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

[Steve Ireland]

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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