
>> There is no continuity from the input to the output when powered off.
>> Therefore no receive signal passes trough. Also the transmitter goes to
>> high swr.  I know at a minimum that the  vacuum relay is bad.
>>
>> I have the following questions:
>>
>> Are the vacuum relays high failure ?
>> Anything that typically causes them to fail.
>> Any other thoughts as to what might be bad ?
>> Does anybody have a schematic of the qsk board with only 3 relays ?
>> Best place to buy a replacement vacuum relay ?
>> Any other mods or thoughts while I am working on it ?
>>
>> Thanks in advance.
>> Mike Stokes
>> KK9V
>
> --
> 73,
>
> Vic, K2VCO
> Fresno CA
> http://www.qsl.net/k2vco/
>
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