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G8MNY > TECH 05.12.24 11:30l 72 Lines 3283 Bytes #999 (0) @ WW
BID : 21239_GB7CIP
Read: GUEST
Subj: IC 735 Battery Backup Mod
Path: IW8PGT<LU4ECL<I0OJJ<GB7CIP
Sent: 241205/1002Z @:GB7CIP.#32.GBR.EURO #:21239 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Jul 22)
(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.
SYMPTOMS
I found the 12 memories can occasionally be lost, as the old memory battery was
going flat. My cure is suitable for many rigs if the battery is difficult to
change, and it can still be revived with a very small charge current!
SIMPLE CURE
Looking inside I found the battery was not completely flat, and it was a
soldered in type that can be difficult to change without removing the whole
large PCB.
D4
+5V>ÄÄ´>ĆÄÄÄæ So I looked at the circuit and found
³ a very small trickle current,
Ś-10K-æ ³ bridging around the batt steering
| | ³ diode D3, would bring back the
+ŚÄĮÄ´>ĆÄĮÄĮÄÄ>RAM battery to give a good voltage,
_³_ D3 MEMORY and give many more years of life.
Ü Also a lower battery volts is now needed
³ BT1 to corrupt RAM with 10K path there too.
ÄĮÄ
FIXING IT
Access is fairly straight forward, but a few screws!
1/ Remove power lead, remove top and bottom covers, including the 4 anti
rattle 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 and 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 and carefully
solder in (with isolated not static iron) a small 10K across it. The 10K
limits charging current to less than 100uA.
7/ Now put everything on its side, and make power safe, power up the rig and
check D3 volts. You should see +4.6V on the Ram side and an increasing
battery voltage.
8/ Reassemble and test memory stays OK. It should do a many more years if the
rig is used occasionally!
Also see tech buls "IC 735 No RF Output Fault", "IC 735 No PA Bias Fault",
"PA instability in ICOM IC735", "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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