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MCS 3233 with several issues to fix

starcopy

starcopy

Active Member
Hi, MCS fans. Just found a decent-condition MCS 3233. I see and hear the potential in this well-made receiver. Not sure if it will need components replaced -- that comes later. Right now I’m working through the 3233 functions, switches, dials, connectors, jacks, etc. to see what I’ve got here. I’ve done considerable research on AK, cleaned controls, repaired the cabinet, ordered new LEDS/sockets, etc. But I'm stalled on a few issues. And 3233 documentation is hard to find. Any advice would be greatly appreciated.

1. Has a stepped (click) volume control, but no sound in right channel at the lowest volume (first click up). Otherwise fine. Probably needs a better DeOXIT cleaning? Or I can live with it. Minor issue.

2. 3233 Phono 2 function = very, very faint music -- even at highest levels. Conversely, the Phono 1 setting delivers EXCELLENT sound with my MM cart. Are both phono inputs identical? Or is it possible that one of the phono inputs is/was meant for a different type of cart? Maybe a ceramic cartridge? (The transition from ceramic carts to magnetic carts did occur during the time this unit was built.) I have cleaned this switch with D5. Twice maybe.

3. Felt a slight electrical current when touching the 3233 metal faceplate while standing in my garage in my socks. But no electrical current was felt when I reversed the power cord and made sure that the “ribbed” side of the power cord was in line with the larger slot in the electrical outlet. Do I replace the entire power cord with one that has a wide blade -- making sure that the ribbed wire is always in line with the wide blade and properly grounded? Or just replace the plug (but that would look clunky.)

4. Also RE above: The slight electrical shock was only felt when I touched the faceplate, and not the rear painted panel. Did the paint act as insulator?

5. The “signal strength” meter does not move – buried at the “O” (rest) position. (But, the tuning meter just started working this morning. No kidding. Really. Yeah!)

6. Hear a loud, real-time thump in speakers when powered up. My temporary workaround to protect speakers is to turn the unit on “in headphone mode.” Should I be looking for a dirty, faulty relay? I had the unit opened up for an initial cleaning, but did not think to look for a relay at that time.

7. Am in the process of replacing the four dial sockets/bulbs with the help of an AK member but no affiliation. It appears that each of the original bulbs were "surrounded” by a clear, blue plastic “bowl.” Now very faded, these bluish “bowls” look like they were meant to produce a blue dial light. Can anyone confirm that the 3233 dial lighting was blue? (Please, no “Captain Obvious” jokes here, okay LOL?)

Many thanks. BTW, sorry for such a long post with so many questions. It just seemed like a very efficient way to tackle a number of issues at one time with this one machine.
 
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Hey, thanks for your quick response. That's a good thread you suggested. The Billy Dio post looked especially relevant. Looks like DC offset is not adjustable, but bias is. I checked the fuses earlier -- they looked identical, but mine was just a quick "is the fuse good" inspection, so maybe they're all good but not a matched set? I'll spend some time with that entire thread. Cheers.
 
As a first step in restoring my MCS 3233, I'd like to eliminate a loud thump in the speakers during power-up b/4 I do damage. I make sure I have my cheap headphones connected when powering up so the cans get the thump.

The three fuses are not all identical. One fuse is a 3A 250V 312. The second and third fuses (both speaker fuses) are identical BUSS AGC4 250V with "UL" and "SA" logos on them 9. (The back panel specifies that 3AMP/3AG TYPE fuses be used.) In another thread @Billy Dio noted that "...These amps are actually VERY sensitive to mismatched fuses as I believe the audio actually transmits through them."

DC offset is 20mv Left and 10mv Right. If you owned a 3233 and you were me, what would be your first step toward chasing away that nasty thump? I can handle a solder iron for minor, easily accessible repairs. Thanks much.
 
The thump is sorta normal. Looks like there's a differential transistor pair at the very start of the amp stage. I'd replace those will close matched new transistors. New caps will also help. There's not gonna be much you can do if you don't have a DMM and decent solder skills.
 
Many thanks. I do have some solder skills, the proper equipment, and some solder knowledge. And, I do have a DMM, but so far my testing abilities consist of testing batteries and measuring DC offset -- pretty basic stuff. I hope to find a 3233 service manual with schematics and learn as I go.
 
1. If the sound at louder levels is balance between the two, more than likely the volume pot is the culprit. Try cleaning it again.

2. Phono 1 is MM and Phono 2 is for ceramic cartridges. Ceramic cartridges generate a louder signal (voltage) and does not require a preamp for it.

3. Have you tried plugging it into a different outlet? The room that the receiver is plugged into may have a ground fault issue. If that doesn't resolve the issue, there could be a PS issue in the receiver or a voltage leak to the chassis.

5. The meters have issues sometimes. I manage to take mine apart and readjust the pivots to free them. Put a DC volt meter across the terminals and see if the signal is going to it.

6. Every 3233 I came across has the turn on thump. There is no speaker delay in these receivers, so there is a current rush from the capacitors charging (causing a thump). I just put the receiver on headphones then switch to the speakers after it is on. The wattage on the receiver is pretty low (33 watts), so I guess the engineers felt that the thump would not be enough to damage the speakers. Do not put in higher farad rated caps in there. The thump will get worse.

7. There are blue liners in the plastic surrounding the bulbs. I think the main purpose of the blue liners was to give the dial a whitish-blue/green hue instead of yellow. My dad bought a 3233 new and I never remembered the dial straight blue at all.
 
BTW, I found a MCS ad on youtube. Its in a video that has many commercials in one. At the 8:07 mark, is the ad for the 3233, 6500 turntable, and the 8226 speakers. The matching tape deck was a 3551. This was the system my dad bought when I was a kid. Just found it tonight surfing around.
 
Thanks @MCS Guy. Great info on so many levels. So glad you jumped in. A few comments for closure....
1. I'll try a better cleaning. Maybe remove the bottom panel to get a different angle on those pots.
2. Good to hear that Phono 1 and Phono 2 are operating normally.
3. Have tried various other electrical outlets with no issues. Just had that one "mild shock" in the garage while standing almost barefoot.
5. I'll service the meters -- try to loosen them up. Assuming that I'm looking for low DC voltage with my DMM.
6. So, the thump is normal. Good news, actually. Wish it didn't have the thump at all. But glad It's not a problem that needs attention.
7. Thanks for your experienced observation on the color of the dial.

This 3233 does not appear to need a whole bunch of servicing. I have the "wooden" case looking great. The metal on the face plate needs some further cleaning, but not much -- am trying to clean with just cold water to maintain the lettering. Dial glass is clear. Best of all, this unit does look and sound terrific -- was pleasantly surprised. Cheers from the Buckeye state (and from a fellow Kansas fan.)
 
MCS Guy said:
BTW, I found a MCS ad on youtube. Its in a video that has many commercials in one. At the 8:07 mark, is the ad for the 3233, 6500 turntable, and the 8226 speakers. The matching tape deck was a 3551. This was the system my dad bought when I was a kid. Just found it tonight surfing around.
Click to expand...
Nice find. Thanks. I checked out that video this morning. JC Penney was really promoting the quality of its gear. Do you have any/all of those components that your dad originally bought? It would be interesting to see who made those other MCS pieces. BTW, I did pull a pair of 3-way MCS speakers from a tree lawn a while back. Many of the drivers looked of decent quality, but cones were ripped, etc. Cabinets were rather low grade -- needed bracing. I moved them. But this was before I discovered the quality in these MCS receivers. And thanks again for answering pretty much every question on that long list. I'm sure other AKers and MCS fans will benefit from all that knowledge.
 
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The only things left from my dads system is the 6500 TT. The 6500 to me is Hitachi made (the motor and other things inside have the Hitachi symbol on them) and its pretty decent. The cartridge is a Audio Technica AT12 cart. Mine still has the original technical banner that is tape to the inside of the lid from the factory.
The original 3233 was "destroyed" by me when I was a teenager. I pushed the receiver as hard as I could at the time, frying the amp board to oblivion. I ended up buying another used 3233 to replace it. That one still works.
The 3551 Cassette deck was used so much that the tape head had a groove worn through it. I don't remember what happened to it. My dad made some really good tapes back in the day with it.
The 8226 Speakers ended up with blown tweeters (wonder why?) and I used the cabinets to make a sub woofer box for a car I had at the time. The speakers are actually pretty heavy and sounded pretty good. The tweeters were a little lacking, but everything else was good (12" woofers with fried egg mid-ranges).
Love to get a hold of the cassette deck and speakers again.
 
The nice thing is that all of this MCS stuff is still available -- and at decent prices, although prices continue to drift upward.... The MCS speakers that I had (and sold) were Model 683-8952 3-way bass reflex speakers. Only got $5 for the pair, which gives you an idea of their condition. Again, many thanks for taking the time to share so much knowledge on these 3233 receivers -- it was invaluable.
 
Hi, everyone. Thanks for your above info on my thrift-find MCS 3233 receiver. Partial restoration yielded quite a nice unit.

Signal strength meter not working but the tuning meter is - and both meters have seen excessive soldering by previous owners -- might be best to leave well enough alone? They are accessible, though. @MCS Guy when you say "Put a DC volt meter across the [meter] terminals," should the MCS be off/on? The lowest DC volt setting on my DMM is 2 volts. (I am obviously not too skilled yet at vintage audio repair.)

Speaking of soldering, looks like a prior owner also replaced (successfully) a fried resistor in the left channel (photo). Not sure if other upgrades were done. I replaced all four light sockets and am testing four light-blue LEDs (photo) and four cool-white LEDs. (It was tough to get a good photo, but in person the blue light is very even across the entire dial. Probably not too "original looking." I've repaired the cabinet to almost like new.

And this receiver sounds wonderful. One AKer suggests that these Taiwan-built MCS receivers are not as good as some of the other MCS receivers (Japan built?). But mine is a keeper. Hope to find one of those 125-watts/channel units.

Again, thanks!!!
 

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I pulled out my best unit and took some voltage readings.

With the FM tuner between stations, voltage should be near .000 volts. On a strong station with a 4 strength, should be about .113 volts. This is with the DVOM red lead on the yellow wire and the black lead on the other.

If you wish to Ohm out the meter, the DC resistance should be about 635 ohms. Make sure to UN-solder the yellow lead before you check resistance. Also, the Meter should deflect halfway with the test leads on the same terminals.

Also, I took a pic of the back of the meter to make sure they have the wiring right on the meter.

I would check the resistance of the meter first and make sure its not open or shorted. If that's good, check to see if the voltage is there. If it is, the meter is stuck. You can take it apart and try to clean and lube it. Sometimes if it has a pivot adjustment, you can back the screw off just a hair and see if it moves freely.
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Might be time to put my 3233 under the knife. It's in rotation right now -- am really liking the looks and general sound of this unit. It's no Nakamichi, but the overall experience has been pleasant, especially with the new blue dial lights. However, vinyl through the MCS has been sounding super-bland lately. Lazy sound. Poor highs. Did a direct VINYL / CD comparison of several Thomas Dolby songs -- no contest. Big difference. CD player connected through the AUX input sounds terrific -- clean, open, and with no music playing, the AUX input is super quiet even at max volume. But the PHONO 1 input is noisy -- hums even at very low volume esp the right channel. Disconnecting the TT made some hum difference I think, but hum is still there. Time to give this thing some serious attention. Will start with a good cleaning of the controls. Looks like a resistor was replaced at one time.

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These units benefit from a full recap. Since this is a Taiwan made receiver, Capacitors are not of the Japanese quality (they seem to be fine otherwise, not to many leakage issues).

That resistor was replaced, but they need to be matched in order to keep the DC offset correct.
 
Hey, thanks MCS Guy. I always appreciate your MCS knowledge and guidance. The recap suggestion sounds dead on, especially given the age of these units. I'll pull it from my rotation and see if recapping and matching up those resistors is something I can handle. I'm thinking it is. (I have decent unsoldering / soldering skills. Just need to make sure I properly deal with the stored cap voltage or this might be the last post I ever make LOL. (But not really funny.)

And your thinking about the recap is interesting when it comes to replacing older (and lesser quality?) Taiwanese caps with newer (higher quality?) Japanese caps. Theoretically, that should deliver an extra-nice jump in performance? Had not thought of that.
 
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