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  1. Yaesu-FRG-7
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Almost ready to give up but...

 

..I thought I'd give the group a try.

Friend gave me an old FRG7 to fix for him.? No fine tune on the front & has some corrosion on the chassis.

Symptoms:

  • Only a light hiss from the speaker with volume turned all the up

  • No stations or s meter movement

  • Can hear the 455 IF (I think on 1455) if I mess with LOCK

So I check for the obvious:

  • PS voltages OK.? Electrolytics ESR are fine.

  • All connections seem fine

I suspect Q101 & find only G2 is working & replace it.? No change.

When I was checking component voltages I notice Q102/103 Emitters somewhat high at 2.5 & 2VDC

Also find that Q401 has 5.2vdc on G2 (vs 2.7).? I pull 401 & it checks fine.? I start searching for cause & misread the schematic looking for R133 to find R135 on the RF board completely missing (missing from Yeasu's component view also??).? So I install it, no change.

I then check Q407 voltages (connects up to Q401) & they are fine.? Further inspection of the IF/AF board I find a big solder blob left behind from another incompetent tech.? Remove it & no change.

I do insert a 3MHz signal into the the IF/AF board & get a loud report.

So I find 3 issues & still have a non working radio.? I am very surprised how quiet the AF is even at full volume.? I know it can get pretty loud when I inserted the 3MHz.

Any suggestions before I return the unit with a sad face.

Thanx - Bob W8RMV

ps - is there a good (cheap) source for 3SK40's?
 

Check this out in reference to the 3SK40
 

Also this thread is very useful for you
 

Is your "lock LED flashing when tuning through the megacycle tuning?

On Fri, Apr 7, 2023, at 9:50 AM, Bob W8RMV wrote:

..I thought I'd give the group a try.

Friend gave me an old FRG7 to fix for him.? No fine tune on the front & has some corrosion on the chassis.

Symptoms:

  • Only a light hiss from the speaker with volume turned all the up

  • No stations or s meter movement

  • Can hear the 455 IF (I think on 1455) if I mess with LOCK

So I check for the obvious:

  • PS voltages OK.? Electrolytics ESR are fine.

  • All connections seem fine

I suspect Q101 & find only G2 is working & replace it.? No change.

When I was checking component voltages I notice Q102/103 Emitters somewhat high at 2.5 & 2VDC

Also find that Q401 has 5.2vdc on G2 (vs 2.7).? I pull 401 & it checks fine.? I start searching for cause & misread the schematic looking for R133 to find R135 on the RF board completely missing (missing from Yeasu's component view also??).? So I install it, no change.

I then check Q407 voltages (connects up to Q401) & they are fine.? Further inspection of the IF/AF board I find a big solder blob left behind from another incompetent tech.? Remove it & no change.

I do insert a 3MHz signal into the the IF/AF board & get a loud report.

So I find 3 issues & still have a non working radio.? I am very surprised how quiet the AF is even at full volume.? I know it can get pretty loud when I inserted the 3MHz.

Any suggestions before I return the unit with a sad face.

Thanx - Bob W8RMV

ps - is there a good (cheap) source for 3SK40's?


--?
? Dayle Edwards
??dayleedwards@...
 

Mike - I've seen many of those posts.? Looks like the SMD part is most promising.
Dayle - Yes.? All 1MHz segments lock fine.

-Bob
 

Well, it seems the tuneable IF section, 2 to 3 megs is working, the loop section, ie, megacycle selector is working, so the money goes on the second mixer back. This is a juncton FET, it may be open. There is little to go wrong with the 55 meg first IF section, there is a dual gate FET in there, that never gives problems, neither does the front end balanced mixer. So, i would check the second mixer, just replacing it is easy and cheap? and will eliminate that one.
 

And, if the previous guy has twiddled the 1st IF? coil tuning slugs, it will need a realignment in that section. Correct alignment here is crucial.
 

As the saying goes, I am self taught & I had a bad teacher.
I got the scope out (means I am desperate) I can see the 1st & 2nd ocs.
I can see the lock unlock working & the comb freq on the scope.
I pulled Q105 2nd Mixer & Q104 and both tested fine.
But I see very little at TP107 coming out of the premixer IC Q106.
And I do not see the 3MHz coming out of the good Q105 over to the IF/AF board.
So I am thinking it maybe that IC Q106 or maybe someone messed with the alignment.

Thanx for the comments.? The slog continues...
--
-Bob
 

No need to worry about IC Q106, all that section is working, else you would not have the megacycle lock light flashing, this is the mixer chip for the Wadley loop, it takes the VFO and the harmonic gen products and converts them to the 52 meg IF. The output of this IF strip is rectified and used to light the LED, so this signal is present and correct.
The problem seems to be upstream from the second mixer, between this and the first mixer. Place a short wire to TP103 and see if any signals appear, this will eliminate the RF amp and front end tuning.

On Sat, Apr 8, 2023, at 11:05 PM, Bob W8RMV wrote:
As the saying goes, I am self taught & I had a bad teacher.
I got the scope out (means I am desperate) I can see the 1st & 2nd ocs.
I can see the lock unlock working & the comb freq on the scope.
I pulled Q105 2nd Mixer & Q104 and both tested fine.
But I see very little at TP107 coming out of the premixer IC Q106.
And I do not see the 3MHz coming out of the good Q105 over to the IF/AF board.
So I am thinking it maybe that IC Q106 or maybe someone messed with the alignment.

Thanx for the comments.? The slog continues...
--
-Bob

--?
? Dayle Edwards
??dayleedwards@...
 

Update:
New 3SK40 I bought off of Ebay is bad.? Same problem as the old one: G2 is kaput.? So I ordered a NTE222 from Amazon.? Awaiting delivery.
I also found the ATTN switch has seen an EMP.?? Many of the resistors are fried & one was blown in two.
So now I wait....
--
-Bob
 

Most transistor sold on eBay are fakes. You should file a claim and get your money back.
 
Edited

I would not be so scathing, most transistors sold on Ebay/Aliexpress? are not fakes. Also bear in mind these dual gate FETs are static sensitive and may have been stored/handles incorrectly by previous warehouses/distributors, or even inadvertantly damaged by the purchaser without any knowlege. Dual gate FETs , even NOS are getting on in years, they are becoming a rare component these days.? Many sellers too, have no idea of what they are selling. The early 2/3 SK series dual gate FET lacked any internal gate protection diodes and were prone to gate "punch? through" by static voltages, the later types, the 40673 for example did have the protection diodes, and therefore more robust with handling.
 

thats not what the people on all the audio sites say, do the research please
 
Edited

this is one of the many many threads on fake semi conductors from China and eBay



this article is most useful
 

You stated unequivocally that "most transistors sold on Ebay are fake".? This is untrue and an unfair generalisation.
More correctly, SOME transistors sold on Ebay are fake. .
There is a simple reason for this.? Any supplier repeatedly selling known fake semiconductors would soon not be in business.
It is also very common for a failed repair by an untrained hobbiest to be blamed on faulty components. I repair this type of equipment regularly, its been a very good little earner.
I operate an electronic design and repair shop, concentrating mainly on the repair of legacy equipment. I have been reliant mostly on the same Ebay suppliers you mention,? to supply discontinued/obsolete semiconductors, and have twice in 30 years had occasion to question a supplied component/product. This suggests that the "fake" semiconductor problem is not as widespread as is liked to be believed., and I buy a large amount of random semis from random overseas suppliers.? Others in the industry also tell me similar, I have no reason to doubt them.? They also derive a large part of their repair revenue from well meant but? failed repairs? based on youtube videos or mods? performed by the hapless owner.....
 

I am just passing along what almost EVERYONE on audiokarma and DIYAUDIO websites says…..
they are full of ordinary people getting fake semiconductors!
many of the people giving these warnings are pro, who have been in the audio hobby for many years…..

could you provide a list of eBay sellers who can be trusted to sell genuine semiconductors, there are many many people including myself would would LOVE to know who we could buy from on eBay
 

By the way, did you just call Mr. Elliott a liar? He is A PROFESSIONAL
 

This is getting off topic, my final comment.
If fake transistors predominate just the audio world, it does beg the question, why??
Vacuum tubes for instance , they look for the brand name, the colour of the getter, the gold plated pins.
We look for heater? to Cathode voltage, Gm, Mu, plate dissipation and grid bias. Transistors we look at HFe, SOA, Ft, Vsat, among others, not the colour, the hype or the "sound" or whether its recommended by some audio expert down the road, we care not about such things.
Do you seriously expect me to give a "list" of my suppliers, this would take hundreds of pages.
As I have said, only VERY occasionally you "may" have a problem, in which case, if suspicious, or suspect, simply MEASURE the component parameters first ,thats what? competant techs do. There is no excuse for fitting suspect parts , or substitute parts without..... potentially damaging the equipment under repair.
 

Clearly we disagree
 
Edited

Accusing Mr Elliot of lying? Certainly not, and what a stupid allegation.
I do however question the parroting of unsolicited allegations of fake components from unknown sources. For instance, unwanted parasitic oscillations are common in high gain audio designs, and can destroy ANY? output transistor even at quiescent .
Many of these reported failures are from non technical people who either lack the knowlege or equipment to track this phenomena, let alone cure it, they are merely following a diagram, or a plan, with the expectation it will work.
One contributor sites a? 2N3055 transistor failing at 4 amps, so it must be a fake. The genuine transistor is rated at 15 amps Ic, max CE voltage 60 by memory. Without any more technical context by the contributor, we cannot diagnose anything. What was the supply? voltage? What was the base current? Was the transistor in saturation? What were the thermal conditions.????Not enough evidence here to allege fakery.
?Was? this gentlemans expectations rather? too high, his understanding too low? perhaps?
To accept this as evidence of a fraud is ridiculous.
?I am sure fake components do exist, but not on the scale you would like to believe.... my initial point.
Even your friend Mr Elliot agrees with me that distributors making a living knowingly selling fake transistors are unlikely to remain in business long, so in that regard, its a self levelling process.?

So, please do not offend me with your assumptions.

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