Radio Head Unit (EU 1992) Repair and Capacitor Replacement

[Heineken]

A fellow NSX driver approached me after fixing all three of his amplifiers (http://www.nsxcb.co.uk/showthread.php?15973-Speaker-Amplifer-Repair-and-Capacitor-Replacement) reporting issues with his radio. It worked but when listening to stations they were distorted and he mostly used it together with a CD changer adapter. The unit arrived last week, with an interesting modification to supply power to an extra set of speakers but nothing to worry about. Time to grab the active speakers, a cassette and a CD changer for a test run.





14381
front


14382
back


14383
bottom





Radio tuning and sensitivity were fine. The sound was indeed distorted - an effect that wasn't audible when playing cassette (which worked fine - including reverse and track skip so no belt replacement (http://www.nsxcb.co.uk/entry.php?2659-Radio-Head-Unit-Cassette-Belt-Replacement) required) or CD. The sound got better after warming up but then the CD playback, which was working on one channel only, completely dropped out - suspect here is the OP amp near the CD changer socket as it's often affected by acid creep.
Since the distortions were only present when the radio was playing it couldn't be the Z-diode from the last radio repair (http://www.nsxcb.co.uk/showthread.php?15911-Radio-Head-Unit-(EU-1992)-Repair-and-Capacitor-Replacement) since that affected all sound sources equally.

Next step was opening the case and investigating the PCBs for damage. It's the typical European RDS NSX radio with the extra large voltage stabilizing capacitors that leak substantially.
Two capacitors had blown and, three where bulged and the two large ones leaking. The capacitors on the small power where leaking too but no damage had happened to the PCB yet.



14384
bulged and vented capacitors


14385
soaked connectors and OP amp


14386
large leaking caps







14387
acid leaks on the PCB ..


14388
.. underneath the flat cable connector ..


14389
.. and on the power board





To ensure a proper repair, the CD changer and the left flat cable connector were removed and investigated. Since there was no corrosion beyond the soldering points they were deemed fit for service and later re-installed. The OP amp and all contaminated silk screen was removed, no damaged tracks observed and everything cleaned, including the connectors.

<to be continued>

[Heineken]

A new OP amp, cleaned connectors and new capacitors were installed. Since only the larger capacitors are replaced (identified by venting marks on top) the small one on the middle PCB, under the metal shield, was replaced, too (no image). Note that the so-called semiconductor crisis isn't only about these but regular parts, too. Some of the capacitors have doubled their price in the last six months ..



14391
new operational amplifier


14392
re-capped lower PCB


14393
.. and power board





After successful re-assembly the unit was powered up and played without any issues. Stable sound during radio usage, both channels when listening to CD and no warm-up effect. Summing it up, the dying capacitors where the reason for the radio distortions and the CD changer OP amp died of being soaked in acid for too long.




14396old capacitors


14395
strengthened CD player port


14394back in working condition



I'm happy to announce another working OEM radio looking forward to supply his owner with hopefully many trouble free hours to come :)

[ozon02]

Nice work !!!

[Heineken]

Thank you very much :)