Sony CRF-5090 "Eart...
 
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Sony CRF-5090 "Earth Orbiter"

 
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered

I was asked to look at this set some long time ago, by a friend on behalf of a friend of his. The set has sentimental attachments for the owner, so I thought that I really should have a look at it after a long period.

The main problem is it crackles very loudly at switch-on, which can be reduced with the volume control and continues to do so, although it is much more prominent on AM than it is on FM. That immediately raises a big worry in my mind; what if it's an IF transformer breaking down? You can see the effect of this problem clearly on the tuning meter.

I took it apart and one thing I noticed was that I was not the first person to have been in this radio. I also downloaded a service manual for it; but on closer examination I discovered that it bore little relationship to the set in question. In fact, the later CRF-5100 manual is much closer to the physical and electrical layout of the set, save for the extra VHF 'Air' band. It is also very difficult to dismantle beyond removing the chassis from the cabinet: it is nowhere as easy to work on as say, a contemporary Grundig Satellit. On closer examination the wiring to the loudspeaker via the earphone socket was replaced incorrectly, so that has been corrected and the wiring replaced more neatly. The switches have had DeOxit sprayed into them, but it doesn't 'sound' like switches. It sounds like component breakdown. I may have to break out the analogue 'scope for this - the one I recently fished out of a skip!

So as a first measure, I've ordered some new 2SC710 transistors to try in the IF stages. I'll let you know how I get on: I'll try and post up some pictures later.

I have a number of sets I'm meant to be looking at for other people (one indeed being a Grundig Satellit 2000): how nice it will be to get them repaired and returned, so I can look at my own collection.

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Topic starter Posted : 28/07/2019 4:36 pm
crustytv liked
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered

Just a quick picture of the interior: all on one PCB bar the VHF tuner and the fuse panel. Note the set being powered from my trusty old Farnell PSU.

CRF5090 1
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Topic starter Posted : 28/07/2019 8:27 pm
Anonymous
(@anonymous)
Group Deactivated Account

I have one of these radios came from NY in the 70s still got the sony sales sticker on it, I had this trouble on my Grundig Melody Boy, on the Grundig it was C82 coupling from Volume Control to Base T8. just an Idea.

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Posted : 29/07/2019 6:13 pm
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered

At long last... an update!

Finally, after getting fed up of looking at this sat on my bench, but also spurred on by repairs to a set in my collection prior to it going for auction (I'm downsizing) I decided to look at this with fresh eyes.

First step was to isolate the fault, and to do this I realised I could short the collector of the first AM IF amplifier transistor to earth without any ill effect. Switching on the set, I was rewarded with the usual loud crackling and so I shorted the collector down, to be rewarded with silence. So the fault is either here, or prior to it.

Now, these are not the easiest sets to work on but that transistor is accessible with care and a long-nosed pair of pliers. I thought I might prod around the area to see if I could provoke anything - and when I prodded the transistor, all sorts of noises and goodness knows what occurred. Noting carefully the orientation, I removed it and connected it to my little Peak tester. It told me it was a transistor, and these were its connections - emitter and base at the edges, collector in the middle.

Some time ago, I bought some 2SC710s from a reputable supplier, but these didn't look like the one I removed; they were smaller. Noting the orientation, I soldered a new one in and switched on.

Nothing. Not a sausage. Rats!

Out comes the new transistor, and pop it on the Peak. Yes, it's a transistor. Compare it with the old one, which briefly said it was a couple of diodes. Eh?! Retry, and this time it says it's a transistor. But hang on... where did you say the base and emitter were? Oriented the new transistor the same way, connected the leads up... and no wonder it didn't work. The base and emitter are swapped! So, repositioning the leads, I re-soldered the transistor back into the set and switched on. Radio Caroline boomed out, free from crackle!!

If anybody can offer an explanation for that, I'd be grateful.

A quick play showed lots of life on the AM bands (even LW had life) and also on the FM band, so it would seem IF alignment is unnecessary - but it does need a tweak on the FM band as the stations don't come in anywhere near where they should do on the dial.

That, however, is for tomorrow...

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Topic starter Posted : 09/02/2020 11:57 pm
turretslug, Nuvistor, ntscuser and 2 people liked
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered

To wrap up: the set was adjusted to get the tracking right on FM and then soaked on Radio Caroline for the rest of the day. Further reinforcing the fact that the set is a CRF-5100 in disguise, I noticed the VHF tuner had all the components for the missing "PSB" band fitted - it's just you can't switch to them!

Also is a photo of the defective transistor, which my Peak DCA75 now just sees as two common-anode zeners. But what's that around the legs on the body?

Earth Orbiter
defective transistor
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Topic starter Posted : 11/02/2020 1:21 pm
Nuvistor liked
turretslug
(@turretslug)
Honorable V-Ratter Registered

I wonder if that is a similar problem to the notorious Lokfit lergy- perhaps an incomplete adhesion of plastic encapsulant to the lead-outs, allowing atmospheric degradation of the silicon sliver.

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Posted : 11/02/2020 8:49 pm
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered

@turretslug

I have to admit I was having the same thoughts, especially as you could mechanically provoke the transistor into noise and failure by moving it about even though the joints were sound.

 

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Topic starter Posted : 11/02/2020 9:59 pm