Realistic MPA-100 Model#32-2023 - diyAudio
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Old 28th October 2009, 09:02 PM   #1
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Default Realistic MPA-100 Model#32-2023

When I got this delivered I plugged it up and got nothing but the power light. So, I cracked it open and started poking around. First off I found signs of overheating on the preamp board along with a resistor that was disconnected on one side. I started taking the board loose so I could examine it better. I disconnected 4 wires. Stopped, and when I started again a week later I forgot which wires I took off from which post.... So now I am stuck. I can't even find the service manual to buy it, let alone find one to download. I'll work on that. When I got the board loose enough to flip it looked terrible. I'll definitely have to clean and re-solder it before I re-apply power to it. I didn't see any burnt traces though. Just a lot of corrosion. I am going to replace the two resistors where it looks burnt. That's all I think it might need. If any one has any schematics or knowledge of this amp I would appreciate the input.

Cheers!

Last edited by Bas Horneman; 29th October 2009 at 09:44 PM. Reason: At the request of the poster.
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Old 29th October 2009, 02:43 PM   #2
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Angelfire doesn't allow external linking,try photobucket or some other pic hosting site.
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Old 29th October 2009, 03:17 PM   #3
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i thing you are in a bit of a mess ....this will be not easy ....as about the schematic that will be twice as hard

only chance is to try hard
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Old 29th October 2009, 08:42 PM   #4
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Third try, this time using photo bucket.

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Old 29th October 2009, 08:56 PM   #5
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Quote:
Originally Posted by sakis View Post
i thing you are in a bit of a mess ....this will be not easy ....as about the schematic that will be twice as hard

only chance is to try hard

I don't think I am in to much trouble. I only have three wires disconnected that I need to figure out. The rest I will carefully mark and document. This will be a nice amp when I finish!
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Old 23rd April 2010, 01:19 AM   #6
dp19 is offline dp19  Canada
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Did you resolve your problem? I have a same amp like that here and I could take pics of the inside if you still need help.

Thanks
Denis
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Old 9th July 2012, 06:19 PM   #7
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Denis, Honestly I had put this one the back burner and forgot about it. I found another one on ebay and bought it so now I have a guide to go by. The Second one I got is working but, it has a "high" , "Tinny" sound to it; Absolutely no bass or lower register whatsoever. So now I have two amps that basically do not work right. I will be diving back into them both in the coming months so I will take any advive or suggestions, and I will post my progress. Cheers!
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Old 10th July 2012, 02:59 AM   #8
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Default PA systems as audio

PA amps don't or perhaps didn't always offer a full hi-fi audio range, as old shopping mall sound systems would suggest. It may still require the schematic or reverse engineering to locate any preamp filters that intentionally cut bass and high treble for announcement or background music. Otherwise, the usual treatment of replacing the electrolytic caps, main ones in particular, will restore weak sound with hum that occurs as these dry out with age and heat.

My recollection of old Realistic and similar equipment from the '70s is that that that's how they sounded, so they will be disappointing for home audio use. Mods may help but just how much, is down to the original design. As it appears to be transformer coupled to the speaker system, like most 70 or 100V line systems, there is one big limitation on bass.
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Last edited by Ian Finch; 10th July 2012 at 03:07 AM.
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Old 10th July 2012, 12:13 PM   #9
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Thanks Ian, I was thinking along the same lines; replacing/upgrading some caps. Also I was considering replacing the output transistors. I found identical ones on ebay-- 2PCS D675 2SD675 Audio Power Transistor MOT TO-3 | eBay
But, I was hoping maybe to find a newer cross part with better performance. I will keep looking at datasheets.
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Old 6th October 2012, 10:06 AM   #10
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try 2N3055

2N3055 STMicroelectronics | Mouser

But the Toshiba made (in red) is better than one posted on the web
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