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Old 31st Aug 2020, 2:16 pm   #1
Phantomrose1999
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Default FRG-7. Very quiet

As this is my favourite site, hope there are some FRG-7 experts here

Bringing one back to life but time to reach out

It has low RF sensitivity, can’t peak the front end could, the S meter doesn’t move. On AM it’s very very quiet. On LSB I can hear some noise. Was able to pickup an AM station one day with a very long wire.

Have replaced the 3x 3SK40 fets with originals. All voltages ok. The two oscillators are working. But there is virtually no signal at TP104. At under 1mhz I get a 180mv signal at 52mhz (I do hear noise at the speaker) but at any other frequency there is no output at TP104

Does the mixer IC fail ? SN76514 ?

Any other suggestions ?

David
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Old 31st Aug 2020, 3:03 pm   #2
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Default Re: FRG-7. Very quiet

Just at the moment all the HF bands are amazingly quiet. THere has been a geomagnetic storm, so don't judge things just now.

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Old 31st Aug 2020, 3:49 pm   #3
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Default Re: FRG-7. Very quiet

Itís embarrassing but I can now pick up an AM station on broadcast band. But itís so quiet off station. Zero noise. And the peaking knob is so sensitive a few mm and I will lost the station.

To actually find another station is ridiculous! The peaking knob and 1mhz tuning know must be moved in synchronisation.

The S meter barely moves on AM local stations and thatís with a 6 ft wire. This canít be normal.

See photos of both oscillators working.

Does this unit need a long outdoor antenna to work ?

I even used a RF generator a few feet away and it can pick it up. But itís just so insensitive. Driving me batty !
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Old 31st Aug 2020, 3:53 pm   #4
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Default Re: FRG-7. Very quiet

Quote:
Originally Posted by Phantomrose1999 View Post
Does this unit need a long outdoor antenna to work ?
Yes. For any decent sensitivity.

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Old 31st Aug 2020, 3:54 pm   #5
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Default Re: FRG-7. Very quiet

I can pick up 40m SSB as clear as AM stations with my old Marc dual on my kitchen table with the telescopic aerials

https://youtu.be/Ghj0oZWW32U

Was thinking a triple conversion Unit should be better or st least as sensitive.
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Old 2nd Sep 2020, 5:30 am   #6
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Default Re: FRG-7. Very quiet

The Drake SSR1, which is very similar, circuit-wise, is normally fitted with a telescopic whip.
Using this, or a fairly short length of wire on the ordinary aerial terminals, it is quite lively.

I remember going to the radio store, clutching my hard-earned cash in hand, to buy a FRG-7, but they were out of stock, & I got pointed at the Drake instead, otherwise I could have been more helpful.
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Old 2nd Sep 2020, 5:54 am   #7
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Default Re: FRG-7. Very quiet

After submitting the previous post, a bit of information came back to me.
It may not be useful, but here it is, for what it's worth.

The normal method of operation with "Wadley loop" radios like this one, is to:-
(1) Set the MHz control to the required band.

(2) Adjust the peaking knob for maximum noise.

(3) Tune across the band with the kHz knob.

It is, thus, a bit more "structured" than a conventional superhet, where the bands are changed with switches, so each range change presents you with virtually a separate radio for that band.
With such radios the "peaking"control just tweaks the aerial input tuning.

With the SSR-1 & the FRG-7, the MHz control tunes to each of the harmonics of 1MHz, "which one", depending on the required band.

The SSR1 MHz control was always a "bit off" the markings.
You would move it to the "MHz" marking, then a little bit off, & up would come the noise.

The Drake used, from memory, a 10 MHz crystal, which was then divided down to 1MHz, a popular modification being to change the oscillator to 1MHz directly.
I think this was because Drake, or the Japanese OEM were miserly, & 10 MHz crystals were cheaper.
I dunno if Yaesu did the same.
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Old 2nd Sep 2020, 8:20 am   #8
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Default Re: FRG-7. Very quiet

10Mhz crystals are cheaper but you can usually get them at better stability.

The bandchange switch and what you've called the peaking control are the range and tuning controls for a basic preselector. The preselector is needed to protect a fairly soft mixer from strong signals away from your wanted frequency.... Even the Racals relied a lot on their preselector.

You do indeed set the MHz dial appropriately then tune the kHz dial, but, go back to the MHz dial and twiddle slightly to peak your wanted signal. This dial being off a bit is usually NOT the crystal, but a tuning error in the Wadley system filters. There are two of them and famously a nightmare to adjust. on't touch them unless you really really need to. to adjust them you need a sweeper (wobbulator) and some experience in adjusting higher order filters.

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Old 2nd Sep 2020, 5:56 pm   #9
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Default Re: FRG-7. Very quiet

I've just had a quick look at the circuit diagram,

http://www.monitor.co.uk/radio-mods/...it-diagram.pdf

I see that there is an awful lot of switchery in front of the receiver.

I am assuming that the DX/Off/Atten switch has been set to 'DX' throughout?

One thing you could try is to connect a long length of wire directly to C101, not the side which goes to Q101 G1, but the side which goes to the junction of VC1 / S2c common. Connecting an aerial here bypasses the input bandpass filters, but if the receiver livens up when you do that, that would suggest a fault between the aerial input and the beginning of the receiver proper.
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Old 2nd Sep 2020, 6:57 pm   #10
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Default Re: FRG-7. Very quiet

That snippet shows a 1MHz crystal, X301, as the basis for the harmonic generator.
Any old MW radio should be able to hear that running when held in proximity.

No 1MHz and there will be nothing else. It could be a sleepy crystal.
Maybe the weak AM station was just breakthrough at tunable IF?

Last edited by Jon_G4MDC; 2nd Sep 2020 at 7:09 pm.
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Old 2nd Sep 2020, 8:02 pm   #11
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Default Re: FRG-7. Very quiet

does it have a fuse ie a lamp fuse on the input? ei7ka
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Old 2nd Sep 2020, 8:16 pm   #12
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Default Re: FRG-7. Very quiet

As per FT747 / FT757? Not according to the diagram (post #9).
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Old 3rd Sep 2020, 2:51 pm   #13
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Default Re: FRG-7. Very quiet

Quote:
Originally Posted by SiriusHardware View Post
I've just had a quick look at the circuit diagram,

http://www.monitor.co.uk/radio-mods/...it-diagram.pdf

I see that there is an awful lot of switchery in front of the receiver.

I am assuming that the DX/Off/Atten switch has been set to 'DX' throughout?

One thing you could try is to connect a long length of wire directly to C101, not the side which goes to Q101 G1, but the side which goes to the junction of VC1 / S2c common. Connecting an aerial here bypasses the input bandpass filters, but if the receiver livens up when you do that, that would suggest a fault between the aerial input and the beginning of the receiver proper.
Been poking my CRO around. Will post the findings. The DX switch is in the middle. At DX the radio is dead. Could be a clue. Will try your suggestion.

Itís the AM BC that has zero background noise until I find a station. But the preselected and kHz tuner are incredible sensitive and this difficult to align both to get a station on BC.
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Old 3rd Sep 2020, 3:47 pm   #14
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Default Re: FRG-7. Very quiet

I think the bottom band, for doing AM broadcast medium wave reception may have an inbuilt attenuator, in the assumption there will be bigger signals. I seem to recall FRG7s were quieter. A number of other sets played this same trick.

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Old 3rd Sep 2020, 3:54 pm   #15
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Default Re: FRG-7. Very quiet

I think you are right David. The Local DX Switch Attenuator path is different between range A and the other three ranges.

The other thing this has is an LED indicator that shows when you are tuned on a 1MHz band segment.
It seems it is lit when off tune and it goes out when MHz dial is correctly tuned. I wonder whether that behaviour can be observed on this set?

It works by detecting the level of 1st LO mixed with the 1MHz harmonic as observed at the end of the narrow (52.5MHz) filter.

Do these paths through the Local/DX switch meet general agreement?
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Old 3rd Sep 2020, 4:40 pm   #16
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Default Re: FRG-7. Very quiet

Quote:
Originally Posted by Jon_G4MDC View Post
That snippet shows a 1MHz crystal, X301, as the basis for the harmonic generator.
Any old MW radio should be able to hear that running when held in proximity.

No 1MHz and there will be nothing else. It could be a sleepy crystal.
Maybe the weak AM station was just breakthrough at tunable IF?
Both oscillators are working. Pls see 1st post.

There is almost no measurable output at pin 3 of the mixer IC.

The output from the RF board to the IF/amp board is 40mv during a broadcast station. Thought it should be higher ? If I put my finger on the same connection I get static from the speaker so the issue is in the RF board.

Will post waveforms at the key test points
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Old 3rd Sep 2020, 5:07 pm   #17
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Default Re: FRG-7. Very quiet

Quote:
It seems it is lit when off tune and it goes out when MHz dial is correctly tuned.
To save battery life?
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Old 3rd Sep 2020, 5:19 pm   #18
Jon_G4MDC
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Default Re: FRG-7. Very quiet

You won't see much at Q106 Pin3. It takes 3 stages of gain before they can do anything useful with it.

What about the Lock LED behaviour? If you want to look for mixer output look after the gain at TP110 - this is where the detector for the LED is so we know there should be some go there - if all is well...

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Old 3rd Sep 2020, 8:31 pm   #19
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Default Re: FRG-7. Very quiet

Some thoughts, does the OP have the instruction/service manual, the Yaesu one? It has all the test voltages and alignment info in there, and the instructions on how to drive the radio, it really isn't like anything else. The input attenuation switch oddly is at its most sensitive on the middle "normal" setting, the DX setting drops the signal, and the local setting even more. Which aerial input is being used? Linking SW1 & BC then feeding the aerial into the coax socket should give the best sensetivity on the BC band.

If the voltages look good when checked against the service manual, check the 2nd tunable IF, it tunes 3 to 2 MHz, backwards, with the L.O 455kHz higher than the input signal, if that works OK, then turn attention to the 1st IF / RF board.

Can the OP report back if the tunable IF section is functional first.

Is there any known history to the set that may help an online diagnosis?

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Last edited by Tyso_Bl; 3rd Sep 2020 at 8:35 pm. Reason: typo
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Old 3rd Sep 2020, 9:17 pm   #20
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Default Re: FRG-7. Very quiet

The well documented modification replacing the "lock" LED with a dual-colour one is
simple and worth doing.
I have noticed that near the ends of some preselector bands it is worth selecting the
next band up or down and tuning for mximum signal, there is some overlap.
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