Pooklord 7 Posted July 20, 2020 Share Posted July 20, 2020 Hi All, I just acquired a somewhat broken MXR-130. I had no idea there was so much info on fixing these receivers! I've already ordered some refurbish kits on Ebay, plus deoxit etc. I am a little concerned though that I may have screwed something up; after I took off the covers, blew the dust out, etc I though I wanted to run some of the basic sm alignment procedures to better understand it's current condition. The first one I ran, per the sm, was to clip onto the D626 diode and chassis with my voltmeter and see if it's at 61.1v. It was at ~42v, so I adjusted the SVR603 trim pot to ~61v. At that point the tuner came back and I was able run up and down am/fm, listen to stations etc. BUT I noticed the top two big resistors on the tuner board were running (what appeared to me) to be super hot -- the top one was at 163 degree F and climbing. I turned off the receiver, turned it back on, clicked the FM tuner button and the back panel 6a fuse blew. I'm waiting for new fuses. I later learned some stuff---the tuner resistors typically run hot (I've ordered some new ones at the same ohm value, but higher power 5w) . I've also ordered a kit to replace the main power board resistors. I'm thinking I should not have changed the existing SVR603 trim pot value until I had performed a general refurbishment (new caps, relays, higher rated resistors etc) I'm thinking of turning the trim pot BACK to the 42v value before I proceed with the ebay kit refurbishment. I should also add that BEFORE I did any of the things I described above, I hooked it up to my CD player and listened to Beethoven, it sounded both loud and awful--crackling, distortion, just terrible. But both channels worked and no fuse blew until I adjusted that trim pot to the sm spec'd value. I also maybe should have been using a true 8 ohm dummy load (I don't even know what that is) before screwing with the trim pot? Probably. I'm sure more experienced techs have spotted a bunch of dumb things, but I am new to fixing receivers and am still learning. Anyhow, I'm so glad this site exists! I hope to learn and eventually be able to pass on real knowledge to others in this forum. I am looking forward to continue working on this receiver till it works as spec'd in the sm. I am genuinely appreciative of any and all advice and comments related to this project. I am sure many of you are old hands at this stuff, but I am still somewhat new to power amp design and troubleshooting procedures. Thanks in advance, Matthew 2 1 Link to comment Share on other sites More sharing options...
Sk1Bum 9,803 Posted July 20, 2020 Share Posted July 20, 2020 Hello Matthew, and welcome to thecarversite.com. We're glad you're hear. There is a lot of information here, much technical know how, and a pretty good bunch of folks that are happy to help. While I know next to nothing about the MXR-130, there are several here that do, and I'm sure one of them will chime in and help you sort out your issues. Once you get to Novice status, please consider uploading some pics of your gear in the Members Systems area. We all like pics of all kinds of audio gear. In the meantime, kick your shoes off, turn up the music, and welcome aboard. 1 Link to comment Share on other sites More sharing options...
Pooklord 7 Posted July 20, 2020 Author Share Posted July 20, 2020 Thanks for that friendly welcome! Appreciated. I will upload pics, as soon as I am able. Matthew 2 Link to comment Share on other sites More sharing options...
Sk1Bum 9,803 Posted July 20, 2020 Share Posted July 20, 2020 Once your reputation gets to 6, you'll be able to upload pics. Link to comment Share on other sites More sharing options...
kve777 6,640 Posted July 21, 2020 Share Posted July 21, 2020 The relays on the speaker terminal board SP-508 are in need of replacement, no doubt, along with a plethora of electrolytic caps, plus R635 needs to be 3.3KΩ 1W. Spend the time to check for shorted or open caps! Fix the main amp board MA-508A first, then the smaller boards. Leave the main tuner board TIM-510A and Noise Reduction board CNR-527D for last. Give the two switches for TAPE functions on FEQ-508A a good shot of DeoxIt. 3 Link to comment Share on other sites More sharing options...
Rob 4,229 Posted July 21, 2020 Share Posted July 21, 2020 Welcome. I have had an MXR for 33 years. Those resistors on top of the noise reduction board are always hot. Unless it’s off. 😄 1 Link to comment Share on other sites More sharing options...
Pooklord 7 Posted July 21, 2020 Author Share Posted July 21, 2020 2 hours ago, kve777 said: The relays on the speaker terminal board SP-508 are in need of replacement, no doubt, along with a plethora of electrolytic caps, plus R635 needs to be 3.3KΩ 1W. Spend the time to check for shorted or open caps! Fix the main amp board MA-508A first, then the smaller boards. Leave the main tuner board TIM-510A and Noise Reduction board CNR-527D for last. Give the two switches for TAPE functions on FEQ-508A a good shot of DeoxIt. According to the sm, r635 is currently 1/2w -- More business for Digikey! Once my parts arrive, I will follow that fix order . . . thanks Link to comment Share on other sites More sharing options...
dennismiller55 4,717 Posted July 21, 2020 Share Posted July 21, 2020 Welcome! If you want to eliminate the hot resistors all together here is an option available from a trusted eBay seller CircuitsAndConcepts. Les is also a member here though not very active anymore. I have used this regulator in both of my MXR-130 recievers. A bit pricey for a repair and flip unit but well worth it for personal equipment. High Efficiency Regulator to repair refurbish CARVER MXR-130 -150 THE RECEIVER 3 Link to comment Share on other sites More sharing options...
Charlie 16,429 Posted July 21, 2020 Share Posted July 21, 2020 Greetings @Pooklord ! Looks like you are well on your way!!! 1 Link to comment Share on other sites More sharing options...
Community Admin AndrewJohn 8,030 Posted July 21, 2020 Community Admin Share Posted July 21, 2020 Welcome @Pooklord, that looks like a super project. Can't wait to see some pictures of your results! 1 Link to comment Share on other sites More sharing options...
Pooklord 7 Posted July 21, 2020 Author Share Posted July 21, 2020 8 hours ago, dennismiller55 said: I was considering that regulator the other day--looks neat, but I am trying to stay on budget for this project. I have already ordered some of the circuitsAndconcepts refurbishment kits, after that work is done I may reconsider. Thanks for the tip! Matthew 1 Link to comment Share on other sites More sharing options...
Brian_at_HHH 2,607 Posted July 21, 2020 Share Posted July 21, 2020 Welcome to the group. I can see exactly what your problem was and yes, you made a terrible mistake - blowing the dust out is guaranteed to make it all fail in bizarre and spectacular ways - the magic dust is what makes it all work! Obviously I can't offer any good assistance in helping you get that receiver going, but as you've seen, there are lots of folks here who do know there way around the circuits and are happy to offer good help and guidance. Personally, I admire anyone willing to dive in there and have a go at things. Good for you. I'm sure it will get sorted out and making beautiful music in no time. Tanks again for joining! 2 Link to comment Share on other sites More sharing options...
Pooklord 7 Posted July 21, 2020 Author Share Posted July 21, 2020 13 minutes ago, Brian_at_HHH said: Welcome to the group. I can see exactly what your problem was and yes, you made a terrible mistake - blowing the dust out is guaranteed to make it all fail in bizarre and spectacular ways - the magic dust is what makes it all work! Obviously I can't offer any good assistance in helping you get that receiver going, but as you've seen, there are lots of folks here who do know there way around the circuits and are happy to offer good help and guidance. Personally, I admire anyone willing to dive in there and have a go at things. Good for you. I'm sure it will get sorted out and making beautiful music in no time. Tanks again for joining! Thanks for the kind words, Brian--I should have been more careful with the magic dust. lol 2 Link to comment Share on other sites More sharing options...
Dadvw 2,800 Posted July 22, 2020 Share Posted July 22, 2020 17 hours ago, Pooklord said: Thanks for the kind words, Brian--I should have been more careful with the magic dust. lol Well, just don’t let out the magic smoke too. Everything electronic has magic dust and magic smoke, let them both out and.........😔😔😔😔😔 Link to comment Share on other sites More sharing options...
RPA-1 Man 594 Posted July 22, 2020 Share Posted July 22, 2020 Welcome Matthew! With a little patience and help from the good folk here you'll have that receiver singing. Link to comment Share on other sites More sharing options...
Circuits & Concepts 311 Posted July 22, 2020 Share Posted July 22, 2020 Welcome, Matt! I suggest you get the power supply sorted out before doing anything else. I typically probe the rectifier diodes to do this. Red meter lead on the diode of interest and the black lead on the chassis. Measure and log both the DC and AC voltages. The AC voltage (on the rectified side of the diode) should be lower than 0.1 VAC. Something higher indicates a bad power supply capacitor, which will mess up the regulation. The kit you ordered from C & C includes the resistor R635, new speaker relays and a trim cap for the tuner. The high efficiency regulator I make replaces the 4 hot resistors on the main/amp board, and includes replacements for the 4 hot resistors on the noise reduction board. You shouldn't do that upgrade until the rest of the receiver is fully functional. Hope it goes well! Les 2 1 Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now