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