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Old 11th January 2014, 11:35 AM   #1
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Join Date: Jan 2014
Default Alesis RA150 burns power resistor

Hi All,

I am new to audio electronics tinkering and hope my diyAudio participation proves valuable to others as well.
Jumping right in: My recently repaired Alesis RA150 worked for 2 wks then quit, again burning out the power resistor.
What happened: Heard a “click” thru spks, volume increased on its own, “searing” noise thru spks, sound died amid smoke.
What I found: 1. Mains Fuse burned; 2. R401 (470/2W) burned; 3. C403 (220uf) bulging at top but testing normal with analog vom; 4. Z1 (15V) shorted.
Repair Status: Changed those 4 parts and reconnected LED indicator circuit, Driver amps and Pwr amps to Pwr Supply board one at a time.
Bench running at low volume for a couple hours now. DC at spk terminals: Rt – 0.1mV Lt – 0.5mV
Question: What else should I check and/or replace before putting amp back in service? Previous fix included change of all el’tic caps except main filters and 2 in the LED circuit. Schematics can be viewed here
Big thanks.
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Old 18th January 2014, 11:59 AM   #2
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Join Date: Jan 2014
Default Update to Alesis ra150 burns resistor

Update on Alesis RA150:
Bench run unit for 6-10 hrs daily since replacing 470R and zener.
Rigged 12 volt fan above area of PS board and ran unit thru Polk LSI9s for 2 hrs with enough volume to fill my ~ 24x24 room. No problems (Right ch slightly lower volume than Left).
Next project is a Kenwood KR-2090 Receiver with crackly controls and a misfiring phono stage. CD input to Aux gives no discernable distortion. Anyone with a schematic?
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