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Old 21st Aug 2020, 3:06 pm   #1
Dylan85
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Default Sony ICF SW7600 lives again.

Well after a bit of a protracted battle to order a replacement part, this set is fit for purpose again.
A short precis of the repair folows:
This set is now 28 years old and has never let me down until approx 2 weeks ago when the audio failed. Having worked on other examples of this set previously, I was fairly certain that this was due to that recurring problem of leaky /dried out aluminium electrolytic capacitors that seems to plague these sets. This is where Murphy steps into the picture - having sourced and replaced all of the electrolytic capacitors I was greeted with silence again, no audio. Curses.
After carrying out a few more checks and measuring a few key voltages it was apparent that the audio amplifier chip was dead. This is not unknown on these sets but this was the first occurrence that I had come across. This chip was made by Sanyo (LA4550) but in the intervening years has been made obsolete. However there are still one or two places they can be purchased. I was very wary of purchasing from the majority of advertisers on that well known auction site due to the proliferation of counterfeit devices. However, I managed to narrow my search down to 1 UK supplier and placed my order. This wasn't straight forward though and after much chasing up it eventually turned up about a week later than it should have done.
Removing the old device is best done by cropping all of the leads close to the IC body and then removing the pins and heatsink tabs one at a time. Once all of the pins have been removed the pcb pads can be carefully cleaned up with solderbraid and any excess flux cleaned off. Before fitting the new device I took the opportunity to carry out a few resistance / continuity tests using the circuit schematic as a guide. All tests checked out ok so I went ahead and fitted the new audio chip. The tabs on each side of the IC act as low thermal resistance paths to the underlying heatsink ( pcb groundplane) so care is needed to use a large enough soldering iron bit to get sufficient heat into the heatsink tabs and pcb groundplane without overheating the amplifier chip.
This done, the radio was then reassembled which is a little fiddly and upon applying power was rewarded with audio good clean audio. Welcome back old friend.

Just a few additional comments to make as a result of carrying out a bit of research whilst awaiting delivery of spares.
The original audio device fitted was a LA4550 made by Sanyo. As stated above this device is now obsolete but a few do still seem to be available. As time goes on this stuation will no doubt get worse. However, there is a second alternative i. e. LA4555 also made by Sanyo which is also obsolete but for some reason seems more readily available at present and it seems cheaper. The only difference between these 2 devices seems to be slightly inferior THD figures for the LA4555 but as far as I can tell all other parameters were practically identical.
I also managed to turn up a third option which in the long term may be turn out to be the only option. This device is the KA2206 made by Samsung and as far as I can tell is still a current production item. In the context of the Sony ICF SW7600 this is a pin compatible item with parameters very similar to those of the LA4550. The main difference seems to be the quiescent current figures. The LA4550 states typ 15mA to max 30mA whereas the KA2206 states typ 40mA to max 55mA. It may be worth a punt if all else fails.
I hope the above is useful should anyone else have the same problem.
Photos below show the removal /replacement of the amplifier.
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Old 21st Aug 2020, 3:20 pm   #2
Vintage_RC
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Default Re: Sony ICF SW7600 lives again.

Well done on reviving the Sony ICF SW7600. These are good sets and well worth some time spent on repairing.
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