ICOM 751 (not A) - UK Vintage Radio Repair and Restoration Discussion Forum

thx1138 · 28th Jun 2014, 1:40 pm

Hi,
I took the risk of buying a dead on arrival Icom and luckily apart from the known EPROM PCB issue which I had prepared a new one, the main PSU inside is dead.
I fired up the radio from my ext 12V 20A psu and all modes and tx are fine, so all good luckily.

So, can anyone point me in direction of help regarding fixing this switchmode power supply. I note there's 2 680uF 200V caps and a few other obvious things but any further advice would be greatly appreciated.

Alternative is to try to find something pre built but at 20A max, I assume that would be rather expensive?
73s OM-EI8FIB

Radio Wrangler · 28th Jun 2014, 3:17 pm

I fixed an IC761 switch mode PSU some 25 years ago. The owner had imported it to the UK via Australia from the US.

Someone had tried to convert the PSU from 110v to 240v. There are some obvious links on the PCB, but there was another link UNDERNEATH the bridge rectifier. They had plugged it in and destroyed the main switch transistors which had destroyed the control chip.

The control chips have been obsolete for 20 years.

I think the Icom switch mode power supplies of that era were all similar.

David

28th Jun 2014, 1:40 pm	#1
thx1138 Tetrode Join Date: May 2007 Location: Bratislava, Slovakia Posts: 65	ICOM 751 (not A) Hi, I took the risk of buying a dead on arrival Icom and luckily apart from the known EPROM PCB issue which I had prepared a new one, the main PSU inside is dead. I fired up the radio from my ext 12V 20A psu and all modes and tx are fine, so all good luckily. So, can anyone point me in direction of help regarding fixing this switchmode power supply. I note there's 2 680uF 200V caps and a few other obvious things but any further advice would be greatly appreciated. Alternative is to try to find something pre built but at 20A max, I assume that would be rather expensive? 73s OM-EI8FIB

28th Jun 2014, 3:17 pm	#2
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,902	Re: ICOM 751 (not A) I fixed an IC761 switch mode PSU some 25 years ago. The owner had imported it to the UK via Australia from the US. Someone had tried to convert the PSU from 110v to 240v. There are some obvious links on the PCB, but there was another link UNDERNEATH the bridge rectifier. They had plugged it in and destroyed the main switch transistors which had destroyed the control chip. The control chips have been obsolete for 20 years. I think the Icom switch mode power supplies of that era were all similar. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done