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

Thu Nov 7 11:43:20 EST 2024

I am unfamiliar with the schematic bus notations.  I am trying to see why the cathodes from V507B and V510 are reading as open.  It could be R544 the cathode bias resistor opened but in case not, the other places would be outside the IF module.  I see the cathodes go into J517-10 / P117-10 but I cannot find on the schematic where they come off the harness into what module?

Can someone point me in the right direction?

Thanks
Jerry

-----Original Message-----
From: k1jos at att.net <k1jos at att.net> 
Sent: Thursday, November 7, 2024 11:30 AM
To: 'Barry' <n4buq at knology.net>
Cc: 'Barry Scott' <72volkswagon at gmail.com>; 'R-390 Mailing List' <r-390 at mailman.qth.net>
Subject: RE: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?

Ooops please I see that J517 plugs into P117.  Yes and removed and reinserted a few times with no change -----Original Message-----
From: k1jos at att.net <k1jos at att.net>
Sent: Thursday, November 7, 2024 11:28 AM
To: 'Barry' <n4buq at knology.net>
Cc: 'Barry Scott' <72volkswagon at gmail.com>; 'R-390 Mailing List' <r-390 at mailman.qth.net>
Subject: RE: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?

Hi Barry,

Do you mean J517, the large multiwire amphenol?  Arte you measuring a R390 or 390A?

Jerry

-----Original Message-----
From: Barry <n4buq at knology.net>
Sent: Thursday, November 7, 2024 11:03 AM
To: k1jos <k1jos at att.net>
Cc: Barry Scott <72volkswagon at gmail.com>; R-390 Mailing List <r-390 at mailman.qth.net>
Subject: Re: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?

Hi Jerry,

OFF: 520k
CW: 583k
CCW: 638k

Those don't exactly meet the specs.  I probably have more than one drifted resistor that I need to address at some point.

So strange that so many of those readings are so far off in your radio.  It's almost as if another connector is loose or making poor connections.  I presume you've reseated P117?

Hope that helps,
Barry - N4BUQ

> Hi Barry,
> 
> Could you do me a favor and also check resistance on V507B (Neg Peak
> Limiter) pin 8 cathode -- It should read 500k (Limiter knob at full
> CW) and 450k with Limiter switch OFF - I read an open circuit or 
> resistance > 10Meg.  The cathode of V507B is tied to the cathode of
> V510  (pin 3) which also reads open on my DMM.
> 
> Thanks in advance
> Jerry
> 
> -----Original Message-----
> From: Barry Scott <72volkswagon at gmail.com>
> Sent: Wednesday, November 6, 2024 10:52 PM
> To: k1jos at att.net
> Cc: r-390 at mailman.qth.net
> Subject: Re: [R-390] R-390 (non-A) - Low RF Gain or bad Antenna relay?
> 
> I just checked resistance from V506 Pin 7 to ground in my R-390/URR 
> and it checks a few ohms over 820 ohms.
> 
> Thanks,
> Barry - N4BUQ
> 
> On Wed, Nov 6, 2024 at 8:38 PM Barry Scott <72volkswagon at gmail.com> wrote:
>>
>> That resistance measurement seems quite odd.  R536 is supposed to be
>> 820 ohms.  Unless C523 is bad, I don't see how there should be 
>> anything much less than 820 ohms at pin 7 of V506 yet the resistance 
>> diagram shows 700 ohms.  99 ohms seems very wrong.
>>
>> Thanks,
>> Barry - N4BUQ
>>
>> On Wed, Nov 6, 2024 at 8:12 PM <k1jos at att.net> wrote:
>> >
>> > Update....
>> >
>> > I checked voltages and resistances per TM  11-5820-357-35 (09 March
>> > 1962) for the IF amps V501 - V506.  I don’t know if my R-390 had 
>> > any mods, its SN 1256, but all the results were very close to the 
>> > listed values except for V506, 6th IF amp.  The cathode should read  700 ohms to ground and 8.2vdc and I find 99
>> > ohms and 2.3vdc.   The schematic shows the cathode bias resistor of 800 ohms
>> > and a 15ohm pot for carrier meter adjustment.  There is a 
>> > decoupling cap 0.1uF off the cathode that if leaky could bring the resistance down to my reading.
>> > But would this be enough to drop my gain so dramatically?
>> >
>> > Jerry
>> >
>> >
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