Omega Owners Forum
Chat Area => General Discussion Area => Topic started by: danzigfan on 01 January 2012, 19:17:47
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So, I'm trying to repair an old Marantz cd player. Till now I found a power supply unit is dead. Searching for fault and following the connections on circuit board I found out that voltage 230v doesn't even reach the transformer because of this (at least I think so) faulty thingy - the roundy in the middle (http://i1103.photobucket.com/albums/g480/danzigfan1/IMAG0025.jpg) Does anyone know what it is? I think it's a capacitor but there's been a "few" years from my school times... :o Sorry for such an off topic TID Stan
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Oouhh... matey. I am but that's almost impossible to repair anything by remote control... ::) ::) ::) Do you have digital multimeter?
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I have, that how I found that...I'm not giving up yet till it will resurect...
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At first I propose you deciding that is this part on line or parallel to the other?
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Whar consfuses me is: Voltage is fine between transformer's input 1 and 2 if I measure between input 1 and voltage before it reaches this element. After this element, voltage between is 20V which is definetely too low to even convert into somethong usefull at the transformers exit...
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It isn't capacotor's purpose to lower the voltage but to smooth it and stabilize it
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The round thingy is a capacitor (tantalum i think) normal use of that type to remove any high freq when converting to dc. Will normally appear open circuit to a meter.
The things to check are two diodes next to it (ac to dc convertion here) and the transistor attached to the heat sync (may be a switch mode psu)
you will have to diconnect diodes to check high resistance one way low the other
Transistor will be a combination of high and low resistance between the three legs.
There should be no open (very very high resistance) or short circuits
Voltage smoothing is done by a different capacitor which is cylinder shape (normally blue) with wires out both or one end.
Sure TB or others will be along soon with more recent experience on this (20+ yrs since i did any of this)
Phil
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Very impressive, thank you. I'll check all of these matters tomorrow morning before going to work.
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In this case it can be a Voltage stabiliser IC if it has three leg. But not if doesn't have any. With two leg either a condensator or a resistance or diodes can work. Or a coil but here it is irrelevant. My guess is a condensator. Check that it is parallel or on line to others...If parallel it'll be a condensator, if line mostly a resistance. When you use condy one leg of it has to be connected to the "-" or negative pole (ground) to help it the electronic circle get smoothed (faulty signals to be filtered ).
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Phil is the Master! ;) follow him! :y
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Given its proximity to the mains input, it could also be a thermal fuse, they look like that. They go high resistance and stay that way until the over current is gone and they cool down. Although the numbers 103M suggests a cap, 0.01uF ?. If you can trace the flow of current, does the mains go into the diode, thro the unknown device and into the circuit, or is it across the main rails, maybe with a diode each side, or just one in the "hot" feed. Is there any markings on the PCB next to the component, like C23 ?. If it says C then most likely a capacitor something to do with interference, so can be ignored. Switch off and feel it, if its hot then it prob is a thermal fuse with an overload somewhere else. However if it isn't hot it could just have gone bad, so check its resistance when cold and supply disconnected.
Ken
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I agree, that looks like a ceramic cap to me, so almost certainly not the problem.
Diodes close to the mains input make me wonder if it's switched mode, in which case an entirely different approach is required to debugging it.
I would have a look online for a service manual with a schematic in. Failing that, can you post a photo showing the whole power supply circuit so we can get a better understanding what we're dealing with.
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Yes, I will. For now I'll try to find (what I think capacitor is - 0.01 micro farad, 1 KV) another one somewhere, replace it and see what happens. Diodes, all four are fine, opening in one way only, transistor on cooling plate is also fine - no open circuit (AFAIK)... will post a pics of a plate
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Diodes close to the mains input make me wonder if it's switched mode
I was thinking that as I honestly can't remember the last time I saw a "normal" PSU in devices such as CD/DVD players.
If it is an SMPSU, I'll go in "blind" with a bid that it's an electrolytic that has popped.
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Diodes close to the mains input make me wonder if it's switched mode
I was thinking that as I honestly can't remember the last time I saw a "normal" PSU in devices such as CD/DVD players.
If it is an SMPSU, I'll go in "blind" with a bid that it's an electrolytic that has popped.
Good call.. :y Although I can't help thinking that an "old Marantz" CD player would probably have a linear PSU.. For a certain value of "old". :-\
Can we have the model number / name? ;)
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Few pics of it (I'm at work and forgot which model it is but I'm searching for it) (http://i1103.photobucket.com/albums/g480/danzigfan1/IMAG0026.jpg) (http://i1103.photobucket.com/albums/g480/danzigfan1/IMAG0028.jpg) (http://i1103.photobucket.com/albums/g480/danzigfan1/IMAG0029.jpg) (http://i1103.photobucket.com/albums/g480/danzigfan1/IMAG0030.jpg) (http://i1103.photobucket.com/albums/g480/danzigfan1/IMAG0031.jpg)
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Found it Marantz MX550 (http://i1103.photobucket.com/albums/g480/danzigfan1/trio.jpg)
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This is definately a switch mode psu. There does not seem to be any visible problems so this is a good sign
Problem is that some have to be connected to actually work and be tested, If I recall correctly
Obvious things to check are the fuses next the transformer
Also the two transistors 7431 & 2. These are the ones that do the switching (with the chip 7352) and tend to be the ones that fail. Look up online the type and you should be able to find an uprated replacement. RS components or even Farnell.
Also 7351 & 2 may not be able to be tested by resistance. re-connect and see if they get hot. if so replace if you can find
Best of luck
Phil
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Its a proper linear supply.
Measure those three round fuses and check they are ok.
I suspect connector 1345 has AC volts on it so check for AC here when its on (if you tried measuring for DC you would get weird readings).
The rest of the components look to be a HT power off circuit (7353 is an opto to support issolation for the switching) and hence for the rectifier diodes to support generation of a low current standby supply.
The disc in question is a ceramic cap and in conjunction with the common mode choke next to it (the toroid with the wires) its allowing the unit to meet emc emmisions by blocking the common mode noise.
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This is definately a switch mode psu. There does not seem to be any visible problems so this is a good sign
Problem is that some have to be connected to actually work and be tested, If I recall correctly
Obvious things to check are the fuses next the transformer
Also the two transistors 7431 & 2. These are the ones that do the switching (with the chip 7352) and tend to be the ones that fail. Look up online the type and you should be able to find an uprated replacement. RS components or even Farnell.
Also 7351 & 2 may not be able to be tested by resistance. re-connect and see if they get hot. if so replace if you can find
Best of luck
Phil
Nah, not convinced it it :y
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This is definately a switch mode psu. There does not seem to be any visible problems so this is a good sign
Problem is that some have to be connected to actually work and be tested, If I recall correctly
Obvious things to check are the fuses next the transformer
Also the two transistors 7431 & 2. These are the ones that do the switching (with the chip 7352) and tend to be the ones that fail. Look up online the type and you should be able to find an uprated replacement. RS components or even Farnell.
Also 7351 & 2 may not be able to be tested by resistance. re-connect and see if they get hot. if so replace if you can find
Best of luck
Phil
Nah, not convinced it it :y
Not going to argue - been a long time since i did this type of stuff. will give in to more recent experience :-X
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A few reasons
1) No secondary control section
2) Transformer has a LOT of iron in it (key reason you use a switch mode is to reduce the iron and hence the size and weight)
3) Marantz pretty much always have linear supplies which gives a better transient response for the audio
4) No large HT cap to create the required HT DC supply required switcher primary
5) No where near enough EMC filtering
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A few reasons
1) No secondary control section
2) Transformer has a LOT of iron in it (key reason you use a switch mode is to reduce the iron and hence the size and weight)
3) Marantz pretty much always have linear supplies which gives a better transient response for the audio
4) No large HT cap to create the required HT DC supply required switcher primary
5) No where near enough EMC filtering
Yep, agreed. Although on first glance the amount of circuitry on the primary side suggests it might be a switcher, It's not.
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My face at the moment is like this...(http://i1103.photobucket.com/albums/g480/danzigfan1/images.jpg) After I get home and take a sleep I'll take another detailed read trough all posts and hopefully make some progress. Guys, thanks for help. I will keep you informed of progress
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A few reasons
1) No secondary control section
2) Transformer has a LOT of iron in it (key reason you use a switch mode is to reduce the iron and hence the size and weight)
3) Marantz pretty much always have linear supplies which gives a better transient response for the audio
4) No large HT cap to create the required HT DC supply required switcher primary
5) No where near enough EMC filtering
Yep, agreed. Although on first glance the amount of circuitry on the primary side suggests it might be a switcher, It's not.
Right ok guys have given up - your right :y :y what does he do to fix it ??? ???
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looks like a normal old fashion transformer to me, so if its got 240 volts going in to it (and thats confirmed) I would check if theres a link some where in the middle for the 110 v market, normally goes 110v, plus link, 110v, check for dry joints etc, failing that I would diss one side of the output of the transformer so as to isolate the the rectifiering cct and see what its pushing out AC wise, guessing 20v AC o/p would give around 24v+ DC once rectified and smoothed, if the AC o/p volts drop with the rectifier cct back in play the check the DC rectifier, smoothing Caps and Voltage stablisers etc.
Chris.