Re: {Collins} 75S-3 S-meter Issue



To All:

Found R57, the RF gain pot located on the chassis, under S-meter was bad.
Wasn't responding at all, applied some contact cleaner, now that 1K pot
measures 400K-700K, Ah, no longer a pinned S-meter, no indication at all,
however, still hear the calibration signal.  Located a replacement pot,
will plan to order it later today.

Again, Thanks to all for getting my brain into 1st gear!

Chuck W9KR

On Mon, Aug 19, 2019 at 3:07 PM Chuck Curran <chuck53012@xxxxxxxxx> wrote:

> Steve & Glen:
>
> THANKS to you and others who offered suggestions
>
> I seemed to have rushed into my CCA posting, without thinking this
> through.  It started with a bad R13, the S-meter zero adjust pot.  Zero
> would jump from close to zero, then up to S-8 or so.  Found a suitable
> replacement, brand new and installed it.  Zero adjust is now very stable.
>
> Then I noticed how high the S-meter display was on most signals, and as
> already mentioned, a full scale needle position when the crystal calibrator
> was turned on.
>
> I checked the R57 setting, it was 100% clockwise.  With the crystal
> calibrator on, I backed it counter-clockwise in steps, but S-meter remained
> at full scale deflection, all the way to full counter-clockwise.
>
> I do have a good HP-5687B RF Signal generator, so I will first see if I
> can spray some DeOxit into the R57 pot, work it around then try the signal
> injection and see what happens.  Not sure what type of pot R57 is, will it
> have an opening to actually get any cleaner inside?  Will check pot
> continuity first too.
>
> Also plan on checking the AGC, another potential issue.
>
> Chuck W9KR
>
>
>
>
> > On Aug 19, 2019, at 1:04 PM, Steve Berman via Collins <
> collins@xxxxxxxxxxxxx> wrote:
> >
> > Chuck,
> >
> > As Glen suggested, check the receive gain pot.  It may be dirty or
> defective.  The rec gain pot will interact with the S-meter zero adjust.
> You'll need to inject a -70dbm (50uv) signal at
> > 14.1mhz and set the rec gain to S-9.  After that go back and reset the
> S-meter zero.  Basically what you're doing is balancing out the bridge
> circuit.  You may have to make this adjustment a few times until you get
> S-9 with -70dbm and have the S-meter perfectly zeroed.
> >
> > Steve N6HK
> > ________________________________
> > From: Collins <collins-bounces+n6hk=hotmail.com@xxxxxxxxxxxxx> on
> behalf of Don Rasmussen via Collins <collins@xxxxxxxxxxxxx>
> > Sent: Monday, August 19, 2019 8:28:27 AM
> > To: Glen Zook <k9sth@xxxxxxxxxxxxx>
> > Cc: Collins <collins@xxxxxxxxxxxxx>
> > Subject: Re: {Collins} 75S-3 S-meter Issue
> >
> > IS YOUR AGC WORKiNG ??
> >
> > On Mon, Aug 19, 2019 at 11:23 AM Glen Zook via Collins <
> > collins@xxxxxxxxxxxxx> wrote:
> >
> >> Check R-57 the RF gain adjust potentiometer.  It is a 1K in series to
> >> ground from the cathode of V-6.
> >> Glen, K9STH
> >> website:  https://k9sth.net
> >>
> >>    On Sunday, August 18, 2019, 07:09:14 PM CDT, Chuck Curran via
> Collins <
> >> collins@xxxxxxxxxxxxx> wrote:
> >>
> >> Hello the Group:
> >>
> >> I received a S-Line for repair, all items not having been on the air
> for 20
> >> years.  I started to repair the 75S-3 receiver for the owner, and was
> >> pleased with the success, after replacing electrolytic's and the Sangamo
> >> coupling caps.  PTO was messed up, as far as end stops and pointer being
> >> vertical, but that was resolved too.  Alignment followed, with great
> >> success, all ceramic trimmers were NOT frozen, a real surprise!
> >>
> >> OK, now on to the issue.  S-meter was jumping all over, the zero pot was
> >> junk.  Found a suitable replacement and installed it after lunch today.
> >> That totally cured the jumping problem, when trying to set zero.
> However,
> >> I now see that the S-meter response is way high.  The calibrator signal
> >> PINS the S-meter, without a problem.  I checked pin voltages on V6 and
> V7,
> >> both were within spec.
> >>
> >> All on the air signals I have listened to are also WAY high, crazy high
> >> S-meter levels.
> >>
> >> All tubes were checked on my Hickok 752, three weak tubes were replaced,
> >> V3, V8, and V11.  Supply voltages are to spec.
> >>
> >> So, any suggestions on where to go next?
> >>
> >> Thank You in advance,
> >>
> >> Chuck W9KR
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