Marantz PM-4

[Guest]

Well finally getting my arse in gear and sorting this amp out.

Due to age some of the big capacitors have leaked and some are just starting to bulge. So I thought I would get it sorted.

First off pictures of the inside and the bits you have to remove to open her up.

Pretty easy really. First remove the screws at the side and bottom of the front panel. Then lever off the toggle switch covers and the volume control. Then lever off the balance control. The others don't need to be removed.

The front then slides off.

You can now start to remove the mesh cover. Do this by undoing the two newly revealed screws which where behind the front cover. Then the four screws (two each side) on the top of the heat sinks. Finally the three at the back of the mesh. It will now lift off revealing the amps internals.

Luckily the amp I got came with the circuit diagram. Which should help.

But I have only ever built DIY kits and have never changed parts inside an old amp. So it is a bit of a mine field.

To start with I think I have identified all the electrolytic capacitors and will replace them.

Main board; 4x 55v 6800uF, 2x 16v 100uF, 2x 16v 1000uF, 2x 63v 470uF, 2x 50v 47uF, 2x 55v 220uF, 1x10v 220uF, 1x25v 100uF, 1x10v 100uF

Front left;

2x 35v 100uf, 2x 25v 4.7uF, 2x 10v 100uF, 4x 10v 10uF, 2x 50v 0.22uF

Front right;

2x 35v 220uF, 2x10v 2200uF, 2x 16v 10uF, 4x 35v 10uF

Not sure it is worth replacing the others? They shouldn't need it, I wouldn't think.

So off to order some replacements. Not looking to hot rod the amp, just replace like for like or as close as possible.

I will replace the rear screw down posts, as they are utterly useless. with any cable thicker than a human hair.

Give it a good clean/dust and probably if I ever get the time re-soldering all the boards.

Anyone know what else might need changing or is worth looking at?

 

[BD Audio]

Fit some valves to it?

 

[It Cost How Much!?!]

How about, fitting better speaker connectors as the standard ones are shite with larger cables and fitting an IEC socket instead of the mains cable, so you can try other mains cables (which make no difference of course)?

 

[murray johnson]

I'll be watching with interest to see what you think of the end result. I might have to do mine at some point although caps etc seem healthy enough at the moment.

I suppose the tricky aspectindoing this kind of refurbishment is to keep what's nice about the amplifier intact.

 

[Guest]

earlofsodbury wrote:

Dom - I know it's a PITA, but it is worth relacing all of the electrolytics in a class A amp of this age - they may not be showing obvious signs of distress, but they are all long past their use-by date.

Yep already listing them now

It is also worth uprating the smoothing caps - check the voltage coming off the secondaries as 55V is an uncommon rating nowadays - 50V should be plenty, 63 or 80v if you have room, and take them up to 10,000uF - Panasonic TSUPs should work nicely and not break the bank.

Looks to be around 48v

If you find any carbon comp resistors (brown, straight-sided drums usually) then junk these too, as they may well have drifted; carbon films will maintain tonality and hold their values pretty well.

Spotted a couple of these already so will replace them too.

While it's unquestionably a good idea to retouch solder joints, do take proper ESD precautions as much of the sandware will be out of production and hard to replace, and keep the times and temps down.

In reality I'm probably too lazy so I may or may not retouch all joints!

 

[Guest]

murray johnson wrote:

I'll be watching with interest to see what you think of the end result. I might have to do mine at some point although caps etc seem healthy enough at the moment.I suppose the tricky aspect in doing this kind of refurbishment is to keep what's nice about the amplifier intact.

Indeed, the last thing I want to do is change the sound. Just want her to perform at her best and keep going for a few more years yet :^

 

[i_should_coco]

dom_ wrote:

earlofsodbury wrote:

Dom - I know it'sa PITA, but it is worth relacing all of the electrolytics in a class A amp of this age - they may not be showing obvious signs of distress, but they are all long past their use-by date.

Yep already listing them now

It is also worth uprating the smoothing caps - check the voltage coming off the secondaries as 55V is an uncommon rating nowadays - 50V should be plenty, 63 or 80v if you have room, and take them up to 10,000uF - Panasonic TSUPs should work nicely and not break the bank.

Looks to be around 48v Use 63V.

If you find any carbon comp resistors (brown, straight-sided drums usually) then junk these too, as they may well have drifted; carbon films will maintain tonality and hold their values pretty well.

Spotted a couple of these already so will replace them too.

I'd replace with carbon comps such as Allen Bradleys, or you may fuck up the sound.

While it's unquestionably a good idea to retouch solder joints, do take proper ESD precautions as much of the sandware will be out of production and hard to replace, and keep the times and temps down.

In reality I'm probably too lazy so I may or may not retouch all joints!

 

[Guest]

Cheers, will be changing things in steps anyway to make sure any change isn't bad.

Another quick question, the wires are wire wrapped to pegs in the pcb. What is the best way to remove and replace these as/when I lift boards.

Just snip the wire down and solder it to the peg with a couple of twists?

 

[Guest]

Yep pretty sure they are wire wrap, square peg and all.

 

[russ abbott - royds broth]

Nice to see properly inside one...even though i don't have a clue what any of it is. :nuts:

Mines going in for a check up this week as it needs a once over.

 

[murray johnson]

Where? Knobs & Buttons?

let me know if you need the circuit diagram for whoever is looking at it.

 

[russ abbott - royds broth]

murray johnson wrote:

Where? Knobs & Buttons?let me know if you need the circuit diagram for whoever is looking at it.

d&m in stoke.

tape 2 needs the toggle wiggleing to get sound and then usually only one channel and all other inputs 5 times out of ten only one channel but a tap on top gets it sorted.

Will give you a shout if he needs diagram. :^

 

[Guest]

Caps and resistors ordered. Will fit them bit by bit and see how it sounds as I go.

Will leave the binding posts and other bits and bobs till the end when I know the amp better.

Also looking into wire wrapping tools! Not cheap. So leaving the wires attached will make my life a bit harder, but still easily doable as the wires have plenty of give length wise to allow lifting of the pcb's.

Have attached the schematic and will scan the manual/spec sheet soon and upload that too.

 

[Guest]

Will do :^

Just scanned the manual and spec sheet. Attached to this post.

 

[Guest]

Can you guess what I will be doing tomorrow afternoon?

 

[Guest]

She is alive!!!!!

j:

So today I have been dusting/cleaing everything inside. Cables, pcb, metal bits the lot.

Then I replaced every electrolytic with new with the same value except for the smoothing caps which are 63v 10,000uF instead of 55v 6,800uF. Used Panasonics through out.

Will leave her on for a while, then test the output to make sure all is well.

Will look at bypassing some caps and changing the resistors after I am used to the new caps and the sound. Have ordered up new rear speaker binding posts and am still contemplating changing the mains cable.

Uploading the pics at the moment and I will post them soon.

 

[russ abbott - royds broth]

how much have all the bits cost dom?

 

[Guest]

About £55 without the resistors or back panel bits. All in probably £85 by the end.

 

[russ abbott - royds broth]

dom_ wrote:

About £55 without the resistors or back panel bits. All in probably £85 by the end.

:^

will see if i can get mine done methinks.