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VCC problem on a Microtech1200


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#1 Electrochap

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Posted 10 July 2012 - 07:41 AM

Hi, first post here so Hello to you all !

I'm desperate.... I did repair a Microtech1200 for a friend ( some burned outputs, BIAS diodes, drivers ) And everything tests good except on the repaired channel, VCC + sits at 93 volts and VCC- at -.6V. And as soon as I turn the power switch off I see voltage getting to normal @ +/- 45 Vdc. The BIAS on the high side can't get lower then 490mv and it is impossible to do BIAS on the low side; get no voltage at all...  I've been looking everywhere and the only thing I saw odd is on the N102 pin5 I have 8.2 Vdc where the other channel gets 0 V. I swapped N102 with N202 and get back to the same result. I measured the resistors in it and they look all OK.

All components I've measured were OK. I've been looking and looking but it is the first time I work on that kind grounded bridge amp and am not familiar at all...

I'm sure I'm not the first one with that kind of problem but I didn't find any topic on it. I'm using Macrotech schematics. I've red it is the same on the 1200 power.

Probably a loopback problem or ODEP ?

Well, thanks any of you !

#2 rodr@fse_Crown

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Posted 11 July 2012 - 01:58 PM

Please Call Crown and ask for Kip or Kevin for assistance.  They are repair type of guys and are in our FSE Department.

#3 Electrochap

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Posted 19 July 2012 - 09:16 PM

Well I've received an E-mail from KIP with the exact schematics and the advise to look at Q115 & Q116 and exactly Q116 was EC short. Replaced it and I was able to adjust bias and everything.

Great help guys ! Thanks a lot Kip !