A while back (January 2022) I somewhat randomly got an old Yamaha CA-410 II. It's a pretty neat amp but had some issues. The right channel was kind of failing and the lights for the VU meters were dead. So I did 2 things. The first is get a new Yamaha A-S501 which has now been my daily driver for just under 2 years. The second was to buy an expensive capacitor kit for the CA-410. It was a good kit and got me into an area I knew nothing about. However there were a handful of caps not included and a couple that had bad spacing for the board. Looking up prices I realize the kit itself probably would not have been that expensive to put together. That said it did get me started on a project I was otherwise kind of lost on, so it was still a good purchase.
Initially, I only replaced a couple caps that I thought were likely the issue. I honestly don't remember if it fixed the issue, but it must not have since I didn't put it back together. So it sat in pieces for a good year or so before I finally picked it up again. One of the reason I hadn't been working on it was a lot of the caps were hard to get to. I was worried if I took the pieces fully apart I would never get it back together. But just letting it gather dust in a corner wasn't useful either. Finally, I cut the wires and finished pulling the boards out of the chassis.
It was the right move. I was able to redo the small board in just a couple hours. I took a picture and labelled all the caps I took off. It also helped that they were all matched pairs. The main board had a lot more caps with some singles. I tried taking pictures and labeling the caps, but made some mistakes and also lost some of it that had only been partially saved. Falling back on the circuit diagram from the service manual I figured out most of what I had missed. But there are still some weird things I can't really explain. There's a set of about 4 3.3 uF capacitors that exist on the physical diagram but not in the parts list. I also can't find them on the logical diagram. These caps were also missing from my kit which I didn't realize until I had already removed them. There are another couple that I didn't track closely that are spec'ed differently than what was physically on the board. Again, I have no idea if those were intentional changes or just mistakes in the documentation.
The major problem I ran into was destroying one of the solder pads. Ultimately, I went ahead and bought another main board for $50. It seemed like the better way rather than trying something janky and also now I have a good reference for capacitors if I do need to replace any.
So I got the "new" mainboard, some heat shrink tubing, hot air gun, and a wire wrapping tool. And also importantly, I now felt set up for success.
To start off, I unwrapped the weird tube of wires that connect the primary and secondary boards. The next question is what to do for the connections to the little boards that have the volume. I suppose heat shrink just to be on the safe side. I think there are a few that will be done at the solder layer.
So I de-soldered some leads. I also got a cool magnifying glass/light combo that is super nice. But now it also shows how much I'm messing stuff up. Or at least it looks that way.
I dropped the soldering iron temp way down from like 380 to 325 C. It still seems to kind of singe the surround a bit but not sure if that's avoidable or not. Also I did not have good luck with the narrowest tip but I did go down to a slightly smaller one than I had been using previously.
Then I got the small volume board and it's buddy back together. I broke most of the connecting leads when I handled it indelicately during the original cap replacement phase. I got the gray multiwire thing soldered to the new mainboard.
I got most of the wires that connect to the smaller boards stripped.
I still need to fix up the connections to the VU meters.
I made some more progress on reconnecting wires. It's still going to be a miracle if this thing ever works again.
I ran into some wires using the same color that I forgot to label. Luckily the service manual has the connections so I can do it right. I am slightly curious if it actually matters though. Good thing I checked because I was wrong on a few.
I finished the right half of the main board. I'm pretty happy with how it turned out. I did ditch the silly plastic tube around the wires connecting the primary and function board, hopefully that wasn't actually needed.
Next up were the VU meters. I cut the wires before so the leads still have a soldered mess on them. They proved to be more challenging than I expected. I got one lead freed, but had to leave the other for a bit to avoid doing something regrettable.
I got the power supply wires connected. I didn't have any blue wire so had to use black instead. Another attempt at the remaining VU meter and I was able to get the clipped wire out cleanly. Taking a break from it really paid off, since it ended up coming out easily once I could approach it with a clear head.
Now, for the moment of truth. I powered it on with nothing connected and it lights up. Connecting up to computer and a single classix speaker... and it worked!
Hooking it up to the JBL 4312SE and computer. It works and I think sounds good. Vocals are crazy nice sounding. Guitars seem to have a bit more grit on the low end of things, but I can't tell if I'm making that up or not. If distortion was coming through I would have expected it to impact across the range but maybe that wouldn't be true. In any case I like the sound, but I'm also just happy it works. Seems to be able to handle anything I throw at it.
I let it sit for a couple hours after dinner and the left channel is a bit weak at times. I must have a bad connection somewhere as fiddling with the wires seems to have straightened it out again.
Hmmm things got weirder. The right headphones channel only is working, but when I switch back to speakers only the left works. And I found a bad connection coming from the speaker into the a/b selector part. B speakers also had the issue. Fixing the bad connection helped somewhat but still having some troubles with the left channel. Again headphones were also impacted.
I replaced another bad cable and both channels are doing good now. The lights are a bit flaky but I'm calling it good and put it all back together. Of course, I forgot to tighten the balance knob before I did though so I had to take the top off one more time. I also managed to not break the power light which I think was extremely lucky.
Overall, I'm extremely happy with it now. Someday I'll pull it apart again and redo the caps, but it's good for now. I let it sit overnight and it worked in the dreaded morning cold start! I got all the knobs put back on and it's still going strong. At this point I can't decide what to do with it. It'll probably end up in the living room with the JBL 4312SE but I am tempted to keep it in the office. I do like the VU meters, but in the office I can't play it loud enough to get much movement on them.
It's a bit strange, I didn't grow up in the 70s or what not but there's just something about this era of amps. The aluminum knobs, the soft lights on the VU meters. And the fact that I brought it back from half dead is cool too. Surprisingly the power usage is fairly similar to my A-S501, about 18 watts idle vs 25 on the A-S501. I ended up spending about $400 total, which again is pretty close to the new A-S501. Finishing this rebuild has been like finishing a good book. Even if it's a happy ending, you'll still miss the characters.
I'm also at a loss for what to do next. Do I try to find a broken amp for cheap and fix it up? Should I get a tube amp kit to put together? Maybe I go something totally different and do a frame up dream bike build? Or maybe build a model car?
I do have a couple projects in the hopper. I need to do the vinyl covering on the c-note speakers and make some fancier stands for the JBL 4312SE. I also have a trip to Norway coming up so I really shouldn't worry too much about finding new projects.