[ICOM] Icom 7800 Problem ?

[Adam Farson]

Hi Larry,

The IC-781 PSU is also switch-mode. In fact, it incorporates a shunt
regulator which causes a severe heat problem. 

The PSU was designed for the Japanese 100V mains supply. When fed from 120V
mains, the shunt-regulator dissipation increases by a whopping 44%! Over a
period of several years, this causes heat damage to the PSU regulator unit.
One way around this is to buck the mains voltage down to 110V by means of a
step-down transformer or Variac.

I had an IC-781 from 1993 to 1998. The IC-756/IC-756Pro series replaced it.
Never looked back since.

Cheers for now, 73,
Adam VA7OJ/AB4OJ

-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
Behalf Of Lawrence Young
Sent: Wednesday, May 02, 2007 18:56
To: icom at mailman.qth.net
Subject: Re: [ICOM] Icom 7800 Problem ?

Phil; Sorry to hear of your 7800 problems. As a retired RF and reliability
engineer,I would say, the only way to know the cause of your failures would
be to have the failed parts returned to their manufacturer for a failure
analysis. Anything else would be speculation. Regarding the difference
between the 781 having an analog supply and the 7800 having a switching
supply. In a well designed supply there should be no difference regarding
the supply loads. Good luck, Larry K4LXV.




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