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AR3000 FM question ANYONE FEEL FREE TO HELP!!!

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mancow

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Here's my issue...

I bought a used non working AR3000 (not A model). Everything works except the audio is extremely distorted in FM and WFM. I first thought it was off frequency above HF but in AM mode I clearly received milair stuff on 327 Mhz.

When tuned to the 100Mhz broadcast FM band it plays a sound that's similar to fast forwarding a cassette tape. In narrow FM on something like the weather channel it is just all a distorted mush. When I switch to AM I can hear the WX channel try to come in (obvious distortion from AM) and the signal seems to be on frequency.


I'm thinking that this may be something to do with a filter. There is a small silver crystal looking filter marked X3 near the wide FM 3 pole filter. Is it possible that there could be one single filter somewhere that is damaged?

I believe this unit was dropped in the past because the knobs were slightly bent.


Any ideas would be appreciated. A legible schematic would be a blessing...... ;)
 

wa8vzq

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When I worked in a two-way radio shop back in the mid 70's we replaced a lot of crystal filters in handheld radio's that were dropped. It's been a bit to long to remember all of the symptoms but I'd venture to say that most of them were just plain dead on receive. If a filter was made up of individual crystals as they were in the 50's & 60's, I'd guess that you could be correct. But by the 70's, most of the filters in handhelds were monolithic crystal filters. I'd guess that most units today most likely use monolithic filters as well.

AM mode may use an entirely different IF than the FM mode. If that is the case then your off frequency theory may still be correct. Could be that the xtal oscillator that injects for that conversion has shifted freq.

Dan
 

mancow

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If anyone cares...
It ended up being a fractured chip capacitor near the FM demod chip (MC3357). It was killing the audio chain right from the discriminator.

I guess those parts tend to fracture due to age and thermal and mechanical stresses.


BTW, does anyone know the best way to calibrate the receiver tuning? It was off by about 7 khz due to my dinking around with the VCO PLL adjustment in a desperate attempt to narrow things down. I think I have it pulled back in as closely as I can by ear when tuning in WWV and various narrow FM frequencies.

I'm looking for an idea of what to do to try to get the most accurate read of where the tuner sits.
 

timmer

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I have had a aor3000a for several years. It has always been a little off on the tuning in the shortwave band. For example, 11.176 is actually 11.1777.3 on mine. I don't use it for shortwave only once in a great while so I'm not too worried about it. I would like to fix the volume switch, though. I has a short of some kind in it.
 

mancow

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The VCO adjustment is right under the top cover and is labeled PLL ADJ.

All you need is a plastic tuning stick and a steady hand. I calibrated mine on SSB to one of the 11.175 USB Airforce transmissions. It's as simple as listening and turning the tuner.
 

Rui

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same problem with my ar3000

TO Mancow and all you guys,

I have the same problem with my ar 3000 as mancow did, my NFM on 106mhz it sound "mushy" or "fuzzy" can any one tell me where on the pc board is the (mc3357)... and by change it did it work?

also if I may did any one try to connect your your ar3000 to your pc/laptop and what software did you guys used and how is it done?

Thank a lot

Rui
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