TS-870S CW-monitor audio mod
----- Original Message -----
Sent: Wednesday, September 11, 2002 9:31 AM
Subject: [CQ-Contest] TS-870 (S)
> I also use the TS-870 and I like it very much.
> Where can I find the "CW-monitor" mod?
> Can you help?
Unfortunately I lost the file with this mod.
But let's try to remember what is it.
Symptom: some samples of TS-870 has (but maybe your doesn't) such a symptom - CW audio monitor bacome hoarse or even like a claps in some conditions (especially with bad power supply or in portable application with battery etc.)
Cause: in CW mode final audio amplifier is swithching sinchronously with keyer manipulation. High speed keyer manipulation results in low average votage level in one of audio amplifier inputs.
Modification: you should add resistor 10k between 1 and 4 inputs of audio amplifier IC33 (LA4422) on TX-RX UNIT (X57-4620-00) (or - it is the same - in parallel with R435-4.7k). (Some guys additionally recommend to add capacitor 4700.0x25V on 14A voltage bar.)
Another way, simply cut swithching circuit in CW mode and made it as in SSB mode.