Hey everyone! New to the thread, but wanted to show my gratitude to the community here and share my recent, and first time experience repairing an SX-434 receiver.
After digging an old turntable (Thorens TD 165 MKII) out of storage, I wanted to pair a vintage receiver with it, so came across the AK forum and started reading about different receivers, how to think about buying vintage etc. I wasn't looking for anything crazy and eventually came across a very clean looking SX-434 that fit the bill. When I went to test it out, it sounded good on FM, but the right channel was completely out on the phono input. After explaining the issue to the guy and planning to walk away, he offered it to me for $20. Outside of using a soldering iron once or twice, I had no electronic repair experience, but for some reason, after reading a few threads here, I had the blind optimism that it was worth taking a crack at. So I decided to take the deal and brought it home.
I took to the threads to do some research, and started trying to diagnose what the issue could be. Clear sound came through both speakers through FM, AM, and AUX. Tried swapping speakers, issue was still in the right channel, borrowed a friends turntable, issue was still in the right channel. If I turned up the volume there was faint sound coming from the right channel. Toggling controls didn't make a difference (although the pots definitely gave off some distortion when toggled). Hitting mono brought sound to both channels though. So with that, and other info from a few different threads here, I decided the issue was most likely with the pre-amp, but that I should still start with a deoxit to see if that solved anything.
Time to take things apart for a deoxit! Sounded easy enough until I watched a couple videos of people fumbling to dismantle their 434s to get to the pots...turns out the 434 is a pain in the a** to clean up. After finally getting the power and amp board detached and accessing the pots, I ran a couple rounds of deoxit, which did a nice job eliminating any static/noise when manipulating the controls...but still no dice on the right channel.
Guess this was going to cost me more than $20 and a can of deoxit to rectify. So I went back to the boards and started reading more about different people's experiences diagnosing issues with their 434s (typical problem transistors etc). Didn't know how to read a schematic to save my life, and looking through the service manual felt like I was reading a treasure map, but I eventually decided that this (photo below) was probably the phono pre-amp and the best place to start. Rather than shopping for each individual transistor, caps, etc, I bought a full replacement kit on eBay for about $50 (figured the higher price was worth the time saved).
So I started with what I assumed to be the right channel section of the pre-amp. I replaced two SC1344 transistors (Q2/Q4) with two KSC1845, making sure to pull up the datasheets to solder them in correctly (lots more reading about NPN/PNP and ECB/BCE differences). Turned on the unit, and...SOUND IN THE RIGHT CHANNEL! Nice! Unfortunately, while there was now sound in the right channel, there was a lot of distortion and static, so something still appeared to be off.
I figured I would continue to make my way down the rest of the right channel section of the amp board, replacing transistors, caps etc and periodically testing as I went. There were definitely some transistors with black corroded legs and some leaky looking caps, but I replaced everything in the right channel and still found no noticeable improvement in sound. So then, thinking that maybe I was misreading the schematics, and because I really still didn't know what the heck I was doing, I went and did the same thing in the left channel. Still no change to the right channel.
At this point I was a little frustrated, and continued to read some more threads, contemplated making some replacements on the power board, or replacing the output transistors. The kit I bought didn't come with output transistors, so I sent a message to the seller asking about them. He said that he doubted I needed to replace the output transistors and we went back and forth running through what I had tested and replaced. He then asked if I had tried swapping the RCA plugs of the turntable into the phono input (Right into Left and Left into Right) to see if the problem persisted in the right channel...
Well, since I had already tried another turntable (my friend's turntable that I knew worked properly) before replacing anything, it never dawned on me that there was an issue with my turntable. Who would have thought that my receiver, with a right channel issue, would be perfectly paired with a turntable that had a bad right RCA connection. So when I replaced the transistors in the right channel of the phono pre-amp, it brought sound. It just so happens that the distortion that came after was coming from the turntable, not the receiver. I borrowed my friends turntable again, and viola, everything was working and sounding great!
So I guess moral of the story is, make sure that the equipment that you are using to test on the receiver is all in proper working order. That said, I'm still glad that I replaced everything, because it was kind of fun, and will hopefully prevent the need to go back in there any time soon.
But now I have a great working receiver that now has some sentimental value from fixing it up. I also have a working turntable after replacing the RCAs. Huge thank you to everyone that has put in time to help others with repairs like this, I wouldn't have been able to figure this all out without the help, and now I have a much deeper appreciation for the vintage gear that I'm using!
Happy to share anything else about my experience (replacement parts etc) if helpful.
After digging an old turntable (Thorens TD 165 MKII) out of storage, I wanted to pair a vintage receiver with it, so came across the AK forum and started reading about different receivers, how to think about buying vintage etc. I wasn't looking for anything crazy and eventually came across a very clean looking SX-434 that fit the bill. When I went to test it out, it sounded good on FM, but the right channel was completely out on the phono input. After explaining the issue to the guy and planning to walk away, he offered it to me for $20. Outside of using a soldering iron once or twice, I had no electronic repair experience, but for some reason, after reading a few threads here, I had the blind optimism that it was worth taking a crack at. So I decided to take the deal and brought it home.
I took to the threads to do some research, and started trying to diagnose what the issue could be. Clear sound came through both speakers through FM, AM, and AUX. Tried swapping speakers, issue was still in the right channel, borrowed a friends turntable, issue was still in the right channel. If I turned up the volume there was faint sound coming from the right channel. Toggling controls didn't make a difference (although the pots definitely gave off some distortion when toggled). Hitting mono brought sound to both channels though. So with that, and other info from a few different threads here, I decided the issue was most likely with the pre-amp, but that I should still start with a deoxit to see if that solved anything.
Time to take things apart for a deoxit! Sounded easy enough until I watched a couple videos of people fumbling to dismantle their 434s to get to the pots...turns out the 434 is a pain in the a** to clean up. After finally getting the power and amp board detached and accessing the pots, I ran a couple rounds of deoxit, which did a nice job eliminating any static/noise when manipulating the controls...but still no dice on the right channel.
Guess this was going to cost me more than $20 and a can of deoxit to rectify. So I went back to the boards and started reading more about different people's experiences diagnosing issues with their 434s (typical problem transistors etc). Didn't know how to read a schematic to save my life, and looking through the service manual felt like I was reading a treasure map, but I eventually decided that this (photo below) was probably the phono pre-amp and the best place to start. Rather than shopping for each individual transistor, caps, etc, I bought a full replacement kit on eBay for about $50 (figured the higher price was worth the time saved).
So I started with what I assumed to be the right channel section of the pre-amp. I replaced two SC1344 transistors (Q2/Q4) with two KSC1845, making sure to pull up the datasheets to solder them in correctly (lots more reading about NPN/PNP and ECB/BCE differences). Turned on the unit, and...SOUND IN THE RIGHT CHANNEL! Nice! Unfortunately, while there was now sound in the right channel, there was a lot of distortion and static, so something still appeared to be off.
I figured I would continue to make my way down the rest of the right channel section of the amp board, replacing transistors, caps etc and periodically testing as I went. There were definitely some transistors with black corroded legs and some leaky looking caps, but I replaced everything in the right channel and still found no noticeable improvement in sound. So then, thinking that maybe I was misreading the schematics, and because I really still didn't know what the heck I was doing, I went and did the same thing in the left channel. Still no change to the right channel.
At this point I was a little frustrated, and continued to read some more threads, contemplated making some replacements on the power board, or replacing the output transistors. The kit I bought didn't come with output transistors, so I sent a message to the seller asking about them. He said that he doubted I needed to replace the output transistors and we went back and forth running through what I had tested and replaced. He then asked if I had tried swapping the RCA plugs of the turntable into the phono input (Right into Left and Left into Right) to see if the problem persisted in the right channel...
Well, since I had already tried another turntable (my friend's turntable that I knew worked properly) before replacing anything, it never dawned on me that there was an issue with my turntable. Who would have thought that my receiver, with a right channel issue, would be perfectly paired with a turntable that had a bad right RCA connection. So when I replaced the transistors in the right channel of the phono pre-amp, it brought sound. It just so happens that the distortion that came after was coming from the turntable, not the receiver. I borrowed my friends turntable again, and viola, everything was working and sounding great!
So I guess moral of the story is, make sure that the equipment that you are using to test on the receiver is all in proper working order. That said, I'm still glad that I replaced everything, because it was kind of fun, and will hopefully prevent the need to go back in there any time soon.
But now I have a great working receiver that now has some sentimental value from fixing it up. I also have a working turntable after replacing the RCAs. Huge thank you to everyone that has put in time to help others with repairs like this, I wouldn't have been able to figure this all out without the help, and now I have a much deeper appreciation for the vintage gear that I'm using!
Happy to share anything else about my experience (replacement parts etc) if helpful.
