[Amps] Alpha 91b anomaly

[Alek Petkovic]

Sadly, not much that will help.

Steve, VK6VZ has a 91B that burnt out the transformer. He has a new 
transformer but I'm not sure that he has installed it yet.

I thought that he may be able to follow the record of your investigation 
and either verify or offer a different result.

I'm pretty certain he is a subscriber to this list.

73, Alek.

On 27/09/2021 8:45 pm, gudguyham wrote:
> Alek tell me more?  What do you know? Please??????
>
>
> Sent from the all new AOL app for iOS 
> <https://apps.apple.com/us/app/aol-news-email-weather-video/id646100661>
>
> On Monday, September 27, 2021, 8:15 AM, Aleksandar Petkovic 
> <vk6apk at bigpond.com> wrote:
>
>     Steve, VK6VZ. Are you reading this?
>
>     73, Alek, VK6APK
>
>     On 27/09/2021 7:34 pm, gudguyham via Amps wrote:
>     > Hey guys, hope everyone is staying safe these days.  We’ll just
>     as you thought you’ve seen it all something weird comes along.
>      I’m working on a 91b that belongs to an ARRL director.  He bought
>     it recently from a ham that was liquidating an estate of an SK.
>      The seller doesn’t know anything about the history of the amp and
>     the guy that does is SK so I guess it ends there.  Well anyway the
>     amp comes to me with the problem “ it won’t turn on”.  I won’t
>     bore you with the step by step troubleshooting process but if you
>     look at the schematic, the start up process is a major series of
>     logic circuits to get the damn thing to turn on.  I fully checked
>     it all out and suddenly I discovered a couple wires going off the
>     schematic diagram and over to another diagram of the screen board.
>      When I followed those wires on the schematic I see a closed loop
>     going through the contacts on K1 on the screen board.  If connects
>     via J4.  I pulled the connector off J4 and I looked on pins 1 and
>     2 for a 15 ohm reading which would confirm a closed loop through
>     K1 common and NC contacts.  This loop completes the logic circuit
>     that latches the contractor relay.  K1 energizes in a major Plate
>     current fault and opens the contractor and kicks the amp off line.
>      As you’ll notice on the schematic the K1 loop is closed when the
>     amp is de-energized and only opens in a fault.  Well when I tested
>     for 15 ohms on pins 1 and 2 I read open.  Well ah ha that explains
>     why the amp won’t turn on.  It wasn’t hard to figure there’s
>     something open in that loop.  There’s only a 15 ohm resistor and a
>     set of relay contacts.  What I discovered is nothing short of
>     incredible.  The 15 ohm resistor was not open and the relay
>     contacts were not welded closed.  The problem is that the 15 ohm
>     resistor which is traced over to the NC contact of the relay on
>     the schematic is actually traced over to the NO contact.
>      Subsequently the loop is open and not closed with the relay not
>     energized.  I ohmed out the relay contacts and sure enough the
>     relay is fine and it ohms out according to the cut sheet.  I
>     checked the part number on the relay with the parts list and it
>     agrees.  The trace on the PC board connects to the wrong terminal
>     on the relay.  You can see through the relay cover and tell that
>     the contacts are not welded.  The schematic agrees with the relay
>     logic, but the PC board simply had the trace misplaced.   That
>     said, this amp could have never worked as is.  What’s going on
>     here?  Anybody?
>     >
>     >
>     > Sent from the all new AOL app for iOS
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