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Help needed repairing Marantz 1040 and 2440

D

Dystyrbed

New Member
Hi everyone.

I recently got a Marantz 1040 and 2440 off Craigslist, and have only performed basic stereo repairs in the past. I have been through the junior year of electrical engineering, including building a class AB amplifier to run off a 9V battery, so I'm not completely useless here.

The 1040 outputs no sound on one channel, and the 2440 has no output on the main speakers. I've dusted them as best I could with the canned air stuff, but they're still pretty dirty. I have friends with an air compressor, and will probably eventually take it over there to do a better job cleaning it. I've also used the Radio Shack branded contact cleaner in all potentiometers and rotary switches in an attempt to solve any simple, obvious problems first. I have the 1040 service manual and 2440 schematics. What should I look to solve these problems? Are there any obvious places to start or common failure modes in these models? Also, I have a DMM, scope, and variac.

Thanks!
 
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No, I can't easily reach most of them, partly because the little plastic tube for the contact cleaner was of course lost by the time it got to Radio Shack's shelf. I've pulled the top and bottom covers, but I'm a bit hesitant to go any further with disassembly because I need to move later this month.
 
Everything on the 1040 has been cleaned with contact cleaner, but I still only get one channel. Checked outputs with a DMM on AC mode, and the left channel reads 0V.
 
Okay, I've got the amp board out. One output transistor shows a diode drop from case to one leg, and a short from the other leg to case. Clearly, this transistor needs replacing. The other transistor on that side reads diode drops from either leg to case, but I've heard it's a good idea to replace the outputs as a set.

What would be good replacements for these? They are 2SA837 ans 2SC1667 BJTs.
 
These will probably work. The 2sa837 crossed to the MJ15016, so the complimentary MJ15015 will probably work for the 2sc1667. Read the data sheets for the old and new devices to be sure.
 
Cool, thanks. I found a transistor replacement datasheet, but the replacement for one of them is also outdated and the replacement for the other is a TO-220 packace, not TO-3.
 
You might also want to check the drivers. I repaired a luxman that ran ok for a while until the drivers in the repaired channel opened.
 
The MJ15015 has a lower hfe (40-200 @ 1A, 4V vs 20-70 @ 4A, 4V). Otherwise, all values looked at least as good, and in most cases far superior to the 2SC1667. The hfe shouldn't be a problem though, because it will be matched to the complementary MJ15016 ideally, right? Do they compensate for hfe in push-pull outputs? Thanks!
 
Okay, I got the MJ15015 and MJ15016 transistors to replace the originals. I decided for the sake of consistency to replace all the output transistors rather than just the ones which were out. I have two pots for adjustment per channel, and I'm fairly certain I'll need to adjust these to get a half decent stereo in the end of this, but I can't identify what they do easily from the schematic in the service manual. Can anyone help me? Thanks in advance!
 
Not terribly well, I'm afraid. I ended up giving it to a friend who is far more meticulous than I with these things and after checking factory specs and everything, I think he still had some issues possibly related to other components needing replaced. Best of luck with yours though!
 
That's a bit of a bummer :( Do you think the ouptut transistors you bought to replace the originals were fit for the job? Im having trouble finding parts in Australia...
 
I think so. I forget where since it's been a few years now, but I'm pretty sure I cross referenced them with the OE part.
 
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