Problems with Alesis RA-500

sippo · 30th December 2005, 03:45 PM

Hello,

i have a problem with one channel of an Alesis RA-500 Amp. If i connect a signal generator and an oscilloscope to the amp everything i can see is a distorted signal that decreases from the time i start the amp to a certain point and which is lower in level compared to the other channel. If i play music with this channel the output is very low an distorted. So far i have checked all transistors, diodes, caps and resistors on the main amp pcb O.K., there is no !! voltage drop over the emitter resistors, the supply voltages for output and driver stage are allright. There´s another small pcb attached to this board which seem to include the protection circuit and a small part of signalcircuit.
Maybe someone here could help me with this or have a schematic of the RA-500.

Thanks in advance

Regards

Frank

sippo · 14th January 2006, 08:11 AM

Nobody in here who knows something about this amp ??

Frank

anatech · 15th January 2006, 02:51 AM

Hi Frank,
No diagram, sorry.

No bias could mean a shorted protection transistor or bias transistor. Discharge the caps and go hunting in diode test mode.

-Chris

sippo · 15th January 2006, 12:25 PM

Thanks for the help Chris,

now i have checked everything and finally resolder all joints just for sure but the distorted low level output still remains.I´m running out of ideas. I have asked the Alesis distributor for a replacement board but without a reply yet.

Frank

anatech · 15th January 2006, 02:27 PM

Hi Frank,
Stick your negative meter lead on the positive speaker output terminal. Measure the bases of the outputs and drivers. Record the voltages.

If you can find the differential pair, measure the emitter voltages with respect to ground.

-Chris

eccentricload · 26th July 2010, 10:06 AM

inject a source output on the differential input via R9 .

If there are still low audio, work till you reach the VAS circuits.

sakis · 26th July 2010, 01:08 PM

this amplifier is ...a bad amplifier .... secondary psu caps arround the protection area is a common failure and also poor soldering since amplifier is under thermal stress and show soldering problems also quiet often

also the protection ic fails quiet often

eccentricload · 26th July 2010, 01:31 PM

You can also try swapping the IC on the other amp ( BA4560 ) or have it removed.

oldmaelstrom2 · 27th July 2010, 01:49 PM

take RapidShare: 1-CLICK Web hosting - Easy Filehosting

lm324 · 27th July 2010, 11:28 PM

Hi Frank,

Service Manual here:

Alesis RA500 (manual de serviço) - [Audio List]

Good Luck

Roger

30th December 2005, 03:45 PM	#1
sippo diyAudio Member Join Date: Mar 2004 Location: Northern Germany	Problems with Alesis RA-500 Hello, i have a problem with one channel of an Alesis RA-500 Amp. If i connect a signal generator and an oscilloscope to the amp everything i can see is a distorted signal that decreases from the time i start the amp to a certain point and which is lower in level compared to the other channel. If i play music with this channel the output is very low an distorted. So far i have checked all transistors, diodes, caps and resistors on the main amp pcb O.K., there is no !! voltage drop over the emitter resistors, the supply voltages for output and driver stage are allright. There´s another small pcb attached to this board which seem to include the protection circuit and a small part of signalcircuit. Maybe someone here could help me with this or have a schematic of the RA-500. Thanks in advance Regards Frank

26th July 2010, 01:08 PM	#7
sakis diyAudio Member Join Date: Jan 2006 Location: nea makri athens greece	this amplifier is ...a bad amplifier .... secondary psu caps arround the protection area is a common failure and also poor soldering since amplifier is under thermal stress and show soldering problems also quiet often also the protection ic fails quiet often __________________ SERVICE ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr

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14th January 2006, 08:11 AM	#2
sippo diyAudio Member Join Date: Mar 2004 Location: Northern Germany	Nobody in here who knows something about this amp ?? Frank

15th January 2006, 02:51 AM	#3
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Frank, No diagram, sorry. No bias could mean a shorted protection transistor or bias transistor. Discharge the caps and go hunting in diode test mode. -Chris

15th January 2006, 12:25 PM	#4
sippo diyAudio Member Join Date: Mar 2004 Location: Northern Germany	Thanks for the help Chris, now i have checked everything and finally resolder all joints just for sure but the distorted low level output still remains.I´m running out of ideas. I have asked the Alesis distributor for a replacement board but without a reply yet. Frank

15th January 2006, 02:27 PM	#5
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Frank, Stick your negative meter lead on the positive speaker output terminal. Measure the bases of the outputs and drivers. Record the voltages. If you can find the differential pair, measure the emitter voltages with respect to ground. -Chris

26th July 2010, 10:06 AM	#6
eccentricload diyAudio Member Join Date: Oct 2009	inject a source output on the differential input via R9 . If there are still low audio, work till you reach the VAS circuits.

26th July 2010, 01:31 PM	#8
eccentricload diyAudio Member Join Date: Oct 2009	You can also try swapping the IC on the other amp ( BA4560 ) or have it removed.

27th July 2010, 01:49 PM	#9
oldmaelstrom2 diyAudio Member Join Date: Nov 2005	take RapidShare: 1-CLICK Web hosting - Easy Filehosting

27th July 2010, 11:28 PM	#10
lm324 diyAudio Member Join Date: Nov 2004 Location: São Paulo	Hi Frank, Service Manual here: Alesis RA500 (manual de serviço) - [Audio List] Good Luck Roger

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