FT-757GX (I) Repair success story

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FT-757GX (I) Repair success story

Postby n3eg » Tue May 02, 2017 11:22 pm

Bought a non-working one on Ebay. It was poorly packed, and dropped on the SQL/NB corner in shipment. NB outer concentric shaft broken, left it fixed CCW. Otherwise, it was in bad condition overall with the silver paint on the buttons corroding green.
Previous owner said it went pop and released smoke when powered up, so the first thing I did was check voltages. All were OK, even the critical -8vdc. The memory backup battery was even still useable at 2.8 volts!
Second thing I did was to check crystals - all were OK. Still no display, so I ran through function buttons. At one point I hit the MOX button and tripped the overcurrent on my supply - the darn thing transmits! Found the carrier on my spectrum analyzer and generated back - it receives too! Still no display.
Checked the display board and glitched it to display 50.000 MHz - obviously not right. -8vdc was still there. After trying to troubleshoot the board and finding everything seeming normal, I found a "display reset" procedure where you push two rear panel buttons and power up. BAM! It came up on 7.000.0 MHz, right where I had found it transmitting. Radio is working fine, nothing touched with a soldering iron (except the power plug, which had to be reverse engineered from the radio's jack due to wrong diagrams posted on the always reliable internet) and modifying an old Fujitsu TEN microphone for the 8 pin plug.

Next thing I did was to join Fox Tango, since I now have two Yaesu radios - this one and the FT-817 (no ND.) I have to say, Yaesu receivers beat the Icom 706 II I had for IMD performance. The only thing I miss on the 757 vs the 817 is all the memories for storing bands in and "dialing off" from - example, lower end of 40 meters so with one button I could return to 7.125 after tuning up the band during a contest.

Also got a good deal on a FL-2100F with 10 meters and low voltage relay keying mods. Probably need to re-tube it because I can only get 400 watts out with full drive, and increasing loading does not increase power.
n3eg
 
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