By the way - I have heard of 7 or 8 of these Centurion HV transformers blowing
in recent
years and then being rewound.
I can imagine that there have been quite a few of the transformers replaced by
Tentec also.
I wonder if their other Centurion models are just as vulnerable... you live and
learn.
73 - Bry, AF4K
On 15 Mar 2014 at 22:09, Donald, K6RV wrote:
> 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
> >
> >
> >
> >
> > -----
> > No virus found in this message.
> > Checked by AVG - www.avg.com
> > Version: 2014.0.4336 / Virus Database: 3722/7200 - Release Date: 03/15/14
> >
> >
> >
>
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