[R-1051] Synthesizer Questions

[jan at skirrow.org]

Hi Cecil ....

I put my three defunct six packs on the bench and in turn connected each to 
a 1051 freq std and power supply. They were all set in a good radio to 
15.000MHz before removal. I checked the waveforms etc thru the four 
sections of the spectrum generators for each. Nothing leaped out as being 
wrong.

I then checked the inputs to the translator module (leaving the individual 
synthesizer modules until last). One module had the wrong MHz freq.

As you had suggested the motors in the 1MHz module as a trouble spot, I 
checked each and found one motor was dead. The relay clicks when powered, 
but no current beyond the relay draw shows on the 28V line.

I hoped that this was the only problem with the affected six pack, and 
replaced the bad 1MHz module with one of the other two with good motors. 
Into an operating R-1051 et voila! It worked. So one six pack down, one to 
go for my remaining radio (maybe two to go if I want a spare.)

I also found the problem with that unusual freq std I sent you the pix of. 
The piston trimmer was broken - the shaft had come loose from the piston. 
The rough tuning cap couldn't bring it to 5MHz. So I replaced the piston 
trimmer and this std now is fine.

Two last questions:

First - have you repaired one of the motors?

Second - One of my radios is noticeably less sensitive than the others. I 
had to replace one of the RF amp tubes, and assume this might be the reason 
as it seems equally insensitive across all bands. Have you aligned one of 
the RF modules? I'd understood that these modules were designed to be 
forgiving of some misalignment or tube replacement, but can't think of any 
other explanation. IF gain seems correct.

Cecil - I have to thank you again for your wise advice. It's great to 
finally fix one of these intriguing radios. A synthesized radio before 
digital PLLs is quite an achievement, and this radio is a landmark in the 
progress of the art. Also, your comments have encouraged me to persist with 
the last radio! For me the key was understanding the radio well enuff so I 
could operate individual modules completely independent of the case. My 
cables may not be neat and tidy, but they work!

Jan Skirrow


At 09:29 PM 6/8/03, you wrote:
>Hi Jan,
>
>         I always start at the Frequency standard all synthesizer function
>depend on it being healthy...use a known good one.  I then check the three
>inputs to the Translator from the various synthesizers.  You will find that
>the synthesizers are interdependent...with the exception of the 1 MC
>synthesizer.    The output of some are dependant on inputs from others...it
>gets tricky some times figuring out that the output of one is not there
>because the input from another is missing.  I look for the proper
>frequencies into the Mixers based on the frequency set on the front panel.
>I also look for the proper levels.  That will usually tell all.  Usually one
>of those is missing.  I will also do an alignment on the spectrum
>generator...stepping through it from beginning to end.  The waveforms and
>levels are in the manual.  An alignment problem in the spectrum generator
>will cause improper outputs from the synthesizers.
>
>Try it on different frequencies...sometimes a dead crystal in the 1 and 10
>kc synthesizer will make it seem as though the radio is dead on all bands
>when in fact you are always just sitting on an even 1 or 10 kc setting.
>
>Another problem I have seen several times...the motor that drives the
>crystal switch in the 1 MC synthesizer will stall...the brushes and
>commutator get gummed up...and the switch is not working leaving you sitting
>on one crystal....the results is that the radio only works on one 1 MC
>segment...easily overlooked.  It is most easily found by listening as you
>change MHZ steps on the front panel...you should hear two motors
>running...one to drive the turret assembly in the RF deck and one in the 1
>MC synthesizer. (quieter)
>
>Those should get you going...also be sure to set the IF gain through the
>Translator...There should be around 10 to 12 db of gain...if set improperly
>you will have AGC problems. More is not better!  It works like the
>R-390A...if you set the gain lower the set has greater sensitivity...but the
>R-1051 doesn't have too much audio power to make up for the reduced gain in
>the IF.  I have thought about driving a decent stereo amp with the line outs
>and setting the IF gain very low...probably would make the radio much
>quieter...
>
>Good Luck..
>
>Cecil...