Re: trying to repair FRG-7 receiver
Proud Mary, Fri Apr 06 2012, 05:01PM

No, don't attempt to recalibrate it! Do not fiddle with any of the dust cores in the IF transformers!

First clean off loose mould and debris with a dry paint brush.

1.) Is the power supply reaching the boards? test with meter. Does the front panel display light up?

2.) If power is reaching the boards, inject a ~20mV audio test tone at pin 7 on Q410. If no tone comes from the loudspeaker, it means that the audio output amplifier circuit has failed. If the audio output circuit is good, inject the test tone at the hot end of VR1, the volume control. If the tone still comes from the loudspeaker, and can be varied by varying VR1, then VR1 is good. If no loudspeaker output, then VR1 has failed.

Work backwards along the signal path in this way, until you find the fault. When you get to the detector, and IF stages, you will need an HF signal generator, or function generator to inject your test signals.

The good news is that your receiver was manufactured in a way that makes fault-finding and repair very easy. There are even test points! (marked "TP" on the board) so you will be able to make it work again if you don't rush into it in a hurry.

Re: trying to repair FRG-7 receiver
hsieh, Sat Apr 07 2012, 04:18AM

I did what you said and I found that the audio amplifier and VR1 is OK.So now I have to check the detector and RF part of the receiver.But I don't know how to do it.Can you explain this further or are there any websites to reference?

I will borrow a RF signal generator after this weekend.Should I inject a modulated test signal to every stage of the receiver?What amplitude and frequency should I set?

Re: trying to repair FRG-7 receiver
Proud Mary, Sat Apr 07 2012, 10:56AM


Hi Hsieh, I will study the circuit diagram this evening, and tell you where to inject an AM RF signal to test basic detector operation, and the IF amplifier stages. Stella

Re: trying to repair FRG-7 receiver
Steve Conner, Sat Apr 07 2012, 11:44AM

In the meantime, leave those dust cores alone!

Re: trying to repair FRG-7 receiver
Proud Mary, Sat Apr 07 2012, 09:52PM

Set the signal generator to 455kHz 500mV and AM modulation 500Hz.

With S3 on the receiver set to AM, inject a 500mV signal onto the anode of D402, where it is connected to C428 and L402.

If you hear the audio tone from the loudspeaker, the AM balanced detector and all the circuits after it to the loudspeaker are good.

If NO audio tone comes from the loudpseaker in the AM test, switch S3 to USB/CW and apply the same signal with NO modulation to the junction of D404, D406, and R433. If you can now hear a whistle when you adjust the BFO it means that the demodulator and all the circuits after it are good.

If BOTH of these tests are OK, set S3 back to AM, and inject a 455kHz 50mV AM tone signal onto the hot end of the secondary of T404 where it is joined to C422.

If you can hear the tone in the loudspeaker, Q406 - the final IF amp - is good.

If NO tone comes through, check voltages on Q406 which should be close to Emitter 1.4V, Collector 9.1V and Base 2.0V.

That is enough to be getting along with for now.

Tell me how these tests perform, and we can decide what to do next.

Re: trying to repair FRG-7 receiver
hsieh, Mon Apr 09 2012, 01:11AM

All the test you described are OK.I can hear audio tone come from the speaker in all tests.

My receiver also make a lot of weird sound when I turn it on.Does this mean something?

Re: trying to repair FRG-7 receiver
Proud Mary, Mon Apr 09 2012, 10:22AM


It means receiver not working properly! In triple-conversion superhet like FRG-7, it is best
to work systematically, and not to work on 'hunches' and guesses about what is wrong.

Next:

Set signal generator to 455kHz, with AM audio tone, RF output level 10mV.

With S3 set to AM, inject signal at start of ceramic IF filter - the point where FL-1 is connected to R420 and C417.

If you hear tone from loudspeaker it means IF filter and everything after is good.

Re: trying to repair FRG-7 receiver
hsieh, Tue Apr 10 2012, 07:23AM

OK, I can hear the tone from the speaker when I inject test signal to ceramic filter.

Re: trying to repair FRG-7 receiver
Proud Mary, Tue Apr 10 2012, 09:10PM

That is excellent news, Hsieh!

I will look at the diagram of the analogue frequency synthesizer in the morning, so we can move on to a new set of tests.

Re: trying to repair FRG-7 receiver
Proud Mary, Wed Apr 11 2012, 05:37PM

Next test:

Set signal generator to 2.5MHz, AM audio tone, 10mV.

Set the receiver to AM.

Fixing a small capacitor (say 3 - 10pF) to the end of the probe, inject 2.5MHz signal at junction of R445 and the hot end of T401.

Now tune the receiver very slowly across a 1MHz segment.

Stop turning the main tuning dial when - if - you hear the audio tone from the speaker.

What is the frequency reading on the dial when this happens?

Is there any indication on the signal strength meter - "S-Meter" - on the front panel during this process?

Do you have a counter-timer that we can use to measure the frequency of the various oscillators?

Re: trying to repair FRG-7 receiver
hsieh, Thu Apr 12 2012, 01:23AM

When doing this,I can sometimes hear a very faint/unclear tone when the main tuning dial is tune to 500 and the S-meter also reach 20dB.

Yes,I have a frequency counter.

Re: trying to repair FRG-7 receiver
Proud Mary, Thu Apr 12 2012, 10:01AM


This result strongly suggests that Q401, Q402, Q403, and Q404 are all OK, as the 2.5MHz test signal has appeared where it should at 500 on the main tuning dial - but as you describe the signal as being 'very faint' we must not dismiss the possibility of IF breakthrough.

So we will perform one more test on this 2nD IF/3rd Mixer stage just to be sure.

Set your counter-timer to a range that can detect signals in the range 2.455Mhz - 3.455MHz.

Fix your counter-timer probe to TP404, and observe the counter-timer while tuning the main dial across its full range.

If Q403 and Q404 are working properly, the counter-timer should display 2.455Mhz - 3.455MHz as you turn the main tuning dial across its full range.

Re: trying to repair FRG-7 receiver
hsieh, Mon Apr 16 2012, 01:23AM

I measure TP404 with an oscilloscope.The waveform is unstable,especially when my hand is on the dial.

Re: trying to repair FRG-7 receiver
Proud Mary, Mon Apr 16 2012, 01:58PM


OK Hsieh. That's because the probe is detuning the circuit. Connect it back to TP404 through a very small capacitance ~2 - 3 pf and try again.

Re: trying to repair FRG-7 receiver
hsieh, Tue Apr 17 2012, 09:45AM


I did this but the waveform is still unstable and distorted.

Re: trying to repair FRG-7 receiver
Proud Mary, Tue Apr 17 2012, 11:16AM


It's difficult to be 100% certain what is going on, without being able to see it myself, but here is what I think:

"waveform is unstable" - this is an analogue VFO, being operated without the Faraday screen of the equipment case. Moving your hand, for example, near the variable capacitor may alter the frequency.

"distorted" - remember that this is the switching waveform being applied to 3rd mixer. It is not intended to be a sine wave, but don't expect to see good square waves either!

Were you able to measure the frequency range of the signal at TP404, as I suggested? If you haven't got an instrument to do this, we will put this question on one side for the moment, (as you clearly have a signal of some sort) and move on to the frequency synthesizer.

Synthesizer crystal oscillator test: Measure the frequency of the signal at the junction of L301, L302 and C307. This should be 1 MHz.

Re: trying to repair FRG-7 receiver
Patric, Tue Apr 17 2012, 04:25PM

I do not want to interfere, but it is very stretching and I hope for a good ending!
Nothing wrong with the speaker?

Re: trying to repair FRG-7 receiver
hsieh, Wed Apr 18 2012, 12:58AM

waveform and frequency at junction of L301, L302 and C307:




waveform at TP404(sometimes it is a stabe sine wave):

Re: trying to repair FRG-7 receiver
Proud Mary, Wed Apr 18 2012, 02:46PM

The waveform and frequency of the synthesizer oscillator is excellent.

The VFO signal is within the correct frequency range. The waveform does look a bit sickly, so we will leave it as OK Probable? and come back to it later if we cannot otherwise eliminate the fault.

Now we will get into the heart of the RF.

This next test will show us if there is a failure in the the elaborate RF pre-selector switching, one of the most common types of fault in older equipment.

Solder a small capacitor of approximately 50 - 100 pf to the end of a piece of insulated wire about 100cm long. This is your new antenna!

Fix the free end of the capacitor to the junction of R101, C101, and Q101 Gate 1. This is the input of the first RF amplifier.

Now tune across each of the receiver frequency bands and tell me what signals - if any - you can hear. If all is good, there should be plenty of signals (though not all in the right place, as we have by passed the pre-selector! )

Re: trying to repair FRG-7 receiver
hsieh, Thu Apr 19 2012, 01:18AM

I connect the capacitor and wire to the junction of R101, C101, and Q101,But I still cannot hear any signal.I only can hear some weird sound.

I also measure TP101 with oscilloscope and get a perfect sine wave.and the frequency range seems correct.

Re: trying to repair FRG-7 receiver
Proud Mary, Thu Apr 19 2012, 09:57AM

OK Hsieh.

First we will go back to the doubtful waveform at the VFO (Q403) and VFO buffer (Q404).

Go to the junction of C410 and T403 and look for a signal between 2.455 - 3.455 MHz. This signal should vary in frequency across this range when you turn the main tuning dial.

Setting the receiver to the conditions given at the bottom of Table 5, measure the voltages at Emitter, Collector and Base of Q403 and Q404 and compare these test results with the figures given in the voltage chart.

Re: trying to repair FRG-7 receiver
hsieh, Fri Apr 20 2012, 01:37AM

I test the junction of C410 and T403 and get a perfect sine wave.The frequency range is correct.I test TP404 again and now I get a stable sine wave too.I didn't do anything.I only clean the circuit board with some sort of cleaner.

I also measure the voltages of Q403 and Q404.They are close to the voltage given in the manual.

Re: trying to repair FRG-7 receiver
Proud Mary, Fri Apr 20 2012, 09:18AM

That's good news about TP404!

Do make sure that your probe contacts and crocodile clips are sharp enough to penetrate any surface coatings of varnish, oxidation, or dirt.

Now to some more voltage measurements!

Set the reciever to the condition specified at the bottom of Table 5, measure the voltages on C,B, E of Q101, Q102, Q103, Q104, Q105, Q106, Q107, Q108, Q109 and Q201, and compare with the specifications.

Re: trying to repair FRG-7 receiver
Conundrum, Fri Apr 20 2012, 06:22PM

Another thought, view the board on a thermal imager to look for hot spots from bad transistors etc.

-A

Re: trying to repair FRG-7 receiver
Steve Conner, Fri Apr 20 2012, 06:30PM

Don't listen to Conundrum! He'll have you improvising heat sinks from Sugru and metal filings.

Where are you going to get a thermal imager anyway? You could buy another dozen FRG-7s for the cost of even renting one.

If it were me, I'd be poking the board with a chopstick and banging on the chassis, to check for loose connections. Oh, and check for dirt between the tuning capacitor vanes, if it has a tuning capacitor.

Re: trying to repair FRG-7 receiver
hsieh, Sat Apr 21 2012, 02:09PM

I think probably I can use a thermal imager for free.There is one in our school lab and my teacher once said that I can use it.But will this trick work?

I am curious to know if FRG-7 is a well known model or not.

Re: trying to repair FRG-7 receiver
Proud Mary, Sat Apr 21 2012, 03:01PM


I can't help you with suggestions about fault finding with thermal imaging devices, as I have no experience in this, and will leave it to Conundrum to tell you what would be the best way of repairing your receiver using this technique. I know only the old slow way of doing this, circuit by circuit, until the fault is found.

But I can tell you that FRG-7 was one of the first high quality receivers built for sale to radio amateurs. It offered triple conversion, frequency synthesis, and Wadley loop stabilization, which had previously only been seen in communications receivers for professional use - such as military and maritime.

A Yaesu Musen FRG-7 in good working order and good cosmetic condition will still sell for a good price on ebay.

Re: trying to repair FRG-7 receiver
Conundrum, Sat Apr 21 2012, 03:49PM

Its an accepted technique, industry uses this all the time to locate shorts on multilayer boards.
Its also used for military applications where extreme reliability is essential, when recertifying a repaired board.
I think they compare it with a known good (KG) board and if there are substantial differences then the board gets reworked or scrapped.

-A

Re: trying to repair FRG-7 receiver
hsieh, Mon Apr 23 2012, 01:53AM

Today I measured the voltages and find some transistors that might be bad.

How much error is acceptable?I f the manual says 9V but I get 10V,Is this ok?

Re: trying to repair FRG-7 receiver
Proud Mary, Mon Apr 23 2012, 08:27AM


That would depend on which transistors they were, Hsieh, but mostly a ~10% deviation will not stop the circuit working.

Very generally, the collector or drain voltage should be a bit less than the supply voltage in normal operation. If the collector or drain voltage is the same as the supply voltage, it usually means that the device has gone open circuit.

Re: trying to repair FRG-7 receiver
hsieh, Tue Apr 24 2012, 01:03AM

I suspect that Q101 is dead.But it seems to be hard to find or expensive(10USD on ebay).Are there any replacements?

Japanese or American transistors are easier to find in Taiwan.

Re: trying to repair FRG-7 receiver
Proud Mary, Tue Apr 24 2012, 09:52AM



3SK40 has no ESD protective diode so is vulnerable in position of first RF.

3SK40 is obsolete, so NTE454 is a good substitute, which also has ESD protection on gate 1.

If NTE454 is also hard to get try BF988.

When substituting 3SK40 with a more modern dual gate FET, make sure you re-organize the pin outs!

If the substitute has a higher gain than 3SK40, I would suggest putting a ferrite bead on the drain lead to stop oscillation.

You will need to go through the RF board alignment procedure once you have replaced Q101.

Re: trying to repair FRG-7 receiver
hsieh, Mon Apr 30 2012, 03:13AM

I replace Q101 already.I replace it with 3SK40I.It cost me about 4USD each.

After I replaced it,the voltage still not don't match and I cannot receive anything.

Do I need some sort of antenna or I can just connect a long wire to the terminal block on the back?

What to do next?My friend is now laugh at me that I spent a lot of time and still cannot fix it.

Re: trying to repair FRG-7 receiver
Proud Mary, Mon Apr 30 2012, 12:31PM


Antenna: The FRG-7 has a sensitivity of better than 1 μV, so with only 1 meter of wire as an antenna, you will be able to hear many shortwave broadcast stations when the receiver is working normally. With a really good antenna, FRG-7 can detect very weak, distant stations just as good as any modern receiver.

Ignorant friends: You are restoring a vintage triple conversion analogue communications receiver that has a soul and spirit, and you should thank the fault for teaching you how to think about analogue receiver construction and repair.

How you should proceed: We know that most of the sub-circuits are working correctly, so start the 'maintenance and alignment' process on page 11 of the manual and keep going until you find a procedure that doesn't work. You may need to make alignment tools - like plastic screw drivers - by filing down a plastic knitting needle, or other hard plastic rod.

I am going to replace all the electrolytics on the IF/AF board in my own FRG-7 in the next two or three weeks - when I can find the time - and will post up pictures of the work here in case you want to make the same improvements to yours.

Re: trying to repair FRG-7 receiver
Steve Conner, Mon Apr 30 2012, 12:35PM

The Wadley loop synthesizer is a complicated beast. The Pop-pop noises and bad waveforms are kind of what I would expect from a synthesizer that was failing to lock.

Maybe it would be a good idea to replace the electrolytics before starting to twiddle the IF transformer cores.

Also, dual-gate FETs like the 3SK140 can be extremely static sensitive, so take great care when replacing them. The Art Of Electronics recommends winding wire around all 4 leads and the metal can (if it has one) to short everything together, and not removing it until the device is soldered into the board.

Re: trying to repair FRG-7 receiver
Proud Mary, Mon Apr 30 2012, 03:10PM

Hi Hsieh, you may find it helpful to join Petra's FRG-7 Group on Yahoo

She also runs groups for other makes of classic communication receiver.

Re: trying to repair FRG-7 receiver
hsieh, Tue May 01 2012, 07:25AM

Some suggest that I should measure TP109.I measure it but I cannot get any waveform.So I replaced Q107.Q108.Q109. But I still cannot get any waveform.

I also measures TP107 and didn't get any waveform.

Re: trying to repair FRG-7 receiver
Proud Mary, Wed May 02 2012, 10:27AM


I am going to take my FRG-7 (pictured below) out of its case next weekend to estimate the work and parts needs to replace all the electrolytics and introduce a narrower CW filter, and a crystal calibrator. If you can wait till then, I'll look at TP107 and TP109 and see what signals and voltages are on them in normal operation. I don't have a signal generator that can output a calibrated 1 μV, but last night I listened to the CW segment of 40 metres (7.000 - 7.040 Mhz) while I was doing the ironing, and could hear stations from east Europe and Russia, which is good performance for the receiver with just an indoor antenna. (I also heard a very loud WT station called GB60VUL, a 'special event' station celebrating 60 years of the Vulcan nuclear bomber, an airborne horror of the 'Atom Bomb' era.) Anyway, Hsieh, this is the sort of performance you will get from your FRG-7 when you have finished restoring it.

Re: trying to repair FRG-7 receiver
hsieh, Thu May 03 2012, 02:22AM

Today I tried to send 1mV(lowest voltage on my signal generator) amplitude modulated signal to the antenna terminal of my FRG-7.

First I set my signal generator to 1.2MHz and tune my FRG-7 to this frequency.I can hear the sound but the sound is very faint.

Then I tried to send 10.5MHz signal and tune to this signal.Now the sound is very clear.

Did this mean that I need to calibrate my receiver?

Re: trying to repair FRG-7 receiver
Proud Mary, Thu May 03 2012, 09:15AM


Remember that 1 mV is more than 1000 times larger than minimum sensitivity of receiver, which is 0.7 μV. Such a large signal could bleed through a whole defective stage, and so appear at the audio output.

A problem often found with old communications receivers is called 'finger trouble' or 'the man with the golden screwdriver' - bad work of previous owner, who interfere with circuit to 'improve' it, without knowing what they are doing. This can result in the position of dust cores, trimmer capacitors, and pre-set potentiometers being far from optimum position.

I would now suggest - as I suggested above - that you start whole re-alignment procedure given in manual, and tell me how the receiver performs at each stage.

Re: trying to repair FRG-7 receiver
hsieh, Thu May 03 2012, 09:38AM

In fact, I am now not very sure how to alignment it.I read page 11 already but cannot understand every step.Especially steps that involve sweep signal generator.

The highest frequency of the signal generator in my school lab is 20MHz.

I also don't know what output voltage should I set my signal generator to.

Re: trying to repair FRG-7 receiver
Proud Mary, Thu May 03 2012, 06:51PM

It is possible to align receiver without sweep generator, by plotting frequency response graph on graph paper like Old Times, but you still need signal generator that can output 55 MHz.

So let us leave that problem, and try procedure number (2) on page 11 "Balanced Mixer" - to give us important information.

Re: trying to repair FRG-7 receiver
hsieh, Fri May 04 2012, 12:29PM

Did the manual means that connect drain of Q102 and Q103 to the antenna input and tune to 910KHz?

I did this but there seems to be no change on the S meter.I can hear s sound if I switch to CW mode.

Re: trying to repair FRG-7 receiver
Proud Mary, Fri May 04 2012, 01:31PM


Bad translation Japanese to English! It mean you must connect antenna input terminal to Earth.

Look at back of receiver. Connect wire between SW1, BC, and E. (SW1 mean Short Wave (antenna) 1, and BC mean Broadcast antenna (Medium Frequency) and E mean Earth which Americans call 'Ground')

Now there is no RF signal from outside! Only 910 kHz spurious signal receiver make itself!

Now set BAND to A, and MHz to 0 and do procedure with VR101 and TC105 to make this bad, unwanted signal as small as possible. Slowly adjust VR101 a small amount, and then TC105. Then a little more on VR101. Then a little more on TC105 until you find best combination of R and C to make 910 kHz as small as possible.

Re: trying to repair FRG-7 receiver
hsieh, Mon May 07 2012, 02:35AM

I cannot find TC105.And no matter how I adjust VR101,the volume of 910KHz signal don't change.The S-meter didn't move either.

I also notice that when the main tuning dial is near 0 or 1000,my receiver will make a weird sound.

Now I borrowed a signal generator capable of generating up to 1GHz.But I'm still not sure how to do step 1 on the manual.

Re: trying to repair FRG-7 receiver
Proud Mary, Mon May 07 2012, 03:52PM


These are harmonics of 1 MHz synthesizer oscillator Q301. This is normal. It show that most of receiver working correctly.

Today is public holiday in England. I will work on your problem tomorrow.

Re: trying to repair FRG-7 receiver
Proud Mary, Tue May 08 2012, 08:04PM

OK.

Band selector position: B - 1.6 - 4.0
Main tuning dial: 500
Pre select: approx 2.5 MHz

Now turn slowly MHz between 2 and 3. Does red Lock light go off and then go on again as you turn knob?

LOCK light go off when frequency locked. When red LOCK light on, circuit NOT locked- like warning! Reverse of what you think!

If LOCK light test OK, try at other frequencies and tell me what you see.

Re: trying to repair FRG-7 receiver
hsieh, Wed May 09 2012, 12:34AM

Yes,The red light go on and off when I slowly turn the MHz dial.I tried different frequencies and it works.

I know that the light go off means the circuit is locked.Why they design it this way?why they didn't add an inverter/not gate?

I also replaced all electrolytic capacitor on the IF-AF unit PCB.

Re: trying to repair FRG-7 receiver
Proud Mary, Wed May 09 2012, 10:32AM

Red is warning light. Synthesizer not locked!

Set receiver to 2.5 MHz exactly as above. Set MODE to USB CW.

Connect long piece of wire to terminal SW1. 3 meters is OK, 5 m is better.

Turn up volume control.

Check LOCK light is off.

Now turn PRESELECT slowly between 2.3 to 2.6 MHz. Does the noise from speaker get louder while you turn PRESELECT, and then become more quiet?

Re: trying to repair FRG-7 receiver
hsieh, Thu May 10 2012, 04:06AM

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?

Re: trying to repair FRG-7 receiver
Proud Mary, Thu May 10 2012, 07:27AM


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.

Re: trying to repair FRG-7 receiver
hsieh, Thu May 10 2012, 11:30AM

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.

Re: trying to repair FRG-7 receiver
Proud Mary, Thu May 10 2012, 12:27PM


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.

Good Luck!

Re: trying to repair FRG-7 receiver
Proud Mary, Thu May 10 2012, 06:31PM

Hsieh! This is how I made indoor HF horizontal rectangular loop antenna 3.5 m x 4.5 m. for FRG-7





Regular hammer drill not work on my wall! Hard concrete! I use SDS drill - everything shake and crack plaster!

Re: trying to repair FRG-7 receiver
hsieh, Mon May 14 2012, 02:16AM

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?

Re: trying to repair FRG-7 receiver
Proud Mary, Mon May 14 2012, 09:22PM

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.

Re: trying to repair FRG-7 receiver
hsieh, Tue May 15 2012, 03:39PM

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?

Re: trying to repair FRG-7 receiver
Proud Mary, Tue May 15 2012, 06:13PM

OK.

We test operation of First Heterodyne Oscillator Q201.

Connect oscilloscope or frequency counter between TP101 and TP102 (which is Earth/Ground).

What is the frequency on TP101?

What is RF voltage on TP101?

Re: trying to repair FRG-7 receiver
hsieh, Wed May 16 2012, 12:42AM

I measured the waveform at TP101.I get a sine wave and the frequency is around 75MHz.(MHZ dial set at 20MHz,as specified in the manual)

Re: trying to repair FRG-7 receiver
Proud Mary, Wed May 16 2012, 10:35AM

OK.

Now measure accurately frequency across whole tuning range, and post results here, so we can talk about them.

You may also find this FRG-7 restoration project helpful:

Re: trying to repair FRG-7 receiver
caffel, Wed Feb 27 2019, 08:34PM

FRG-7 tuning. Thanks for this exceptional guidance. As I start the tune up of my own FRG-7 I see an ambiguous instruction on page 11 of the manual "Set the band switch to A and the MHz dial to 0. Disconnect the antenna and connect its output to antenna terminal."
If this makes sense to you, could you explain with a few more words ?
Thanks, caffel

Re: trying to repair FRG-7 receiver
Conundrum, Thu Mar 14 2019, 08:48AM

Would a frequency counter be any use?