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FT-902 Mods, also FT-901




 
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Author Topic: FT-902 Mods, also FT-901  (Read 11896 times)
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WA1FAF
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« on: January 21, 2010, 06:29:15 AM »

These mods were developed in the 90's by the "Timtron", WA1HLR.  I have been using my FT-902DM since using a low impedance dynamic mike and Radio Shack 5 band MONO EQ plugged into the "patch" jack on the rear with excellent results.  Here they are:

Receiver mods:

Obtain and install 6kHz crystal filter in AM filter slot.
On IF Board, PB 1704, change C431, 1uf to 10uf, C430, .002 to 470pf disc ceramic

Transmitter mods, all on PB 1705A, AF board.

C533 1uf to 10uf, 25V
C532 1uf to 10uf, 25V
C501 .01 to .001 disc ceramic
C502 1uf to 10uf, 25V
C505 22uf to 100uf 16V
C504 4.7uf to 47uf 6V
C503 1uf to 10uf, 25V
C506 .01, REMOVE
C509 1uf to 22uf 10V, (you can use C505)
C511 1uf to 10uf, 25V
C513 22uf to 220uf 10V
C518 470uf to 1000uf 10V
C515 100uf to 470uf 10V (you can use C518)

These Rice Boxes can sound terrific!  Run 15-20 watts out or drive a linear amp and you'll have a signal you can be proud of!

Mark ("The Faf")
WA1FAF
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kb3ouk
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« Reply #1 on: January 20, 2012, 08:23:23 PM »

does anyone know if the rest of the caps on those boards are electrolytics, besides the ones listed as disc ceramic? what is C501's value, is it supposed to be mf, pf, uf? and also what is C431 supposed to be? i'm guessing electrolytic, since it doesn't list it as a disc ceramic, but then what is the voltage rating supposed to be? 25 volts like the others similar to it?
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Clarke's Second Law: The only way of discovering the limits of the possible is by venturing a little past them into the impossible
Steve - K4HX
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« Reply #2 on: January 20, 2012, 10:02:42 PM »

I don't think you'll find too many 10 uF disc ceramics, so it's a safe bet that C431 is an electrolytic. But, if you look in the rig, it should be obvious.

The value of C501 is uF.

For any replacement, just match or increase the voltage rating of the part you're replacing.
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kb3ouk
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« Reply #3 on: January 20, 2012, 10:39:15 PM »

ok, that's what i thought.
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Clarke's Second Law: The only way of discovering the limits of the possible is by venturing a little past them into the impossible
kb3ouk
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« Reply #4 on: January 27, 2012, 07:09:47 PM »

ok, another question. i have all the caps i need except for C501. i don't have any .001 disc ceramics, but i did find a .0001 disc. will this make a major difference or cause any problems?
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Clarke's Second Law: The only way of discovering the limits of the possible is by venturing a little past them into the impossible
W4AAB
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« Reply #5 on: January 27, 2012, 11:35:54 PM »

.0001 uF is 100 pF, 10% of the value of the .001 uF(aka 1000 pF).
                                                                   Joe W4AAB
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kb3ouk
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« Reply #6 on: January 27, 2012, 11:57:28 PM »

ok, well now i'm all confused as to what i actually put in it. a .001 cap is coded 102. well, if i remember right, i put a 103 in, thinking that was .0001. no, a 103 is a .01, so i replaced the .01 with another .01. a 101 would've been .0001. but i've had enough of a headache trying to get all those caps shoehorned into the spaces on that board, i'm not tearing it apart again to change one cap, it sounds good enough with the rest of them changed out.
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Clarke's Second Law: The only way of discovering the limits of the possible is by venturing a little past them into the impossible
kb3ouk
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« Reply #7 on: January 28, 2012, 12:30:08 AM »

i should also add that C501 appears to be bypass to ground right at the AF input to the circuit board. so does it make a difference if i leave it as is or to get it sounding the best should i replace it with a .001? to me, changing the rest of the caps made a lot of improvement, so i wouldn't think one bypass cap could be a huge AF bottleneck? i think a have a .0001 that i could stick in there to experiment if i wanted to, but i don't feel like tearing it apart again this soon.
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Clarke's Second Law: The only way of discovering the limits of the possible is by venturing a little past them into the impossible
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