[TenTec] Try again, amp

[Rick - DJ0IP / NJ0IP]

John,

It could be almost anything on the control board (81426).
It controls the signals for the "VAC RELAY", "QSK BYPASS RLY", "P.O. BYPASS"
[relay] and the "INPUT RELAY".

The "VOX KEY IN" line goes through the mode switch and becomes the same
signal (in SSB) as the "KEY IN" line in CW, so there will be no difference
which switching method you use.  The problem is 99% on the control board.

One (or more) of these four signals is/are hanging.
So start by determining which one(s) is/are hanging.
That will help you determine if the problem is in one of the latches (U1 and
U2) or one of the switching transistors.

I assume when you turn everything off, then turn it back on and connect all
the cables and connectors, it comes up in BYPASS mode (so the antenna is
switched to the transceiver directly and you can hear stations in the
receiver).  Of course you should be doing the testing on a dummy load.

With the amp still in receive mode (BYPASS) and using a high impedance volt
meter or scope, measure the voltage on the three signals:
 - QSK BYPASS
 - P.O. BYPASS
 - INPUT RELAY
 - VAC RELAY
And write down the voltages.

BTW, the first 3 of these signals are also present on "J5" on the "Input
Board 81430", so it might be easier to measure there.  I don't know, I've
never seen inside a Herc2.
You can also measure the VAC RELAY signal on the "DC DISTR" board, on the
"LPF" board, and on the "VAC RELAY" board.  

WITH AS LOW OF POWER AS POSSIBLE from the transceiver, key a couple of dits
and then stop transmitting.  
I assume from what you say it hangs in TX mode after that.  The question is,
what's hanging?
OK, now measure the four signals again.
Which one has changed?
That should give you a clue which path to troubleshoot.
  - If all are hanging, it's probably U1.
  - If just P.O. BYPASS is hanging, it's probably U1 or Q9
  - If just INPUT RALAY is hanging, it's probably U2 or Q3
  - If just QSK BYPASS RLY is hanging, it's probably U2 or Q4
  - If just VAC RELAY is hanging, it's probably U2 or Q5

I think possibly the QSK BYPASS is only used in SSB mode, but I'm not sure.

Hope this helps to point you in the right direction.

GUD LUK OM!

73
Rick, DJ0IP


-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of John Farler
Sent: Wednesday, October 03, 2012 5:05 AM
To: tentec at contesting.com
Subject: [TenTec] Try again, amp

The amp put out a good clean up-to-power signal, but did not switch back to
receive.  The relay locked down in the transmit mode, and stays there as
long as the amp is turned on.

I suspect something on the control board.  The amp stayed in xmit mode even
without a control connection of either kind from the the xcvr, as long as
the power is on.

I suspect I should look in that area.  Any suggestions on what to look for?

Thanks,
73,
John, K4AVX
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