Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 81
Default Yaesu FRG-7700 receiver tuning fault

I suppose an amateur radio group would be better but they
are very quiet.

The mechanical tuning dial works as it should but the radio
won't tune above .783 in each band. I haven't had the cover
off yet but I'm thinking the VFO variable capacitor is being
prevented from full movement.
  #2   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 633
Default Yaesu FRG-7700 receiver tuning fault

On 12/1/18 11:38 PM, Lucifer wrote:
I suppose an amateur radio group would be better but they
are very quiet.

The mechanical tuning dial works as it should but the radio
won't tune above .783 in each band. I haven't had the cover
off yet but I'm thinking the VFO variable capacitor is being
prevented from full movement.


There isn't a VFO capacitor. The radio uses phase locked loops.
Operating manual:
http://www.radiomanual.info/schemi/YAESU_RX/FRG-7700_user.pdf
Service manual:
http://www.radiomanual.info/schemi/YAESU_RX/FRG-7700_serv.pdf


--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com
  #3   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 81
Default Yaesu FRG-7700 receiver tuning fault

On Sun, 2 Dec 2018 01:31:27 -0600, Fox's Mercantile
wrote:

On 1/12/18 11:38 PM, Lucifer wrote:
I suppose an amateur radio group would be better but they
are very quiet.

The mechanical tuning dial works as it should but the radio
won't tune above .783 in each band. I haven't had the cover
off yet but I'm thinking the VFO variable capacitor is being
prevented from full movement.


There isn't a VFO capacitor. The radio uses phase locked loops.


Thank you for your reply and the manual links, however you are
wrong about the VFO capacitor.
It uses the PLL to select the band and the VFO to tune within the
band. The Kenwood R-1000 works the same way.

Operating manual:
http://www.radiomanual.info/schemi/YAESU_RX/FRG-7700_user.pdf
Service manual:
http://www.radiomanual.info/schemi/YAESU_RX/FRG-7700_serv.pdf

  #4   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 10
Default Yaesu FRG-7700 receiver tuning fault

On 2018-12-02 06:38, Lucifer wrote:
I suppose an amateur radio group would be better but they
are very quiet.


There is a lively and helpful Facebook group of Yaesu users, look for
"Yaesu-FOX-TANGO". Describe your equipment and take the exam :-;

Arie de Muijnck

  #5   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 81
Default Yaesu FRG-7700 receiver tuning fault

I suppose an amateur radio group would be better but they
are very quiet.

The mechanical tuning dial works as it should but the radio
won't tune above .783 in each band. I haven't had the cover
off yet but I'm thinking the VFO variable capacitor is being
prevented from full movement.


  #6   Report Post  
Posted to sci.electronics.repair
external usenet poster
 
Posts: 201
Default Yaesu FRG-7700 receiver tuning fault

In article ,
Lucifer wrote:
I suppose an amateur radio group would be better but they
are very quiet.

The mechanical tuning dial works as it should but the radio
won't tune above .783 in each band. I haven't had the cover
off yet but I'm thinking the VFO variable capacitor is being
prevented from full movement.


That's possible. It may be purely mechanical - a loose tuning cord (I
can't tell if the design uses one), or a loose shaft coupling, or an
obstruction (e.g. bent plate on the capacitor, or a small dead
cockroach, or etc.) which binds the mechanism at some point in its
rotation.

It's also possible that there's something wrong with one of the
circuits to which a variable-capacitor section is connected. For
example, the VFO might be stopping entirely when you try to tune it
into part of its range. This might indicate (e.g.) a weak transistor,
or a capacitor that has become leaky... something which causes the
gain inside the oscillator loop to drop below 1.

Best way to distinguish would probably be to hook a frequency counter
and/or o'scope to the output of the VFO unit. Tune it through its
range, and see if you get a reasonable output signal throughput the
range.

If the VFO produces a consistent signal, then the next suspect would
be the PLL board, which generates the IF frequencies by multiplying
the output of the VFO. The PLL might be losing lock for some reason,
and shutting down. If the VFO works OK, then scope/count the IF
outputs from the PLL, and see if they vanish suddenly or get "stuck"
somehow.

The manual has the alignment procedures.

You should also do an "eyeball" inspection to look for obvious
failures, such as bulging or leaking electrolytic capacitors. These
units are old enough that it might have been built with some 'lytics
that suffer from the faulty-electrolyte "capacitor plague". If so, a
careful re-capping (with repair of any damaged traces on the board)
would be called for.

Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Porter Cable 7700 Miter Saw [email protected] Woodworking 0 May 30th 15 05:10 PM
LaserLoc 7700 Porter-Cable Miter Saw Interest Will[_7_] Woodworking 0 June 15th 10 10:13 AM
Yaesu FT-897D noisy in CW narrow mode Fox Electronics Repair 3 January 21st 09 08:28 PM
Yaesu FT-757GX Problem rijo Electronics Repair 2 August 31st 06 08:25 PM
Yaesu FRG-7700 display ??? Henry Kolesnik Electronics Repair 21 January 7th 05 01:56 AM


All times are GMT +1. The time now is 11:03 AM.

Powered by vBulletin® Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 DIYbanter.
The comments are property of their posters.
 

About Us

"It's about DIY & home improvement"