Marantz 300DC

[zambrano966]

"Good friends, I'm from Venezuela and I'm recovering a Marantz 300DC, I bought it in very bad condition, but little by little I have been repairing it, it is almost ready but I have a problem, there is a channel that is missing some diodes, according to the electrical diagram says that they are MV-1 varistors, will you know which diode can be placed as a substitute?"

 

[quadmatrix82]

try a 1n4148, i asked about this very varistor nearly a year ago, fellow member catrafter provided the below specs

catrafterMarantz SpecialistSubscriber
My ancient data sheet says:
MV-1; P(mW)=40 If(mA)=50 Vf(V) min=0.58 typ=0.62 max=0.65 @If 10mA. (mV/°C)=1.9

 

[zambrano966]

Thanks quadmatrix82, if I have been researching these varistors and for the STV-3H they say that you can place three diodes 1N4148 in series and for the STV-4H four diodes. I think it was right here (AUDIOKARMA.ORG). It also recommends the same for the SV-2, SV-3 and SV-4. Well I will try to place a 1N4148 to see how it works. In this Power Marantz 300DC this diode and a thermistor are placed on the opposite side of the card, I imagine that it is for that closest to the heat sink where the 4 power transistors are.

 

[bktheking]

Are you sure it's missing? Did you look on the back of the board cause that's where they are on my 300dc. I think you'll find that they are there.

 

[zambrano966]

Hello bktheking, the varistor is not on the back side of the card, as I mentioned earlier, I bought this power in very bad condition and it can be said that I have completely reconstructed it, I could send you photos but I do not know how you are staying in this forum, you explain to me, I send you photos of the cards so you can see how they have been after the restoration. it also lacks the thermistor Q722 and Q723 (SDT-100 which are 1Kohm) the missing varistors are the Q720 and Q721 (MV-1). The thermistors I already got, I'm missing are the two varistors of that card. Luckily a channel I could repair it completely because if I had the aforementioned parts.

 

[quadmatrix82]

You can upload a file photo by clicking the upload a file button

 

[zambrano966]

Ok, thanks quadmatrix82, I will try to do it and publish the photos.

 

[zambrano966]

 

[zambrano966]

Friends as you can see, first I am in the stage of electronic repair and then with the cosmetic restoration, I am very sad the state as it was, but it will be as good as new. The final transistors did not get the originals so I'm going to place the same as the SPEC-2 Pionner uses. that was what I got.

 

[Richs_Trains]

Sad to see such a beautiful amp left to die ........ looking forward to re-birth

 

[zambrano966]

If, after finishing repairing, I will disassemble it completely and paint the transformer and all the panels, it will not be as new but it will remain operative and beautiful.