Marantz 4430 Quad - noise/distortion in left channel after playing so well earlier

[redpackman]

OK. I've got a Marantz 4430 Quad.

Played it today and it sounded great, four speakers - two front, two rear, all 8 ohm, all on the "main" bank, none "remote." Strong and clear, but as the day wore on I noticed distortion/weakness in the left channel. I've cleaned all the controls and will clean them again with ol' De-oxit, but I don't think that's it.

This, of course, is an old unit. Sat idle for a long time. Yet it's been well cared for and not abused except by time.

Primary suspects? Outputs? They are old and one side, after some reasonable play and stress just decided to croak after all this time?

Can one trust the 2SC1403 "NEW" transistors coming out of China on eBay? In the service manual it says the outputs are 2SC1403's, 8 of them!!

Second Question: And then after that notation for the 2SC1403, it says "R or O". What does that signify? OK, if you're guessing by now that I'm in more than a little over my head, you're right.

Any suggestions are appreciated.

 

[Binkman]

On semi; MJ21193G/MJ21194G to replace 2SA745A/2SC1403 I've read. Never had to replace these but forums recommend on semi. I wouldn't trust ebay china but even if good it takes weeks to get stuff.

 

[redpackman]

The noise doesn't start until the receiver has played awhile. It's always in the right channel. Outputs, dirty connectors for the outputs, noisy transistors elsewhere (which are biggest suspects) or more dioxit?

 

[catrafter]

A dirty rear panel Local/Remote switch is frequently the problem, you can spray some DeOxit in from the back side with the top cover removed. Unplug the power cord first.
NEVER EVER cycle the rear panel 'Power Mode' switch with the unit powered on.

Tom

 

[Binkman]

Well you didn't mention the time/ delay and 'noise' hint. I'd say nothing wrong with the transistors aside from perhaps age but I'd not be so sure some reflowing solder joints in the preamp stage. perhaps some caps if low volt rated types like 10-15v. But I have a theory that aged solder is often ignored and I've found bad solder joints on never been touched units. We've had two examples this week on good gear that resoldering fixed it that both had transistor static.

You may also inspect the output transistor mounting for good contact and if heat sauce or mica gaskets? general inspection. Just make sure all major power caps are discharged. Some think the mains hold the majority of risk but some are switched and those switched circuits still hold a charge and I've read 12vdc or more just on a meter discharging on a 30 vdc rated cap. That circuit was still hot.

Recalling other quad units.. I think best results was a recap and transistors were good. It may be driver preamp transistors if suspect if caps and resolder suspect joints don't cure it. Also often ignored is checking diodes.

 

[redpackman]

Newbie question here. Other than time (how much time), what's the proper way to discharge a power cap w/o doing damage to the power cap or any of the other sensitive components?

 

[Rob-F]

Newbie question here. Other than time (how much time), what's the proper way to discharge a power cap w/o doing damage to the power cap or any of the other sensitive components?

I bridge a resistor across the cap terminals. If it is a 50V supply, I might use a 100 ohm resistor, for a 500ma (max) discharge rate. It only takes a few seconds. I might followup with a lower value resistor once the voltage has fallen to 5% or so or the starting point. Power supply caps tend to "bounce back" a little after discharge; but nothing serious.

 

[redpackman]

Does the rating of the resistor matter? 1/4 watt 1/8 watt or does it have to be higher than that?

 

[catrafter]

I use this.
Capacitor discharge unit.

Tom

40 Watt 120V lamp
+

Adapter
+

Two clip leads

Tom

 

[Binkman]

TOM!! I do same.. been thinking of using a hduty xmas bulb. I like watching the glow down' even a smaller bulb on a 30v rated cap will light up small auto bulb rated, too.

 

[Jube marsh]

I have the same issue on mine.

I also would like some suggestions on how to replace all the bulbs.