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Yes the U21 on the A4 card,
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The A7 card cane be the cause of the filters not working correctly, go to CW and vary the frequency up and down and check that it is smooth in both directions.
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Gary ---------- Original Message ---------- From: "thoyer via groups.io" <thoyer1@...> To: <[email protected]> Subject: Re: [RacalRadio] RA6790 Bad Filters? Date: Sat, 28 Dec 2024 21:05:55 -0500 Thanks Gary, ? Is the 10v adjustment you reference the -10v for the DAC (U21)? If so it is -10V. ? Tom ? From: [email protected] <[email protected]> On Behalf Of gewingerd@... via groups.io ? You can force the filters with the attached file, the A2 is +2 to -4 DB of gain, the A3 is +55 DB of Gain and the A4 is about +60?DB of gain, the 10.00 Volt adjustment on the A4 card is critical for the BITE to run the filters. ? Gary After changing out several IC¡¯s on A4, A6 and A9 and replacing the EPROM sockets, that were corroded by a bad battery, I now have my 6790 up and running. Signal levels seem low though and running the BITE I get errors 33 thru 37 ¨C bad filters in slots 3 thru 7. I bench tested the filters using my sig gen and spectrum analyzer - I know the impedances don¡¯t match but this was just to see if they passed any signal. They each seem to have ¡°reasonable¡± response curves and all seem to have the similar peak amplitudes. The LSB and USB filters pass BITE and also tested ok with similar levels through them in my crude setup. ? My question is, I¡¯m wondering if the test level is possibly low (similar to the received signal level being low) and causing these indicated failures. I¡¯m going through the schematics looking for how the test signal is generated but could maybe use some guidance by those that know these receivers better then I. ? Thoughts? ? Tom W3TA ?
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