MC502 and C504 Clean Up

Well was an interesting night or diagnosis. Also updated photos of the cleaned up preamp https://plus.google.com/photos/107630792464950674683/albums/5952862669651686929

Weak channel is preamp related, swapped the output from the preamp and weak channel changed. In the process I discovered how the amps speaker protector works, and just how fast you can blow a speaker. I fryed, at really low volume, one of my hamlin/lafayette/pioneer drivers (pim 8/20 - sk-98)
I tested the amp via the tuner and it's strong both channels.

Now the weird one, I feel the chassis is hot, low voltage, but I swear I felt electricity a number of times as my arm brushed the top and sides, then my knuckled (with cracked skin) touched on the end of the volume control and felt it again. Its just not a feeling you forget. At the same time I also had the amp and tuner powered off the preamp.

So off to search about the preamp and the hot chassis, and of course any advice is always appreciated.
 
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Can someone comment on this troubleshooting guide I found? While this is newish territory for me, I think I can pull it off, I built a kit preamp, so I'm comfortable with what I'm doing. I should most likely have a bit more respect with what I'm doing, i've only hit 110 4 or 5 times in my life. :) I did try to measure voltage and did not get anything, and while testing today I did not feel any voltage. Wondering if I have something that is shorting inside the unit that moved when I moved the unit last night.

http://www.geofex.com/ampdbug/shock.htm
 
Welcome to integrated loudness and balance controls. So when you turn the balance to the right the loudness also increases and vise versa. Doh. And can find nor feel and more chassis voltage. So beats me. Just happy now.
 
Shouldn't turn together, must be some corrosion binding the concentric shafts.

Still have a weak channel?
 
No weak channel deoxit has seemed to cure that. Have been listening to the amp sans the preamp and all is well.

So just the opamp replacement in the phono stage and that will be done. The combo switch seems pretty difficult to get at with deoxit but will try a couple more sessions.
 
Just found the insert image tool. Any suggestions how to clean the combo balance/loudness control? Just spraying deoxit at the end is not enough. It's at the top left of the photo.

IMG_20131210_221910.jpg
 
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Well sprayed a few more times and starting to loosen up a bit. Want to avoid taking it out, will most likely use it before I free it completely, just don't want to keep flushing with deoxit. Have the faderlub will try to get some in from the top but that won't free it.

Started listening to the amp the other night, no preamp, and was really disappointed. Added a bottlehead foreplay and that really improved everything, nice tight bass, highs are great too not too rolled off, was listening to Mariah Carey "feeling emotion" and schrill end notes were really actually pleasant to listen too, not what I was prepared for at all. I'm still uncertain if this will unseat my integra a809, I told my wife unless it blows my pants off, the integra will stay.
 
Have had a few more days listening to these guys and really liking them. One channel on the phono is totally dead, need to order the replacement op amp, thanks c_dk for your help with this.

The seller had mentioned he had 3,000 ish records and until now could not figure out why he would sell these, glad it was just a few dollar item to repair.
 
The Mac saga continues. I ordered the wrong opamps, blah, will need to order again. Now I have 10 extra little NE5534A opamps to decorate my desk.
 
Well it's been a struggle, I ordered the wrong op amps twice and also discovered that install direction matters. So progress has stopped for now. But I have pulled the op amp out, its sitting there waiting for me to order it, again, but this time while I'm looking at it.

I had ordered the wrong op amps, Signetics NE5534N, thinking they were the same as the ones for the phone stage, I tried one anyway, and it started smoking (YIKES) I think it has to do with install direction. I swapped channels, made sure same direction, and the channel still worked fine, thank goodness.
 
Op amp direction definitely matters - as it does for all other IC's. If you look closely at the op amp, there's a little notch at one end - like a tiny mouse took a bite. That end will correspond with a similar notch on the socket or a silkscreened mark (perhaps a dot) on the PCB.

http://www.ti.com/graphics/folders/partimages/OPA627.jpg

On vintage Macs like this, the socket probably doesn't have a notch; it will rather be marked "1" at pin one. You'll need to have the op amp removed and look very closely to see the marking. Insert the op amp with its notch to the marking or the "1".

Sunday night I decided to recap my 30-year old MC502 and place an order with Mouser. Everything was less than $20. Hang in there with your project!
 
c-atle-79bay said:
Well it's been a struggle, I ordered the wrong op amps twice and also discovered that install direction matters. So progress has stopped for now. But I have pulled the op amp out, its sitting there waiting for me to order it, again, but this time while I'm looking at it.

I had ordered the wrong op amps, Signetics NE5534N, thinking they were the same as the ones for the phone stage, I tried one anyway, and it started smoking (YIKES) I think it has to do with install direction. I swapped channels, made sure same direction, and the channel still worked fine, thank goodness.
Click to expand...

Yep, that will do it. Put those puppies in the wrong way and they'll start a smoking'......
 
I'm certainly glad to find this out sooner that too much later, glad I did not just pop one in, close it and go.

I still need order the op amp (will order 2) for the phono stage. I also purchased a matching MR500 tuner, so I have an entire stack, and always keeping my eyes on ebay for another MC502 for dual mono.

But I've been forcing my self to stop, and just listen to my ginormous JVC AVR and decide if I really miss the Mc stuff that much Honestly the amp, when driven (pure analog) from the McIntosh preamp is more to my liking and really more dynamic than the MC502. I might just sell it and keep the tuner/pre combo as my cool analog convo gear, that is difficult for anyone, i.e. kids to mess with. For now at least.
 
I have a new wrinkle. I hooked things up again and the amp has died. It powered down and right back on while running some Linn Sara 9 speakers kept going and was fine for another hour. Next day I had a set of IMF super compacts going for a good few hours with no issues. This morning I hook the Linn's back up and again power off then on twice within a few moments. I un hooked the Linn's figuring they were the issue. Reconnected the IMF's then in about 2min power off but no back on.


I've read the Linn's are 4 ohm and not easy to drive. Have not had a chance to look for loose connections. The power guard lights never came on so don't think that's it. I'm also had power on the unswitched outlet if the c504 preamp and also have the tuner the same way but never lost power to the tuner. Will report back one I check fuses and connect
 
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I checked the fuse, good. So I disconnected the amp from speakers, provided power directly from the power strip and whola, powered up.............then a few minutes later, restart. Also noticed the lights of the amp seemed to dim.

Any idea where to go with this?

Thanks
 
What's the thoughts on using the 5534AN in place of the 5534A opamps? Bad idea?

c_dk said:
I swap in new TI or Onsemi 5534an. I am always concerned about oscillation rolling in non stock ICs.
Click to expand...


Wow, read your own thread dude.
 
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The AN designation was Signetics culled out ICs with a lower noise floor.....alas the seen to be in short supply.....Mac used the AN in phono stages the A in most other circuits. There was a really big price difference back in the 80s.

What am I supposed to read?
 
c_dk said:
The AN designation was Signetics culled out ICs with a lower noise floor.....alas the seen to be in short supply.....Mac used the AN in phono stages the A in most other circuits. There was a really big price difference back in the 80s.

What am I supposed to read?
Click to expand...

That was a comment to me, you'd specifically called out the AN in a prior post. My Mac has the A in the phono section. But it does have AN in the amp.

I ordered a lot of 10 signetics AN's, thinking it might be nice to have them around.
 
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