[ICOM] power supply trouble with ICOM IC-R70 Receiver

[John Hagle]

Actually, the power supply is out of the chassis and on the bench. The 
supply chassis is clipped to the radio chassis with a short clip lead. 
The scope and meter ground are to the power supply chassis. When I 
remove the clip lead ground between the two chassis, the receiver goes 
out because the grounds are then floating.

I am going to see if I can duplicate the problem by loosening the power 
supply circuit board ground again.

Radio is working fine except for the uncertainty with the power supply 
and I need to trim the PLL since it goes out of lock at the bottom 
1.4khz of each megahertz range.

jrh


Clif Holland wrote:
> All of the reading you obtained voltage wise; where was your ground 
> connection for the meter????? Main chassis I would guess. Loos the 
> supply ground and what does that do..... Lets the meter float.. 
> Starnge readings. Same with the scope, the probe was probably grounded 
> to the chassis, not the power supply ground.
>
> Clif Holland KA5IPF
> www.avvid.com
>
>
>
>
> ----- Original Message ----- From: "John Hagle" <jhagle at madbbs.com>
> To: "ICOM Reflector" <icom at mailman.qth.net>
> Sent: Wednesday, November 01, 2006 9:43 PM
> Subject: Re: [ICOM] power supply trouble with ICOM IC-R70 Receiver
>
>
>> You may be right about that ground screw. Thanks. Someone previously 
>> bridge soldered the hexagonal standoff post where that mounting screw 
>> is. The screw was snug, not tight. Will tinker some more. Thanks.
>>
>> But I still wonder about that 60Hz ripple frequency.
>>
>> jrh
>>
>>
>> Clif Holland wrote:
>>> Look around and tighten the ground screw.  They didn't hardwire the 
>>> ground. In their infinite wisdom the ground for the power supply is 
>>> thru a screw that comes loose and causes all sorts of problems.
>>>
>>> Clif Holland KA5IPF
>>> www.avvid.com
>>>
>>>
>>>
>>>
>>> ----- Original Message ----- From: "John Hagle" <jhagle at madbbs.com>
>>> To: "ICOM Reflector" <icom at mailman.qth.net>
>>> Sent: Wednesday, November 01, 2006 9:28 PM
>>> Subject: [ICOM] power supply trouble with ICOM IC-R70 Receiver
>>>
>>>
>>>> I am having some trouble with an old Icom IC-R70 receiver. From 
>>>> time to time it develops a loud hum and the S-Meter light goes dim. 
>>>> The problem is probably in the power supply.
>>>>
>>>> The power supply is conventional, non switching. It uses a power 
>>>> transformer tapped for both 110vac and 220vac feeding a bridge 
>>>> rectifier, filter capacitor (47,000mfd) and a three transistor 
>>>> regulator circuit including what appears to be current limiting 
>>>> circuit followed by some additional RF bypass caps and a small 
>>>> electrolytic. Pretty standard stuff.
>>>>
>>>> However, the condition is intermittent. It is not sensitive to a 
>>>> bump or to thermal changes. It occurs at completely random 
>>>> intervals, hot or cold.
>>>>
>>>> At first I thought "electrolytic" but now I am not so sure. When in 
>>>> the working condition there are several volts of saw-tooth ripple 
>>>> at the output of the bridge. However, the ripple is at 60Hz rather 
>>>> than the 120Hz I would expect. Again, this is when the radio is 
>>>> working. And when working, the raw B+ measures about 15 volts.
>>>>
>>>> If a single diode in the bridge rectifier is open, then the bridge 
>>>> would function as a half wave rectifier and the ripple would be at 
>>>> the AC line frequency of 60Hz. If a second diode were to open, then 
>>>> the bridge could still function as a half wave rectifier.
>>>>
>>>> With the hum condition in the radio, the raw B+ measures only about 
>>>> 7.5 volts. And I believe that the saw tooth ripple voltage is still 
>>>> 60Hz. (I didn't get the scope probe on it in time).
>>>>
>>>> Are these bridge diode packages known to be intermittent like this 
>>>> in older Icom receivers.
>>>>
>>>> Or should I be looking elsewhere.
>>>>
>>>> thanks in advance
>>>>
>>>> de N2JH
>>>> ex AA2GV es WA2SXH
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> ----
>>>> 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/
>>>>
>>>>
>>>
>>>
>>> ----
>>> 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/
>>>
>>>
>> ----
>> 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/
>>
>>
>
>
> ----
> 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/
>
>