Sony ICF SW7600

[Dylan85]

I know that what follows doesn't relate to 'vintage' or 'valves' but I have a bit of a soft spot for these radios. They may not conform to the average view of what qualifies as an antique radio, but humour me, some of them, like me, are getting on a bit now. For their age they still perform remarkably well and in their day Sony were one of the market leaders with a radio that had features that many rival sets did not have at that time.
When I purchased mine, I was due to take my morse test and I needed a portable means of listening to real SSB / CW transmissions. In those days I was using a R1155 at home for most of my listening and apart from it's lack of portability, my wife wasn't hugely enthusiastic over it's presence in the dining room.

I now have two of these Sony radios, the first I bought new in 1991 I think it was, so has now come of age at a venerable 21 years old and is still going strong. Although it was expensive at the time, it has turned out to be one of my better investments. The second 'SW7600' was aquired recently and the FM band wasn't working on this one.

The one weak spot of the ICF SW7600 is the surface mount electrolytics, they gradually fail with age, some leaking electrolyte and some drying out. No different in that respect to a lot of older 'valved' radios. There is some debate as to whether the capacitors were just unreliable or whether in fact during the pcb assembly stage too much heat was used to solder them in place. Either way, the end result is the same.

Getting into the SW7600 is strraight forward and 4 screws are all that is required to release the front / rear case halves. The rear case can then be removed to expose the main radio pcb. The majority of the components used on this pcb are surface mount but are not too small (by today's standards) and so replacement is possible with care. To remove the main pcb, 4 wires have to be unsoldered from the internal ferrite aerial and the 2 speaker wires also. A single screw once removed from the centre of the pcb allows the pcb to be released from a couple of moulded latches. A ribbon cable on the other side of the pcb that connects to the display / control pcb has to be released and then the pcb can be safely removed. The display / control pcb can also be unclipped from it's moulded support frame.

There are a total of 27 electrolytics that need to be replaced, 26 on the main pcb and 1 on the display / control pcb. When I checked the board over under a magnifier, only 3 or 4 of the electrolytics apppeared faulty, showing signs of leakage. One of them clearly had caused corrosion to nearby tracks by leaking electrolyte over the pcb.

The original electrolytics were end mounted aluminium devices and have to be removed carefully to avoid damaging the pcb tracks. I found the easiest way was to 'chop' the can off and then remove each lead separately. Once removed from the board I could then see that almost every single capacitor showed signs of leakage but it was underneath the plastic capacitor support pad and so was invisible until the capacitor was removed. So, I would say if you get this far, it would pay to replace all of the electrolytics regardless of whether there are signs of leakage or not.

The most awkward capacitor to access is probably C127 which is connected across the output of the DC converter. This generates the 14 volt supply for the varicap tuning and runs at a nominal frequency of 1.8MHz. The DC converter is surrounded by a screening can on both sides of the pcb and this has to be removed to acces C127. Awkward but take it steady and it's all fairly straight forward.

Once all the capacitors were removed, the board was given a good scrub and clean with IPA taking care to avoid IF coils, trimmers, potentiometers etc.

The display / control pcb has only one electrolytic and that has plenty of room around it and so is an easy one to replace.

Replacement capacitors were obtained from CPC and Farnell and all seem to be readily available. Capacitor technology has moved on a bit since these radios were made and now it is possible to find low voltage ceramics up to 47uF, cheaper than their electrolytic equivalent. So that was the route I took, especially on the output of the DC converter where the high frequency ripple current and the capacitors ESR causes internal heating of the capacitor. The electrolyte susequently dries out followed by the eventual demise of the capacitor. The ceramic replacements should avoid this particular issue.

Capacitors of 100uF or larger I replaced with the modern electrolytic equivalents. There are 3 radial leaded high value capacitors around the audio stage and I replaced these with the same style.

Putting it all back together was the reverse of disassembly and when power was applied I was rewarded with a fully functioning radio once more. I am hopeful that this radio will now give many more years of reliable service.

For anyone who may have one of these radios and it has started showing problems, I would say that if your soldering skills are upto it then give it a go. I found that a good 10x magnifier or headband magnifier was essential not only to cope with the repairs but to also read the schematic!

The full service manual for these radios is freely available to download online and should have all the information you need to carry out 'recapping' of these radios.

Another job jobbed!

Dylan

[fetteler]

Dylan,
Very good to read your comments. I bought one of these in about 1992 I guess... At that time I was travelling a great deal, often to fairly inhospitable and out of the way places and the little Sony radio was my companion and link back to a saner world.
I'm mostly at home these days but your post has made me want to get the Sony out again and try a set of batteries in her.

Cheers,
Steve.

[cmjones01]

Originally Posted by Dylan85

Capacitor technology has moved on a bit since these radios were made and now it is possible to find low voltage ceramics up to 47uF, cheaper than their electrolytic equivalent. So that was the route I took, especially on the output of the DC converter where the high frequency ripple current and the capacitors ESR causes internal heating of the capacitor. The electrolyte susequently dries out followed by the eventual demise of the capacitor. The ceramic replacements should avoid this particular issue.

It would be worth checking the output of the DC converter with a scope after replacing its output capacitor with a ceramic. There are some types of voltage regulator which get upset with the extremely low ESR of ceramic capacitors and start oscillating. The chances of this are fairly small, I'd have thought, in a radio of this vintage - the fussy regulators are generally a certain era of linear low-dropout ones from about 5 years ago - but it's something I'd look at just to be sure.

Chris

[SeanStevens]

These are lovely radios - I have had at least two from this family (ICF SW-40, ICF 7600d).

My last one was a Sony ICF 7600d - it would not turn off its amplifier, no matter what buttons were pressed. I wonder if it was a capacitor?

Nice write-up - you must have very keen eyes!

SEAN

[Dylan85]

It would be worth checking the output of the DC converter with a scope after replacing its output capacitor with a ceramic.

It's funny you should mention that Chris, the same thought went through my mind. I did have a quick look at the 14 volt rail with a scope - just in case. No signs of instability and normal mV levels of ripple. The other thing I have come across with ceramics is that they can be very microphonic depending on where they are used in a circuit and what function they are performing. I would think in this case though, they are all supply decouplers and the risk of microphony problems low.

I'm very tempted to look at my original 7600 and see what state those capacitors are in. although it is performing flawlessly I'm now getting visions of leaking electrolyte doing nasty things to the pcb. Trouble is I'm a great believer in leaving well alone if it is working ok. Maybe a bit of preventative maintenance would prevent tears later on. I get the impression that these radios benefit from being in continuous use but who knows?

you must have very keen eyes!

I wish! Long gone are the days when I could do a bit of surface mount with the MK1 eyeball, hence my comments about a x10 magnifier. Thinking about it, I'm fairly sure it is actually a x20 magnifier. As long as I can see it I'm prepared to have a go at it, but if I can't see it then I've got no chance. At work we are now using 0402 devices (1mm x 0.5mm) and I won't even try to work with these unless I really have to, they are like specks of dust!

At that time I was travelling a great deal, often to fairly inhospitable and out of the way places and the little Sony radio was my companion and link back to a saner world.

Me too. I've used mine a few times when abroad and it has never let me down. The alarm feature has also proved useful too, though I guess these days most people have everything built into their mobile phone, including the FM radio.

nice write up i got one i picked up in the summer boxed all bits for a fiver

Thanks for the comments. That's an absolute bargain Vince, well worth a bit of effort to get it going.

Dylan

[Andrewausfa]

Nice write up Dylan. I have the more recent 7600GR which comes with me on trips around the world. The manner of tuning on the GR is slightly annoying but other than that I love it.

Andrew

[Hybrid tellies]

Very impressive job. Your eyesight must be A1. These radios were sought after by anyone into DXing and their performance is still good even by today's standards.

[dave cox]

Dylan, how to you chop the can off without stressing the pcb? Thanks, dc

[Dylan85]

Carefully, taking care not to 'pull' the capacitor body.
The capacitor lead outs will sometimes 'peel' away from the copper foil but this is not a technique I could recommend.

dylan

[HamishBoxer]

Use "desoldering braid".

[boiss]

I also have one of these and changed all the electrolytics. I tried solder wick
but the best way as stated is to use end cutter snippers and carefully cut the cap in half and then remove the rest, tweezers etc. Latest problem ;- it didn't work with batteries. Resolved by reapplying solder to the pads contacted by the battery connectors on the pcb.
Have fun although SW is a bit dead these days !!

[brunel]

@ Dylan85.

Thanks for your excellent write up. You have spurred me on to have a further look at my 7600.

A few of the surface electrolytics are showing signs of distress, so will need replacing.

You mentioned that you obtained suitable replacements from Farnell/CPC.

I am slightly confused about the types and physical size of the replacements, do you have the details of the ones that you obtained from Farnells and if possible the various stock numbers.

Regards

IKB......!!

[Dylan85]

I am slightly confused about the types and physical size of the replacements, do you have the details of the ones that you obtained from Farnells and if possible the various stock numbers.

Sorry, it would take rather a lot of ferreting through old orders paperwork to track all of these down. If I were a bit more organised I would have made a note of them all for future reference.

All I can suggest is measure all of the capacitors you need to replace i.e. can diameter, dimensions of the base and solder contacts and overall height. Then when you look through suitable capacitors for value / voltage rating on CPC / Farnell etc, they will also have data for capacitor diameter / height etc. It takes a little trawling through the data sheets but the information is all there.

I have just had a look through an old order and some (maybe all)of the capacitors you need will be on the CPC website. Listed below are the part / order numbers on my order, so look them up on the CPC website and you should find what you want.
A word of warning, some of the capacitors below were for another job, so you won't need those.

CA05526
CA07901
CA06318
CA05527
CA05532
CA07446
CA05131
CA07521
CA05498
CA05562

Good luck.

Dylan

[brunel]

Thanks for the info.

[maginot]

Hi,

I have a 7600DA model and already replaced the DC converter related caps. It should generate 17.5V but I can only get around 1.5V after turning on the radio which decays down to 0.5V. Would be very grateful for any other ideas (apart from replacing the caps)? Presumably the oscillator is not working correctly but which component is key to triggering the oscillator that could be at fault?

many thanks