Any Ideas on How to find a Radio Shack MPA@250 amp shematic? - diyAudio
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Old 23rd April 2013, 08:56 PM   #1
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Default Any Ideas on How to find a Radio Shack MPA@250 amp shematic?

I've had no luck trying to find a schematic for Radio Shack MPA250. I have 2 that are in the protect mode. I'd love to get them working again....
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Old 24th April 2013, 01:20 AM   #2
sregor is offline sregor  United States
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I've found a parts list but no schematic. One question - is it a 250 or a 250A or 250B. The MPA250 has analog meters, the 250A and B have digital displays. As far as I can tell, the A and B versions are the same except B is black front. One possible problem with the A or B is that the heat sinks tend to pull on the boards in shipping,and can cause cracks at the other end of the board around the mounting screws.
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Old 24th April 2013, 02:40 AM   #3
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Steve thx for the reply. Mine have the arch shaped LED meter & use Tosiba 1943 & 5200 outputs.2pr. per channel.Who make thesea Amps? Pyramid made something very similiar. Pyle also sold similiar amps.NOT sure how to contact these companies....
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Old 24th April 2013, 06:28 PM   #4
sregor is offline sregor  United States
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250A is silver, 250B is black. I mispoke - by digital I meant LED display. I've also heard that pyramid or pyle makes these, but haven't verified anything.
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Old 25th April 2013, 02:16 PM   #5
JMFahey is offline JMFahey  Argentina
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Sorry but even if you find who actually made them, OEM factories do NOT talk to the end supplier , your only bet is Radio Shack itself or *maybe* some Authorized Service guy , although obviously he'll prefer you send the dead amp to him.

Of course, if you are experienced and have a well stuffed Lab you can service them anyway without schematic, by applying "general purpose" diagnostic and service procedures, such as checking for presence of correct rail voltages, shorted power and driver transistors, dead PSU diodes , open or missing or unsoldered filter caps, etc.
Living in Argentina I have to do it all day long.
Probably many who live outside USA have a similar experience, working without schematics and lacking access to original parts.
Oh well.
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Old 26th April 2013, 02:19 AM   #6
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I uaually work with schematics, I guess I have try your way. I spent hrs. looking for info, but no luck. Radio Shack does not want to give it up!
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Old 16th June 2013, 06:12 PM   #7
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I was given one of these amps - the one with analog VU meters, because it was not working. The bridge rectifier was shot. I replaced it and the amp works fine and sounds better than I expected. The fan is a little noisy (not a very good fan), but I unplugged it. Even at half throttle, the heat sink is cool to the touch. I think the fan is there in case the amp is rack mounted.

I still have not found a schematic for the amp. I like that it has Toshiba 2SA1302 power transistors.

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Old 16th June 2013, 06:17 PM   #8
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Old 16th June 2013, 06:20 PM   #9
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Note: Since, I unplugged the fan, I run this amp with the top off. When I get around to it, I'll order the quietest fan I can find, and replace the noisy one.

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Old 16th June 2013, 06:56 PM   #10
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I did have a 250B (black) here in working order & the sound was very good.. Still no luck with schematic or repairs. Thx for the reply....
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