Marantz 4400 - tuner MPX board - help needed

[tranguru]

Hi all,

I have a 4400 with no stereo.
tuner works in mono only.

I am trying to remove the MPX board. - any idea on how to do this without taking the 50% of the 4400 apart?
what are the typical components which fails on this board?
I intend to replace all the elcos

Thanks
Robin

 

[tranguru]

after reading many posts here, I decide to remove the MPX board.
will send some pics later .

 

[tranguru]

Had 11V on pin 1 of HA1156 - usually due to bad cap.

So I removed the board and recaped it.
I decided to replace the connectors so that I could avoid resoldering.... not such a good idea. the cables are too short to be able to bend them so that the connectors can easily connect on the pins.
So I ended put putting some wire wrapping pin back in.
I disconnected the AM board and wrapped it in masking tape to avoid any accidental shorts....

Then I recapped the board.



On the pictures you can see the pins I tried to replace.

Important note: Muting will not work because the 13,5V come thru the AM board to Pin J303.
When I wanted to mute I put a jumper between J304 and J303.

I replaced the caps and the board back in.
12,4V on pin 1 of HA1156.
Still no stereo.

 

[tranguru]

what made the biggest the difference is the tuning of L201.
as these units get older the ferrite core loses its permeability ==> the transformer L201 needs to be re adjusted.
his is tricky of course because according to the SM you need the FM and stereo generators for a perfect job.
The goal is get 0V on pin J204 when a channel is perfectly tuned.

I put the MPX board in muting mode and measured voltage on J309 (J204 in under the 4400 chassis).
Then with a PLASTIC hex screwdriver (see picture - green stick) I screwed (very carefully) the ferrite core inwards on L201 - and the tuner came alive!
stereo came back and tuner plays nicely again.

Careful: L201 has 2 parts.
1 = top part accessible on top of the chassis - see picture. it right next to the power supply heatsink.
2= bottom part used to set distortion - I did not touch that one.

don't break the ferrite core - those are very difficult to find.... if you break it the tuner will probably never work again.

I will take some picture of the signal from my scope (not the 4400 one).

Next step is to adjust the scope circuit because tuning and multipath display don't work.

will keep you posted.

 

[tranguru]

Here are some pictures of the amp recap and resoldering
I am quite proud of my solder points which look a lot like the original ones..

 

[catrafter]

Nice work!
Did you replace the two failure prone 2SC458 bias transistors under the edges of the driver heat sink? You can use KSC1845s for these, they are a different package but fit OK. Note that one is face up and one is face down. The silk screen on the circuit board will tell you how to install them.

I would also replace those two little tantalum capacitors with film types, C701 and C702
Tom

 

[tranguru]

Thanks for the advice. No I have not replaced them. I will go ahead and do so.
The amps work quite well, but these 2 xtors are failure prone I might as well replace them.