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Old 10th July 2013, 09:11 PM   #1
pinyoro is offline pinyoro  United Kingdom
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Default Need help adjusting Alto Macro 2400

Hi,

I recently repaired a Alto Macro 2400 power amplifier. I had to replace the plus and minus HV switching transistors and output transistors on channel B. (All output transistors replaced). Amp is now operating but unfortunately the service procedure does not contain a setup procedure.

Service manual with schematics can be found here:


http://diagramas.diagramasde.com/aud...00,%202400.pdf

There is mention of the test procedure in the document but it is not in the document.

There are pots R23,R239 and R240 for adjustment.

May someone please advise how they would go about setting up this amp.

Thanks,

Mike
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Old 10th July 2013, 09:42 PM   #2
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If you haven't changed Q105/6 then the bias will still be correct. If you have, use a scope and set for no xover distortion with 8R load. Should be about 2mV across the output stage emmiter resistors.
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Old 10th July 2013, 10:35 PM   #3
pinyoro is offline pinyoro  United Kingdom
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Quote:
Originally Posted by JonSnell Electronic View Post
If you haven't changed Q105/6 then the bias will still be correct. If you have, use a scope and set for no xover distortion with 8R load. Should be about 2mV across the output stage emmiter resistors.
Thanks for your response. Q105/6 were not changed. If there is xover distortion, should I adjust R131? Does R139 and R140 control the voltage accross the emmitter resistors? Thanks.
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Old 10th July 2013, 10:45 PM   #4
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R131 adjusts the bias. the other pots set the mid point. Best left alone!
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Old 11th July 2013, 04:34 PM   #5
pinyoro is offline pinyoro  United Kingdom
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Quote:
Originally Posted by JonSnell Electronic View Post
R131 adjusts the bias. the other pots set the mid point. Best left alone!
Thanks
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