Marantz 4400 power fail

blhagstrom

Mad Scientist, fixer.
Subscriber
This came to see me a few days ago.

Supposedly played but low volume.

Arrived and no sound at all.

All lights, scope fired up (adjusted that, it was out of focus).
Had tuning and sound out of preamp (pre-outs OK).
Nothing from the amps, 2 or 4 mode.

Main caps test showed almost no DC on one cap.
Amps and power supply were recapped (good work, nice caps).
SO, someone may have been hunting a problem.

Tore into it and suspected bridge rectifier or blown cap (blown caps are rare, I've only found 3-4 in 100s of units).

Trying to unmount the half bridge, something was wrong.
Pulled hard and pin missing.
AH HA!
Trying to remove pin proved fruitless.

The pin had failed and the arc melted the pin and welded it into the socket!

I tore is all out and grabbed a nice 35A full bridge and reworked the mount a little.
Wired it all back up and dim bulbed it and A-OK on 150W bulb so back to line power.

NICE!

When I find a free week, I will finish the re-cap.
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Those sockets for the rectifiers are so delicate, one of them was broken in my 4400. I soldered the wire directly to the pin. Maybe I'll replace the whole mess like you did. Got a pic of the new rectifier?
 
Those sockets for the rectifiers are so delicate, one of them was broken in my 4400. I soldered the wire directly to the pin. Maybe I'll replace the whole mess like you did. Got a pic of the new rectifier?

It may be tough to see.

Directions:

Pull the red and white leads off the caps.
Pull the screws holding the rectifier mount, they are in the bottom of the bracket from the top.
Work the rectifier mount up (that's why the leads need to come off the caps).
Tear all the rectifiers apart. Unsolder the AC tranny lines and red and white cap lines, the black ground line.
Keep the bypass caps and the terminal. Toss the rest.

I flipped the rectifier bracket around so I could put the big bridge in the setback.
You need to drill a hole in the bottom of the bracket to realign the holes and account for the screw relief in the bottom. there is a screw up from below that needs the relief which is the old screw hole and you need a new screw hole to align with the chassis. You'll understand when you do it.

I took a big salvaged 35A bridge and screwed it to the bracket through one of the holes that the old half bridge had.
( When I first started fixing, I ran into a lot of blown bridges so I tend to salvage nice ones and odd ones. A bone pile of parts comes in handy. I have boxes full of bridges now.)

I soldered the AC lines and +/- cap lines on along with the bypass caps and screwed the terminal into one of the existing holes.
Solder the black ground lead back on the bypass cap terminal.
( NOTE, the leaded bridges solder much easier than the terminal types, soldering on terminal spades is a pain. )

Work the bracket in, working the leads back down.
Screw the bracket down. Reconnect the cap leads (red and white).

Test fire.
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Wish you were closer to me. I've got one that needs some help. I've got one with an issue in the protection circuit and haven't been able to solve it, yet.
 
Wish you were closer to me. I've got one that needs some help. I've got one with an issue in the protection circuit and haven't been able to solve it, yet.

Have you started a thread dedicated to this issue? If not.. do it.
 
This came to see me a few days ago.

Supposedly played but low volume.

Arrived and no sound at all.

All lights, scope fired up (adjusted that, it was out of focus).
Had tuning and sound out of preamp (pre-outs OK).
Nothing from the amps, 2 or 4 mode.

Main caps test showed almost no DC on one cap.
Amps and power supply were recapped (good work, nice caps).
SO, someone may have been hunting a problem.

Tore into it and suspected bridge rectifier or blown cap (blown caps are rare, I've only found 3-4 in 100s of units).

Trying to unmount the half bridge, something was wrong.
Pulled hard and pin missing.
AH HA!
Trying to remove pin proved fruitless.

The pin had failed and the arc melted the pin and welded it into the socket!

I tore is all out and grabbed a nice 35A full bridge and reworked the mount a little.
Wired it all back up and dim bulbed it and A-OK on 150W bulb so back to line power.

NICE!

When I find a free week, I will finish the re-cap.
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I have a 4400 that worked before I recapped it now I’m not getting any sound but if I ran a signal directly to the main in it works? So I’m guessing my power amp boards are working. Could this also be the bridge rectifier issue?
 
No

Without a working bridge things get wonky or dead.

Does the service manual give voltages for the power supply pins? I’d start there looking for right voltages. You may have futzed the power to the preamp section.

If power supply voltages are OK, then I suspect you futzed the preamp.
 
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