Marantz MA500 thread

[Bratwurst7s]

And the frame relief for the filter caps is cut.


Also the extra mounting hole for the speaker binding post plate is drilled. Now I just have to fab that plate and I can get to the fun stuff.

Cheers,
James

 

[Bratwurst7s]

Further information concerning using 35mm diameter main filter caps.
While working the 5th amp I took some more careful measurements and photos.

First off, measuring from the bottom of the main connection plug to the center of the top through hole I got 15.5mm.



Not shown in a photo, but looking at one of the 35mm dia caps I measured 12mm from the center of a connection lead to the OD of the cap. So concerning shifting it's position up there is 3.5mm to play with.

Cheers,
James

 

[Bratwurst7s]

So I drew a vertical line through the through hole centers.



And, barely visible in the next photo marked the new positions, 3mm towards the top, but only for the upper cap.



And drilled with a 1.5mm bit.



You can't shift the hole toward the middle of the board because G808 (a combined cap and resistor in a epoxy body) will interfere with the filter cap. Any higher than 3.5mm and the cap will interfere with the plug socket. Ideally getting as close as possible to 3.25mm high for the new holes would be perfect as far as spacing between the connection socket, the caps and the lower mounting frame. Except, as you can see the upper hole is nearly at the edge of the pad, so I stuck with trying to get as exactly as possible at 3mm.

One thing that I have done on that upper cap lead where is is so close to the edge of the pad was to wrap a short section of 1.5mm solid core wire around the lead after inserting it in the hole and laying the wire across the rest of the pad before soldering. This gives some extra contact area and stability for the cap.

Doing all of this allows the lower filter cap to be mounted in the original holes without drilling. This is good because trying to shift the lower cap down just makes the interference problem with the steel mounting frame worse and partly negates the space won by cutting the relief in the frame.

So this works, but there is darn little extra room to play with.

Cheers,
James

 

[Bratwurst7s]

After that I got ready to work the board. As well as the filter caps the binding posts and RCA jacks were removed.



This lets me mount the board in my PC board fixture.



Cheers,
James

 

[Bratwurst7s]

Btw, earlier I failed to measure the height of the original blue Elna main filter caps. 55mm. Which makes me guess that the ones in my '99 amp were probably 50mm.
Also before I did anything with this 5th amp I put it on the dim bulb tester, which it passed and then let it warm up directly on line current. Before doing that I realized that I had neglected to check and of these amps for DC offset.



Well, color me surprised. After warming up the amp settled in at 7mV idle current, right where is is supposed to be. But the surprise was DC offset.
I did not actually believe what I was reading at first. Tested it with 2 different meters, Fluke 77 and Fluke 79, on V and mV scales, and got the same reading. 1.4mV.

Not bad.

Cheers,
James

 

[painttoad]

Btw, earlier I failed to measure the height of the original blue Elna main filter caps. 55mm. Which makes me guess that the ones in my '99 amp were probably 50mm.
Also before I did anything with this 5th amp I put it on the dim bulb tester, which it passed and then let it warm up directly on line current. Before doing that I realized that I had neglected to check and of these amps for DC offset.

View attachment 3092739

Well, color me surprised. After warming up the amp settled in at 7mV idle current, right where is is supposed to be. But the surprise was DC offset.
I did not actually believe what I was reading at first. Tested it with 2 different meters, Fluke 77 and Fluke 79, on V and mV scales, and got the same reading. 1.4mV.

Not bad.

Cheers,
James

i believe there is circuitry that clamps dc. it should never have much dc on the outputs.

 

[Bratwurst7s]

Note that all through this thread so far I have been writing that I used Panasonic ECQ caps in place of 4.7µF elcos. That was just totally incorrect. In fact I used ECW series caps. The previous posts have been edited and corrected. Sorry for the confusion.

Cheers,
James

 

[Bratwurst7s]

I made some good progress the last few days.


All except for 2 of the ceramic caps have been replaced with MLCC C0G (NPO). I missed seeing CS05 (1200pF) and somehow forgot to order a 20pF for C704. Those were ordered yesterday along with a bunch of other stuff. I just got shipping notice from Mouser a few minutes ago so the order might be here Monday, Tuesday for sure.

The service manual parts list shows all of the ceramic caps as 50v parts. Because I was unsure as to what voltage C704 is really seeing I ordered a 100v part for that.

The entire power supply section, V-Amp section except for the idle current setting area in the middle of that heat sink, and much of the inverting section have been worked. The relay has been replaced.

Cheers,
James

 

[Bratwurst7s]

I replaced the 470µF/35v C805 and 806 with Panasonic FC 680µF/50v. The other 3 caps with the same MKS2 as the earlier amps.

G802, that long green epoxy module next to the filter caps has just enough lead length left that I was able to raise it up a bit and offset it towards the middle of the board a couple of mm to make some clearance for the big filter cap.



I bought some 1.5mm thick copper sheets last week to replace the pre-drive chip heat sink. There will be enough extra to cut a heat spreader to mount on top of the bridge rectifier. There is not enough clearance to mount a proper heat sink but as hot as these amps run every little bit might help. In that same direction I ordered a few clip-on TO-92 heat spreader blades, I will see about mounting some on those 2 +/-15v voltage regulators.

Cheers,
James

 

[Bratwurst7s]

Got some partial work gone in the center section. All 4 carbon film resistors replaced with metal film, and 2 of the 3 ceramic caps. After the replacement for C704 gets here I will finish that area, including replacing the trim pot with a 20 turn part.



Cheers,
James

 

[Bratwurst7s]

The entire rest of the V-Amp section has been worked. All of the resistors replaced with metal film. The SM shows a number of resistors marked with a safety warning and specifies 1/4w for them. But only R718 and 719 (22ohm) are shown as fusible in the parts list. I replaced them with Yaego FRN metal film fusible. They are 5% parts but I sorted through what I have and was able to find 2 that are inside 1% tolerance.

R714 (220ohm) and R710, 711, 720 and 721 (10ohm) were replaced with Vishay Dale RN military grade 1/4w 1% metal film. All other resistors in the section were replaced with VD SFR25 and SFR16 1% 400mW metal film.



Cheers,
James

 

[Bratwurst7s]

R715 (10ohms 1W) looks abused so I ordered a new metal film for that position.

Starting in the protection section, CN01 (22µF/16v) was replaced with an FC 100v.
CN02 and CN03 (47µF/16v) rere replaced with FC 50v parts.



Cheers,
James

 

[Bratwurst7s]

In the signal inverting section all of the signal path resistors will be replaced with RN types where I can find room for them, otherwise the rest of the section will get SFR types. That is partly finished, I am waiting on more RN resistors and will finish that section when they get here.

The NJM4558 has been removed and replaced with a socket. There are still a number of caps to change (and add) here but that must wait until I deal with the resistors.



My brother-in-law over in Arizona told me yesterday that he was able to buy a "parts unit" for me to strip for a replacement main circuit board. Supposedly it does not work but he said that optically it is in perfect condition. We decided to wait on that one until I am over there at the end of April and we will look it over and decide on what to keep and what to toss.

That's it for now. Time for a beer.

Cheers,
James

 

[Bratwurst7s]

Change of direction for a moment.

My plans include replacing the RCA jacks with panel mounted types. I have a roll of 0.75mm shielded microphone cable to connect them to the board. This will completely unload the board from pressure from the rear panel and prevent damage to the board like my first amp.

All well and good but sometimes plans go sideways when one doesn't think them through clearly.
I bought these jacks a few weeks ago. Anyone see the problem?


So today I ordered some more jacks that insert from the interior of the panel and have the jam nut installed from the outside. That is going to eat up another week.

Cheers,
James

edit 17 Feb 2024: 0.75mm microphone wire turned out to be too thick. See post #98 and #111.

 

[Bratwurst7s]

Got a bit more done today.

Managed to bend the leads on the new trim pot for a vertical installation. They were barely long enough but it worked. Bourns 25 turn 500mW 4.7k ohm.
https://www.mouser.de/ProductDetail/Bourns/3296Y-1-472LF?qs=T%2BU9C%2B7w6dKpLx/xkLRwig==

I measured the old pot setting after removing it and pre-set the new one before installing it.



I also replaced the two 33µF/100v with Panasonic FC as was done in the other amps.

After the new ceramic cap gets here I will replace the last 3 elcos.

Cheers,
James

 

[Bratwurst7s]

Lastly I got some more of the signal inverting section done. 4.7µF and one 10µF elcos replaced with MKS2 and ECW film caps. The 2.2µF was replaced with a MKS2 100v.

Concerning the op-amp, the two 10µF/16v local filter caps CS10 and CS11 were replaced with Panasonic FR 47µF/50v with a 0.1µF/50v MLCC ceramic piggybacked in parallel. It would have been better theoretically to install the 0.1µF directly between the socket pins 4, 8 and ground but the nearest ground is in fact at the elco and I would have had to stretch the cap so far to do that that in the end I don't think that it makes much difference.

A JRC version of the 2068DD in now installed in the socket. I just have to wait for the Mouser order and I can finish up this section.



At this point there is nothing else that I can do except for resoldering all of the rest of the connections on the board so that is my project for tomorrow.

Cheers,
James

 

[Bratwurst7s]

FedEx finally delivered my Mouser order today. The longest that I have ever waited for a Mouser order, 6 days! Usually they arrive in 2 working days.

C705 and 707 (100µF/16v) were replaced with Panasonic FC 220µF/35v. These are 8mm in diameter and 15mm tall.
For C704 (20pF) I used a Kemet part, one of their GoldMax series. They are nice and rated at 125°c. Because I was unsure what voltage this cap is actually seeing I bought a 100v part.
https://www.mouser.de/ProductDetail/KEMET/C315C200J1G5TA?qs=7JStj/jQ2SHVAVZ760Uvzw==

After that I finished up that section with a ECW 4.7µF as in the other amps.



Cheers,
James

 

[Bratwurst7s]

That 10 ohm 1W R715 with the chipped body was replaced with a Vishay Dale CMF industrial grade 1% 1W part.



Cheers,
James

 

[Bratwurst7s]

After that I was almost done. There was just no room to install and RN or CMF resistors in the last 4 resistor positions remaining, all in the signal path. RS06, RS14, RS07 and RS02. I ended up using SFR25 parts there.
RS14 is shown in the schematic as a 5.6kohm part. All 4 of the later production amps had a 2.2kohm resistor actually installed. This early production amp did have a 5.6k part installed. I pondered this for a while and decided to go with what was in the later amps and used 2.2k.

Also, another discrepancy. The schematic shows RS12 as 10kohms. There was actually a 100kohm part installed there. I thought that I had read the tester wrong and tested it 3 times. 99.86k ohms. So I installed a 100k part.

Again the last 2 signal path 4.7µF caps were replaced with ECW.



Cheers,
James

 

[painttoad]

i stopped using fedex from mouser/digikey.

they've been dragging their feet the last ...oh, probably 6 months or so.