I still need to check the 3rd LO injection frequency and I do have to adjust
the LSB / USB BFO injection frequencies.
It appears that the main board for this unit is underneath the convertor /
regulator assembly.
The service manual is not clear on how to dissamble the unit. Can anybody
give me any tips on how to get this thing apart? Do the front and rear
panels need to be removed in order to do this?
Pete
"Pete KE9OA" wrote in message
...
I did check the varactor diode voltage and it checked ok..........I wanted
to make sure that the thermistor didn't open up.
Thank you also for your tip, Bob.
The problem did turn out to be the crystal........apparently, some of the
metal from the plates that hold the quartz element itself migrated to the
element, increasing its mass.
It's funny..........on Icom's website they mention that this is an ongoing
problem with the R7000. One would think that they would address this
problem in later iterations.
I did repair the unit. First of all, I replaced that cheap plastic trimmer
with a good microwave unit (Ceratrim). Next, I removed that 1pF shunt
capacitor that was in parallel with the old cap. As it stands right now, I
can tune the 2nd LO up to 1.5kHz above the desired frequency. Not as much
range as I would like, but hopefully, the crystal has done its ageing
process and I won't have to go into the receiver again.
I am going to order a replacement for the reference crystal, just to have
on hand.
Overall, the 7100 is a good receiver. Looking through the service manual,
it appears that all 3 of the mixers are doubly-balanced diode ring mixers
that operate with +10dBm of LO rejection, so the IMD performance should be
pretty decent. It also appears that Icom finally decided to use glass
epoxy circuit boards. I didn't know when they had decided to start doing
this, since this receiver was designed during that "transition time" when
there was a mix of both FR4 and Phenolic being used.
Maybe they finally got tired of repairing those cold solder joints that
would develop over time.
Oh, their quality control................it was pretty funny when I
removed the covers from the shield assemblies and found fingerprints on
the inside!
I've got the receiver burning in right now........after another half hour
of running, I will do the final calibration on the 2nd and 1st LOs.
Thanks again for the tips, Mike and Bob!
Pete
"Bob Parnass" wrote in message
news
On Sat, 27 Aug 2005 23:18:37 +0000, Pete KE9OA wrote about
his ICOM IC-R7100:
Apparently, the reference crystal has drifted down in frequency over
the years.
I have serviced multiple IC-R7000s, IC-R7100As, and other ICOM radios
(e.g., IC-275H) with the same problem. The reference oscillator crystals
in those radios aged after use and shifted frequency. In some cases,
like yours, they go too far off frequency and must be replaced. Check
with ICOM USA for a replacement crystal.
Too bad ICOM didn't burn in the crystals *before* final factory
alignment.
I've not had this problem with the IC-R8500.
--
================================================== =======================
Bob Parnass, AJ9S GNU/Linux User http://parnass.com