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MCS 3253 Receiver Service Manual?

JamVal

JamVal

Addicted Member
I'm looking for a Service Manual for MCS (Modular Component Systems - JC Penny) 3253 Receiver- If one even exists?

From what I've read here, it was probably made by NEC, similar or same amp section to the NEC AUA-7000E whose service manual I haven't found either.

I'm looking for procedure to check the bias on this MCS 3253.

Under the hood there are 2 trim pots on the main amp board: VR201 (left, I think) and VR202 (Right). 15 test lead posts scattered around that board shown in yellow. The outputs attached to the heat sink are TR213, TR215 (Left side), TR214, TR216 (right side)
PowerAmpPCB.jpg

To my ears, left and right channel are balanced. It might be my imagination, but the power meters seem to show a very slight difference, with the right being a hair lower, hard to tell depending on what I'm listening to. It just occurred to me that I could play a test tone to get a better idea.

Thanks for any assistance.
 

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Following the traces on the PCB, I'm quite sure that Test Points13,15 are for the left channel bias
and TP12,14 for the right. The traces from these test points are connected to the legs of the
emitter resistors (white ceramic resistors) for the outputs (TR213,215 Left and TR214,216 Right).
Two of the resistors are marked .47ohm, so I'm assuming they're all .47ohm.

The unanswered question is what is the manufacturer's idle current (ma)?

In a warmed up state I read mV across the left, then the right channels.

Left channel read 47mV - calculates to 50mA
Right channel read 44mV - calculates to 47mA

Would 50mA be a reasonable assumption on manufacturer's recommended bias current for this amp?

Is the difference between left and right channels (50 vs 47) enough to worry about?

Thanks again, (I don't think a service manual exists for this receiver.)
 
I have the SM for the NEC AUA-7000E. It's in a large file that includes the AUA-6000E & AUA-8000E.

Start a conversation with me and include your email address, and I'll send it your way. Hopefully, it will help.
 
JamVal said:
There is a Product Service No.: 683-3253-00

Never thought of googling that, I will give it a try.
Thanks for the reply.
Click to expand...

Ok, Sams Publishing lists that model in their Modular Hi Fi (MHF) series.
That's the only place I could find it for an MCS Integrated I'm working with.
https://www.samswebsite.com/en/photofact/details/index/id/74260

If that receiver is like the amp I have here, the controls on the amp section would be to calibrate the power meters.
There would be no DC offset or bias adjustments.
 
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glen65 said:
Ok, Sams Publishing lists that model in their Modular Hi Fi (MHF) series.
That's the only place I could find it for an MCS Integrated I'm working with.
https://www.samswebsite.com/en/photofact/details/index/id/74260

If that receiver is like the amp I have here, the controls on the amp section would be to calibrate the power meters.
There would be no DC offset or bias adjustments.
Click to expand...

Hifirob2 just sent me the service manual for the NEC AUA-7000E which I had read has the identical amp to the one in the MCS 3253.

After comparing the layouts and schematics in that NEC manual to the board in my MCS3253, I can safely say they are identical amp boards. The power supply looks the same too, I haven't compared beyond that yet.

The test pins to measure across the output emitter resistors (13-15 Left, 12-14 Right) in the photo above are identical to what's shown in the NEC service manual which says to adjust the trim pots VR201 and VR202 to 28mV for the bias.

Agreed, there is no adjustment for DC offset, but my unit is measuring under 7mV. The bias seems to be on the high side, but the amp is not running hot. I'm getting 30 degrees (86F) directly off the heat sink when running at above average listening levels.

I think I may leave well enough alone, it sounds very good. But then again it's always fun to fiddle with those old trim pots. I popped a bunch of transistors on an SX-9000 once. The worst part of that was that my wife heard it, and said : "I told you it sounded fine and to leave it alone. You never LISTEN!!!"

Thanks to everyone that replied, it's been very helpful.
 
JamVal said:
Hifirob2 just sent me the service manual for the NEC AUA-7000E which I had read has the identical amp to the one in the MCS 3253.

After comparing the layouts and schematics in that NEC manual to the board in my MCS3253, I can safely say they are identical amp boards. The power supply looks the same too, I haven't compared beyond that yet.

The test pins to measure across the output emitter resistors (13-15 Left, 12-14 Right) in the photo above are identical to what's shown in the NEC service manual which says to adjust the trim pots VR201 and VR202 to 28mV for the bias.

Agreed, there is no adjustment for DC offset, but my unit is measuring under 7mV. The bias seems to be on the high side, but the amp is not running hot. I'm getting 30 degrees (86F) directly off the heat sink when running at above average listening levels.

I think I may leave well enough alone, it sounds very good. But then again it's always fun to fiddle with those old trim pots. I popped a bunch of transistors on an SX-9000 once. The worst part of that was that my wife heard it, and said : "I told you it sounded fine and to leave it alone. You never LISTEN!!!"

Thanks to everyone that replied, it's been very helpful.
Click to expand...

Good deal, I don't have much in the way of NEC literature so I wasn't sure. As for the excessive bias, could be some passive components in the control circuit which have drifted off spec including the pots themselves. The levels are high but not enough to destroy the amp.
 
glen65 said:
Good deal, I don't have much in the way of NEC literature so I wasn't sure. As for the excessive bias, could be some passive components in the control circuit which have drifted off spec including the pots themselves. The levels are high but not enough to destroy the amp.
Click to expand...

PM me with your email if you want a copy of the NEC service manual. It includes the NEC AUA-6000E, 7000E, and 8000E. I'm pretty sure the NEC AUA-7000E integrated amp is the same as the MCS 3847 integrated. Not sure what the other two equate to.
 
JamVal said:
PM me with your email if you want a copy of the NEC service manual. It includes the NEC AUA-6000E, 7000E, and 8000E. I'm pretty sure the NEC AUA-7000E integrated amp is the same as the MCS 3847 integrated. Not sure what the other two equate to.
Click to expand...

Just for reference:

NEC AUA-6000E = MCS 3837
NEC AUA-7000E = MCS 3847
NEC AUA-8000E = MCS 3865

NEC AUR-8055E = MCS 3253
NEC AUR-8075E = MCS 3275
NEC AUR-9060E = MCS 3260
 
Hi,
I'm the new guy here, and I've been reading up on MCS equipment. Sounds like most were rebranded NEC stuff. I sure like the looks. Is there a reason that most people on these threads don't post photos of their equipment? Just curious. I'd love to see some images of any nice receivers. Thanks! :)
 
richartistic said:
Hi,
I'm the new guy here, and I've been reading up on MCS equipment. Sounds like most were rebranded NEC stuff. I sure like the looks. Is there a reason that most people on these threads don't post photos of their equipment? Just curious. I'd love to see some images of any nice receivers. Thanks! :)
Click to expand...


Welcome to AK. There's probably a few reasons that there aren't more pictures of MCS gear here on AK. One big one is probably due to the change of software used by AK. It was switched over to XenForo in early October of 2015. With that change, the "MCS receivers group" was lost - and there were photos located in that section. Some pictures in regular threads were also lost - some of mine included. With the switch to XenForo in my particular case, AK lost most of it's useful features (and appeal), so I have pretty much stopped posting like I did in the past. That I received an email notification of your post to this thread is a small miracle - I almost never do anymore. If you google "MCS receivers", and click on images, you'll see a pretty good representation of some of the more popular models.

The NEC made models are my favorites. All of the Modular Component Systems receivers that were made in Japan were made by NEC. Three of them (3253, 3275, and 3260) were true rebadges. All the other MIJ models were built to JC Penney's specs. Top notch build quality, and a sound that I absolutely love. Find a MCS 3125, and you will probably think you've found audio heaven. Most people reading that comment probably just rolled their eyes, but that's because they have never heard one.

The receivers that were made in Taiwan were sometimes worthy (like the 3245), and sometimes barely mediocre (like the 2240) - but I prefer the feel and the sound of the NEC ones. Just my opinion, though.
 
Hi, not to bring up an old thread, but I was looking for some help on the 3235, service number 683-3235-00. I inherited it from my Dad and I am trying to get it working again. It was sitting for some time. I remember it sounding amazing when I was young. Anyhow, when I turn in on, there is a pop, which sounds like it is coming from the receiver/amp itself and nothing.. No lights, nothing. I was wondering if I could also get a copy of that service manual, there is a good local shop that works on vintage equipment and maybe it could help them restore this for me... Thanks!
 
Mr_Wayne said:
Hi, not to bring up an old thread, but I was looking for some help on the 3235, service number 683-3235-00. I inherited it from my Dad and I am trying to get it working again. It was sitting for some time. I remember it sounding amazing when I was young. Anyhow, when I turn in on, there is a pop, which sounds like it is coming from the receiver/amp itself and nothing.. No lights, nothing. I was wondering if I could also get a copy of that service manual, there is a good local shop that works on vintage equipment and maybe it could help them restore this for me... Thanks!
Click to expand...

Hi - and welcome to AK - The service manual for the 3253 would be so different from the 3235 that it wouldn't be of much help. The 3235 (from what I learned recently on here) is nearly identical to the 3233. If you search the site for info. on the 3233 service manual - that may be helpful. Or a google search for "JCPenney 3233" or "JCPenney 3235 service manual" may turn up something. MCS service manuals are tough to track down, and always said "JCPenney" instead of MCS on the cover. Also, some sources misspell JCPenney as JCPenny, so that may turn up something.

Hopefully, you can get it back up and running. :)
 
I'm having tuner problems with my 3253. I cleaned and deoxed all the pots and switches. After a few minutes of FM play it cuts out to silence. Turning the tuning dial results in loud pops and clicks. The stereo light is out but the tuning meter indicates some signal strength. After a long cooldown it will play again normal, only to cut out again after awhile. All other inputs and AM work OK at this point. I assume something is heating up in the FM board. The only visible issues are some white chalky discoloration on the back side of the tuner board and the controls board near the mute and stereo switches. None of the electronics appear overheated or discolored. I'm not a tech so my next step is to use my infrared thermometer to see if I can tell what is heating up. I too, would like a service manual or info on the tuner section if for no other reason than to bring it with to a service tech. Do you know what NEC model might have a similar tuner section? I don't want to invest too much into it. If it was my 3125 I would probably say cost is not an issue. I kind of have an affinity for MCS gear. 3125, 3253, 3233, 3223 and 6700 TT. I would like to get a 3275 just to complete my MCS by NEC receiver collection.
 
The tuner section in the 3253 is the same as the NEC AUT-7000E. That tuner was also sold as the MCS 3700 and 3701. The tuner in the MCS 3275 is also nearly the same. I don't have a service manual for it, but I have the schematic for the 3275. Maybe that would help? If you'd like it, I can send it to you. Just start a conversation with me, and include an email address where I should send it.
 
Hifirob2 said:
The tuner section in the 3253 is the same as the NEC AUT-7000E. That tuner was also sold as the MCS 3700 and 3701. The tuner in the MCS 3275 is also nearly the same. I don't have a service manual for it, but I have the schematic for the 3275. Maybe that would help? If you'd like it, I can send it to you. Just start a conversation with me, and include an email address where I should send it.
Click to expand...

Thanks Rob. I see HFE has a service manual for AUT-7300E but not 7000E. When I dig back into it I will take some pics and post them then send a PM. I bookmarked this thread awhile ago in anticipation of this. I appreciate the help.
 
Hifirob2 said:
I have the SM for the NEC AUA-7000E. It's in a large file that includes the AUA-6000E & AUA-8000E.

Start a conversation with me and include your email address, and I'll send it your way. Hopefully, it will help.
Click to expand...
Hi there. I started a conversation with you and requested the service manual also.
 
I got your message asking about the 3275. This file won't help with the MCS 3275, but I'll send it to you just in case.
 
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