Marantz PM66KI amp.

[Fidelity Audio]

I have rebuilt many output stages on these amps.

Change Q764 Q762 Q752 Q754 Q758 Q756 Q760 QN02 QN03 (or equivalent on other side). Change them all as said previously its not worth it going bang again.

Once rebuilt set volume to minimum , balance to center position , set the bias VR to center position (R756 or R755).

Set your digital (not analogue) multimeter to mV and connect to the two outer test points of the output resistor (R767 or R768).

Now switch power on.... Hopefully nothing has gone bang!!!!

Adjust the VR to 14 mV as follows......

Elapsed Power on ¦ idle current setting
-------------------------------------------------------
30 sec to 1 min ¦ 5mV
1 min to 2 min ¦ 8mV
2 min to 4 min ¦ 10.5mV
More than 6 mins ¦ 14mV

If after this time period the mV will not stay stable then there is another problem and you run the risk of it going bang again.

Changing all the above components should be fine though.

The capacitors used in the KI are Elna 'FOR AUDIO' 56V 12000uF.

The regulators Q801 and Q802 do get hot, they supply the protection, relay and volume circuits.

I fitted mine to the heatsink. Remove them, clean the pcb with a fiber pen and resolder, put new ones in on longer legs too.

Hope this helps

 

[toman_9]

Thanks al a lot for the help so far...

This means I have to order new transistors, I hope I can find them all. I shall update you guys once I change them.

Please use toman9 at googlemail.com for the pdfs.

Tim

 

[Fidelity Audio]

All the components used are common items so you will be ok.

Try these...

http://www.electronicsrepair.net/scemes.html

I find them very good and efficient.

EDIT:- Just noticed they don't have the Schematics for this model. lol.

I will try to copy mine once my scanner is repaired

 

[toman_9]

Hi Hugo,

You have suggested to desolder the output stage transistors.
If I do that, is it OK to turn on the amp to see whether other parts are working ? I have in mind to check the regulators for example to see whether to supply the correct voltage.

Hi Rowemeister,

Ok I will order all the transistors you named.
Anything else you think necessary ?

BTW The SI E model also have the same ELNA capacitors. I do not think they are broken, but if...
Does someone know where to order them I can not seem to find any...

 

[Netlist]

The idea behind it is that, if they still work, you surely save them from frying while testing.
It is perfectly possible to turn on the amplifier without output stage to perform most DC measurements.

/Hugo

 

[Fidelity Audio]

Everything listed should cure your problem.

And yes you can power up without the output in. Also you can run the channel that appears ok and test the audio from it.

You may also be better getting hold of a pair of better quality caps but this may be too expensive.

 

[toman_9]

The regulators Q801 and Q802 do get hot, they supply the protection, relay and volume circuits.

I fitted mine to the heatsink. Remove them, clean the pcb with a fiber pen and resolder, put new ones in on longer legs too.

So do you place them on the big heat sinks and wired them to the PCB ?
Or added small heatsinks to those transistors.

If this help I might try it also, do you have a photo ?

 

[Fidelity Audio]

I fitted mine to the main heat sink and wired them.

I'll look for a pic

 

[toman_9]

Grrrrr......

I have ordered 2SC9141 instead of 2SA1941....and recieved them... Very annoying...
Have to order them once again...

Thanks Hugo!
I have received the KI spec, there is list of parts that are different.
Any idea what "Blue SE" caps are ?

 

[Netlist]

Blue SE

Not really; are they listed in the manual?

Thanks for the mail.

/Hugo

 

[toman_9]

Yup..
But never mind.. I shall repair the amp first, upgrade to KI would be the second prio...

 

[chicco_36]

Can someone pass schematic of K.I. version of this amp to me?
janevski_69@yahoo.com
Upgrading 66SE versions to K.I. is nice option!
Chicoo

 

[Fidelity Audio]

The blue SE caps are ok but I changed C709/710/753/754/755/756 with silver mica caps and this did improve the sound on my KI.

The sound was a little bit more open and the treble is a little crisper.

The caps I changed were upgraded on the SE and KI from the PM66, so I thought I would change these for even better caps

 

[toman_9]

Thanks for the info I will look for those caps...

Meanwhile I have realized that PM66 and PM6010 actually have different sets of end transistors, unfortunately or fortunatlely I have ordered the parts for my PM66, the parts from PM6010.

So,
Which one is better :

2SA1941 or 2SA1265 ?
2SC5198 or 2SC3102 ?

Or doesn't make any difference ?
Shall I stick with the PM6010 spec as assumably it is newer ?

 

[Fidelity Audio]

looking @ my transistor data book they are both 140v 10A 100w 18j.

So interms of working they are fine, but if one side is different to the other you may get a different sound between channels.

Try them and see what happens, the worst that can happen is the output goes bang again lol

 

[Fidelity Audio]

Here is a pic from my amp so you can see where I placed the regs, + the blackgate caps and Schottky bridge etc

An externally hosted image should be here but it was not working when we last tested it.

 

[toman_9]

Wow! You did quite a lot of improvements...
Does rectifier upgrade worth the effort ?
I saw that in the other discussion thread, but your schematics was under discussion, and I think it is not up to date.

Also, I know it might sound silly to to some experienced guys, but how do I make sure that the capactors are Blue SE and Silver Mica... I have lots of them but not sure which is which... I assume the "Blue SE" are the blue ones... ;-)

 

[Fidelity Audio]

The rectifier gives a much quicker tighter bass and the treble is better too. The caps help further.

I also fitted 10n and 100n plastic caps with 1ohm 3w resistors across the smoothing caps. Some sort of snubber circuit.

After fitting those two (blackgates were fitted previous) the sound is more open and I could here noises on tracks I could not hear before.

On my pic the yellow caps on the input and the output sections are silver mica. Yours will be blue in your amp.

So yeah the Blue SE are blue

 

[toman_9]

Some more findings from my amp :

I removed the faulty transistor and powered up again and saw that it the amp is working again, at least no shortcut hence no fuse blow. And also after like 5 seconds the relay turns on. And I can at least hear (from one channel) music. Great !!!!

Sounds good up to this poit...
BUT... If I turn the volume up, after like 15 %, the relay goes off again. Which means there is still someththing wrong...

Any idea what could be faulty ?

May be I can save some time if I can pinpoint it...

 

[Netlist]

BUT... If I turn the volume up, after like 15 %, the relay goes off again. Which means there is still someththing wrong...

Congrats.
You didn't forget to put the output transistors in place?

/Hugo