Problem with Macrotech 3600 VZ

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#1 gustaudio

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Posted 30 September 2006 - 09:57 PM

Dear friends I´m repairing a Macrotech 3600 VZ, the channel 2 have a distorsión. When I turn up the volume at the medium level (aprox), teh output wave form is ok, but when turn it up a little more, the negative portion of the sine wave desapear. I check the output transistors, they are ok, check the power supply voltage they look like teh other channel (the good one), I interchange teh PCB´s that have the 6900 uF capacitors...nothing happened, the problem still in channel 2, I think that the problem is in the switching area of the amplifier, but I need some sugestions, Please any body...
Thank you and best regards.
Gustavo Contreras smile.gif

#2 dannyavila

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Posted 04 October 2006 - 07:19 AM

Hi Gustavo:

If the amp's sine wave negative side "disappears" at certain power level, it could be caused by an output current control circuit defective part. Did you check all the 0.33 Ohm/5 Watt output resistances, Q107-108 and Q124-125 BJTs or U104 (MC33079) conditions? In some cases, a missing cooper trace in the main board around the "Mode" switch area caused this symptom to appears randomly.

Kind regards,
<span style='color:blue'>Danny Avila.</span>
Tech Service Chief.
Inaudio - Servicios Integrales.

#3 gustaudio

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Posted 04 October 2006 - 08:49 PM

Danny my friend thank you for your answer, I will check. Thank you again and best regards.  smile.gif