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G8MNY  > TECHNI   10.10.21 10:00l 58 Lines 2734 Bytes #999 (0) @ WW
BID : 49102_GB7CIP
Read: GUEST
Subj: IC 735 No RF Output Fault
Path: PI8DRE<PI8CDR<DB0RES<DB0ERF<DK0WUE<GB7CIP
Sent: 211010/0754Z @:GB7CIP.#32.GBR.EURO #:49102 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                               (Update Jan 20)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
 ________________________________________________________
³         ŚÄÄÄÄÄÄÄÄæ ŚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄæ  ==  ==  == ³
³ ßßßß == ³  \     ³ ³ Rx 14.273.5 vfo A 12³    _    _   ³
³ /~\     ĄÄÄÄÄÄÄÄÄŁ ĄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄŁ   (_)  (_)  ³
³ \_/                          ____  IC-735              ³
³      ßßß ~~~~~~""""""~~~   /'    `\    ßßß   /"~"\  [] ³
³  0   ÜÜÜ                  |(~)     |   ÜÜÜ  |     |    ³
³           Ž Ž Ž Ž Ž Ž    ³  ~       ³        \._./  [] ³
³ /~~\ ßßß  Ž Ž Ž Ž Ž Ž     |        |   ßßß  ==  ==  == ³
³ \__/ ÜÜÜ  # # # # # #  []  \.____./    ÜÜÜ  [___] [___]³
ĄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄŁ
I have 2 of these old rigs, a heavily used one for /P use, club events &
training courses etc. & a cleaner one in the shack. I've been looking into a
problem with my older well used IC735. It developed this no O/P fault while in
use on a /P demo HF station, so I had to go back home & get the shack one to
continue!

SYMPTOMS
Indicating clues to this fault's whereabouts, were the rig's O/P SWR meter
showing power & infinite SWR (internal protection SWR/over Current ALC circuits
cut the power back to a safe level), but external kit to rig showed no power!

Initially it looked like it was something to do with the rig's rear Rx phono
patch lead, as it came & went with any movement in that area. But it turned out
to be the nearby SO239, where the centre pin is allowed to float slightly to
make good connections. The thin hard wire used in the PA box to the filter PCB
had eventually fractured due to this small movement.

FIXING IT
Access is fairly straight forward, but lots of screws!
 1/ Remove power lead, remove top cover including the 4 LS anti rattle screws.
 2/ Unscrew the 4 screws for PA unit, remove external Phono Rx patch lead,
    release LS lead, RF drive lead from underside PCB & 2 other connectors to
    the upper PCB. then rotate the PA unit.
 3/ Remove all the screening plate screws & lift it.
 4/ Inspect the aerial socket. If broken as mine was or loose in PCB continue,
    or go to 8/.
 5/ Remove the filter PCB (loads more screws) unsolder Rx phono wire & earth.
 6/ Replace the hard wire link with fine flexible multi-strand wire. (I kept
    the original wire's insulation tube)
 7/ Put back the PCB & solder up, check the slight SO239 pin movement will not
    break the new wire.
 8/ Reassemble & test.


Also see tech bul "IC 735 Battery Backup Mod", "PA instability in ICOM IC735" &
"Autocaller with old Maplin kit"


Why don't U send an interesting bul?

73 de John G8MNY @ GB7CIP


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