MCS 3236 Receiver

[OctalSocket]

Found this unit locally on CL. Ad said both channels work and it looked good in the picture. Picked it up from the seller's wife, who didn't know anything about it, just said he didn't sell junk, unless he advertised it as parts. For the price, not much of a risk at all.

At home, I brought it up on my variac and listening through headphones, I noticed a fair amount of 60 Hz hum, especially with no volume. I then ordered two 6800uF 65V filter caps, and removed the originals. One of the caps had leaked and dried out, so there's a smoking gun.

I installed the new caps last night, and brought it up gently again. Bummer, there still was a hum. However, I found it diminished greatly when I touched any metal part of the chassis. I then remembered having a piece in the past that hummed with the panels removed. Put the metal top back on. Less hum. Put the perforated pressed board bottom back on, even less hum.

It wasn't quiet (comparing to my Mc C45 and MC7300, I know, not fair), but I was still using headphones. I hoped it wouldn't be noticeable through any of my medium efficiency speakers. Connected to a pair of 90dB Boston HD8s, and I hear no noise from a couple feet away. Not bad at all for for a 37-year-old cheapie.

I read a few MCS receiver posts by people saying the better the speaker you put behind it, the better the receiver sounds. I did hear more potential through the Sony on-ear headphones than I did through the little two-way Bostons, so I will withhold sound quality judgments until I hook it up to my Bose 601 Series II or my Genesis II.

 

[MCS Guy]

That one filter cap was definitely bad. Hard to see from the first pic, but there is some smaller ones behind them that looks like the jackets are slipping down. You might want to just recap the power supply section.
The hum could also be poor ground connections. Tighten all circuit board screws and check the star ground for loose or poor connections. Receiver looks like and NEC one.

 

[quaddriver]

replace any <3.3uf-ish caps on the inputs or outputs of any section (phono, tone control) and replace any tants and see if that goes away. any 1uf cap in the signal path in the same section, go BP on. those are great hum removers on marantzes so mebbe it will work here.

check for poor grounding on the tone control section.

 

[EngineerNate]

What's the vintage on this model? Early 80s? Definitely doesn't have the look of the Taiwan sourced low-power models.

 

[OctalSocket]

EngineerNate - Date code says 106, and according to HifiRob2, this model was sold between 1981 and 1984. So I gather my unit was built in June 1981. I can validate what others have said about MCS receivers. Yes, this was made by NEC. The boards start with YEC, and there are a lot of NEC-labelled components within. The back panel also says Made In Japan.

Some complain about build quality, but for the physical size, weight, and price range it sold for, I find the build entirely appropriate. It's as solid as it needs to be. Just don't use it as a foot stool.

Quaddriver/MCS Guy - thanks for the advice on cleaning up the remaining hum. I was hoping the quick and dirty filter cap replacement would do the trick. I can be quite OCD at times, so I want to make sure I wasn't making a mountain out of a molehill. Through the headphones, there still is a low level hum with volume at zero, but as soon as you give it any volume, the slight hum gets swamped by music.

But you both are correct, I should and will replace all aforementioned caps and check the grounding points. From what little listening I've done so far, this unit's well worth the effort. BTW, the tuner is still spot-on, both the analog and digital frequency display match perfectly, and selectivity is quite good with just a split piece of 300 ohm ribbon as an antenna.

 

[OctalSocket]

This evening I checked all board mount screws and the only thing not tight was a heat sink mount screw for a transistor in the power supply. Tightened, no change. I also checked DC offset, 10mV on the right, 8mV on the left. That's good news. With the bottom cover on, me touching the chassis has no effect on hum now. That pressed board bottom cover has a foil layer bonded to its inside, so that plays a big part in reducing hum. Looking at the schematic and the circuit board, there are about ten, maybe more, caps in that section. So I'll make a laundry list and order some to see if that helps.

BTW, I couldn't find any kind of star ground. Not on the boards, nor on the schematic.

The only thing on this receiver that doesn't seem to work is the MUTE button. Makes no difference whether in or out. Not a big deal, just curious how much of an effect it's supposed to have.

 

[Hifirob2]

The mute button, I think, is not for the volume - but for the FM. It's just labeled Mute instead of FM Mute. The 3253 is the same way.

 

[OctalSocket]

That's what I figured it was for as well, since it's situated right next to the FM button. However, it doesn't reduce or eliminate the static when tuning between stations. Not a deal breaker by any means. Will not worry about it, unless it's an easy fix, of which I don't have enough electronics know-how to determine what new parts would fix it.

Recapping to lessen the minimal hum it has now is first priority. Saying that, looking at the schematic, there are dozens of caps within the AF/Power Supply section. Besides doing a wholesale recap of all those, I can't figure out which ones directly affect the power supply, or perhaps they all do need to be changed.

 

[quaddriver]

scan up the SCM and we can tell ya which ones are power supply or local filters

 

[OctalSocket]

AK says file is too large, so see if you can access this. First time using this feature, so I hope the link works..

https://drive.google.com/file/d/1u6hHmAtpOsfUHbBVIepbOzpeq8aZOXjv/view?usp=sharing

BTW, thanks to HifiRob2 for the pdf.

 

[OctalSocket]

Regarding the hum, it appears the following are in the power supply section:
C704 through C718

For me, it's easier to figure out how to isolate the sections by looking at the circuit boards. All of the above cpas are on the same board, save C716 through C718.

 

[Hifirob2]

OctalSocket asked me if I had any of the same hum in my 3236, so I got it out (along with it's little brother, the 3226) to compare.

My 3236 doesn't have any hum, but there is some backround hiss through the AUX input at any volume level. Gets worse the louder the volume goes. Same with the phono input - although I would expect a bit there. It's annoying enough that it probably needs service.

My 3226 has no hum, and only a tiny bit of hiss once the volume goes up past half way. It's really quiet - even the phono input is very quiet. Also - with no antenna, the 3226 picks up many more stations than the 3236. Maybe my 3236 has drifted out of spec - but no hum. I wish there was a tone defeat on the 3236 to see if that gets rid of the hiss. Probably some noisy transistors on the tone board. My 3865 integrated has some of that hiss, and it goes away with the tone defeat engaged.

 

[OctalSocket]

Thanks for that feedback. To put it in perspective, (through headphones) the hum at zero volume (with any input) is at least as loud as the hiss. Once I turn the volume up (no signal) to halfway or more, the hiss then overpowers the hum. Turning the balance left or right takes the hiss with it, but the hum stays constant and centered. As far as overall hiss, I don't find this receiver any worse than any of the older SS amps or receivers I've had in the past.

 

[quaddriver]

ok iirc, you did C702/703.

so do the following: do c704/705 as is. c 717 same value, but 35cv, do c718, do d702 with one much larger in PIV, d703 with 1n4148, c173 and c175 with 50v units.

If your DC is not rock stable, look at swapping out the zeners and upgrading tr703, 704, 705, In fact, the D313 is almost a shoot on site for an onsemi mje15032? and the c945/c1815 can be had with a KSC2383 c710/711 with higher voltage units

not a lot of $$ in parts, and here, you can get gp caps if you so desire, perhaps with a 105* rating depending on how packed in...

you can also replace c301/302 with wimas and c313/314 in the phono section and c321/322 and c529 in the tone amp. others may chime in but I personally would look there. skimming over the power amp. if ya blow it, this is an easy sub in...

 

[OctalSocket]

Thanks for the suggestions. If you don't mind, how about a bit of education.

Why not do C716? I see it's on TR704's collector leg, whereas C717 and C718 are on the base and emitter legs, respectively. Would a bad cap on the collector leg not cause hum?

I looked and looked, but cannot find C173 or C175.

 

[quaddriver]

Thanks for the suggestions. If you don't mind, how about a bit of education.

Why not do C716? I see it's on TR704's collector leg, whereas C717 and C718 are on the base and emitter legs, respectively. Would a bad cap on the collector leg not cause hum?

I looked and looked, but cannot find C173 or C175.

because I am lysdexic....713/715 sound better?

 

[OctalSocket]

You'd think after four months, I would have replaced all the above mentioned caps. Since October, I've had the MCS in the garage powering a pair of Boston HD8s. With the Boston's 90 dB efficiency, I hear none of the subtle hum I was picking up with headphones. I've decided not to dig into it for two reasons: (1) If it ain't broke..., and (2) My laziness can sometimes offset my mild case of OCD.

Every time I've turned it on, I've been thoroughly impressed by what I'm hearing, especially in light of its humble pedigree.

We're currently having a sub-freezing, snowy spell, so I'm going to bring it in and hook it up to my pair of Bose 601 IIs, and see how they do together.

 

[OctalSocket]

Set up the MCS 3236, an ADC CD-100X, and Bose 601 Series II in front of the main system. Forced a Sterilite plastic 3-drawer file cabinet into service as a gear rack.

I played the Redbook layer of Steely Dan's Gaucho SACD and Yes' remixed by Steven Wilson Close to the Edge CD/DVD-A/V set, and here's what I determined with this system, in my room, drinking my beverage of choice for the moment.

This trio of 1980s outcasts (maybe not the 601s, according to auction-site results) is a real hoot! They do have great synergy together, but each is quite good in its own right.

Regarding the MCS 3236, I am using my memory to compare it to a couple of cheap used units I've had over the years. None had been gone through by a tech to check whether they met original specs. In addition to a listening test, I've done a visual inspection of every old unit I've ever owned. If I heard any objectionable hum or noises, I'd dig deeper to try to correct the noise. The MCS is the only one I dug into and I replaced the filter caps. With that...

I had a Technics SA-5270 receiver, and did not care for it. No matter the source, its sound was thin, threadbare. Because of that, it sounded bright since there was no body to the mid-bass. Moved that one on quickly.

Next was a Pioneer SA-7500 II, and it was almost the opposite of the Technics. Somewhat dark and recessed. Unfortunately a bit too polite, kind of boring. Kept it a little longer than the Technics, but moved it on anyways.

As a side note, as I type, I am listening to Jackson Browne Solo Acoustic Vol. 1, and I must admit his vocals through the 35-year-old Bose are not as holographically real as they were through the main system I had 10 years ago, a McIntosh C35/ MC7200/Harbeth Super HL5s. I'm still enjoying what I'm hearing right now, though. Hell of a bargain.

Back to the MCS, I can wholeheartedly recommend this model to anyone wanting a quality second or third system centerpiece. I am a little curious how much better a 3275 or 3125 sounds than my 3236, but not enough to buy one. This receiver scratches that itch enough to not tempt me.

 

[EngineerNate]

Excuse me if this has been answered already-is this an NEC unit or Taiwanese build?

 

[OctalSocket]

NEC, due to the IC chips saying such and the circuit boards saying YEC (secret code for NEC), and it says Made in Japan on the back panel.