Marantz 4240 repair, help please

K

kryzpo

New Member
Hi!

I'm new here :yes:
http://www.audiokarma.org/forums/showthread.php?t=427288

This is my first post, forgive my basic english, I'll use google translator ;)

I have only basic knowledge of electronics, but enough to make a typical maintenance on this device.

I found it near the trash. When turned on, it worked almost perfect, with the typical noise of the "knobs" and after 5 minutes began a noise typical of capacitors, so I started to change.

I checked some diodes and transistors, all apparently work well.

Unfortunately, my inexperience and my lack of concentration I made a mistake. I changed all the capacitors of the power supply and amplifiers, noticing that all were in their position. In turn, exploded lol. My mistake, a capacitor of 10000uF 35v plugged it backwards :cry: The result, a capacitor burst, and a rectifier dead.

My second error, improperly connected cable, resulting in a transistor (H801) died.

(I know I was stupid, I need not say it haha)

OK,

- I changed the two 10000uF 35v capacitors, for new (50v 10000uF).
- H801 transistor changed for a new one.
- I changed the rectifier with a new one. The original was 6 amps and placed one of 1000v 8 amps.

My third mistake, broke the diode H005, I changed with two diodes 4148, as I found in this link: http://www.audiokarma.org/forums/showthread.php?t=373582

p700sq.jpg


Now on!! :music: (almost happy)

Calibrate the bias of the P700 and P800, all perfect values. Noise no longer exists :banana:

But still I have a couple of problems. :tears:

At first everything looked fine until I went up the volume :thumbsdn: is an overload and the lights go down in intensity. The sound is perfect, but a very low noise in the background, which sounds for any of the 4 outputs (in 2x40 and 4x17 as well).

(see the video)
http://youtu.be/YUypipyJoCs

If the load increases, raising the volume, connecting the decoder (sqa-2b) and put the FM radio, I can not go much volume because the source is not able to maintain the signal and the sound becomes noise and voltage to the speakers, the lights go out. It seems that AC pass. Apparently the decoder is not good, do not know, for now I will not use.

I disconnected the two amplifiers (P800) and capacitor voltage is 35v (in the rectifier), but when connected, the voltage is 52v (in the rectifier) Is this normal?

capsku.jpg


By spending 5 minutes in the power supply components R805 and R809 are heated much. The H801 is heated too. (C, B and A in the picture)

psupply.jpg

p800.jpg


I checked all the transistors and diodes of the P800 and P700, apparently they are all OK. I checked all connections and are all ok.

I do not know what to do: '(

What else I can check?
 
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I don't have the skills to help you, but if AK member Echowars reads this thread he might chime in and help you out. He's the best. :thmbsp:
 
My first guesses would be the H804, a 14V zener diode is shorted or that something connected to the 14V power supply (J803) is shorted to ground.

Tom
 
Thank you! I have checked the diode you mention, seems to be good, I will change it anyway and I will check the connections again.
 
If those components still get hot, try removing the wire(s) from J803. Then try to find the down stream short.

Tom
 
Hi!

I'm back! Thanks Tom for your help, unfortunately still can not find the problem.

I can not turn the volume up more than one third, because it seems that consumption is very high.

I have reviewed all the transistors and all diodes are good. I checked all connections and position of each of the capacitors I changed, I found a capacitor connected in reverse on the plate of the oscillator :bash: (my fault), I solved it, now there is no noise, but the problem of high consumption continues :(

R805 and R809 components are kept warm, but stabilized, should be normal.

I did the next test. I pulled out the fuses of the right amplifier. When I switch it, the opposite side obviously sounded, but consumption remains high. Then I tried it in reverse and the result is the same. Is there another way to rule out the problem in amplifiers?

How I can isolate the power amp and preamp to connect another preamp and discard both stages? I do not know which pins correspond to the amplifier input.

ampv.jpg


Although all bias voltages and amps and the power measured well, I do not know why the measured rectifier 52v when the amplifiers are connected, but when I disconnect the amplifiers (from the rectifier), measured 35v. I think that's the problem, or not?

capsku.jpg


What voltages other areas I can check?

Thank you very much!
 
I am unsure how we went from a P800 power supply problem to a power amp problem.
Why do you think the power consumption is too high?
Is something on the power amps getting hot?
Are you using a dim-bulb test by any chance?
If you are turning the volume up over half way I think you will be over driving the amplifiers.

Since this unit has no pre-main jumpers, it's going to be hard to separate the pre amp from the power amp.

I have no idea as to why the rail voltage would go down when you disconnected the amplifiers unless you also disconnected the filter capacitors (C002 and C003).

Tom
 
Thanks for your quick response.

I do not know if consumption increases too much, or is the source of power that is not being able to deliver the power required (or transfo, or maybe d315 transistor, or capacitor?, the transistor d315 is not original.). If you look at the video, when the music has a lot of bass, with the loudness on, dial lights begin to fade (The sound is a bit outdated).

http://youtu.be/YUypipyJoCs

I don't have a dim-bulb tester, but if I did, should I use to check the power supply or transfo right?

The amplifiers are kept completely cold, yet have spent over 15 minutes.

I have no idea as to why the rail voltage would go down the amplifiers disconnected when to you UNLESS you disconnected the filter capacitors Also (C002 and C003).
Click to expand...

Yes, it happens when I disconnect the capacitors too. What should be the correct voltage? The voltage should be 35v right? influences that I have changed the capacitors C002 and C003 by 50v - 10000uF? (The originals were 10000uF - 35v)

When I select the option of 17x4 the intensity of the lights does not come down much, however, when I place it in 40x2 turn off even more.
 
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It's easy and cheap to build a dim bulb tester. It will help prevent more damage by powering up the receiver under safe conditions to see whether there are still problems in its power supply etc.
 
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What speakers are you trying to use with this?
It's possible that your Marantz is fine and that you are driving it into clipping. Try it with some more efficient speakers and see what you find.

Tom
 
What speakers are you trying to use with this?
It's possible that your Marantz is fine and that you are driving it into clipping. Try it with some more efficient speakers and see what you find.
Click to expand...

I'm using the same speakers since I have it, I built a generic for any purpose. With them, initially worked well (before modifications). I thought it might be that the problem, then connected it to a yamaha ns-690, then I can not turn the volume up more than 1/4 without the lights go down. But when in 17x4 mode I can get to 1/2 the volume.


do you have h005 attached to heatsink ?
Click to expand...
All H005 are attached to the heatsink. Except one, which changed by two 1N4148 diodes. This is not attached to the heatsink. Maybe I could get a better replacement?

I did this:
http://www.audiokarma.org/forums/showthread.php?t=373582

Thank you all again. Next week I will make a "dim bulb".
 
Hello! I'm happy because I found a problem. Are 1:30 a.m. in my country. Now I sleep a while. In a few hours will tell.

Good night!
 
I forgot that this device is quad.... :scratch2:

Previously, I had selected the 17x4, but I kept only the front speakers connected. :headscrat

The right rear channel is weak.

I have reviewed all the knobs and work well. Then I will do some tests, I guess the problem must be in the PE01 (though I have not tested yet)

tonod.jpg


Unfortunately, I have no time. I back in a week.

For now I leave a video, unfortunately is mono. In it, the speakers are connected to the right and left rear. When turned on, the noise comes from the right rear, then disappears, but the volume is very low and no bass or midrange. The left rear works fine. If you think the problem is something else, do not forget to comment.

VIDEO (The sound is a little bit lagged, the pot that I move is the right left rear):
http://youtu.be/e5FDTydoSdQ

Thanks!!
 
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Picked up a 4240 known not working. Supposedly had been sent successfully repaired, but upon receipt (actually, from a nationally known vintage stereo repair shop) the owner plugged it in, and found it still didn't work. Using a DBT (100w), I powered it up and the bulb came on bright.

Figuring the last owner had already done damage by plugging it in, I plugged it into 120v w/o the DBT while keeping one hand on power switch. Within moments smoke was emitting from power supply board, specifically diode group H805-H808, one actually sparking inside. Of course I shut it down pronto.

Three more things: 1) there are all new output transistors on the L channel, so that must have been the original problem. 2) Not watching wire routing during reassembly, who ever worked on this pinched - and nearly cut - a transformer wire connecting to PS J807. It all but cut into copper, but I'm wondering if some stray voltage got through to cause this this problem. I doubt it, but thought it worth a mention. 3) Plugged into the DBT, all channels show 0.43+ volts at the speaker outputs when in the 17w x 4 mode. When set to 40w x 2, it drops down to 2 mV on the L channel, 32 mV on the R.

Anyway, In my experience, rarely is the smoking component the culprit, but an indicator of something more that caused this to happen. I'd appreciate any guidance on where to go from here. Thanks!
 
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Hi Markallen, You need to start a New thread on your problem. Using this old thread will just confuse the crap out of us:scratch2:
 
KutzlerTrans said:
Hi Markallen, You need to start a New thread on your problem. Using this old thread will just confuse the crap out of us:scratch2:
Click to expand...

Really? I've piggybacked before on threads that have evidentally run their course but have titles that well fit my situation. My thinking is that it would consolidate similar info on that model and problem.

Having said that, I'll take your counsel on my next question! But, since we're here now, any info on the described issue would be appreciated! Thanks.
 
I have the original, full size schematic for this 4240, but like other schematics I've seen, there are no listed voltage readings to compare with actual. Anyone have any ideas on where to start to identify problems as I've described a couple entries ago? Could this actually be a problem limited to the power supply?
 
Late to the party, as usual.
I always test in 17x4 mode as then you are dealing with 4 independent power amps instead of 2 bridged amps.
Never, ever cycle the rear panel 'Power Mode" switch with the unit turned on.

If you have one power amp with problems, you have 3 others to compare it to.
With the volume down, you can take DC measurements and record them on a good channel, then do the same for the bad channel. Set your meter to read DC volts, measure with the red meter lead, black meter lead to chassis.

As far as the power supply goes, H805 thru H808 can be replaced with standard rectifiers, 1N4004 thru 1N4007 should be fine.
Collector of H801 should be around +50VDC, Base at around +35.6, Emitter at +35VDC.
Collector of H803 at around +35VDC, Base at around +14VDC, emitter at +13VDC or so.
J805 should be at around 9VDC or so, I think it's just for the Dolby lamp, but I'm not sure.

Tom
 
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