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[danzigfan]

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 Does anyone know what it is? I think it's a capacitor but there's been a "few" years from my school times... Sorry for such an off topic TID Stan

[Johnny English]

Oouhh... matey. I am but that's almost impossible to repair anything by remote control... Do you have digital multimeter?

[danzigfan]

I have, that how I found that...I'm not giving up yet till it will resurect...

[Johnny English]

At first I propose you deciding that is this part on line or parallel to the other?

[danzigfan]

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...

[danzigfan]

It isn't capacotor's purpose to lower the voltage but to smooth it and stabilize it

[SIR Philbutt]

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

[danzigfan]

Very impressive, thank you. I'll check all of these matters tomorrow morning before going to work.

[Johnny English]

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 ).

[Johnny English]

Phil is the Master!    follow him! 

[Ken T]

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

[Kevin Wood]

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.

[danzigfan]

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

[Martian]

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.

[Kevin Wood]

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.. 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?