IC-735 Powering on problems

[VE2HKW]

Hello

This video outlines the basic problem: http://www.youtube.com/watch?v=CtnKM...ature=youtu.be

In a few words: The radio gets power, but it won't power on.

In Many words: When I push the power button, it looks like the radio is getting power, but not enough power. I remember reading about how sometimes a 5V regulator can go bad, but I wouldn't know where to look for the regulators. I've done some investigating: it's not the switch, and it's not the power connector on the back. I don't know what is the problem is thought. Any help - ether by pointing me to another post, or a website - will be greatly appreciated.

Harrison -- VE2HKW

[VE1DAY]

looking at the schematic the power comes off the PA unit to a 4 pin connector (that looks like an old computer drive power connector in the vicinity of the power switch). it goes from there to the display unit where the power switch is attached. After the power switch it branches off to the rest of the radio boards. So, I can tell you what connectors to check for 13.8 v on but not all of them are marked on the board. P8/j4 on the main board pin 4 should be 13.8v if you can find it. I cannot remember is the main board is the one under the PA unit or on the bottom of the radio. The speaker plugs into the main board and the ACC1/ ACC2 jacks on the rear are soldered to the other board called the PL board.
If you have 13.8v on p8/j4 then check that there is continuity from pin 5 of p8/j4 to the negative(black) power wire coming in from your supply. Obviously if you are comfortable with using your meter leads in close proximity then just check pin 4 and 5 for 13.8v directly. If you have it there, then you have a board issue... more than likely a regulator etc..If you dont have it then check the condition of the wires going to the main power switch etc.

HTH
Dave

[KO6WB]

While you're in there check the fuse F1 a 3A unit on the PA board. If that's bad you won't be able to power up.
Check the service manual; http://boxspringsonline.com/icom/212...service-manual.
Hope this helps
73
Gary

[VE2HKW]

Thanks for the help so far.

I checked the voltage at the 13.5V pin on P8/J4 and it was less then stunning... the first time I checked it it read 7V, the second after doing the other test was 3V...

The wires to the switch look okay, but I havn't taken a reading directly from the terminals on the switch.

Any other suggestions?

Thanks
VE2HKW

Edit: I looked at the fuse a small while back and it was perfect, so I know it's not the fuse. Also, I have the Wiring diagram here as well as the original owners manual. I can reference those if needed at all.

[K2WH]

How many amps is your power supply good for? Can it supply the needed current required by the radio? Is your power supply putting out the voltage required IE. 13 volts DC?

You need to confirm you are supplying the correct voltage and amperage in the first place. Check the voltage with the power supply disconnected from the radio then check it again after you connect it to the radio and then check it again after turning the radio on.

K2WH

[VE2HKW]

Okay, I was talking to a friend and he said to try and test the power switch. I thought I had already done that with an ohm meter, but it tested fine back then (the radio was deadish when I tested it) but now with a little jumper wire I got it to work, os I need a new switch. Just goes to show you "check once, wait 4 months, and test again )

As for the power supply, it's an Astron RS-20M and it's good for the radio, it's powered it since 1992, so I think it's still good. it's a great point to look at though.

Thanks for the help.

VE2HKW

[KE3WD]

If you put a 0.1uF/600V cap across the new switch, it will last almost forever.

The old one dies because there is no cap to snub the spark when the contacts are opened and eventually that spark takes its toll on the contacts as well as the heat generation from the carboned contacts working on the switch metal internals.

73

[VE1DAY]

The power switch was what I was going to suggest you check again. A high resistance was in there somewhere. Drop another one in and it should be good for another 20 years.
What you could do if you cannot locate another switch that would buy you some time is to disconnect and make safe the other 2 wires going to the switch and use those contacts instead. these 2 wires run to the extra contacts in the power plug on the rear to switch the ac for the icom supplies. So im assuming that you have a power switch on your supply.
Good luck.