[ICOM] Ailing IC-745 - any thoughts?

[Richard Peterson]

Well, Gary. We came close, but no cigar. The resistor (R1) was black from 
heat, but measured about 6 ohms. Voltage from the board was about 8.4 volts, 
on two instruments that were in agreement. I did replace the resistor -- I 
admit I actually had to parallel two ten-ohm units, but I still ended up 
with about 8.4 volts and a radio that still won't behave. I doubt that it is 
critical that the voltage be 8. And soo, I will keep studying this critter. 
I thank you a very great deal for your advice and help thus far!

Richard


>From: "Gary P. Fiber" <gfiber at clearwire.net>
>Reply-To: ICOM Reflector <icom at mailman.qth.net>
>To: ICOM Reflector <icom at mailman.qth.net>
>Subject: Re: [ICOM] Ailing IC-745 - any thoughts?
>Date: Fri, 15 Jun 2007 10:55:15 -0700
>
>Richard,
>
>I am sure the print of the REG UNIT appears on the print. I seem to 
>remember its names as I wrote in caps too. Probably on the logic board side 
>of the print.
>Generally Icom used to outline small boards like that in a dashed square. 
>Most of the time only that resistor goes bad. Seems to me its something 
>like 4.8 ohms but do read the print when you find it there. I certainly 
>would up the wattage on it to a 1/4 or 1/2 watt.. I think its an 1/8 watt 
>now. The REG UNIT outputs +8 VDC. I don't remember any other odd voltages 
>coming from it.
>
>Gary K8IZ
>
>Richard Peterson wrote:
>>Gary, K8IZ, suggested I take a look at the regulator (especially R1) -- 
>>and I have had just done so. R1 is cooked - completely carbonized.
>>
>>I have not yet checked the regulated voltage just for the heck of it, 
>>primarily because I cannot find the fool little regulator board in any of 
>>the schematics. I have found the parts list, but I have spent a good, 
>>honest hour trying to find that little board schematic, and I give up.
>>
>>Does anybody know where that regualtor schematic it is hiden in the shop 
>>manual? Thanks.
>>
>>Richard
>>WB5NEN
>>
>>
>>>From: "Gary P. Fiber" <gfiber at clearwire.net>
>>>Reply-To: ICOM Reflector <icom at mailman.qth.net>
>>>To: ICOM Reflector <icom at mailman.qth.net>
>>>Subject: Re: [ICOM] Ailing IC-745 - any thoughts?
>>>Date: Tue, 12 Jun 2007 07:52:46 -0700
>>>
>>>Richard,
>>>
>>>When ever the IC-745 does strange things check the +8 volt regulator 
>>>generally its at fault. This regulator is located on a small circuit card 
>>>attached to the side in the bottom of the radio. Its quite small about 1" 
>>>by 1" as I remember. Going from my rusty memory R1 on that card likes to 
>>>change value a lot. Its 1/8 watt as I remember replace it with a higher 
>>>wattage resistor. I do not believe it was designed as a resistive fuse as 
>>>they almost never open up. Another problem could be a PA oscillation or 
>>>an RF unit board problem. Sometimes a transistor like to go into 
>>>oscillation on the RF unit and will cause this, generally its involved in 
>>>the receive on the RF unit as I remeber.
>>>
>>>A low +8 volts will make the logic do lots of strange things. I once has 
>>>a caller who told me the radio would only transmit in the memory channels 
>>>one and two even though all of the memories were programmed correctly, it 
>>>was the +8 volts DC supply at fault. I doubt seriously it has anything to 
>>>do with the ram card.
>>>
>>>Gary K8IZ
>>
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>>----
>>Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
>>Icom Users Net: Sundays, 1700Z, 14.316 MHz
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>>
>>.
>>
>
>----
>Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
>Icom Users Net: Sundays, 1700Z, 14.316 MHz
>Icom FAQ: http://www.qsl.net/icom/

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