[R-390] Line Level Meter not working...Help a newbie!

Mon Feb 25 17:58:28 EST 2019

Dave, Swipe your ohm meter probes across the line level meter terminals and watch the line meter movement.If it twitches it is good. If you break your R390 meter movement through an improper test event you will have a life time learning experience. A good cal and BFO mix should drive the meter to zero if not full scale. Over the top inspection and correction has not fixed this problem for you. A popular mod it to rewire the  local audio output by passing the meter circuit. The 600 ohm balanced line output around 0 Vu If you diagramed what's under your audio deck you can see the difference from the production schematic and see what and where the local audio output power is appearing on the rear terminal board. One mod I saw in a Navy receiver  was two small jumper wires atop the front panel terminal board right behind  the  receiver name plate. The meter circuit is by passed and a half watt like local audio is present on the rear apron at the line terminals. AC volt meter and ( 2 ea 1200 ohm 1/2 watt resistors in parallel) a 600 ohm load on the line output.Do you meter 2.5 milliwatts  of 500 mill watts.  Line level is 0 VU is equal to +4 dBu, or 1.228 volts RMS, a power of about 2.5 milliwatts when applied across a 600-ohm load. 0 VU is often referred to as "0 dB".Local Audio level is about 1/2 watt.  I was looking for a dead meter circuit and had a WTF moment while I digested that modification. With a fair looking insulated wire you had to know what production looked like to see the modification when installed. (soldered in) Two jumper wires on the front panel terminal board straps the meter bridge and limited line level output components and deliverers the full line audio output to the rear terminal board. If the meter moves with the battery poke test, then the loss is in the audio deck, harness, back panel chassis terminal board. A couple pins in the wire harness connector may need some solder work. A cold solder joint now different after 50 years and couple transport vibration shock rides. Field engineer employment opportunities. It is time to eye ball the underside of the Audio deck for evidence of some post manufacturing solder flow.And just run the ohm meter through the circuit.Broke wire on the meter range switch behind the front panel.Fuzzy wire short.Broke switch wafer. Mod one use TB 11 - 12 as line out 1/2 watt strap R111 to R112 on the front panel terminal board. Mod two strap R111 to R114 (insulated wire) and R112 to R115 (insulated wire) line out is 1/2 watt and meter circuit just hangs as far more load than the output of 600 ohms. So the meter acts very lame. We would watch line level meters go tick tick tick as we zero beat sub audio. Stay with it Dave as time allows. R390 's are a hands on hobby. Respectfully,  Roger 

  -----Original Message-----
From: R. David Eagle via R-390 <r-390 at mailman.qth.net>
To: larry41gm at gmail.com <larry41gm at gmail.com>; R-390 Forum <r-390 at mailman.qth.net>
Sent: Mon, Feb 25, 2019 2:39 pm
Subject: Re: [R-390] Line Level Meter not working...Help a newbie!

Hi Larry.  Thanks for the tips.  I put 2 new 6ak6's in that tested strong and the same for 5814. Still no movement.  I hooked my meter up to the meter terminals while listening to an local am station and it appears to be deflecting as it should with a small AC signal.  I checked the movement and it is moving freely. So I am betting the meter must be shot?
Thanks again,
Dave

  On Sun, Feb 24, 2019 at 11:51 PM, Larry H<larry41gm at gmail.com> wrote:  Hi  David,  Jacques is right and that is probably it.  But, if not, the
meter might be stuck - try tapping on the face.  Or try turning the line
gain up to 5 or 6 and the line meter switch to 0 or -10 (try exercising
this switch a little, also).  Then try hooking up 600 ohm phones, AC meter,
or speaker to line out on the back.  If nothing there, try swapping the
6ak6 outputs v603 and v604.  If still nothing, try a different 5814 at v602.

Regards, Larry

On Sun, Feb 24, 2019 at 5:09 PM R. David Eagle via R-390 <
r-390 at mailman.qth.net> wrote:

> Hello all,
> I have just started back up restoring my Motorola 390a after taking a
> break from it after moving to a new QTH.  I have gone through it pretty
> well and re-tubed it and deoxed what I could.  The receiver seems to
> receive good, but I noticed that my line level meter doesn't move a bit.
> The carrier meter seems to function OK with received signals.
> Is there a good way to test the meter or is there something else I can
> check in to?  Might be looking for a replacement..???
>
> Thanks in advance for the help!
> Dave
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