Ross Henning
Active Member
Hi All,
I've been an electronics nut all my life, but only recently I've decided to get more serious about my hobby and really dig in and force myself to learn to be a true technician. I'm not after this as a career, at least not now...maybe when I retire. I just enjoy learning new stuff, and although I've got a good understanding of electronics, I find troubleshooting and repair at the component level to be quite a challenge.
I've acquired all of the gear I need to get started. I have an oscilloscope, function generator, bench multimeter, bench power supply, etc., etc., etc.
My first project is to restore my old MCS 3226 receiver which was my very first receiver when I was around 10 - 12 years old. I knew that I had blown out one of the channels years ago, so I went in knowing that I was going to have to replace transistors on the one side. I also knew that I needed to recap it, so I've replaced all of the electrolytics. After replacing all of the caps, I fired it up and when I increased the voltage on my variac up to line voltage then turned up the volume, I burned out the main power supply fuse. I also found that I had major DC voltage at the outputs.
I went back and started checking things and realized that BOTH channels are now out. I checked the output transistors and sure enough, they were toast. I went ahead and ordered a full set of new transistors so that I would have a replacement for every one as I knew this being a DC coupled unit, there's bound to be further trouble.
Long story short, I've replaced every transistor and still have the same issue. This receiver uses a push-pull configuration with a positive and negative power supply. The DC voltage at the output is negative, and is oscillating. I'm about to pull my hair out trying to figure out where the breakdown is. I'm sure that if I had more experience, or if I had a mentor to help me, the place to look would be much more obvious.
I'm hoping some good soul on this board might be able to give me some pointers as to where I should look, or what I should look for. Unfortunately, I do not have a schematic, and I've not been able to find one anywhere on the internet.
Thanks in advance for advice.
I've been an electronics nut all my life, but only recently I've decided to get more serious about my hobby and really dig in and force myself to learn to be a true technician. I'm not after this as a career, at least not now...maybe when I retire. I just enjoy learning new stuff, and although I've got a good understanding of electronics, I find troubleshooting and repair at the component level to be quite a challenge.
I've acquired all of the gear I need to get started. I have an oscilloscope, function generator, bench multimeter, bench power supply, etc., etc., etc.
My first project is to restore my old MCS 3226 receiver which was my very first receiver when I was around 10 - 12 years old. I knew that I had blown out one of the channels years ago, so I went in knowing that I was going to have to replace transistors on the one side. I also knew that I needed to recap it, so I've replaced all of the electrolytics. After replacing all of the caps, I fired it up and when I increased the voltage on my variac up to line voltage then turned up the volume, I burned out the main power supply fuse. I also found that I had major DC voltage at the outputs.
I went back and started checking things and realized that BOTH channels are now out. I checked the output transistors and sure enough, they were toast. I went ahead and ordered a full set of new transistors so that I would have a replacement for every one as I knew this being a DC coupled unit, there's bound to be further trouble.
Long story short, I've replaced every transistor and still have the same issue. This receiver uses a push-pull configuration with a positive and negative power supply. The DC voltage at the output is negative, and is oscillating. I'm about to pull my hair out trying to figure out where the breakdown is. I'm sure that if I had more experience, or if I had a mentor to help me, the place to look would be much more obvious.
I'm hoping some good soul on this board might be able to give me some pointers as to where I should look, or what I should look for. Unfortunately, I do not have a schematic, and I've not been able to find one anywhere on the internet.
Thanks in advance for advice.