Home |
Search |
Today's Posts |
|
#1
|
|||
|
|||
Yaesu FRG-7700 receives AM, not SW
Jon Doe wrote:
Try using some spray tuner cleaner on the backside of the bandswitch.. Looks like it may not be functioning. I'll do that, though it appears that the bandswitch is working okay. At least when I change bands the frequency readout changes too and I hear different levels of white noise. Thanks for the suggestion! ---- |
#2
|
|||
|
|||
Yaesu FRG-7700 receives AM, not SW
It sounds like either your synthesizer is out of lock or the bandswitching
diodes in the front end aren't being switched by the microcontroller. You probably have some sort of current booster chip such as a ULNXXXX or some switching transistors that switch the receiver above the 1.6MHz range. Since you are hearing different levels of white noise, I believe that your synthesizer is ok. You can determine that by connecting a frequency counter to your 1st LO injection point. If everything in this section of the circuit is ok, you will see a frequency that is above your actual displayed frequency by whatever the 1st intermediate frequency is. The key is that when you change your tuning frequency by 1MHz for instance, your 1st LO frequency will change by that amount. I don't know if that receiver uses relay or diode switching to switch different ranges of the preselector when you tune the shortwave bands. You could actually bypass the preselector and connect an antenna wire directly to the low-pass filter that is ahead of your 1st mixer. On a final note.............................is there a switch on the back panel of the 7700 that selects between long wire and 50 Ohm inputs? If so, that could be the cause. Either that switch is set to the wrong position or it is dirty. Good luck! Pete "saki" wrote in message ... Jon Doe wrote: Try using some spray tuner cleaner on the backside of the bandswitch.. Looks like it may not be functioning. I'll do that, though it appears that the bandswitch is working okay. At least when I change bands the frequency readout changes too and I hear different levels of white noise. Thanks for the suggestion! ---- |
#3
|
|||
|
|||
Yaesu FRG-7700 receives AM, not SW
I just downloaded the service manual from mods.dk. Your receiver does use
switching diodes for the preselector, along with an MC14555 chip that drives them. The 50 Ohm input has a 4700pF coupling cap. The long wire input had a different path. If you have a high speed internet connection you can register at www.mods.dk and download the manual. This will give you a good starting point. Pete "saki" wrote in message ... Jon Doe wrote: Try using some spray tuner cleaner on the backside of the bandswitch.. Looks like it may not be functioning. I'll do that, though it appears that the bandswitch is working okay. At least when I change bands the frequency readout changes too and I hear different levels of white noise. Thanks for the suggestion! ---- |
#4
|
|||
|
|||
Yaesu FRG-7700 receives AM, not SW
Forget what I said in the last post..............I was looking at another
schematic. The 7700 schematic itself it blurry, but you will need to take a look at that to get an idea of what is going on. "saki" wrote in message ... Jon Doe wrote: Try using some spray tuner cleaner on the backside of the bandswitch.. Looks like it may not be functioning. I'll do that, though it appears that the bandswitch is working okay. At least when I change bands the frequency readout changes too and I hear different levels of white noise. Thanks for the suggestion! ---- |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
Announcing the 'new' Yaesu FRG-7700 Receiver Users eGroup on YAHOO ! | Shortwave | |||
FS: Icom, Yaesu, Alinco Manuals | Swap | |||
FS: Yaesu FT-897 SERVICE MANUAL | Swap | |||
FS: Icom, Yaesu Service Manuals Etc... | Swap | |||
FS: Icom, Yaesu Service Manuals | Swap |