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Author Topic: FT-707 Polarity reverse  (Read 2325 times)
ZL1MHS
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Posts: 29




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« on: July 26, 2013, 03:51:32 PM »

I have a FT-707 that was working fine as a spare radio until after moving stuff around in the shack, I inadvertently connected it back up with reverse polarity after a puff of smoke and calling myself the best known idiotic names I could think of alas it was to late and the FT-707 was dead.Sad Angry
I was told by a friend that once you have done this to a FT-707 the damage caused is irreversible.
So before I take it to see if it can be repaired I was wondering if anybody out there can please advise me on this as to whether or not it will be fixable or not.
Many thanks
Kevin
ZL1MHS
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W9GB
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Posts: 2600




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« Reply #1 on: July 26, 2013, 04:18:23 PM »

Yaesu FT-707
Service and Owner Manuals at Fox-Tango / Yaesu International Users Group
http://www.foxtango.org/ft-library/FT-Library/Eighties/Eighties.htm

Yahoo Group: FT-707
http://groups.yahoo.com/group/FT-707/

AVR board is VERY TIGHT in this radio (not a novice project),
easy to accidentally shorting wires/components -- due to clearances.
To get to the AVR board out your going to have to pull out the VFO and small display board FIRST ...

C1 may be bad, RL1 could have been damaged.
A section of the schematic diagram can be found on this web site,
your other problem is PARTS.
http://hfdxer.x90x.net/ft-707_avr/ft707-02.html

Good luck with your repair project.
« Last Edit: July 26, 2013, 04:35:18 PM by W9GB » Logged
K8AXW
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Posts: 3692




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« Reply #2 on: July 26, 2013, 10:23:26 PM »

The 707 might indeed be a write-off but before I'd throw in the towel I'd obtain a complete schematic of the unit....open it up and trace the B+ lead from the outside world through the unit to see if some solid state device, either one that protected the radio or one that failed preventing the B+ from reaching the rest of the radio.

I've seen cases where a radio had a reverse biased diode protecting the B+ input and when the radio was wired up  wrong, it not only took out the protecting diode but most of the other solid state components.

You just might be lucky.  Check it out.

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W9GB
Member

Posts: 2600




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« Reply #3 on: July 27, 2013, 06:00:01 AM »

Quote from: K8AXW
I've seen cases where a radio had a reverse biased diode protecting the B+ input and when the radio was wired up  wrong, it not only took out the protecting diode but most of the other solid state components.

Takes about 5 seconds to SCROLL DOWN the OH2FFY web page on FT-707 power & AVR,
view schematic for FT-707 POWER DISTRIBUTION and answer that conjecture.
http://hfdxer.x90x.net/ft-707_avr/ft707-02.html

Many color photos by OH2FFY for the novice tech to see and compare to
Service Manual pictorials and schematic diagrams.

AVR - Automatic Voltage Regulation
A common acronym used by Japanese radio designers for DC-DC conversion and
DC voltage regulation functions in mid-1970s or later solid-state transceiver or DC power supply.
« Last Edit: July 27, 2013, 06:06:42 AM by W9GB » Logged
ZS5WC
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Posts: 410


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« Reply #4 on: July 28, 2013, 11:22:14 PM »

Hi Kevin,

I recently repaired an FT-707 that had also been reverse polarised--The power relay will not pull in on reverse polarity (Diode protected) , so the rig should be fine-BUT-the 3300 uF cap across the power terminals would be blown, and will blow the fuses in the supply line.
Replace the cap and replace fuses , should be OK. Smiley

73 de William
ZS4L
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KC4MOP
Member

Posts: 729




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« Reply #5 on: July 29, 2013, 05:19:53 PM »

Hi Kevin,

I recently repaired an FT-707 that had also been reverse polarised--The power relay will not pull in on reverse polarity (Diode protected) , so the rig should be fine-BUT-the 3300 uF cap across the power terminals would be blown, and will blow the fuses in the supply line.
Replace the cap and replace fuses , should be OK. Smiley

73 de William
ZS4L
This should hopefully let you breathe easier. It's not that bad
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ZS5WC
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Posts: 410


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« Reply #6 on: August 05, 2013, 11:45:10 PM »

Kevin, how are you getting on with this FT-707?..

73! Smiley
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