• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

MAC1700 distortion after fuse blown

smartin53

smartin53

Well-Known Member
OK so I got word that the MAC1700 I gave my family has having problems. Apparently the fuse blew on it one day, they replaced the fuse, and now it comes on fine but the audio is distorted on both channels from all sources. This is one of the older models that didn't have the internal fuse block.

I did a recap of the unit a couple years ago except for the multipart cans so I'm thinking one may have shorted out and taken the fuse, but is now just causing the distortion. I'm going to likely attempt to restuff the cans. Otherwise I'll have to get my eyes on it in a few days to inspect for any failed components. Any other ideas on what might cause the problem? I'm trying to collect any parts I might need.
 
Register to hide this ad
Distortion on all sources and still turning on I would say to check your lower rail supply voltages.
Sounds like you may have lost preamp supply rail.
This would allow the amp to turn on and try to play by have distortion on all inputs like your saying is happening:scratch2:

Hope this helps some...
 
Well I found the problem. Opened up the unit and the issue was blatantly obvious...2 of the replacement diodes blew (in the pic, top two on the left right set of diodes). Swapped out and all is well again. That said, this doesn't address why the diodes blew in the first place. This thing ran with zero problems for a year and a half and then just roasted them one day it seems. They are 4007's which I thought were correct for the circuit...am I wrong?
 

Attachments

  • blowndiodes.jpg
    blowndiodes.jpg
    91.5 KB · Views: 41
Wish I knew. All voltages seem to be within spec but I don't profess to be an expert. The original owner thought that maybe the unit had been hit by a surge. Difference was when I got it, it was the lower left diode in the cluster that was bad (intact but not passing current) and the unit always blew its fuse in that state. I swapped all the diodes out as a precaution and it worked great as mentioned.
 
Diodes need to be at least rated 3A @ 100V for the +/- 37V supply, if for no other reason than the turn on surge.
 
Well that would explain the failure thanks. I'll get some 3A 1N5402 or better diodes to allow a tad of overhead and toss those in.
 
You must log in or register to reply here.
Back
Top Bottom