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??????
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On Monday, September 27, 2021, 8:15 AM, Aleksandar Petkovic
<vk6apk@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?
>
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