Well,i have a QSC22 colecting dust for a wile in the "grandpa's basement lab".so i try to fix it.i have only the schematic.
The main caps (PSU) were bad and as soon i replace,the amp work again,but i want to adjust Bias & pos and neg limiting,i have some info about QSCrmx settings,that use positive and negative limiting and bias adj,but the info say someting about measure ampere consuption,but,and sorry for been so naive,where i have to mesasure this?
Other trim pot i see is one that is for dinamic hum? so please,if one can help me with info about adjust proceed,where measure this that etc etc,and if the info is like i have 6yrold better...i have electronic skills and basic test items,like, oscill,func gen,testers etc...
i know this is an old amp but seem a good knowledge source...so any info,andvice,guide,will be useful not only about adjustment,i have oscillation issues too,where it came,how to measure it,what cause it,...so thanks very much for any answer, E gurus,from a E diy & hobbist...
The main caps (PSU) were bad and as soon i replace,the amp work again,but i want to adjust Bias & pos and neg limiting,i have some info about QSCrmx settings,that use positive and negative limiting and bias adj,but the info say someting about measure ampere consuption,but,and sorry for been so naive,where i have to mesasure this?
Other trim pot i see is one that is for dinamic hum? so please,if one can help me with info about adjust proceed,where measure this that etc etc,and if the info is like i have 6yrold better...i have electronic skills and basic test items,like, oscill,func gen,testers etc...
i know this is an old amp but seem a good knowledge source...so any info,andvice,guide,will be useful not only about adjustment,i have oscillation issues too,where it came,how to measure it,what cause it,...so thanks very much for any answer, E gurus,from a E diy & hobbist...
hi,
I have a service advisory for these 'A' series amp, I recently service an A42, trouble is, I can't find it in my hard drive. These amp has a unique topology develop by Dr.Q called the grounded collector topology (the trannies are mounted directly on the heatsinks, its an AC coupled amp, more at home in P.A. applications. Meanwhile you can post on the QSC Forum for help while I search for that service advisory for these amp.
Best Regards,
audiomachines
I have a service advisory for these 'A' series amp, I recently service an A42, trouble is, I can't find it in my hard drive. These amp has a unique topology develop by Dr.Q called the grounded collector topology (the trannies are mounted directly on the heatsinks, its an AC coupled amp, more at home in P.A. applications. Meanwhile you can post on the QSC Forum for help while I search for that service advisory for these amp.
Best Regards,
audiomachines
Thanks for the advisory,audiomachines,i was worried about those IC ,but they are functionally yet 
,
Twaksak,yes to me this topology looks like a short circuit waiting to be,because the collector to ground and the emiters to vcc
Fotios,i have a pdf but is the same circuit Line up post .thanks for the answers...
well the amp have the same output topology of the RMX series,i have some info about current limiting adjust but the RMX say about 4ampers with the outputs shorted,but this amps are in the range of 800W and higer output ,and this little one are in the 120w/4ohms,so im affraid to burning it trying to adjust the limiting current
thanks a lot...
,Twaksak,yes to me this topology looks like a short circuit waiting to be,because the collector to ground and the emiters to vcc
Fotios,i have a pdf but is the same circuit Line up post .thanks for the answers...
well the amp have the same output topology of the RMX series,i have some info about current limiting adjust but the RMX say about 4ampers with the outputs shorted,but this amps are in the range of 800W and higer output ,and this little one are in the 120w/4ohms,so im affraid to burning it trying to adjust the limiting current
thanks a lot...
the dynamic hum null is use for canceling the power supply ripple. QSC are tough amps. Have you check the output devices for leaks? just to be sure. Since you mention that you have replaced the filter/output caps. The newer QSC (i.e.RMX) models where DC coupled. JBL mpx, mpc, mpa and some old electrovoice amps uses the same ckt. topology.
Best Regards,
Audiomachines
Best Regards,
Audiomachines
Thanks...
djk,the op amps are the orig. only i did is cleanning all and replace the main caps,so i dont try adjust the limiting?
audiomachines,yes when i clean the heatsink and replace the thermal compound i check it,and i dont see any PSU oscillation at the output..its that you mean?
when i replace all the caps i only get 4700mf/100v,and the orig are 3300mf/75v,any advice in this matter?? thanks very much
djk,the op amps are the orig. only i did is cleanning all and replace the main caps,so i dont try adjust the limiting?
audiomachines,yes when i clean the heatsink and replace the thermal compound i check it,and i dont see any PSU oscillation at the output..its that you mean?
when i replace all the caps i only get 4700mf/100v,and the orig are 3300mf/75v,any advice in this matter?? thanks very much
qsc anps
howdie,
I am gathering info on a QSC A41,QSC has been helpful,seems like the A 21-42 are all the same layout maybe the only difference is the number of output transistors,I am attaching a folder,I hope that will help you too,I am looking for a parts placement guide as some of the stuff is gone and parts don't measure out right,lol.
howdie,
I am gathering info on a QSC A41,QSC has been helpful,seems like the A 21-42 are all the same layout maybe the only difference is the number of output transistors,I am attaching a folder,I hope that will help you too,I am looking for a parts placement guide as some of the stuff is gone and parts don't measure out right,lol.
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