[ICOM] IC PS-35 Problem

[James T Wassell]

IC PS-35 ProblemJim,  HK1NI'm glad to hear the 1K ohm resistor "fix" worked for you. There is a limitation you should know about and tell your 
friend.  The PS-35 should be in a "no load" condition
when you first turn it on.  Otherwise, IC2 may not get 
the needed "start up" pulse voltage and R5 will fail.  I found that when I installed my PS-35 back into the IC-765 
that R5 burned out when I turned it on (disappointing failure!).
I think there is a 5-6 amp load on the powersupply
at start that is causing the problem.   Nothing else
has changed and when I replaced R5 and the circuit worked
under "no load" startup conditions, so other components
are not the problem. I have looked at circuits for similar Icom powersupplies
(PS-20 and PS-30).  the PS-30 has a diode in place of 
L4 that I may try next.  PS-20 has a time delay transistor
switch for the relay that shorts out R5, that I may try.
User manuals for the PS-20 and PS-30 explain that
the power supply should be turned on in a "no load" condition.It seems as if I can't avoid the "no load" startup condition, 
that the IC2 must be first powered up to start the oscillation
that is generated by pins 12 and 13 of IC2.  And this must
start before Q2-Q5 get full power and start to deliver power.So, the fix has it's limitations, but I'll keep looking to get 
this figured out!73,   Terry   K3JT. 
 Terry
K3JT, 5X1X, V26JT
http://www.qsl.net/k3jt