QSC 22 Adjust advice please... - diyAudio
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Old 11th January 2009, 03:42 AM   #1
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Default QSC 22 Adjust advice please...

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...
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Old 11th January 2009, 04:33 AM   #2
Twaksak is offline Twaksak  South Africa
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Default Bias adjustment

Bias adj depend on output stage confiuration. is yours CF or darlinton? the bias setting can be done while measuring voltage across emitter resistors. I do not know the QSC22. If you supply the schematic it may be of help.
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Old 11th January 2009, 06:09 AM   #3
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The file is about 400k and i can t post it,please send me your mail and i be glad to send it....
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Old 11th January 2009, 06:12 AM   #4
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well this is but larger
Attached Images
File Type: jpg qsc__a21-a22.2.jpg (80.5 KB, 249 views)
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Old 11th January 2009, 06:44 AM   #5
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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
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Old 11th January 2009, 06:52 AM   #6
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ah found it
Attached Files
File Type: pdf service advisory qsc a42.pdf (57.1 KB, 80 views)
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Old 11th January 2009, 10:31 AM   #7
fotios is offline fotios  Greece
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Quote:
Originally posted by artcarmo
well this is but larger
Is this schematic of that amplifier you have? If yes, post it to me to i get a better view.

Regs
Fotios
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Old 11th January 2009, 12:26 PM   #8
lineup is offline lineup  Sweden
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Here is a bigger image, fotios.
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File Type: png qsc_a21_a22.png (87.8 KB, 213 views)
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Old 11th January 2009, 04:42 PM   #9
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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...
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Old 11th January 2009, 04:55 PM   #10
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Here is the adjust i have,and i realize now where i have to measure the current,but still in the dark about the "donamis hum"pot or "null" i think acoord to the schem...thanks
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File Type: pdf qsc__limit adj.pdf (93.5 KB, 68 views)
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