Optonica SM-4545 Repair And Restoration

This Optonica SM-4545 integrated amplifier is in pretty good cosmetic shape but is in need of some repairs and restoration.

The top cover of the Optonica SM-4545 is now removed. This integrated amplifier has a nice internal layout.

All of the individual boards use plug in connectors which make restoring or servicing much easier.

Have the cover that hides the equalizer(phono) assembly now removed on this Optonica integrated amplifier

With the cover removed we also have access to clean some of the controls with deoxit like the volume control shown below.

You can use a paper towel or cloth to help soak up or block areas where you don't want the deoxit to go.

Like all vintage stereo restorations this Optonica SM-4545 integrated amplifier was going to have it's faceplate removed but there's a problem.

I could not remove the cosmetic covers from the toggle switches. I believe at some point they were glued on. Not worth the risk to remove them.

Not getting the toggle switch covers off means not getting the faceplate off. Getting to the controls for cleaning is more of a challenge.

This Optonica SM-4545 makes it so easy to remove assemblies. Remove two screws and pull the assembly off the pins.

The pins had no corrosion but I used a little deoxit on a Q-tip anyways.

All of the connectors in this Optonica SM-4545 integrated amplifier were marked with numbers for easy service. Something you don't always see.

I had an intermittent problem where the amplifier protection circuit would disconnect the speaker relay. Tapping helped me find the problem.

The picture below has a black circle around a questionable solder joint that was not perfect when this assembly was flow soldered 40 years ago.  

Many times it takes decades for a soldering issue to cause a failure. I reflowed every solder joint on this assembly. It only took a few minutes.    

The bottom cover of this Optonica SM-4545 has been removed. Again, a nice clean layout.

Just like on the top side all of the connectors on the bottom are clearly marked and neatly dressed. 

The filter capacitors in this Optonica check out fine and will stay for a while longer. Modern test equipment is helpful with vintage stereo restorations.

Another issue found was that there was excessive noise from the phono input of the left channel.

Interesting that the only wire wrapped pin in this unit was used to hold the equalizer board(phono) tightly to it's connector. Middle pin below.

 I tried to "see" the distortion on the scope using a test tone. I couldn't see it but I sure could hear it. Sometimes your ears are the best tools.

I use my computer for my service manuals. Service manuals for most models of vintage stereo equipment are available online.

After troubleshooting I found that one of the 1345 NPN transistors was causing the phono left channel noise issue. I replaced the transistor.

I used my transistor tester an Atlas DCA75 to help me troubleshoot the 2SC1345 transistor noise issue.

 This DCA75 doesn't measure noise but the bad 2SC1345 transistors gain(Hfe) measured in the high 200's which was different then the good 1345's.

The other five good(noise free) 2SC1345 transistors that I measured had a gain(Hfe) in the mid 400's.

The DCA75 includes software that you can run on your computer. The graph below shows some comparison data between the good and bad 1345.

 After the transistor replacement I hooked up a turntable and had a listen. This Optonica SM-4545 phono section is now sounding like it should..

This Optonica integrated amplifier is fully featured. Don't forget to clean the RCA and speaker connectors.

This SM-4545 has support for 2 turntables, cartridge impedance adjustments and moving coil support.

The back panel has been loosened so that I could clean the phono input switches.

This Optonica SM-4545 integrated amplifier repair and restoration is complete.

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