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G8MNY > TECH 11.07.24 09:22l 60 Lines 2793 Bytes #999 (0) @ WW
BID : 11439_GB7CIP
Read: GUEST
Subj: IC 735 No RF Output Fault
Path: IZ3LSV<I0OJJ<GB7CIP
Sent: 240711/0819Z @:GB7CIP.#32.GBR.EURO #:11439 [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 now have 3 of these old triple convertion HF PLL rigs, a heavily used one for
/P use, club events, & training courses etc. a spare one, and a cleaner one in
the shack.
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 and 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 and 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 had been 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 and 2 other connectors to
the upper PCB. then rotate the PA unit.
3/ Remove all the screening plate self tap screws and 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 and 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 and solder up, check the slight SO239 pin movement will
not break the new wire.
8/ Reassemble and test.
Also see tech bul "IC 735 Battery Backup Mod", "PA instability in ICOM IC735",
"IC 735 Lamps Mod", "Autocaller with old Maplin kit" & "CW/SSB Rig Frequency".
Why don't U send an interesting bul?
73 de John G8MNY @ GB7CIP
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