[R-390] R-390a not receiving below 8 MHz

[Larry H]

Hi Gary,  Pin 7 on V201 was changed to go directly to ground, so that is
good that change is on your RF deck.

Regards, Larry

On Sun, Nov 26, 2023 at 12:36 PM <gary.biasini at shaw.ca> wrote:

> After pulling the RF module and tracing the wiring on V201, I am not sure
> how this radio ever worked.  Pin 7 has a wire that goes through the hollow
> metal center of the tube socket and across the bottom tube and is hooked up
> to pin 3 on the other side of the tube socket which is the ground side of
> the filament on the tube.  Of course it reads 0 ohms!  Unfortunately,
> everything is so tight in there, I am not sure I have the skills to
> unsolder and re-solder.  Before I move forward with trying, can anyone
> confirm that the schematic is correct and that I won’t bugger everything up
> if I rewire as per the schematic?
>
>
>
> Thanks.
>
>
>
> *From:* gary.biasini at shaw.ca <gary.biasini at shaw.ca>
> *Sent:* Sunday, November 26, 2023 12:44 PM
> *To:* 'Larry H' <larry41gm at gmail.com>
> *Cc:* 'R-390 at mailman.qth.net' <R-390 at mailman.qth.net>
> *Subject:* RE: [R-390] R-390a not receiving below 8 MHz
>
>
>
> To continue the story, I used tube extenders and measured the voltages and
> resistances of V201 to V206 (I couldn’t get both the tube extender and tube
> on V207).  The most interesting readings come from V201 as follows:
>
>
>
> Tube V201
>
> Pin #
>
> V to Gnd
>
> Reading
>
> Ω to Gnd
>
> Reading
>
> 1
>
> -0.4
>
> -0.07
>
> ∆1 M
>
> 729K
>
> 2
>
> 2.8
>
> 1.94
>
> 220
>
> 242
>
> 3
>
> 0
>
> 0
>
> 0
>
> 0
>
> 4
>
> 6.3VAC
>
> 5.9VAC
>
> 0.1
>
> 0.2
>
> 5
>
> 185
>
> 185.3
>
> 20K
>
> 23.7K
>
> 6
>
> 154
>
> 160
>
> 24K
>
> 26.4K
>
> 7
>
> 2.8
>
> 0
>
> 220
>
> 0
>
>
>
> From a review of the schematic, pins 2 and 7 are supposed to be connected
> together so they should both have the same voltage and resistance.
> However, you can see that it not the case.  When I pulled the tube and
> checked the resistance between pins 2 and 7, it was infinite so, whatever
> connection the schematic says should be there, is not.  So, time to pull
> the RF module but I may have to wait until later to do that.
>
>
>
> Thanks for reading.
>
>
>
> 73
>
> Gary
>
>
>
> *From:* gary.biasini at shaw.ca <gary.biasini at shaw.ca>
> *Sent:* Sunday, November 26, 2023 9:09 AM
> *To:* 'Larry H' <larry41gm at gmail.com>
> *Cc:* 'R-390 at mailman.qth.net' <R-390 at mailman.qth.net>
> *Subject:* RE: [R-390] R-390a not receiving below 8 MHz
>
>
>
> Folks,
>
>
>
> The saga continues (but so does the fun!).  I think I have narrowed the
> problem down to either the VFO Oscillator or the RF module.  I have put
> known working IF, audio and Power Supply modules in the radio and no
> difference.
>
>
>
> I did find out why I couldn’t get a calibrate signal below 6 MHz.
> Apparently, Z213, the middle one, had some sort of obstruction in the coil
> form that prevented the ferrite slug from going in more than about half
> way.  If I had some sort of boring tool that was exactly the right size, I
> might be able to bore out the obstruction.  Instead, I replaced the coil
> with one from a parts RF chassis and now I get the calibrate signal below 6
> Mhz.  But, still very low audio (and noise) – both almost non-existent.  I
> can receive WWV at 10 MHz and 15 MHz (I will try 5 MHz tonight, now that I
> appear to have some reception below 6 Mhz) but I still cannot receive
> strong BCB stations in the area.
>
>
>
> Time to figure out how to troubleshoot the RF module and the VFO Module.
>
>
>
> Stay tuned, if you’re interested.
>
>
>
> 73
>
> Gary
>
>
>
> *From:* gary.biasini at shaw.ca <gary.biasini at shaw.ca>
> *Sent:* Monday, November 20, 2023 6:44 PM
> *To:* 'Larry H' <larry41gm at gmail.com>
> *Subject:* RE: [R-390] R-390a not receiving below 8 MHz
>
>
>
> Larry,
>
>
>
> Thanks again for all your comments.  I found a half hour to check out the
> radio further today and tightened all of the screws on the IF module
> including the ones on ground lugs and tube sockets.  The readings are now:
>
>
>
> IF Subchassis
>
> J512 Pin
>
> Ω to Gnd
>
> Reading
>
> 1
>
> Inf
>
> Inf
>
> 2
>
> 50K
>
> 54.2K
>
> 3
>
> 54K
>
> 55K
>
> 4
>
> 500K
>
> 486K
>
> 5
>
> Inf
>
> Inf
>
> 6
>
> Inf
>
> Inf
>
> 7
>
> Inf
>
> Inf
>
> 8
>
> Inf
>
> Inf
>
> 9
>
> Inf
>
> Inf
>
> 10
>
> 440K
>
> 458K
>
> 11
>
> Inf
>
> Inf
>
> 12
>
> 27
>
> 66
>
> 13
>
> Inf
>
> Inf
>
> 14
>
> 0 to 20
>
> 16
>
> 15
>
> 132K
>
> 135.4K
>
> 16
>
> 100K
>
> 108.4K
>
> 17
>
> 0
>
> 0.4
>
> 18
>
> 0
>
> 0
>
> 19
>
> Inf
>
> Inf
>
> 20
>
> 0.5
>
> 0.6
>
> As you can see, the only out of tolerance reading is J512-12.  On review
> of the schematic, there is supposed to be a 27 ohm resistor to ground,
> R548.  When I looked at the colour bands on the resistor, it is actually a
> 68 ohm resistor.  I guess the question is – should I change this to a 27
> ohm resistor?
>
>
>
> More to come, I am sure.
>
>
>
> Regards,
>
>
>
>
>
> *From:* Larry H <larry41gm at gmail.com>
> *Sent:* Monday, November 20, 2023 12:47 AM
> *To:* gary.biasini at shaw.ca
> *Subject:* Re: [R-390] R-390a not receiving below 8 MHz
>
>
>
> Hi Gary,  I see that a lot of readings that should be 0 are not -  this is
> an indication that the grounding on these points is a problem.  That is a
> very important item to fix.  Now for j208-E, that is the agc line in the rf
> deck and should read as you have listed, 1.8 M Ohms, so that's ok.  j208-F
> is the filament line and may be ok.
>
>
>
> J512-6 is the open agc line in the IF deck and should read open - your
> reading indicates this is a very bad problem and must be fixed.  J512-12 is
> in the c/l meter bridge - 69 ohms may be ok there.  This higher value may
> allow it to read higher and reach 100 db, where 27 may not.  Leave it and
> check the c/l with 100,000 uv in.
>
>
>
> J620-5  & 7 are indeed the 800 cps filter.  You don't need it for the
> basic function of the rx.
>
>
>
> Have fun.
>
>
>
> Regards, Larry
>
>
>
> On Sun, Nov 19, 2023 at 3:36 PM <gary.biasini at shaw.ca> wrote:
>
> Folks,
>
>
>
> Here are my findings with respect to the substantially “off” resistance
> readings:
>
>
>
> AF Module – J620: 5 This goes to the 800cps bandpass filter and, since it
> is infinity instead of the expected 200Ω, I will have to assume that the
> filter is open and non-functional.  When I try it with the current issues I
> am having, rather than hearing an incredibly faint WWV, I hear nothing.
>
>
>
> IF Module: 6 – this is the AGC line and appears to go to ground in 3
> places – 1. Through R516 (22K) and C519 (5000pf); 2. Through R507 (22K) and
> C512 (5000pf); 3. Through R501 (22K) and C502 (5000pf);  Since this is
> supposed to read infinity but reads 33.5KΩ, would it be an appropriate test
> to check the 3 capacitors for leakage?
>
>
>
> RF Module: E - – this is the AGC line and appears to go to ground in 1
> place – Through R206 (22K) and C319 (5000pf); Since this is supposed to
> read infinity but reads 1.795MΩ, would it be an appropriate test to check
> the capacitor for leakage?
>
>
>
> Thanks in advance for your help.
>
>
>
> Regards,
>
>
>
>
>
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>
> <snip>
>
>