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Registered Member #1412
Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278
Yes.When I turn preselect slowly from 2.3Mhz~2.6Mhz,the sound from the speaker first become slightly louder than become quiet again.If I remove the wire on SW1,this sound disappear.
What is the propose of this test?Is this signal come from outside of the receiver?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
hsieh wrote ...
Yes.When I turn preselect slowly from 2.3Mhz~2.6Mhz,the sound from the speaker first become slightly louder than become quiet again.If I remove the wire on SW1,this sound disappear.
What is the propose of this test?Is this signal come from outside of the receiver?
It means receiver working!
Correct operation of receiver: Example: Set frequency to 9740 kHz
1. Set BAND to C - 4.0 - 11
2. Set main dial to 740
3. Set MHz to 9 so LOCK light go off.
4. Turn PRESELECT slowly between 9 - 10 until you get loudest signal, or noise.
Every time you change the main tuning dial, you must re-tune PRESELECT for loudest signal. This is very important on the lower frequencies, where a small change in frequency on the main dial will need a larger change in PRESELECT.
Registered Member #1412
Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278
Now I know I have to adjust the preselect dial while tuning and I successfully received one or two local AM station.But seems that the sensitivity of my receiver is very low.With a cheap pocket radio I can receive many AM stations.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
hsieh wrote ...
Now I know I have to adjust the preselect dial while tuning and I successfully received one or two local AM station.But seems that the sensitivity of my receiver is very low.With a cheap pocket radio I can receive many AM stations.
Transistor radio has internal ferrite rod antenna!
To listen on HF (BAND B, C, and D on this receiver) Connect SW1 (Short Wave 1)to a long wire antenna - 20 meters is enough - as high off the ground as you can make it.
Connect E to a good Earth.
To listen to AM Broadcast stations 0.5 - 1.6 MHz BAND A connect long wire antenna to BC.
You will hear very much noise on frequencies below about 10 MHz. This is normal today. Try to learn about HF radio wave propagation - which frequencies work well during day, and which frequencies are best at night. A band on which no stations can be heard during the day may be full of stations at night. A band full of stations by day may be dead at night. It all depends on ionosphere.
Registered Member #1412
Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278
Today I also replace Q104.I found the one in my receiver is 3SK51 instead of 3SK40 in the manual.I replaced it with 3SK40 because I bought several 3SK40 and someone on another forum says that loss of sensitivity might because 3SK40 is damaged.
But there is no improvement.Probably I need to re-alignment it.If I am going to use signal generator preform alignment procedure in the manual,what output voltage should I set my signal generator to?
And why the schematic says Q104 is 3SK40 but I found 3SK51 in my receiver?Is this because manufacturer changed its design without changing the manual/schematic or because the previous owner repaired or modified it?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Injected RF and AF signal levels from generator must be appropriate for part of circuit under test.
Example: Maximum receiver sensitivity at antenna is 0.7 μV. An RF test voltage of 100 μV injected onto SW1 will be equivalent to a strong signal, but not enough to do damage.
Generally, you must select a signal generator output to be within the normal range of RF/AF voltage for the stage you are testing. You may increase this if you are sure that no damage will be done by a higher voltage applied at that place.
You have changed active parts in the signal path without good reason, and I expect it will be necessary to completely re-align the receiver for it to function correctly.
Registered Member #1412
Joined: Thu Mar 27 2008, 04:07PM
Location: Taipei Taiwan
Posts: 278
Today I tried to do the first step of alignment in the manual.I don't have a sweep signal generator.So I tried to inject different frequencies but I found that no matter what signal I inject,the waveform on TP104 didn't change at all.Even if I disconnect the signal generator.So what should I do now?
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trying to repair FRG-7 receiver
