[TenTec] More details on correcting weak signal reception on TT Corsair II

[Barry N1EU]

Congrats on the repair and thanks for the update Steve!

The entire thread along with supplemental info is viewable here:
http://tentecwiki.org/doku.php?id=561lpftr

73, Barry N1EU

On Sun, Apr 2, 2017 at 9:12 AM, Steve Ireland <vk6vz at arach.net.au> wrote:

> G’day TT users
>
> After a lack of use for a few months, my TT Corsair II developed the
> classic ‘weak reception’ problem, whose fix is described by Rick VE3ORY on
> the Ten Tec Corsair wiki (Thanks, Barry N1EU) and later expanded on by
> Marco IS0KYB in his email to the TT reflector (Corsair II weak reception -
> Tues 20 December 2016).
>
> My friend ‘Dr Phil’ VK6PH, with my ‘Igor-ish’ assistance, fixed a similar
> weak signal fault yesterday and we discovered a couple of additional pieces
> of information, which may help anyone who has to fault-find/make a similar
> fix.  The main sign of this problem is if the Corsair II receiver suddenly
> goes deaf, but when you connect an antenna to the Corsair II ‘receive
> antenna’ connector and switch to receive on this antenna, the receive comes
> back to life.
>
> *This isn’t an easy fault to fix, so go slow and take plenty of pictures
> with a digital phone/camera.*  *It is not a fault to try to fix yourself
> unless you are used to making your own repairs to radios of this
> sophistication.*
>
> 1. The problem usually is a failure of components on either the LPF-TR
> board (80970) or on the SWR board (80969). The SWR board is where the
> ‘optional’ High Pass Filter (for potentially cutting out interference from
> a nearby Medium Wave transmitter is located). *The HPF is not a separate
> board but is actually a set of components that are mounted on the SWR
> board.*
>
> 2. T
> he SWR board (80969) and the LPF-TR board (80970) are mounted together
> piggy-back style behind the TT Corsair II bandswitch. As Marco IS0KYB
> describes in his email, unscrewing the back panel and slipping the
> two-board assembly board off the back off the bandswitch meant the repair
> could be made without disturbing the bandswitch wiring.  *Do not change
> the bandswitch position once you have the board assembly off the
> bandswitch.*
>
> 3. My impression is the HPF may have started out as an option on early Ten
> Tec Corsair IIs, but perhaps became standard at some time during
> manufacturing manufacturing process. It seems an awful lot of Corsair IIs
> have this option – best thing to do is to assume that yours has it.
>
> 4. The HPF inductors are resistor-body choke-type potted inductors (which
> are perhaps prone to failure from old age) rather than conventional
> inductors.  In our case, one inductor had failed without any obvious
> cause.
>
> 5. Because of the potential failure of these potted inductors and the
> difficulty of making this repair, consider removing/bypassing the HPF
> whether or not this is the source of your weak reception signal, unless you
> really do have a high power Medium Wave transmitter nearby.  This removes
> the possibility of a future failure...
>
> 6. We dealt with bypassing of the HPF without affecting the operation of
> the SWR board Q2 transistor by re-connecting the capacitor (which
> originally ran from the Q2 collector to the HPF *but is not shown on the
> schematic*) between the Q2 collector and the receive antenna input
> socket.  From memory I think the Q2 collector capacitor is actually mounted
> on the back of the SWR board and was a factory modification.
>
> See also the comment from VE3ORY:  “Trouble shooting eventually led me to
> disconnecting and bypassing the High Pass Filter and receive performance
> issue was resolved. I did this by opening the circuit at the input to the
> High Pass Filter and bypassing it with a capacitor between Q2 collector and
> the RX connector to avoid interfering with operation of Q2. It has worked
> fine ever since and no noticeable issue without the "Optional" High Pass
> Filter.”
>
>
> Vy 73
>
> Steve, VK6VZ
>
>
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