[R-390] R390A- Intermittent sensitivity variation

[rbethman]

Roger,

Please post those 20 pages or so to add to the groups "collective 
Knowledge". I'm sure that the group would appreciate it.

If not, please "cc:" my address, <rbethman at comcast.net> .

Thank You!
Bob - N0DGN

On 5/6/2012 8:28 PM, Roger Ruszkowski wrote:
> Eric,
>
> I will move back over to the other computer and send you a couple of long posts.
>
> The up shot is you have a dirty switch contact in the RF deck band width switch.
> An easy fix.
> All you have to do is pull the RF deck, clean the switch and readjust it a bit.
> Watch for about 20 pages of detail to explain " all ".
>
> You describe a fairly common problem. It likely has been in the receiver for some time.
> It is just a mechanical adjustment of the RF deck band switch.
>
> Do not set this adjustment as it says in the TM.
> You will want to pull the RF deck and do this adjustment by eye.
>
> The band switch has 6 segments and 6 stops. Thats 36 contact points. Moving both up and down.
> Some have B+ (some power) on them. Its a matter of wanting the most surface area between the wiper and the contact on each switch segment possible.
> So it becomes a subjective adjustment. What looks best for the RF band switch you are trying to get adjusted is the correct answer.
>
> You may feel the need to clean a contact or wiper in the RF band switch.
> Take the time to get good stuff.
> Go slow.
> Be carfull how you touch it.
> Repairing a band switch wafer after it has been over petted is hard to do.
> Better to go gentle first.
>
> Roger AI4NI
>
>
>
>
>
> Hi Group,
>                   I have mentioned in previous posts (Greetings from Sydney,
> ustralia) that I have noticed variation in calibration signal levels with my
> 963 Imperial R390A.  After a longer period of investigation, I note that the
> roblem is actually confined to the 16 –32 MHz octave. On any one of the 16 –31
> Hz segments ,  a calibration signal level of say 20dB as read on the carrier
> evel meter can suddenly shift downwards to 10 dB or lower.  The problem is not
> n the calibration signal, because  if I switch back to a signal off the
> ntenna, it has also dropped in level.   This shift in sensitivity is
> ntermittent – it does not coincide with warm up after switch on , but can occur
> t any time – another observation is that sometimes sensitivity can be restored
> y moving the MCs knob a few notches – but not always- sometimes the sensitivity
> estores by itself after an unpredictable period.   I am quite new to the group,
> ut have been studying the Y2K manual , and the wealth of information on the
> 390A FAQ page, as well as past posts to the group, but have not yet seen any
> pecific mention of my problem.  Since the sensitivity variation is confined to
> he 16- 32 MHz range, I suspect a problem with the RF deck 16-32MHz circuitry.
> ould it be a problem with the bandswitch contacts in the 16-32MHz section or
> ould it be a problem with the coils and/or capacitors in this section?   Any
> dvice from the group would be most appreciated.   There are no problems with
> ensitivity variation below 16 MHz.
> Best Regards to all,
>                                      Eric.
> _____________________________________________________________
>
> ______________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:R-390 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html