MC2100 To Do's

jbailey930 said:
Almost done. Some progress on the PO boards. Next step transistors on the heat sinks and test.
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Change `almost done´ to `done now.´ Got the NEW heat sinks in place.

boards_done_77_700x.png

They're all straight enough so no one can tell without a close inspection. The BIAS transistors (lower center-right above) were NOT replaced. We'll find out how it goes, maybe tomorrow.

The finish on one of the heat sinks wasn't too good, surprised we missed that, should have done incoming inspection. See the TWO disc ceramic caps below are originals. Newer ones would have been ~half that size.

heat_sink_finish.jpg

Mc should have rejected that part and not shipped it to a customer.


-Greg
 
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SaturationPt said:
I'm looking forward to hearing about the audition. Too bad you're so far from Richmond or I'd invite myself to hear it!
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OT — I thought you meant Richmond VA at first when the reply notice hit the email filter. Richmond IN was the first night's stop for lodging when I used to drive across the America. In later years and with better planning (standard carload, etc) the west side of Indianapolis near Ind Intl Arpt was the first night's lodging. So you'd be looking at a day's 500 mile drive.

-Greg
 
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SaturationPt said:
No, I'll be in Richmond, VA in a couple of weeks. I didn't know there is a Richmond, IN!
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Ok never mind, I got burnt again—now looking out for the OT patrol. Speaking of that, will edit the post above and put OT in front of it so everyone knows it's off topic.
 
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SaturationPt said:
I'm looking forward to hearing about the audition. Too bad you're so far from Richmond or I'd invite myself to hear it!
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Not super far, about 2 hours. My daughter and her husband are down there.

We will post good, bad, indifferent soon. Have to pair this back up with new to me Snell Es, or the usual AR 2ax or the Vandys........
 
Ok, drum roll.......its up and running in my workshop! I am driving a pair of AR 2ax's hard with electronic music. Lots of dynamics to push the amp. It is a night and day difference since I have been using Yamaha receivers with those speakers. Nice to have a receiver but musically the restored/rehabbed improved 2100 is the clear choice. @Gregory will post the tech details on following posts. Thanks for all your help those here that chimed in and provided guidance.

We spent more time and money but the project provided a great learning experience. Have to thank Greg immensely for his time, expertise and patience.
IMG_0702.jpeg IMG_0703.jpeg
 
The amp came to life last Saturday!

There were a couple weeks where nothing happened, not surprising with the upheaval going on everywhere. Last work effort was 3/8 – 3/10 when John came over to install the NEW outputs. Later close inspection found 5 places where transistor `shoulder´ sockets were not seated in the heat sinks, some of them from the 1985 service job. One has to look closely and carefully to see these, especially the middle outputs.

Trans_socket.jpg

I insisted that all outputs and sockets be installed correctly. This was done on 3/10/2020 with much drama over a misplace 1/4" socket. :idea:

On Saturday 3/21 with schedule conflicts, I just went ahead and got the boards back in and powered it up. Amazingly the heat sinks were cool.

After 20 mins, transistors and heat sink idle Temps were under control.
Code: 
Heat Sinks Temps, 2100 upside down, LEFT to RIGHT

  1)    88.3°     76.1°     77.1°     87.6°
  2)    90.8°     77.8°     79.7°     89.3°

Then it started making 136 Watts LEFT and 128 Watts RIGHT before onset of clipping. :idea:


Overall the following measurements at 1,000 Hz on Sunday:
Code: 
            Ea Chan      Both Chan
LEFT        137.6 W       119.4 W
RIGHT       130.0 W       112.6 W


John came over this morning to pick up the amp, and he witnessed it exceeding 100 Watts, both channels driven at 20Hz, 1kHz, and 20 kHz. It was a great feeling of success!

And the TEMPS were stable and uniform.


-Greg
 
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Bogus reference docs

A lot of time was wasted head scratching over the confusing Service Manual diagrams. The `bottom view´ posted in this thread on Dec 10th from SI booklet 038-554 was INCORRECT.

MC2100_bottom_view_02.png


This is the CORRECT `bottom view´ diagram for the MC2100, at least for this old clunker with no visible S/N.

diagram_corrected_v01.png


It took a few hours on Sunday to PROVE the correct diagram by tracking every signal path cable, voltage line, and scope waveform.

2100_diagram_bottom_view_v01.png

Of course you're welcome to rebut the diagrams and statements here.


What a cluster flock. It means ALL of the comments and diagrams above in this thread are BACKWARDS, Left being Right.

As John said earlier, it was a great learning experience.


-Greg
 
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This is a view of the `Transistor Locations´ in FIVE available Serv Info docs:

MC2100-SM_038-275.png MC2100-SM_038-554.png MC2100-SM_038-754.png MC2100-SM_038-907.png MC2100-SM_038-948.png

Either the heat sink or transistor configuration changed at least twice over the production run, or the drafting guys were smoking pot. :rflmao:

Best advice is to get a hold of the latest SM/SI doc (attached).


-Greg
 

Attachments

Motnick said:
Did you guys make any updates to the input board or replace the multi cap?
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@Gregory insists that we tackle the input board next. The tech that serviced this unit in the past updated caps with various brands. He was the one that also said it played fine, hence our journey. It sounds very good and will run it in a bit. Greg has several Nichions on hand. That should take all of a couple of hours once I get the parts needed. Going to give him some time to put his gear on the bench now too.
 
Motnick said:
Did you guys make any updates to the input board or replace the multi cap?
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The input board was serviced by a local shop some years ago and has miscellaneous and mismatched cap pairs L-to-R. They look like `on hand´ junk.

John is understating. I have scores of various Nich audio grade electrolytics that are new-old stock by now.

MC2100_Input.jpg

You can see the inside has dust, dirt, and debris on everything.

Actually said to him the multi-can should be next, but the Input caps are available immediately. If the amp is working really well after 6 months and he likes it, I suggested to replace the original main PS cans.


-Greg
 
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I am at the same point with my 2105 project, planning my attack on the input board next. I do have a Hamfest multi cap on hand to install. I debated about using a hobby board and doing my own thing, but decided to spend a few extra $$ for the hamfest solution since it should be an easier install.

The main caps hurt $$, but I had no choice as one capacitor had vented in my 2105. The new caps sure look nice with the blue jackets though...
 
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We have to test the amp in MONO mode before long. That's connecting a speaker [load] to the COM and 16-ohm LEFT terminals? and jumping 16-ohm LEFT and RIGHT terminals with a single wire?

John didn't have time for the mono test today, and I understand he wanted to get it home and hook it up. He was very patient with me over 3-4 months trying to make sure everything was right, and he could have discontinued the project or stopped buying parts at any time.

-Greg
 
Motnick said:
I am at the same point with my 2105 project, planning my attack on the input board next. I do have a Hamfest multi cap on hand to install. I debated about using a hobby board and doing my own thing, but decided to spend a few extra $$ for the hamfest solution.

The main caps hurt $$, but I had no choice as one capacitor had vented in my 2105. The new caps sure look nice with the blue jackets though.
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Good input.

I have a Hamfest multi-cap in my 2505. It suits the purpose and looks pretty good, with mirror surface on top. Speaking of main cap cans, those were removed on 3/10/2010 to more easily get at the middle outputs on the inboard heat sinks, and to inspect the caps /chassis underneath.

before.jpg after.jpg
Before and after.

The vent plug was dark and a bit wet, I'd say. Overall not in bad shape. The can weights were: Outboard 1 lb 4.2 oz, Inboard 1 lb, 4.5 oz.

-Greg
 
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Was wondering the other day—what caps to replace the 0.47 mylars on the MC2100 Input PCB with? Those are the two yellow caps (see input board photo four posts above) with yellow(4)-violet(7) stripes. There are many supposedly high-end pics with red WIMA film caps installed.

I've replace mylars in the MC2505 with Nich ES non-polar (green) and have a lot of them on hand. Can remember Terry telling me ~10 years ago to `bump up´ the Nich ES value on the input signal-path from 0.47uF to 1uF for improved `bass slam´.

What are the pros and cons?
MKS_4.jpg NICH-ES.jpg
 
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Hunted11 said:
When I did mine, I used these https://www.mouser.com/ProductDetail/Nichicon/QXL2E474KTPT?qs=/ha2pyFadug0ud%2Bc7PQ1kYiGJpcnIr35qNuaSat9BJPpBD3pmgIeYQ==
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Hey thanks, how everything up country there?

Those are metallized film caps. I'm wondering why 250V and 400V caps are needed there. Suppose they last a LONG time.

These are what I put in the MC2505, all Nichicon radials. That was before the axials (left) arrived.

MC2505_Input_PCB.jpg MC2505_input_PCB_II.jpg

Other Mc guys recommend the green NP Nich ES.

I'm thinking of using Nich FG (fine gold) radials for the output signal path now, have plenty on hand.

Here's a cap article from the guitar community.
https://www.coda-effects.com/2015/04/capacitors-which-one-to-choose.html

-Greg
 
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