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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