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