[ICOM] IC PS-35 Problem

[James T Wassell]

Jim, HK1NI measured the voltage across the neon lamp in circuit at 63 VDC.  
It looks like R3 and R4 serve as voltage divider and current limit resistance.I checked the old neon lamp using regular 110 VAC house voltage 
(with fuses of course) and the current limit resistor was 33K ohm 
and also tried a 100K ohm resistor.   I think it would be a challenge to make a circuit using LED opto-isolator
when the control voltage is 63VDC.  I found a voltage chart in the 
IC765 service manual that shows +140 VCD on the "hot" or plus (+) side of D1 and
-140VDC on the minus (-) side of D1.(http://www.radioamateur.eu/schemi/IC765_serv_IW1CKR.pdf)I reassembled my PS-35 last evening with the 1k ohm resistor in place of 
the LDR and a working neon lamp on the other side of IC1.  So far, it 
continues to work OK.   Let me know if you design a circuit or find some other solution. 
It seems there should be another easier way to "protect" Q1 from 
a spike or possible damage from voltage coming through D2.at one point, I thought I would need to replace IC2 upc1042c chip, but 
searching on the internet, I had no luck finding it.  Usual suppliers don't have
any substitute, so I guess it's not available.  If that IC2 fails, I 
think redesign and a new modern circuit would be the only solution. So, if you know of a way to "protect" IC2, that would probably be a 
good idea, considering it's about irreplaceable. Let me know what happends with your repair.73,  Terry   K3JT