Question for the Tech Experts - Marantz 1550 Hum

[Whaleman]

I recently got this Marantz 1550 in excellent condition. However, there is transformer hum coming through the speakers. It is hardly noticeable at all, but not normal I think. It is equal on both sides and is affected by the bass control. Meaning you decrease the bass and it almost completely goes away. Can only hear in the wee hours, is that little, but my other Marantz don't do it. The pots seem to operate cleanly.

Any help appreciated.

[markn2wae]

I'm not familiar with that unit, but it sounds like weak or bad power supply capacitors or power supply related.

Re-capping, that is, replacing all or most of the power supply\signal path electrolytic caps. and maybe some others is what most people do to restore the sound of these vintage units.

Mark T.

[willyrover]

I have the same marantz with the same problem. There is a hum that becomes louder as you increase the BASS. At the zero position the hum inaudible (to me) and as you DECREASE the bass, it becomes slightly louder. The same happens with some noise in the midrange control and some buzz in the Treble control.

I am going to try replacing the 2 50V 10000uF capacitors in the power supply and go from there. I'll post back with the results.

[Whaleman]

I ordered most of the capacitors that seemed to be in the power path from the power supply from www.digikey.com, will let you know what I find out once they are in.

[willyrover]

Great! I was going to order the caps - 2 of the 10000uF Panasonics 50V 105oF. They were about 7$ each. But then shipping and handling was another 15$!!! I'm going to try to find them locally next week.

What model caps did you order for the two biggies?

[Whaleman]

I am leaving those alone for now, I am concentrating on the others near the power supply, I will post a pick if I still have it. 13 in all.

[marty-alex]

Are you sure it cannot be the ground loop? Nothing's connected, I mean...no sound source?

Well, I think whole power supply unit could be dead ("leaking", damaged, whatever...). If you have another similar Marantz, I would suggest to connect the PSU from working unit to see if it doesn't help.

Capacitors and/or resistors related problems IMO usually don't affect both channels...not in the same way...

[willyrover]

No...nothing connected except the speakers.

As for the capacitors, I would have thought the big filter caps would be the first ones to replace since they are the ones that are going to pass that 60hz line noise.

[mjr4077au]

As the capacitor ages, its capacitance decreases while its equivalent series resistance (ESR) increases. When this happens, the capacitors no longer adequately serve their purpose of filtering the direct current voltages.

It's even worse if the capacitor leaks. I would be seeking replacement caps from manufactorers such as Rubycon, Nippon Chemmi Con, Nichicon, United Chemmi Con, Sanyo, Elna, or Panasonic. These are the most reliable brands

With a multimetre... You can check the capacitance of your caps and if they are reaching that rated microfared rating (eg... 10,000uF).

[Whaleman]

Here is a pic of the capacitors I am replacing, all except #2 and #3, and yes, either Panasonic or Nichicon. Also a pic of my neighbors capacitor tester, but not sure how reliable. When I put them in, I will report.

Also, look at that power transistor, does it look fishy? if so, what the heck is it, or how do I match it?

[Whaleman]

OK, got my capacitors from www.digikey.com and replaced all 15 on this board except the 2 tiny ones all the way to the right. NO DIFFERENCE AT ALL! Hum is still there, it is just like a transformer hum and not like a missing ground hum.

However, that large gray cylindrical resistor next to the fishy power transistor w/cooling sink got way hot (too hot to touch) in a minute or two. Is this normal? You can see the resistor in two pictures, it is light gray and has the following writing:

5W 200 Ohm J
JRM ARH

Can someone identify the above?

One last question, can I substitute a 100uF 50V capacitor where a faulty 100uF 16V was?

Sorry Will, thought I'd provide a solution to our 1550 problem, not yet!

[willyrover]

Hmmm...

Just checked that resistor on my unit. It got VERY hot to the touch within seconds of turning the Marantz on as well. It's probably been doing this since I got the Marantz several years ago - so, I'm not too concerned with it. It's probably so beefy because it's meant to get hot.

I am VERY confident that replacing those 2 main filter caps (the big ones) will solve our hum problem. I'm just not sure I want to spend 30+$ on the caps and shipping at the moment.

[Whaleman]

Try playing with your mid control, you will see a big difference, at leat mine does. What makes you think it is the big ones? THanks.

[willyrover]

For a while I was into vintage tube radios and bought several from the 30's and early 40's. Many, you would plug in and get nothing but buzz and hum. Replacing these main filter caps right off the rectifier was always my first step. This got rid of the hum.

I'm not 100% sure it's those cap, but that hum is all too familiar.

[Whaleman]

Willy, where are you looking to get these capacitors? Saw some on eBay for $16, made by Hitana...but none at partsexpress or digikey.

Thanks

[willyrover]

I was looking at digikey. Part number P6691-ND or P6690-ND.

These are Panasonic Caps. ECO-S1HA103EA and ECO-S1HA103DA. The only difference is the size of the can. Here is the link to the datasheet:

http://pdf1.alldatasheet.com/datasheet-pdf/view/117551/PANASONIC/ECOS1HA103DA.html

I was going to go with the 35mmx40mm. Same diameter but not as long as the originals. Should still fit side by side in the same bracket though.

What do you think?

[Whaleman]

Willy, I think you found the best fit. Thanks for the part numbers, I was having a hard time finding them. I will go with the 30x50mm can Panasonic. I think they are more like the oriniginal in size. I am ordering it right now from www.digikey.com, let you know what happens. I am algo going to replace that hot resistor. I think it gets too hot and it may be a fire hazard. I heard of things just going up in smoke in the Marantz and it must be that resistor catching fire.

[willyrover]

Sounds good. Looking forward to hearing what happens. Glad you're the one doing the experimenting.

I've been wondering about that resistor. You can really feel the heat radiating off it even at quite a distance above the case. Going to post a "Hot resistor" thread and see what happens.

http://audiokarma.org/forums/showthread.php?p=815143#post815143

[Whaleman]

Willy, thanks for doing research on the hot resistor, I got one from digikey but it is about 1/3 of the size, so I am gonna leave it in there. Yes, there is evidence of heat all over that area.

Took the main caps out last night, the new ones are quite small and I will have to mod the setup somewhat. I also replaced all the caps on that board excpet 2 3.3 uF that were too hard to reach. No change.

When I get the 10,000s in, I'll let you'll know what happens. These seem to be wired in series and I was about to wire them both negative to ground, good thing I checked.

Check out the pics.

[willyrover]

Yes...I noticed that "unusual" wiring of the caps. I figured - just put the new ones in the same way and not ask any questions. Except one. I'm guessing since there is a resistor across each of the caps, they discharge themselves when you turn off the receiver?

You ordered the 30mm diameter caps? Do you think the 35mm would be closer to originals? Length is not a problem. The connections would just sit deeper in the receiver and you could use the original clamp.

Looking forward to hearing if this change eliminates the hum!

[Whaleman]

It was a no go! put both caps in and same thing all over again, and yes the 35mm would be a better fit, but there is a piece of metal that will keep the wires quite far from the caps. I wish I could post the picture but I can't resize it now. I'll try tomorrow from work.

Back to square 1! I did replace all capacitors on the power board, I mean ALL! The resistor tested smack on, that is the hot one.

Thanks.

[willyrover]

:tears:

Damn! I guess the next place to look would be in the tone controls themselves. I know when mine are all zeroed out the noise is virtually gone. When you increase the bass or mid the noise comes back. And strangely, when you decrease the bass or mid, the noise comes back.

[Whaleman]

Going to bed frustrated! Thanks for the help though.