I'll post pictures later but I wanted to share a bit on my ongoing project for an SCR-8 I found at the thrift store recently for $16. I first want to say THANK YOU to the Boomboxery forum for having schematics and the manual for this boombox. I'm not sure how I'd have fixed it without those resources This thread was also quite helpful to get started. I had the exact same capacitor (C127) go bad! But that wasn't the end. Probing around on other caps, I found that either C164 or C264 was bad so I replaced both. The voltages around the HA1392 power amplifier were all wrong, too. So I replaced all the caps directly attached to the pins with wrong voltages (I had them on hand) even though I didn't suspect they were bad. Sure enough they were just fine and the voltages remained wrong. So I replaced the HA1392 and now the sound works! I didn't see it right away but I'll share a picture of the old amp IC. There was a significant hole blown out of the face of the IC! I never noticed this until it was removed from the PCB. No wonder it was bad. I wonder if the bad output cap caused the amp to blow but who knows.
At this point I decided that I wanted new speakers for it so I got the cheapest I could find on parts express that would fit the mount (Part no. 299-609). I knew the new speakers would be about 1/2" deeper but I just eyeballed it and decided they would fit. Oops! They do not fit. The left speaker hits the power transformer and bulges out by less than 1/4". Lame. But I have to keep these speakers because they sound soooo much better than the old ones. Much better bass response. I'm considering replacing the tweeters, too, but I decided I'll actually measure out the performance before I do that. So my planned solution is to replace the power supply with a switch-mode power supply I got from Mouser recently (15V, 50W). If nothing else it will remove about 600g of weight! I'll remove some plastic that held the power transformer to fit the SMPS. That's where I am right now, waiting for a Dremel part to be able to do that.
I have done zero testing of the cassette deck. No offense to those who may care but I have zero interest in that working. If it works, fine. If not, also fine. I'm planning on adding a BT module to the AUX line. The FM radio works well. The pots mostly sound fine though a few get scratchy. Maybe I'll clean them later. I also have this jump-starting battery and I'm planning on cutting some of the plastic in the battery bay to fit it in there. It has a 15V output which is perfect for this. I'll use a couple of Schottky diodes to make a power OR gate to protect the supplies from each other. Finally I'm planning on seeing how a PAM8406 would improve efficiency (i.e. battery life). I don't think I'd get much if any more power output but it should be sufficiently powerful. I'll wire out the inputs to the HA1392, remove that IC, and have the PAM8406 module live on the faceplate with the speakers. Just looking at the datasheets of the two, I figure I should be able to save up to 5W that's currently just lost to heat. But I'll measure that out, too.
I'll try to keep this thread updated. I'll also post some pictures, later.
At this point I decided that I wanted new speakers for it so I got the cheapest I could find on parts express that would fit the mount (Part no. 299-609). I knew the new speakers would be about 1/2" deeper but I just eyeballed it and decided they would fit. Oops! They do not fit. The left speaker hits the power transformer and bulges out by less than 1/4". Lame. But I have to keep these speakers because they sound soooo much better than the old ones. Much better bass response. I'm considering replacing the tweeters, too, but I decided I'll actually measure out the performance before I do that. So my planned solution is to replace the power supply with a switch-mode power supply I got from Mouser recently (15V, 50W). If nothing else it will remove about 600g of weight! I'll remove some plastic that held the power transformer to fit the SMPS. That's where I am right now, waiting for a Dremel part to be able to do that.
I have done zero testing of the cassette deck. No offense to those who may care but I have zero interest in that working. If it works, fine. If not, also fine. I'm planning on adding a BT module to the AUX line. The FM radio works well. The pots mostly sound fine though a few get scratchy. Maybe I'll clean them later. I also have this jump-starting battery and I'm planning on cutting some of the plastic in the battery bay to fit it in there. It has a 15V output which is perfect for this. I'll use a couple of Schottky diodes to make a power OR gate to protect the supplies from each other. Finally I'm planning on seeing how a PAM8406 would improve efficiency (i.e. battery life). I don't think I'd get much if any more power output but it should be sufficiently powerful. I'll wire out the inputs to the HA1392, remove that IC, and have the PAM8406 module live on the faceplate with the speakers. Just looking at the datasheets of the two, I figure I should be able to save up to 5W that's currently just lost to heat. But I'll measure that out, too.
I'll try to keep this thread updated. I'll also post some pictures, later.
