[R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?

[Barry]

Also, when inspecting the slug racks, check to make sure none of the slugs have let go of their spring or have broken and only the top part of the slug is still attached to the spring.  One of the slugs in mine had broken in half.  I don't know how that happens but it's not that rare.

Barry - N4BUQ


> A couple of other things.
> 
> When you replaced that loose connector, did you lock it down fully with the
> twist lock?
> 
> Are all the slug racks moving up and down as they should with changes to both
> the MC and KC controls?  If not, you might have a loose/broken gear clamp.
> 
> Barry - N4BUQ
> 
>> Hi Jerry,
>> 
>> Not an expert and using those symptoms to zero in on a problem is a bit beyond
>> me; however, since it's "partially deaf" would seem to point to a stage in the
>> RF deck isn't working properly causing the overall gain to be too low.
>> Switching to CAL may not produce the effects it once did because the gain is
>> already way too low so you don't notice the difference.
>> 
>> If you have a way to check for dead tubes, I think that would at least be a good
>> start.
>> 
>> If you have another receiver that can tune in 455kHz, you could try using the IF
>> OUTPUT (J106) to feed into the other receiver's antenna connection.  If the
>> other radio hears properly, then that could indicate the trouble is past the
>> 5th IF amplifier circuitry.
>> 
>> Hopefully others will chime in with more/better suggestions.
>> 
>> Good luck with it,
>> Barry - N4BUQ
>> 
>>> Several years ago, Don W5OR (SK) asked me to share administrator
>>> responsibilities with him to manage the r-390 mail list server.  While I have
>>> several R-390/R-390A, I never had the need to repair any.  So, this is my first
>>> post for help…
>>> 
>>> 
>>> 
>>> My R-390 has gone partially deaf.  It sits in a fan-ventilated rack which rarely
>>> gets rolled around.  Its last maintenance was in 2002 when Don Heywood did an
>>> incredibly thorough job.  It worked great until a few weeks ago when it became
>>> completely deaf.  My initial inspection found something bizarre, the RF cable
>>> had popped loose (see attached picture).  After reconnecting, it was only
>>> partially deaf.  I could tune in moderate and strong signals across all bands
>>> but I need to set Local Gain to 7 or higher just about where hum comes into the
>>> speakers.  The best description is what you might expect to hear if RF Gain is
>>> not at maximum. Also, another ‘clue’ is I noticed that switching to CAL does
>>> not remove or attenuate a CW or phone signal.. sounds same as if in AGC.  I
>>> checked that the antenna relay is working:
>>> 
>>> 
>>> 
>>> *	On powering to STBY – the relay clicks and pulls in visually and checking both
>>> twin-ax connector pins, I confirmed both 2 pins are grounded.
>>> *	On switching to AGC or MGC – the relay clicks off and neither of the twin-ax
>>> pins are grounded.
>>> *	On switching to CAL – the relay clicks on again and the twinax pins are
>>> grounded. The manual says in CAL, unlike in STBY, +180 volts de is applied to
>>> the rf. if., af, and calibration oscillator stages and in both STDBY and CAL,
>>> terminal 2 of CR801 is grounded to apply 6 volts dc to relay K101.
>>> 
>>> 
>>> 
>>> I also checked Break-In and that works in AGC giving complete silence, but the
>>> manual says that’s achieved by grounding the AF output in addition to grounding
>>> the antenna inputs.  How does that prevent overloading the RF section with a
>>> local transmitter?
>>> 
>>> 
>>> 
>>> My 1st question is, why is there no signal attenuation when switching to CAL?
>>> Is there anything in the electromechanics that could explain this?  Is this
>>> coincidental to the R-390 partial deafness or part of the same problem?
>>> 
>>> 
>>> 
>>> Pending some replies, my next step is to check the tubes in the RF and audio
>>> stages but I’m hoping that my description may sound familiar to the many
>>> experienced members of the list.
>>> 
>>> 
>>> 
>>> TIA Jerry
>>> 
>>> 
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