Thanks to everyone for their thoughts.
Carl was right, as usual. Mine has 4 relays, 3 DIP and the vacuum. I mis
spoke when I said 3.
Mike
KK9V
On Thu, May 29, 2014 at 10:35 AM, Carl <km1h@jeremy.mv.com> 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.
>>
>
> My late 500ZC has 4, 3 DIP and the vacuum, earlier ones had 5 and I cant
> recollect seeing a 3.
>
>
>
> 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 ?
>>
>
> Nope, Ive replaced mine once and later found out it was OK after I ran a
> bit of real RF thru the RX contacts, a common fault/fix. It likely has
> more heavy contesting and DXing hours on it than most others.
>
>
>
> Anything that typically causes them to fail.
>>
>
> Wrong antenna, an open/short, or contact resistance since they werent
> meant to switch microvolt signals and didnt use a contact wiping motion.
>
>
>
> Any other thoughts as to what might be bad ?
>>
>
> The electrolytics on the QSK board plus the DIP relay at the board edge.
> Ive repaired a few that took out a diode and resistor on the same board.
>
>
> Does anybody have a schematic of the qsk board with only 3 relays ?
>>
>
> Here is the 4 relay.
> http://bama.edebris.com/manuals/ampsuply/lk450-550>
>
>
> Best place to buy a replacement vacuum relay ?
>
> Lots on Fleabay, Max Gain when he has them, etc.
>
>
> Any other mods or thoughts while I am working on it ?
>>
>
> Replace the ancient filter caps plus relay PS cap on the same board, and
> change plate choke to the big Ameritron who also has the best price for the
> HV electrolytics. I use Mouser for other parts.
> Change fixed padder cap values as needed for your 160 and 80M antennas.
>
> Carl
> KM1H
>
>
> Thanks in advance.
>>
>> --
>> Mike Stokes
>> KK9V
>> _______________________________________________
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>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>
>
--
Mike Stokes
KK9V
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