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Kenwood TS450-TS690 Micro-input RFI modification [message #308] Tue, 18 January 2011 03:50 Go to next message
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Registered: December 2004
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By Pedro M.J. Wyns, RF- and biomedical-engineer.

After buying a ts690 I had considerable trouble with the vox circuitry.
The vox gain was always too high due to an excessive feedback resistance in the vox amplifier. Apparently a PCB-mounting failure as the schematic carried the right value. After correcting this problem I still had RF problems with nearby antennas, blocking the transmitter in TX.

Lack of decent RF-filtering on the micro-input circuitry.

Adding ferromagnetic cores and adjusting the rc-filters on the IF-board.

Action: Remove the connectors on the right hand side of the IF board (underside transceiver front towards you). Unscrew the board and fold over to the left. Add 22nF parallel to R282 1k on t he micro entry close to Connector 6. Add 1nF parallel to C177 close to the IC-15 input. Add 1nF parallel to C217 close to the vox amplifier.
Remove the micro in and ground from the number 6 connector. Feed the white micro wire through a two hole ferrite core. Feed the inner conductor through a small ferrite core as well Reconnect...

If you might be using an MFJ voice keyer, disconnect the junky-unshielded micro cable and replace by high quality twin balanced micro cable. Only use PTT, Mic and GND.

This concludes the mod. Don't even think of doing this without the service manual and some smd-practice.

Good Luck

Pedro M.J. Wyns Pedro.Wyns@emmaus.be Moutstraat 7 B-2220 Hallaar Belgium-Europe Fax +32 15 303115

[Updated on: Tue, 18 January 2011 03:52]

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icon14.gif  Re: Kenwood TS450-TS690 Micro-input RFI modification [message #1359 is a reply to message #308] Tue, 15 May 2012 07:33 Go to previous message
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