Powersupply voltage problem

[u301021]

Hi there.

I have a Marantz MR 2020 (MR2021) there is dead
A fuse in the house installation was blown and all the power in the house was gone.
I replaced the fuse at got power again, but after that little episode the Marantz MR 2020 was dead.

I have tried to measure some voltage on the power supply, and found a "funny" thing.

In the schematic there is a point where there should be -27 V but i´am measure -43 V
I believe it is on the board (6.2) in the schematic the makes the trouble.

Here is a little cut of the schematic and also the complete schematic.

Can somebody help me to get this fixed ?

The schematic = https://www.google.dk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=2ahUKEwjyuYLYgMXlAhVDdJoKHT-SBtgQFjABegQIBhAC&url=https%3A%2F%2Fwww.vintageshifi.com%2Frepertoire-pdf%2Fpdf%2Ftelecharge.php%3Fpdf%3DMarantz-MR-2020-Service-Manual.pdf&usg=AOvVaw3ozfOJwTFq7AlqAhReJq0Q

 

[Vovk Z]

Measure voltage across D812 zener - it must be 27V.
And make sure that your DMM battery is ok.

 

[u301021]

Done
It measure 27 V (27,3)

 

[rayma]

Then the 2SB1240 regulator pass transistor is likely to be shorted C-E, and needing replacement.
There may be other problems as well, if your house breaker tripped.

 

[u301021]

Then the 2SB1240 regulator pass transistor is likely to be shorted, and needing replacement.
There may be other problems as well, if your house breaker tripped.

The house breaker was because of a defective LED bulp

Just measured the 2SB1240 and between emitter and collector i measure 56 ohm - both ways

 

[rayma]

Just measured the 2SB1240 and between emitter and collector i measure 56 ohm - both ways

It's an ex-2SB1240.

 

[u301021]

It's an ex-2SB1240.

Thank you - i will try to find a new or a replacement and replace it.

But can a transistor really go dead cause of housebreaker is turning off ?

 

[rayma]

Thank you - i will try to find a new or a replacement and replace it.

But can a transistor really go dead cause of housebreaker is turning off ?

Could have been a voltage transient, the Vceo rating is 32V.
Maybe the regulator's output to ground was (is) shorted.
That would impress the entire 39V across the transistor, not good.
Do some more checking before replacing parts.

 

[u301021]

Could have been a voltage transient, the Vceo rating is 32V.

Maybe !
It was a LED bulb where 3 LEDs where mounted the wrong way, and when I screwed the bulb in (with power on) it said bang and the bulb exploded in my hand and the house turned dark

 

[rayma]

Maybe !
It was a LED bulb where 3 LEDs where mounted the wrong way, and when I screwed the bulb in (with power on) it said bang and the bulb exploded in my hand and the house turned dark

I think you've got it.

 

[u301021]

I think you've got it.

I will try to replace it, but 10.000 thanks.
This forum is the top

 

[rayma]

I will try to replace it, but 10.000 thanks.
This forum is the top

Can you post a photo of the transistor and its heat sink?
Have you repaired pcbs before?

 

[u301021]

There are no heatsink and the 2SB1240 is a really small "thing"

 

[u301021]

 

[rayma]

Ok, if you haven's reworked pcbs before, practice on some junk boards before doing this one.

 

[u301021]

Ok, if you haven's reworked pcbs before, practice on some junk boards before doing this one.

I have done a lot of soldering and replacement of transistors and so, so this should be an easy one

Hope it turn on in a day or two

 

[u301021]

And again, 10.000 thanks

 

[rayma]

I have done a lot of soldering and replacement of transistors and so, so this should be an easy one

Great, let us know how it works out.

 

[u301021]

Great, let us know how it works out.

Yep.
I have just ordered 2 x 2SB1240 and hope i get it before the weekend

But i will post as soon as i have tried it

 

[u301021]

A new 2SB1240 mounted and the there is -27 V between the pins as there should be.
BUT, the hole display is lighting up (all funktions) and no buttons are reacts.

I dont think its worth working more on this MR 2020, but thank for your help