sony: Sony ICF-SW1: FM selection fails & audio motorboating

Hello fellow members, 

My unit refuses to accept the FM band selection.

Pressing FM button seems to select FM band, but the frequency digits do not appear on the LCD. When presssing the Up or Down keys, the radio switchtes itself back to AM mode. EDIT: This behavior seems to be normal, as we need to type in a frequency in order to be able to commit the RF band selection. However, the radio was not accepting some digits, at least the ones I tried in my brief testing before dismantling the unit.

At least the AM seems to be working, showing the frequency digits, despite with apparent low sensitivity.

That said, the radio also shows the usual motorboating sound at the speaker (but not on headphones), typical of poor decoupling caused by the infamous SMD aluminium electrolytic capacitors that plaged so many equipment of that era.

Contrary to some public information, all SMD electrolytic caps should be replaced at once, not only those two directly afecting the audio power IC Filter and Bias 1 (C607 and C608). 

Why? Because all were manufactured at the same time period using the same deficient manufacturing technology and soldered using the same perfectible technique, so all of them are suspect. Additionally, other operating conditions besides the obvious motorboating noise may be negatively affected by the other defective caps and overlooked at a summary analysis. 

The six SMD electrolytic caps that would need to be replaced are:

In my unit, C420 220uF for VCC decoupling of the IC401 CXA20111 RF IC have leaked as well as the others.

I ordered new capacitors from my local shop and wating for delivery.

The battery contacts also shows signs of corrosion.

As usual, I will clean the PCB's and keyboard membrane with proper IPA spray to remove any electrolytes and other residues. 
I hope this would solve the above FM band selection issue, otherwise it seems I will have a troubleshoot session ahead.

As for the battery contacts, I use cleaning vinager with good results.

(to be continued)

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The three PCBs were cleaned with IPA spray and the keyboard membrane was washed along with the other cabinet parts. Small black particles were released from these parts, I wonder what kind of residues entered inside this unit.

SMD capacitors arrived and installed.

I could not find the small, 4V working voltage caps in my local suppliers, so I had to fit larger ones (6, 10 and 16V) that took extra space in the PCB, taking a few more minutes to solder them in.

A little tricky procedure, as I did not want to use hot air guns on these kind of caps, so I used the thinnest solder iron tip at hand, at less than 1mm diameter at the extreme tip, and I have it bent at an angle of 120 degrees to allow it to apply heat between the capacitor terminal at the bottom and the PCB. I have set the temperature at 420 degrees, and used the good old 60/40 low melting point solder alloy, for a fast soldering operation avoiding excess temperature on the capacitor. And obviously before laying the capacitors on the PCB, I pre-tinned the pads on the PCB as well as the capacitor terminals, to allow for quick soldering.

I could use tantalum caps in smaller sizes, but I wanted to keep with the Sony original design choice and spirit.

After joining the parts for testing, I finally managed to set the FM frequency band correctly. I believe the issue was related to the keyboard membrane contamination. 
And of course the radio unit works fine on the speaker now. No more motorboating sounds.

One last observation on the radio current consumption. I measured around 37mA with volume pot at minimum, and around 45mA with a confortable volume sound.

 

 

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As a final testing, and just for fun, I have changed the radio variant from the original Type 2 to the fully fledged Type 1, despite the radio front panel still says it covers only from 87.5 MHz on FM and up to 26100 kHz on AM.

 

My original Type 2 radio:

 

After changing the radio to Type 1:

 

And it works as advertised, although in my region the now extended FM and SW coverage is basically useless:

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Thank you Jose for posting these pictures & text how you got your SONY going. I did the same work on mine, which had the same "sickness". Got it going this weekend mid Jan 2024. It was Purchased 1989 but works fine now.  Thanks

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