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I finally have some progress to report. After testing a bunch of components, I found 5 wrecked transistors and a fried diode. I replaced all of that and built a dim bulb tester. When I powered up, there was no bright light! No smoke! I have sound! But (always a but), when there's no signal (or...

OK, so I just found that the emitter leg on TR419 was completely detached from the transistor. Obviously this needs to be replaced. Any suggestions for an A817? Would it be reasonable to assume that the damage would have stopped there? I didn't see any other signs of damage, but if I'm going to...

Well, I'm an idiot. The thermal paste I grabbed from my box was silver based. Oops. I'm still hopeful that the damage is limited to the one transistor. I need to get some new washers and clean off that paste. I'll report back when I make some progress.

Ah, so isolators are the little plastic insulators between the back of the transistors and the metal bracket? Those looked to be in good shape, but I suppose it's smart to replace them. I put some cpu thermal paste on both sides of the plastic when I replaced the outputs. When I short my leads...

Measuring in-circuit, it seems like everything is in good shape. The emitter resistors measured 0.8 ohms vs 0.47, but I was surprised my meter measured anything. I couldn't find any flameproof resistors on the schematic. There's a few big red resistors that are marked as 'metalized oxidation' on...

I've pulled the transistor and it looks like there was some arcing between the retaining screwing and the back plate. The little screw insulator just fell apart too. The base to collector is definitely shorted. Can I turn on the receiver without the transistor or would that damage something?

Mouser. Any thoughts on what to start testing?

So there's some interesting results. After I pulled the transistors I tried testing them and didn't see the short. I went ahead and put in the new TIP41C/TIP42C for the left channel. It sounded great and the signal from my little oscilloscope looked great. For about 20-30 minutes. And then the...

Reading JPromo's thread about a very similar issue with his right channel, I tested my output transistors and one in the left channel does appear to have a short. Smacking that transistor also seems to bring it back for a few minutes (it's also near the relay). I'm going to go ahead and order...

Well, I'm back and still having troubles. Life got in the way of playing with this for a few months. Anyways, I haven't gotten a new relay yet, but I was poking around and I learned that the voltages on TR401 all tank when the distortion kicks in. They're supposed to be ~28V, but at low volume...

Good to know. I'll just order a new one then. Thanks again for all the help

The noise came back on mine after a bit and tapping wasn't doing much. I still haven't gotten the cap off, but I reflowed all the solder connections on the relay and I haven't had a problem since. I think replacing or cleaning the relay is probably going to be necessary. I'm actually thinking...

Well, I tapped on the relay a bunch and now things are working. I think you guys have this figured. I'll check out that other thread later and see if I can't clean this thing up. Thanks! You guys definitely know your stuff

Is there a trick to getting the cap off of the relay? I couldn't see how to get into it to clean anything. I haven't taken apart the selector switches, but did hose them down and cycle them a bunch. Seems unlikely that both switches would have the same issue in just the left channel. The relay...

I haven't tried cleaning the protection relay, so that'll be first on the list. I've cleaned all the other switches a couple times, so I'd be a little surprised if that was it. But, you know a lot more than I do so I'll give it a go! Thanks

So I've cleaned this guy and replaced all the capacitors in the power supply section. I thought I finally had it working and it sounded great on headphones. I hooked up some speakers and it initially sounded good, but I've started to get an intermittent distortion only in the left channel. It's...

Thanks guys, the 25V was the only one in that section that was an Elna. The 2 big 6800 uF ones are also, but the rest in it's neighborhood were smaller, purple/violet ones that I didn't see a manufacturer on. I wouldn't say the solder looked any different, but I didn't really pay attention...

Hey folks, I started working on my CR-420 again. I actually pulled a couple capacitors in the power supply to try and test them and then realized that my meter wouldn't work on the big ones. Duh. Anyways, I put them back in (with the correct polarity) and did some more cleaning. Powered up and...

Nailed it! It actually wasn't anything to do with the receiver. I was listening to it and playing around with everything again (interestingly the noise got much louder with loudness on flat but was pretty much constant for 1-10), but I was thinking about your power supply suggestion when I...

So I scored a nice CR-420 at the thrift shop recently. It doesn't have any major issues and after cleaning all the pots work well. I haven't replaced any caps yet and the receiver is making an odd noise. Without any signal, I can hear a low dut-dut-dut kind of noise. It's on all inputs and all...

I took a peek at the crossover, but I haven't checked it beyond toggling the switch in the back. It sounded like it's working, but without taking some measurements or just replacing the cap, I can't say much. Yesterday at work I was bored (or at least more interested in my speakers!) and I made...

Doug, you are right again. I'm just an idiot. I pulled one out and plain as day, there was a foam gasket. Yay! Back to listening. I'll take some pictures after I've cleaned the grills. Thanks again everybody!

Glenn, I got every bit of the old stuff off the basket ledge and inner lip, but I did leave a bit of old glue on the basket above the ledge. I figured that wouldn't be getting in the way... and I'd already scratched the basket pretty good trying to get some of that upper stuff off. Sorry I...

Hrm. Mine didn't have a foam gasket. One wasn't even 'stuck' to the cabinet. As soon as I pulled the screws it lifted right out. The other was a little sticky, felt like removing tape. Any suggestions on how to fashion a gasket? Thanks

Refoaming was a tedious PITA! Took me hours to get the glue off the steel. But you guys were right. Not hard and these speakers were worth the effort! I just hooked them up this morning and they are the best speakers I've ever owned! What impresses me the most is the clarity and how the music...