[ICOM] R70 issue

Gary Fiber gfiber at comcast.net
Sat Oct 15 00:11:28 EDT 2016


The IC-R70 was out of production when I arrived at Icom America in 1989 
doing product support. I do not remember any VCO trimmer cap issues. 
Without looking at a schematic I could not say there are 4 different 
VCO's Generally with the IC-751 / A; R-71 series experienced VCO trimmer 
cap issues it was not the entire radio but usually a frequency range or 
two as the VCO's cover 4 distinct frequency ranges.

As other's mentioned I would look at the power supplies in the radio. 
Generally there is an 8 volt line running through most of the vintage 
radios, T8 and R8 for TX and RX. Of course the R-70 would not have a T8 
line. The 8 VDC line may also only be called that. Lots of times when 
these radio do strange things the 8VDc is in trouble,  low voltage 
usually. Also as others mentioned since the R-70 is long in the tooth 
you could have some faulty electrolytic caps through out the power 
supply or bringing a line like the 8 VDC down. So it is good to give all 
that a look.

Does the S-Meter still show signals when the fault occurs?
When it all goes out does the R-70 loose power completely or just 
signals disappear?
When the fault appears does the volume control still raise and lower the 
volume? RF Gain control still appear to be working?, usually moving that 
will raise or lower the S-Meter
What do you hear then?
Have you tried powering it from an external DC Power supply? I will have 
to down load a schematic diagram can't remember if it had an external DC 
Input.

Basic test gear is about all that is needed. Most trouble shooting at 
Icom was done with a DVM. Sure they had other test gear but the DVM 
seemed to take the first stab at the fault so I would not worry to much 
yet about your test gear. When messing with possible faulty electrolytic 
caps an ESR meter is handy. Ask around your local circle of ham radio 
friends, they are pretty common anymore and you might be able to borrow 
one if you do not have one. Maybe see if they also have a signal tracer 
or scope too. Look over the caps for leaking electrolyte or bulged ends 
but indicators of a faulty cap.

Wish I could lead you to the fault, maybe the questions I asked might 
spark something in it's operation.

Gary K8IZ

On 10/13/2016 9:37 PM, Steve Sutfin wrote:
> Hello to the list,
>  My Icom (aged) R70 receiver started having a problem after xxx years 
> of good service. When I turn it on sometimes there is no signal, just 
> the usual background noise. But after a bit it comes to life like 
> normal but the signal dies after 30 sec. to 3 minutes. The voice 
> doesn't get distorted when it quits but sounds more like wind blowing 
> across the mic. If left on it comes back and sounds like normal for a 
> bit then goes out. All voltages I've traced on the schematic are fine 
> but my test gear is basic.
> Any thoughts?
> tnx & 73,
> Steve k7dna
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