Bry,
You definitely do have a blown QSK board. Those are the same symptoms I
had - and if you re-read the email of mine below, it gives you all the
info on how to fix the board. That board is very sensitive to any
shorts, spikes or surges. Once I repaired my board, all was well, and
has been ever since. I was just lucky I did not have a transformer problem!
Good luck !
Donald, K6RV
On 3/15/2014 9:48 PM, bcarling@cfl.rr.com wrote:
Interesting developments.
I have a newly rewound HV power transformer installed in my Tentec 422.
It appears to be working. No more blowing primary fuses and I now see the 3000V
or so that I expect on the Ep metering. However the switchover circuits are now
misbehaving.
If anyone has experience with the QSK board please comment - here is what
happens:
When I turn on the amplifier, the OPERATE and TRANSMIT LEDs are illuminated.
The Standby LED is not illuminated. The tubes light up.
If I engage the microswitch on the side of the AC / Relay board then I hear
relays kick in and a small amount if plate current follows. Approx. 100 mA as I
remember.
On checking around inside the amp I find that U2 NAND gate on the QSK board is
not operating correctly. PINS 11, 12 and 13 are all HIGH - around 12V or so.
Power appears to be correct with Pin 7 at 0V and Pin 14 at +13V.
The other NAND outputs of U2 are:
Pin 3 = 14v
Pin 4 = 0.22v
Pin 10 = 14v
Can anyone tell me why U2 would act this way and fail to follow the NAND logic?
Any idea what is going on in my 422 to make it misbehave this way?
Best regards - Brian Carling, AF4K
>From earlier:
It appears after reviewing my QSK board problem and the blown fuses in my Centurion, that
I mis-wrote what happened. I indeed had the same symptoms you had: Blown fuses for no
apparent reason. In my case the QSK board was blown, but in talking to Ten-Tec service
yesterday, they said the sequence happened like this: There was a high voltage short from
one of the 3-500Z tube plates to the top of the cabinet, causing the fuses to blow. Guess
when I had replaced the tubes, one of the plate straps was too close to the top of the
case and arced over. The blowing of the fuses created a surge, or a spike, which blew out
the QSK board. The QSK board is very sensitive to the fuses being blown, for whatever
reason. You may find, that the QSK board is blown in addition to the transformer being
shorted. The symptom will be that the standby/operate switch does not work as it should,
and the transmit light will be constantly on. If that is the case, then you can get the
"kit" to rebuild t
he QSK board, or send the board to Ten-Tec for them to re-build, or have them send you a
new QSK board (Cost = $97), and/or the "kit" to rebuild your old board and have
as a spare. That is what I did. The Kit consists of 2 IC's and 5 Transistors, and cost
about $20, as I remember. I know you are concerned about putting so much money into the
amp., but, in my view, it is both necessary, and worth it, especially since you already
will have the big bucks invested in the re-wound transformer.
Again, Bry, good luck !
73, Donald K6RV
Message: 14 Date: Tue, 4 Feb 2014 06:18:44 -0800 From: Bry Carling <bcarling@cfl.rr.com> To: Discussion of
Ten-Tec Equipment <tentec@contesting.com> Cc: "tentec@contesting.com"
<tentec@contesting.com> Subject: Re: [TenTec] Centurion Amp. Problem Message-ID:
<42FCECBC-F96D-40EC-ACBB-A21415410F44@cfl.rr.com> Content-Type: text/plain; charset=us-ascii Thank you so
much. They never brought up that possibility during my calls to Tentec while troubleshooting. However the
previous owner did mention to me that the QSK board had already been replaced. This amp is trying my patience.
It's not just the money but the time. If I end up replacing the QSK board too then I will have enough into it to
have bought a nicer amplifier. It's disappointing to think a QSK board could cause main fuses to blow. I will try
to learn how to troubleshoot that section while my transformer is away being rewound. Thank you so much for the
insight about the QSK circuit. Bry AF4K
Best regards - Bry Carling
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