[Premium-Rx] Harris RF-590 A12 800khz missing

[w3jn at verizon.net]

 I went down the same path some years ago, had to replace two transistors on that board if I recall correctly.
 
 
-----Original Message-----
From: thoyer via Premium-Rx <premium-rx at mailman.qth.net>
To: 'Gilbert Harris' <gibharris at hotmail.com>; Premium-Rx <Premium-Rx at mailman.qth.net>
Sent: Sun, Jul 21, 2019 8:37 pm
Subject: Re: [Premium-Rx] Harris RF-590 A12 800khz missing

You are spot on and described the path I've been down....... Output is good
out of U6 - 800kHz - I lose it after Q18. Replaced Q18, still no workie. 

I may try an inject 800kHz with a function generator after the coupling cap
on U6 just to verify the BITE stage operation. I'll mimic the dutycycle out
of U6 since it is not a 50% signal due to the divide by counter operation.

Something is funky in that circuit, I just need to find it......... Easier
said then done.

Thanks for the reply!
Tom
W3TA


-----Original Message-----
From: premium-rx-bounces at mailman.qth.net
[mailto:premium-rx-bounces at mailman.qth.net] On Behalf Of Gilbert Harris
Sent: Sunday, July 21, 2019 6:43 PM
To: Premium-Rx at mailman.qth.net
Subject: [Premium-Rx] Harris RF-590 A12 800khz missing

You likely received an A12-2 FAULT indicating bad BITE test located on the
800khz reference. This originates from U5 4mhz reference at pin 5 which is
then divided by 5 at U6 with output at pin 5 (800 khz.)  U5 also provides
4mhz which is divided by U4 for the 1mhz reference output. This is tested
PRIOR to the 800khz during FAULT testing so  the problem is after U5.  Go to
U6 and measure its supply voltage, then if ok press on near by circuit board
for cold solder joint, put oscilloscope on pin 1 ( input 4mhz) and pin
11(output 800mhz).  I'll bet you have done already. I may have a couple
A12/A21 somewhere but can't access for 6 weeks.
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