Marantz 4270 project

[javajam12]

Here is an update to an earlier thread re: a 4270 I got for cheap. I bought it
with the knowledge that it had no output. It was very dirty inside so I figured
that dirty pots and contacts would be the culprit. Upon first testing, I got
sound and static from the phones jacks so at least it was getting something.
The static I believe is from the phones jacks themselves. I can't really see
what I am doing as the jacks are buried in the corner but they either need a
good cleaning or have some loose solder connection. Anyway, no speaker
output. I tested all the different speaker jacks, same result. I was then
going to focus on the speaker protection circuit as it was not engaging on
powerup. I started cleaning the unit inside, just some basic pcb and parts
cleaning. I found 4 fuses on a small raised pcb atop the power board. Two
4A 250V and 2 1A 250V. The 4A were wrapped in wire (one actually appears
to have solder wrapped around it!) and were blown. I think they were the
wrong value also. I have replacements coming for the fuses and will commence
testing the protection circuit. Anyone have an good process for
removing the back panel and getting at the Protection circuit board? I did
look at the two relays but have not cleaned them yet. They LOOK ok but
who knows- I know they can cause all kinds of problems. I suspect a cap
is bad or some other thing. Who knows - maybe I'll get lucky and it will work
with just the correct fuses. Please feel free to advise or share similar
experiences. This is my first Marantz project and I would like to get this nice
looking quad running again. Then, I can proceed with my personal opinion
or Yamaha CRxx versus Marantz. I have read many many threads about this
and I have a CR-1020 and a CR-2020 that I love. Pictures of this 4270 to
follow. Thanks - Jon

 

[Gigapod]

Hi Jon,
The first step in bringing any such vintage gear and particularly Marantz receivers up to daily usage level is to get a copy of the service manual.
The most likely outcome of replacing the burned fuses in your 4270 with new ones is... more burned fuses!
At the very least you should take out the power transistors and check them with a multimeter for opens/shorts.
Check the power supply, replace any obviously defective capacitors, check the relays and switches with a multimeter and the very last thing you'll do is to put back new fuses.
Waiting for your pictures and further comments about your receiver's health status. :yes:

 

[javajam12]

Nudies of 4270!

Here are some shots I took of the 4270.

 

[jstang]

Here are some shots I took of the 4270.

Boy, I thought my 4400 was packed solid with stuff, that is just as bad or worse..... guess the overall demensions are smaller.... Make sure you use Deoxit on the Channel mode switch (remove the bottom cover) and the local/remote control switch (from the top).

Both of those have an affect on the sound as they are in the signal path.

Also, because these are packed so tight, they run hot....which means all the more reason to re-cap the unit. I just did my 4400...really helped it.


johnk

 

[ruesselschorf]

Hello,

the 4270 sure is a nightmare to service, no Marantz receiver is so tightly packed.
For a quick check, to find out if all four amps are ok, set the mode switch on the rear to 4x25Watt, all balance faders in the middle position, the front mode switch to stereo, select a good FM station and connect a headphone to front and then rear headphone jack. Do you hear all four amps clear and undistorted?
Since the headphone outputs are connected prior to the relays in the 4270, you can check DC offset by inserting an empty headphone plug and measure there with a multimeter.
If you find DC offset ok (not more than+/- 30mV)with all four amps, the protect circuit probably is bad
Do get to the Protect/power supply board, I always unscrew the back-panel, fold it back 4-5cm and also unscrew the right side power amp, to have a little more space to work on that board.......
Oh, yes those relays 95% have bad contacts, best is to replace them, but you need relays that have pcb-contacts a 24V DC coil for 4270, and 48V coil for 4300/4400......

Helmut

 

[javajam12]

Thanks Helmut

Thanks for the tips Helmut, very helpful. Does anyone know what part I
would use to replace these 2SC897 output transistors? I haven't checked them out yet but just in case, any On Semi replacements? I am also having
trouble locating replacements for the rectifier diodes that are marked as
U11C and U12C, pairs of two. Not sure what or where to get them. The
service manual is not very helpful in determining replacements. Thanks for all
the help. Jon

 

[Gigapod]

Hi,
The first thing is don't replace them unless they are toast.
If you replace a PNP power transistor, you also have to replace the corresponding NPN transistor i.e. always replace the pair of output transistors, never a single one. Matching is recommended but not compulsory.
I don't think there are any modern exact replacements.
Possible alternatives are MJ15024/15025 pairs usually, or MJ15003/15004.
http://www.onsemi.com/pub/Collateral/MJ15003-D.PDF
http://www.onsemi.com/pub/Collateral/MJ15022-D.PDF
IIRC the 2SC897 is also used in the Marantz 1060 amp, so you can ask here in this forum who has replaced the output transistors in a Marantz 1060 and what worked for them.
But then again don't replace anything unless you know for sure it's toast/bad.