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4230 DOA Amateur Needs Help

Richs_Trains

Richs_Trains

Well-Known Member
Hey All,

My newest project came in sad shape with the power cord cut off and a monster fuse in the fuse holder. It is a Marantz 4230 Quad unit. I put a new cord and proper 3a fuse and put it on the DBT. I get a bright light and no power in the unit (I don't know if I should get anything if the bulb is lit, I am guessing the DBT is sucking the power from the 4230). Anyway, I don't know where to start, I was going to re-cap this unit anyway and don't know if I should do that and see what happens with the DBT, or try to find the problem first. Any thoughts or ideas how I should proceed? As always, Thanks!! Rich

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Is there a way to disable (pull power from) the power amps to see if they are the problem and if so what would be the easiest way? Thanks Rich
 
I suggest fixing it first because you will not be able to test any of your work as you go along.

Disconnect the red wire going to each amplifier from the filter capacitors. I think this applies to capacitor coupled models like the 4230 as well as non-cap coupled models.
 
Thank you Runningdog, I pulled each amp power one a a time (red from filter cap) lead and still have a short. I am guessing that means most likely a problem in the power supply, is there a way to test this, or remove the input power to the power supply board? This unit has been apart before, but I don't see that any work was done. Thanks Rich
 
While poking around, I noticed something that does not look right, but I don't know. In the picture, about the center, there is a resistor that is soldered in at one end and the other leg is off in space. Is it supposed to be this way?

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Tom, I pulled the power to the power amps, and still have a short. Removing the power to the amps should take the outputs out of the equation, yes? If so, the short is somewhere else. I am guessing it blew the fuse for the previous owner because the fuse in the holder was a too short 7.5 amp, but no telling what they may have tried before the short fuse. They may have put in a too high rated fuse and done some serious damage, but I don't see anything burned or overheated.

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The resistor at the very front of the PS board looks damaged, could that be my problem?
 
Next is checking the rectifier diode bridge H007 from the transformer to the filter cap and the filter cap C003 (4700uF at 55V) as well. Do an ohms check from the "+" of C003 to ground to see if it's shorted.
 
Richs_Trains said:
Tom, I pulled the power to the power amps, and still have a short. Removing the power to the amps should take the outputs out of the equation, yes? If so, the short is somewhere else. I am guessing it blew the fuse for the previous owner because the fuse in the holder was a too short 7.5 amp, but no telling what they may have tried before the short fuse. They may have put in a too high rated fuse and done some serious damage, but I don't see anything burned or overheated.

The resistor at the very front of the PS board looks damaged, could that be my problem?
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You are using a dim bulb tester, right?

Power to the outputs is supplied directly from the bridge rectifier H007 and filter capacitor (C003) like Randy says. My bet is still on at least one shorted output, maybe more.
I doubt that the condition of R802 has anything to do with your problem.
Tom
 
Yes, using a DBT, but have not let it on for more than a few seconds. I tested C003 + to ground and get 9.55Mohms and counting down very slowly as it is connected. Is that good or bad? How to I check the rectifier bridge? Is there a way to check the outputs with a DMM and still in place?Thanks Tom..... Rich
 
i noticed the trimmers for each channel look set way differently channel to channel ... maybe its correct but they are generally pretty much set same ..
 
Pete, I have not gotten to check the amp settings as I get a short as soon as I hook up the DBT. Both amps have the power disconnected right now and I still get a bright DBT. Any help is much appreciated. Rich
 
Richs_Trains said:
Pete, I have not gotten to check the amp settings as I get a short as soon as I hook up the DBT. Both amps have the power disconnected right now and I still get a bright DBT. Any help is much appreciated. Rich
Click to expand...
yes i realise that .. was in case someone has been fiddling around in there some caps look new to me ...
 
Meter turned off again, when restarted at 3.77 MOhms and decreasing. I did order new filter and coupling caps from Mouser.
 
the output transistors can be tested for shorts in circuit but need pulling to confirm if they appear shorted .
capacitors can be checked with meter on beep test .. it should beep then you should see the numbers counting up or down for a time . reverse probes and it should happen again .. be sure capacitors dont have any charge left in them first .
rectifier diodes can be tested in circuit with meter on diode test . pull any out that appear shorted .
 
Since I still have the bright bulb with the amps power disconnected, would it be best to concentrate on the PS board and it's components? Thanks Rich
 
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