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sony: Repairing SONY ICF-7600A (some of the typical faults)

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Forum » Radios and other type of sets (Physics) etc. » MODELS DISPLAYED » sony: Repairing SONY ICF-7600A (some of the typical faults)
           
Jose Mesquita
Jose Mesquita
 
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Schem.: 208
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31.Aug.20 19:18
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Got this radio model with a good external case and antenna.

I found and have fixed these problems, some are typical issues with this model:

1. Battery corrosion at the contacts: Cleaning using vinegar have fix it.

2. Tone switch contacts oxidation, resulting in audio loss: Dismantling the switch and cleaning have fix it.

3. Missing original Sony speaker: Found a Chinese similar model in UK eBay seller that looks identical to the original, same sizing and electrical specifications. Only difference is the original SONY label printed in the speaker.

4. Short Wave bands are dead (but FM and MW reception works fine):

Power supply rails are OK, oscillators are OK, but the antenna protection diodes (D6 to D9, 1S1555) were burned and in short-circuit. Replaced them with 1N4148 diodes, but it did not fix the issue.

Checked the SW RF AMP FET transistor Q5 (2SK192A) and it was in short-circuit between Dreno and Source. Replaced with a more modern 2SK241 and it resolved the problem.

Original 2SK192A found faulty.

5. Badly worn volume sliding pot, with audio loss: Found a Chinese similar model replacement, but this new component do not fit correctly in terms of size.

I prefer to leave the original potentiomenter in use, but it presents around 200KR instead of the nominal 10KR. The issue looks to be depleted conductive material at the low volume position near the riveted terminal. Also the same issue is shown at the cursor trace.

I have ordered some conductive paint with silver content, to apply on the affected zones and see the result.

Will let you know about the results.

 

  
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