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G8MNY > TECH 15.01.19 11:42l 67 Lines 2822 Bytes #999 (0) @ WW
BID : 54598_GB7CIP
Read: GUEST
Subj: IC 735 Battery Backup Mod
Path: IW8PGT<IR2UBX<F1OYP<F1OYP<JH4XSY<N3HYM<GB7YEW<GB7CIP
Sent: 190115/1026Z @:GB7CIP.#32.GBR.EURO #:54598 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (New Jan 19)
(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 clean one in the shack.
SYMPTOMS
I found the 12 memories can occasionally be lost, as the old memory battery was
going flat.
SIMPLE CURE
Looking inside I found the battery was not completely flat, but a soldered in
difficult to change type.
D4
+5V>ÄÄ´>ĆÄÄÄæ So I looked at the circuit
³ & found a very small
Ś-10K-æ ³ trickle current, bridging around
| | ³ the battery steering diode D3,
+ŚÄĮÄ´>ĆÄĮÄĮÄÄ>RAM would bring back the battery to a
_³_ D3 MEMORY good voltage, & give many
Ü more years of life.
_³_BT1
FIXING IT
Access is fairly straight forward, but a few screws!
1/ Remove power lead, remove top, & bottom covers, including the anti rattle 4
screws around the LS.
2/ Unscrew the 4 screws for PA unit, remove external Phono Rx patch lead,
release the LS lead, RF drive lead from underside PCB & 2 other connectors
to the upper PCB. then rotate the PA unit.
3/ Look at the top PCB & locate the Disk battery BT1 & nearby diodes D3 & D4.
4/ Measure the voltage on BT1 against earth. You should see 3.7V on the +lead.
If you do a poor battery is not the fault!
5/ Check that D3 has the same battery voltage one side & 0.3V less on the Ram
side.
6/ To apply the charging modification, tin both ends of D3 & carefully solder
in a small 10K across it. The 10K limits charging current to just a few uA.
7/ Now put everything on its side, & made power safe, power up the rig & check
D3 volts. You should see 4.5V on the Ram side & an increasing battery
voltage.
8/ Reassemble & test memory stays OK for a few more years if the rig is used
occasionally!
Also see tech buls "IC 735 No RF Output Fault", "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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