[ICOM] Problem with IC-751A

[Jaime Gomez]

Hi Gary, thank you for your prompt answer. I will check the 8 VDC power
supply, and to the ram card sockets solders in the digital card, the
problem is that the VFO is not reeurning to its default setting but to
other band, so it is not possible to operate in split mode,

On Sat, Mar 23, 2013 at 4:22 PM, Gary Fiber <gfiber at comcast.net> wrote:

> Jamie,
>
> Remember the IC-751A will not remember that last frequency you had in the
> VFO as it does not have band stacking registers like the newer Icom's have.
> So its quite normal with you change band for the VFO to return to the
> default setting for that band. Its been a long time since I've been in
> front of a 751A so I can't say changing from VFO A to B will exhibit what
> you are seeing. I will say its very doubtful the lithium battery has
> anything to do with this issue. In my 11 years at Icom, I think I only saw
> less than a dozen actual battery issues. The majority were from operators
> trying to prevent failure by changing out the battery and caused their own
> troubles. We did see cracked solder joints around the sockets the ram card
> used to connect to radio so if you pull out the ram unit have a close look
> at the solder joints on that card. BUT don't remove or short out the
> battery supply on the card.
>
> NOW what I suspect the trouble might be is the 8 volt DC supply. Under the
> bottom cover mounted on the side of the radio where the PS-35 power supply
> slips in is a small PC card with a couple of transistors and a few
> resistors mounted on it. This card supplies 8 VDC for most all of the
> radio. One of the resistors, R1 as I remember liked to change value over
> the years and doing a voltage measurement you will find something other
> than 8 volts. I seem to remember that resistor value being 4.7 ohms and
> renewing it would fix many strange troubles on this radio. Have a good look
> at that circuit board and do check the output voltage.
>
> I suspect it also could be some sort of logic issue but I would not go
> looking for that until you know for sure the 8 volts is correct.
>
> Hopefully some of this helps.
>
> Gary K8IZ
>
>
> On 03/23/2013 08:47 AM, Jaime Gomez wrote:
>
>> Hi fellow friends,
>> I have a friend's 751A wich present the following problem:
>> Anytime I change from A to B VFO or reverse, the VFO changes band, for
>> example if I am in 24.890 in both VFOs and I change from A to B or B to A
>> the frequency in the VFO in use will jump to 20.000, if I am in 1830 and
>> change VFO the frequency will jump to 0.809 or something like that, if I
>> operate on just one VFO A or B the radio works fine, any hint?
>> The RAM card has a second battery added and the voltage is 3.02 volts, the
>> radio was working fine, this happened suddenly.
>>
>> Apprecaite any help,
>>
>>
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-- 
73,
Jim, HK1N

President DXARC - DX Colombia Amateur Radio Club
*Malpe**lo Isl. HK0TU 1990 & H**K0NA 2012 Team Member/ hk0na.com *
Araucaria DX Group